In the aconitase superfamily, which includes the archetypical aconitase, homoaconitase, and isopropylmalate isomerase, only aconitase X is not functionally annotated. The corresponding gene (LhpI) was often located within the bacterial gene cluster involved in L-hydroxyproline metabolism. Screening of a library of (hydroxy) proline analogues revealed that this protein catalyzes the dehydration of cis-3-hydroxy-L-proline to Delta(1)-pyrroline-2-carboxylate. Furthermore, electron paramagnetic resonance and site-directed mutagenic analyses suggests the presence of a mononuclear Fe(III) center, which may be coordinated with one glutamate and two cysteine residues. These properties were significantly different from those of other aconitase members, which catalyze the isomerization of alpha-to beta-hydroxy acids, and have a [4Fe-4S] cluster-binding site composed of three cysteine residues. Bacteria with the LhpI gene could degrade cis-3-hydroxy-L-proline as the sole carbon source, and LhpI transcription was up-regulated not only by cis-3-hydroxy-L-proline, but also by several isomeric 3-and 4-hydroxyprolines.

L-Amino acid ligase (Lal) catalyzes dipeptide synthesis from unprotected L-amino acids by hydrolysis ATP to ADP. Each Lal displays unique substrate specificity, and many different dipeptides can be synthesized by selecting suitable Lal. We have already successfully synthesized Met-Gly selectively by replacing the Pro85 residues of Lal from Bacillus licheniformis (BL00235). From these results, we deduced that the amino acid residue at position 85 had a key role in enzyme activity, and applied these findings to other Lals. When Pro and Gly were used as substrates, TabS from Pseudomonas syringae, synthesized the salt taste enhancing dipeptide Pro Gly and other three dipeptides (Gly-Pro, Pro-Pro, and Gly-Gly) was hardly synthesized from its substrate specificity. However, the amount of Pro Gly was low. Therefore, to alter the substrate specificity and increase the amount of Pro Gly, we selected amino acid residues that might affect the enzyme activity, Ser85 corresponding to Pro85 of BL00235, and His294 on the results from previous studies and the predicted structure of TabS. These residues were replaced with 20 proteogenic amino acids, and Pro Gly synthesizing reactions were conducted. The S85T and the H294D mutants synthesized more Pro Gly than wild-type. Furthermore, the S85T/H294D double mutant synthesized considerably more Pro Gly than the single mutant did. These results showed that the amino acid position 85 of TabS affect the enzyme activity similarly to BL00235. In addition, replacing the amino acid residue positioning around the N-terminal substrate and constructing the double mutant led to increase the amount of Pro-Gly. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.

HpaBC monooxygenase was previously reported to hydroxylate resveratrol to piceatannol. In this article, we report a novel catalytic activity of HpaBC for the synthesis of a pentahydroxylated stilbene. When Escherichia coli cells expressing HpaBC were incubated with resveratrol, the resulting piceatannol was further converted to a new product. This product was identified by mass spectrometry and NMR spectroscopy as a 5-hydroxylated piceatannol, 3,4,5,3,5-pentahydroxy-trans-stilbene (PHS), which is a reportedly valuable biologically active stilbene derivative. We attempted to produce PHS from piceatannol on a flask scale. After examining the effects of detergents and buffers on PHS production, E. coli cells expressing HpaBC efficiently hydroxylated piceatannol to PHS in a reaction mixture containing 1.5% (v/v) Tween 80 and 100mM 3-morpholinopropanesulfonic acid-NaOH buffer at pH 7.5. Under the optimized conditions, the whole cells regioselectively hydroxylated piceatannol, and the production of PHS reached 6.9mM (1.8g L-1) in 48h.

Naturally occurring l-hydroxyproline in its four regio- and stereoisomeric forms has been explored as a possible precursor for pharmaceutical agents, yet the selective synthesis of trans-3-hydroxy-l-proline has not been achieved. Our aim was to develop a novel biocatalytic asymmetric method for the synthesis of trans-3-hydroxy-l-proline. So far, we focused on the rhizobial arginine catabolic pathway: arginase and ornithine cyclodeaminase are involved in l-arginine degradation to l-proline via l-ornithine. We hypothesized that trans-3-hydroxy-l-proline should be synthesized if arginase and ornithine cyclodeaminase act on (2S,3S)-3-hydroxyarginine and (2S,3S)-3-hydroxyornithine, respectively. To test this hypothesis, we cloned the genes of l-arginine 3-hydroxylase, arginase, and ornithine cyclodeaminase and overexpressed them in Escherichia coli, with subsequent enzyme purification. After characterization and optimization of each enzyme, a three-step procedure involving l-arginine 3-hydroxylase, arginase, and ornithine cyclodeaminase (in this order) was performed using l-arginine as a starting substrate. At the second step of the procedure, putative hydroxyornithine was formed quantitatively by arginase from (2S,3S)-3-hydroxyarginine. Nuclear magnetic resonance and chiral high-performance liquid chromatography analyses revealed that the absolute configuration of this compound was (2S,3S)-3-hydroxyornithine. In the last step of the procedure, trans-3-hydroxy-l-proline was synthesized selectively by ornithine cyclodeaminase from (2S,3S)-3-hydroxyornithine. Thus, we successfully developed a novel synthetic route, comprised of three reactions, to convert l-arginine to trans-3-hydroxy-l-proline. The excellent selectivity makes this procedure simpler and more efficient than conventional chemical synthesis.

We examined 66 aromatics for carboxylation by the gamma-resorcylic acid decarboxylase from Rhizobium radiobacter WU-0108 under reverse reaction conditions. The enzyme carboxylated resorcinol, catechol, 5-methylresorcinol and three hydroxystilbenes (resveratrol, gnetol, and piceatannol) with high yields. Except for catechol, the structures of these substrates include a 1,3-dihydroxybenzene moiety. Other compounds gave no reaction products. The reaction products from resveratrol and gnetol were 2,6-dihydroxy-4-[(E)-2-(4-hydroxyphenyl)ethenyl]benzoic acid and 2,6-dihydroxy-4-[(E)-2-(2,6-dihydroxyphenyl)ethenyl]benzoic acid, respectively, as determined by mass spectrometry and nuclear magnetic resonance analyses. Kinetic analyses of the carboxylation reactions indicated that resveratrol and gnetol are better substrates than resorcinol or catechol. (C) 2015 Elsevier B.V. All rights reserved.

RizA is an L-amino-acid ligase from Bacillus subtilis that participates in the biosynthesis of rhizocticin, an oligopeptide antibiotic. The substrate-free form of RizA has been crystallized and the structure was solved at 2.8 angstrom resolution. The amino-acid-binding site appears to be capable of accommodating multiple amino acids, consistent with previous biochemical studies.

Mycobacteria such as Mycobacterium smegmatis strain mc2155 and Mycobacterium goodii strain 12523 are able to grow on acetone and use it as a source of carbon and energy. We previously demonstrated by gene deletion analysis that the mimABCD gene cluster, which encodes a binuclear iron monooxygenase, plays an essential role in acetone metabolism in these mycobacteria. In the present study, we determined the catalytic function of MimABCD in acetone metabolism. Whole-cell assays were performed using Escherichia coli cells expressing the MimABCD complex. When the recombinant E. coli cells were incubated with acetone, a product was detected by gas chromatography (GC) analysis. Based on the retention time and the gas chromatography-mass spectrometry (GC-MS) spectrum, the reaction product was identified as acetol (hydroxyacetone). The recombinant E.coli cells produced 1.02 mM of acetol from acetone within 24 h. Furthermore, we demonstrated that MimABCD also was able to convert methylethylketone (2-butanone) to 1-hydroxy-2-butanone. Although it has long been known that microorganisms such as mycobacteria metabolize acetone via acetol, this study provides the first biochemical evidence for the existence of a microbial enzyme that catalyses the conversion of acetone to acetol.

We developed a novel process for efficient synthesis of L-threo-3-hydroxyaspartic acid (L-THA) using microbial hydroxylase and hydrolase. A well-characterized mutant of asparagine hydroxylase (AsnO-D241N) and its homologous enzyme (SCO2693-D246N) were adaptable to the direct hydroxylation of L-aspartic acid; however, the yields were strictly low. Therefore, the highly stable and efficient wild-type asparagine hydroxylases AsnO and SCO2693 were employed to synthesize L-THA. By using these recombinant enzymes, L-THA was obtained by L-asparagine hydroxylation by AsnO followed by amide hydrolysis by asparaginase via 3-hydroxyasparagine. Subsequently, the two-step reaction was adapted to one-pot bioconversion in a test tube. L-THA was obtained in a small amount with a molar yield of 0.076% by using intact Escherichia coli expressing the asnO gene, and thus, two asparaginase-deficient mutants of E. coli were investigated. A remarkably increased L-THA yield of 8.2% was obtained with the asparaginase I-deficient mutant. When the expression level of the asnO gene was enhanced by using the T7 promoter in E. coli instead of the lac promoter, the L-THA yield was significantly increased to 92%. By using a combination of the E. coli asparaginase I-deficient mutant and the T7 expression system, a whole-cell reaction in a jar fermentor was conducted, and consequently, L-THA was successfully obtained from L-asparagine with a maximum yield of 96% in less time than with test tube-scale production. These results indicate that asparagine hydroxylation followed by hydrolysis would be applicable to the efficient production of L-THA.

We demonstrated the usefulness of a hydroxamate-based colorimetric assay for predicting amide bond formation (through an aminoacyl-AMP intermediate) by the adenylation domain of nonribosomal peptide synthetases. By using a typical adenylation domain of tyrocidine synthetase (involved in tyrocidine biosynthesis), we confirmed the correlation between the absorbance at 490 nm of the l-Trp-hydroxamate-Fe&lt
sup&gt
3+&lt
/sup&gt
complex and the formation of l-Trp-l-Pro, where l-Pro was used instead of hydroxylamine. Furthermore, this assay was adapted to the adenylation domains of surfactin synthetase (involved in surfactin biosynthesis) and bacitracin synthetase (involved in bacitracin biosynthesis). Consequently, the formation of various aminoacyl l-Pro formations was observed.

Vanillin is one of the world's most important flavor and fragrance compounds in foods and cosmetics. Recently, we demonstrated that vanillin could be produced from ferulic acid via 4-vinylguaiacol in a coenzyme-independent manner using the decarboxylase Fdc and the oxygenase Cso2. In this study, we investigated a new two-pot bioprocess for vanillin production using the whole-cell catalyst of Escherichia coli expressing Fdc in the first stage and that of E. coli expressing Cso2 in the second stage. We first optimized the second-step Cso2 reaction from 4-vinylguaiacol to vanillin, a rate-determining step for the production of vanillin. Addition of FeCl&lt
inf&gt
2&lt
/inf&gt
to the cultivation medium enhanced the activity of the resulting E. coli cells expressing Cso2, an iron protein belonging to the carotenoid cleavage oxygenase family. Furthermore, a butyl acetate-water biphasic system was effective in improving the production of vanillin. Under the optimized conditions, we attempted to produce vanillin from ferulic acid by a two-pot bioprocess on a flask scale. In the first stage, E. coli cells expressing Fdc rapidly decarboxylated ferulic acid and completely converted 75mM of this substrate to 4-vinylguaiacol within 2h at pH 9.0. After the first-stage reaction, cells were removed from the reaction mixture by centrifugation, and the pH of the resulting supernatant was adjusted to 10.5, the optimal pH for Cso2. This solution was subjected to the second-stage reaction. In the second stage, E. coli cells expressing Cso2 efficiently oxidized 4-vinylguaiacol to vanillin. The concentration of vanillin reached 52mM (7.8gL&lt
sup&gt
-1&lt
/sup&gt
) in 24h, which is the highest level attained to date for the biotechnological production of vanillin using recombinant cells.

Vanillin is one of the world's most important flavor and fragrance compounds in foods and cosmetics. Recently, we demonstrated that vanillin could be produced from ferulic acid via 4-vinylguaiacol in a coenzyme-independent manner using the decarboxylase Fdc and the oxygenase Cso2. In this study, we investigated a new two-pot bioprocess for vanillin production using the whole-cell catalyst of Escherichia coli expressing Fdc in the first stage and that of E. coli expressing Cso2 in the second stage. We first optimized the second-step Cso2 reaction from 4-vinylguaiacol to vanillin, a rate-determining step for the production of vanillin. Addition of FeCl2 to the cultivation medium enhanced the activity of the resulting E. coli cells expressing Cso2, an iron protein belonging to the carotenoid cleavage oxygenase family. Furthermore, a butyl acetate-water biphasic system was effective in improving the production of vanillin. Under the optimized conditions, we attempted to produce vanillin from ferulic acid by a two-pot bioprocess on a flask scale. In the first stage, E. coli cells expressing Fdc rapidly decarboxylated ferulic acid and completely converted 75 mM of this substrate to 4-vinylguaiacol within 2 h at pH 9.0. After the first-stage reaction, cells were removed from the reaction mixture by centrifugation, and the pH of the resulting supernatant was adjusted to 10.5, the optimal pH for Cso2. This solution was subjected to the second-stage reaction. In the second stage, E. coli cells expressing Cso2 efficiently oxidized 4-vinylguaiacol to vanillin. The concentration of vanillin reached 52 mM (7.8 g L-1) in 24 h, which is the highest level attained to date for the biotechnological production of vanillin using recombinant cells.

We demonstrated the usefulness of a hydroxamate-based colorimetric assay for predicting amide bond formation (through an aminoacyl-AMP intermediate) by the adenylation domain of nonribosomal peptide synthetases. By using a typical adenylation domain of tyrocidine synthetase (involved in tyrocidine biosynthesis), we confirmed the correlation between the absorbance at 490 nm of the L-Trp-hydroxamate-Fe3+ complex and the formation of L-Trp-L-Pro, where L-Pro was used instead of hydroxylamine. Furthermore, this assay was adapted to the adenylation domains of surfactin synthetase (involved in surfactin biosynthesis) and bacitracin synthetase (involved in bacitracin biosynthesis). Consequently, the formation of various aminoacyl L-Pro formations was observed. (C) 2015 Elsevier Inc. All rights reserved.

Vanillin is one of the world's most important flavor and fragrance compounds in foods and cosmetics. Recently, we demonstrated that vanillin could be produced from ferulic acid via 4-vinylguaiacol in a coenzyme-independent manner using the decarboxylase Fdc and the oxygenase Cso2. In this study, we investigated a new two-pot bioprocess for vanillin production using the whole-cell catalyst of Escherichia coli expressing Fdc in the first stage and that of E. coli expressing Cso2 in the second stage. We first optimized the second-step Cso2 reaction from 4-vinylguaiacol to vanillin, a rate-determining step for the production of vanillin. Addition of FeCl2 to the cultivation medium enhanced the activity of the resulting E. coli cells expressing Cso2, an iron protein belonging to the carotenoid cleavage oxygenase family. Furthermore, a butyl acetate-water biphasic system was effective in improving the production of vanillin. Under the optimized conditions, we attempted to produce vanillin from ferulic acid by a two-pot bioprocess on a flask scale. In the first stage, E. coli cells expressing Fdc rapidly decarboxylated ferulic acid and completely converted 75 mM of this substrate to 4-vinylguaiacol within 2 h at pH 9.0. After the first-stage reaction, cells were removed from the reaction mixture by centrifugation, and the pH of the resulting supernatant was adjusted to 10.5, the optimal pH for Cso2. This solution was subjected to the second-stage reaction. In the second stage, E. coli cells expressing Cso2 efficiently oxidized 4-vinylguaiacol to vanillin. The concentration of vanillin reached 52 mM (7.8 g L-1) in 24 h, which is the highest level attained to date for the biotechnological production of vanillin using recombinant cells.

Enzymatic regio- and stereoselective hydroxylation are valuable for the production of hydroxylated chiral ingredients. Pro line hydroxylases are representative members of the nonheme Fe2+/alpha-ketoglutarate-dependent dioxygenase family. These enzymes catalyze the conversion of L-proline into hydroxy-L-prolines (Hyps). L-Proline cis-4-hydroxylases (cis-P4Hs) from Sinorhizobium rneliloti and Mesorhizobium loti catalyze the hydroxylation of L-proline, generating cis-4-hydroxy-L-proline, as well as the hydroxylation of L-pipecolic acid (L-Pip), generating two regioisomers, cis-5-Hypip and cis-3-Hypip. To selectively produce cis-5-Hypip without simultaneous production of two isomers, protein engineering of cis-P4Hs is required. We therefore carried out protein engineering of cis-P4H to facilitate the conversion of the majority of L-Pip into the cis-5-Hypip isomer. We first solved the X-ray crystal structure of cis-P4H in complex with each of L-Pro and L-Pip. Then, we conducted three rounds of directed evolution and successfully created a cis-P4H triple mutant, V97F/V95W/E114G, demonstrating the desired regioselectivity toward cis-5-Hypip.

Enzymatic regio- and stereoselective hydroxylation are valuable for the production of hydroxylated chiral ingredients. Pro line hydroxylases are representative members of the nonheme Fe2+/alpha-ketoglutarate-dependent dioxygenase family. These enzymes catalyze the conversion of L-proline into hydroxy-L-prolines (Hyps). L-Proline cis-4-hydroxylases (cis-P4Hs) from Sinorhizobium rneliloti and Mesorhizobium loti catalyze the hydroxylation of L-proline, generating cis-4-hydroxy-L-proline, as well as the hydroxylation of L-pipecolic acid (L-Pip), generating two regioisomers, cis-5-Hypip and cis-3-Hypip. To selectively produce cis-5-Hypip without simultaneous production of two isomers, protein engineering of cis-P4Hs is required. We therefore carried out protein engineering of cis-P4H to facilitate the conversion of the majority of L-Pip into the cis-5-Hypip isomer. We first solved the X-ray crystal structure of cis-P4H in complex with each of L-Pro and L-Pip. Then, we conducted three rounds of directed evolution and successfully created a cis-P4H triple mutant, V97F/V95W/E114G, demonstrating the desired regioselectivity toward cis-5-Hypip.

Enzymatic regio- and stereoselective hydroxylation are valuable for the production of hydroxylated chiral ingredients. Pro line hydroxylases are representative members of the nonheme Fe2+/alpha-ketoglutarate-dependent dioxygenase family. These enzymes catalyze the conversion of L-proline into hydroxy-L-prolines (Hyps). L-Proline cis-4-hydroxylases (cis-P4Hs) from Sinorhizobium rneliloti and Mesorhizobium loti catalyze the hydroxylation of L-proline, generating cis-4-hydroxy-L-proline, as well as the hydroxylation of L-pipecolic acid (L-Pip), generating two regioisomers, cis-5-Hypip and cis-3-Hypip. To selectively produce cis-5-Hypip without simultaneous production of two isomers, protein engineering of cis-P4Hs is required. We therefore carried out protein engineering of cis-P4H to facilitate the conversion of the majority of L-Pip into the cis-5-Hypip isomer. We first solved the X-ray crystal structure of cis-P4H in complex with each of L-Pro and L-Pip. Then, we conducted three rounds of directed evolution and successfully created a cis-P4H triple mutant, V97F/V95W/E114G, demonstrating the desired regioselectivity toward cis-5-Hypip.

:HpaBC monooxygenase was previously reported to hydroxylate resveratrol to piceatannol. In this article, we report a novel catalytic activity of HpaBC for the synthesis of a pentahydroxylated stilbene. When Escherichia coli cells expressing HpaBC were incubated with resveratrol, the resulting piceatannol was further converted to a new product. This product was identified by mass spectrometry and NMR spectroscopy as a 5-hydroxylated piceatannol, 3,4,5,3',5'-pentahydroxy-trans-stilbene (PHS), which is a reportedly valuable biologically active stilbene derivative. We attempted to produce PHS from piceatannol on a flask scale. After examining the effects of detergents and buffers on PHS production, E. coli cells expressing HpaBC efficiently hydroxylated piceatannol to PHS in a reaction mixture containing 1.5% (v/v) Tween 80 and 100 mM 3-morpholinopropanesulfonic acid-NaOH buffer at pH 7.5. Under the optimized conditions, the whole cells regioselectively hydroxylated piceatannol, and the production of PHS reached 6.9 mM (1.8 g L(-1)) in 48 h.

Dipeptides have unique physiological functions. This study focused on the salt-taste-enhancing dipeptide Met-Gly. BL00235, an L-amino acid ligase from Bacillus licheniformis NBRC12200, synthesizes Met-Gly as a major product as well as Met-Met as a by-product. To alter the substrate specificity of BL00235 and synthesize Met-Gly selectively, we chose to alter Pro85 residue based on the BL00235 crystal structure. We predicted that Met might be not recognized as a C-terminal substrate by occupying the space around C-terminal substrate. Pro85 was replaced with Phe, Tyr, and Trp, which have bulky aromatic side chains, by site-directed mutagenesis. These mutants lost the capacity to synthesize Met-Met, during the synthesis of Met-Gly. Furthermore, they did not synthesize Met-Met, even when methionine was used as a substrate. These results show that the amino acid residue at position 85 has a key role in C-terminal substrate specificity.

We developed a novel process for efficient synthesis of L-threo-3-hydroxyaspartic acid (L-THA) using microbial hydroxylase and hydrolase. A well-characterized mutant of asparagine hydroxylase (AsnO-D241N) and its homologous enzyme (SCO2693- D246N) were adaptable to the direct hydroxylation of L-aspartic acid
however, the yields were strictly low. Therefore, the highly stable and efficient wild-type asparagine hydroxylases AsnO and SCO2693 were employed to synthesize L-THA. By using these recombinant enzymes, L-THA was obtained by L-asparagine hydroxylation by AsnO followed by amide hydrolysis by asparaginase via 3-hydroxyasparagine. Subsequently, the two-step reaction was adapted to one-pot bioconversion in a test tube. L-THA was obtained in a small amount with a molar yield of 0.076% by using intact Escherichia coli expressing the asnO gene, and thus, two asparaginase-deficient mutants of E. coli were investigated. A remarkably increased L-THA yield of 8.2% was obtained with the asparaginase I-deficient mutant. When the expression level of the asnO gene was enhanced by using the T7 promoter in E. coli instead of the lac promoter, the L-THA yield was significantly increased to 92%. By using a combination of the E. coli asparaginase I-deficient mutant and the T7 expression system, a whole-cell reaction in a jar fermentor was conducted, and consequently, L-THA was successfully obtained from L-asparagine with a maximum yield of 96% in less time than with test tube-scale production. These results indicate that asparagine hydroxylation followed by hydrolysis would be applicable to the efficient production of L-THA.

:We demonstrated the usefulness of a hydroxamate-based colorimetric assay for predicting amide bond formation (through an aminoacyl-AMP intermediate) by the adenylation domain of nonribosomal peptide synthetases. By using a typical adenylation domain of tyrocidine synthetase (involved in tyrocidine biosynthesis), we confirmed the correlation between the absorbance at 490 nm of the l-Trp-hydroxamate-Fe(3+) complex and the formation of l-Trp-l-Pro, where l-Pro was used instead of hydroxylamine. Furthermore, this assay was adapted to the adenylation domains of surfactin synthetase (involved in surfactin biosynthesis) and bacitracin synthetase (involved in bacitracin biosynthesis). Consequently, the formation of various aminoacyl l-Pro formations was observed.

CYP199A2, a member of the cytochrome P450 family, is a monooxygenase that specializes in the oxidation of aromatic carboxylic acids. The crystal structure of CYP199A2 determined by Bell etal. (J. Mol. Biol., 383, 561-574, 2008) suggested that the S97 and S247 residues conferred the substrate specificity on this enzyme through interaction between the hydroxy side chains of these Ser residues and the carboxy group of the substrates. In this study, we attempted to design and construct CYP199A2 mutants that recognize hydroxy aromatic compounds as substrates by protein engineering. We speculated that substitution of the S97 and S247 residues with acidic amino acids Asp and Glu, which have carboxy side chains, would provide CYP199A2 mutants that recognize hydroxy aromatic compounds instead of aromatic carboxylic acids. The S97 and S247 residues were substituted with Asp and Glu using site-directed mutagenesis. In whole-cell assays with p-methylbenzylalcohol and phenol as hydroxy aromatic substrates, the S247D mutant regioselectively oxidized these compounds to 1,4-benzenedimethanol and hydroquinone, respectively, although the wild-type enzyme exhibited no oxidation activity for these compounds. Furthermore, the S97D, S247D, and S247E mutants acquired oxidation activity for p-cresol. Especially, the S247D mutant rapidly oxidized p-cresol
the whole cells expressing the S247D mutant completely converted 1mM p-cresol to p-hydroxybenzylalcohol in only 30min. These results also clearly demonstrate that S97 and S247 are important residues that control the substrate specificity of CYP199A2.

Many dipeptides have unique physiological functions such as antihypertensive effects and taste enhancing effects. In this study, we focused on the taste of dipeptides and conducted screening for dipeptides as salt taste enhancers. Dipeptides were synthesized using TabS, an _L-amino acid ligase (Lal) from Pseudomonas syringae NBRC14081. Six kinds of amino acids, which were easily released by the hydrolysis of proteins or peptides, reacted with 20 proteogenic amino acids, and the reaction mixtures were evaluated using sensory evaluation. In the first screening, the reaction mixture or _L-Leu-_L-Ser, a known salt taste enhancing dipeptide, was added to a salt solution containing ATP and panelists judged the salt taste intensities. In the second screening, the reaction mixture or residual substrate amino acids was added to a salt solution containing ATP and subjected to sensory evaluation. _L-Met-Gly was identified as a candidate salt taste enhancer. In addition to sensory evaluation, the salt taste enhancing effect of _L-Met-Gly was evaluated using a taste sensor. Taste sensor analysis showed that _L-Met-Gly had a salt taste enhancing effect, and the relative sensor response for _L-Met-Gly was equal to or higher than that for _L-Leu-_L-Ser. This is the first report that _L-Met-Gly is a salt taste enhancing dipeptide. Furthermore, we propose that the screening method using reaction mixtures of Lal is applicable for the taste evaluation of other dipeptides.

Many dipeptides have unique physiological functions such as antihypertensive effects and taste enhancing effects. In this study, we focused on the taste of dipeptides and conducted screening for dipeptides as salt taste enhancers. Dipeptides were synthesized using TabS, an L-amino acid ligase (Lal) from Pseudomonas syringae NBRC14081. Six kinds of amino acids, which were easily released by the hydrolysis of proteins or peptides, reacted with 20 proteogenic amino acids, and the reaction mixtures were evaluated using sensory evaluation. In the first screening, the reaction mixture or L-Leu-L-Ser, a known salt taste enhancing dipeptide, was added to a salt solution containing ATP and panelists judged the salt taste intensities. In the second screening, the reaction mixture or residual substrate amino acids was added to a salt solution containing ATP and subjected to sensory evaluation. L-Met-Gly was identified as a candidate salt taste enhancer. In addition to sensory evaluation, the salt taste enhancing effect of L-Met-Gly was evaluated using a taste sensor. Taste sensor analysis showed that L-Met-Gly had a salt taste enhancing effect, and the relative sensor response for L-Met-Gly was equal to or higher than that for L-Leu-L-Ser. This is the first report that L-Met-Gly is a salt taste enhancing dipeptide. Furthermore, we propose that the screening method using reaction mixtures of Lal is applicable for the taste evaluation of other dipeptides.

CYP199A2, a member of the cytochrome P450 family, is a monooxygenase that specializes in the oxidation of aromatic carboxylic acids. The crystal structure of CYP199A2 determined by Bell et al. (J. Mol. Biol., 383, 561-574, 2008) suggested that the S97 and S247 residues conferred the substrate specificity on this enzyme through interaction between the hydroxy side chains of these Ser residues and the carboxy group of the substrates. In this study, we attempted to design and construct CYP199A2 mutants that recognize hydroxy aromatic compounds as substrates by protein engineering. We speculated that substitution of the S97 and 5247 residues with acidic amino acids Asp and Glu, which have carboxy side chains, would provide CYP199A2 mutants that recognize hydroxy aromatic compounds instead of aromatic carboxylic acids. The S97 and S247 residues were substituted with Asp and Glu using site-directed mutagenesis. In whole-cell assays with p-methylbenzylalcohol and phenol as hydroxy aromatic substrates, the S247D mutant regioselectively oxidized these compounds to 1,4-benzenedimethanol and hydroquinone, respectively, although the wild-type enzyme exhibited no oxidation activity for these compounds. Furthermore, the S97D, S247D, and S247E mutants acquired oxidation activity for p-cresol. Especially, the S247D mutant rapidly oxidized p-cresol; the whole cells expressing the S247D mutant completely converted 1 HIM p-cresol to p-hydroxybenzylalcohol in only 30 min. These results also clearly demonstrate that S97 and S247 are important residues that control the substrate specificity of CYP199A2. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.

CYP199A2, a member of the cytochrome P450 family, is a monooxygenase that specializes in the oxidation of aromatic carboxylic acids. The crystal structure of CYP199A2 determined by Bell et al. (J. Mol. Biol., 383, 561-574, 2008) suggested that the S97 and S247 residues conferred the substrate specificity on this enzyme through interaction between the hydroxy side chains of these Ser residues and the carboxy group of the substrates. In this study, we attempted to design and construct CYP199A2 mutants that recognize hydroxy aromatic compounds as substrates by protein engineering. We speculated that substitution of the S97 and S247 residues with acidic amino acids Asp and Glu, which have carboxy side chains, would provide CYP199A2 mutants that recognize hydroxy aromatic compounds instead of aromatic carboxylic acids. The S97 and S247 residues were substituted with Asp and Glu using site-directed mutagenesis. In whole-cell assays with p-methylbenzylalcohol and phenol as hydroxy aromatic substrates, the S247D mutant regioselectively oxidized these compounds to 1,4-benzenedimethanol and hydroquinone, respectively, although the wild-type enzyme exhibited no oxidation activity for these compounds. Furthermore, the S97D, S247D, and S247E mutants acquired oxidation activity for p-cresol. Especially, the S247D mutant rapidly oxidized p-cresol; the whole cells expressing the S247D mutant completely converted 1 mM p-cresol to p-hydroxybenzylalcohol in only 30 min. These results also clearly demonstrate that S97 and S247 are important residues that control the substrate specificity of CYP199A2.

Vanillin is one of the most widely used flavor compounds in the world as well as a promising versatile building block. The biotechnological production of vanillin from plant-derived ferulic acid has attracted much attention as a new alternative to chemical synthesis. One limitation of the known metabolic pathway to vanillin is its requirement for expensive coenzymes. Here, we developed a novel route to vanillin from ferulic acid that does not require any coenzymes. This artificial pathway consists of a coenzyme-independent decarboxylase and a coenzyme-independent oxygenase. When Escherichia coli cells harboring the decarboxylase/oxygenase cascade were incubated with ferulic acid, the cells efficiently synthesized vanillin (8.0 mM, 1.2 gL(-1)) via 4-vinylguaiacol in one pot, without the generation of any detectable aromatic by-products. The efficient method described here might be applicable to the synthesis of other high-value chemicals from plant-derived aromatics.

We evaluated the substrate specificities of four proline cis-selective hydroxylases toward the efficient synthesis of proline derivatives. In an initial evaluation, 15 proline-related compounds were investigated as substrates. In addition to L-proline and L-pipecolinic acid, we found that 3,4-dehydro-L-proline, L-azetidine-2-carboxylic acid, cis-3-hydroxy-L-proline, and L-thioproline were also oxygenated. Subsequently, the product structures were determined, revealing cis-3,4-epoxy-L-proline, cis-3-hydroxy-L-azetidine-2-carboxylic acid, and 2,3-cis-3,4-cis-3,4-dihydroxy-L-proline.

Piceatannol, a valuable biologically active stilbene derivative, was efficiently synthesized from resveratrol. Whole-cell catalysis with HpaBC monooxygenase enabled the regioselective hydroxylation of resveratrol to produce 23 mM (5.2 g L-1) of piceatannol. (C) 2014 Elsevier Ltd. All rights reserved.

4-Hydroxyphenylacetate 3-hydroxylases (HPAHs) of the two-component flavin-dependent monooxygenase family are attractive enzymes that possess the catalytic potential to synthesize valuable ortho-diphenol compounds from simple monophenol compounds. In this study, we investigated the catalytic activity of HPAH from Pseudomonas aeruginosa strain PAO1 toward cinnamic acid derivatives. We prepared Escherichia coli cells expressing the hpaB gene encoding the monooxygenase component and the hpaC gene encoding the oxidoreductase component. E. coli cells expressing HpaBC exhibited no or very low oxidation activity toward cinnamic acid, o-coumaric acid, and m-coumaric acid, whereas they rapidly oxidized p-coumaric acid to caffeic acid. Interestingly, after p-coumaric acid was almost completely consumed, the resulting caffeic acid was further oxidized to 3,4,5-trihydroxycinnamic acid. In addition, HpaBC exhibited oxidation activity toward 3-(4-hydroxyphenyl)propanoic acid, ferulic acid, and coniferaldehyde to produce the corresponding ortho-diphenols. We also investigated a flask-scale production of caffeic acid from p-coumaric acid as the model reaction for HpaBC-catalyzed syntheses of hydroxycinnamic acids. Since the initial concentrations of the substrate p-coumaric acid higher than 40 mM markedly inhibited its HpaBC-catalyzed oxidation, the reaction was carried out by repeatedly adding 20 mM of this substrate to the reaction mixture. Furthermore, by using the HpaBC whole-cell catalyst in the presence of glycerol, our experimental setup achieved the high-yield production of caffeic acid, i.e., 56.6 mM (10.2 g/L) within 24 h. These catalytic activities of HpaBC will provide an easy and environment-friendly synthetic approach to hydroxycinnamic acids.

Microbial hydroxylases were screened for the capacity to effect direct hydroxylation of proline and pipecolinic acid, based on genomic information. Of the eight candidates screened, 2-oxoglutaratedependent hydroxylase from Streptosporangium roseum NBRC 3776T and aspartyl/asparaginyl p-hydroxylase from Catenulispora acidiphila NBRC 102108T showed both proline and pipecolinic acid hydroxylation activities. In the case of L-proline hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-L-proline and cis-4-hydroxy-L-proline, and cis-4-hydroxy-L-proline was preferentially produced. In the case of L-pipecolinic acid hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-L-pipecolinic acid and cis-5-hydroxy-L-pipecolinic acid. While the former enzyme preferentially produced cis-3-hydroxy-L-pipecolinic acid, the latter enzyme preferentially produced cis-5-hydroxy-L-pipecolinic acid. (C) 2013 Elsevier B.V. All rights reserved.

:Vanillin is one of the most widely used flavor compounds in the world as well as a promising versatile building block. The biotechnological production of vanillin from plant-derived ferulic acid has attracted much attention as a new alternative to chemical synthesis. One limitation of the known metabolic pathway to vanillin is its requirement for expensive coenzymes. Here, we developed a novel route to vanillin from ferulic acid that does not require any coenzymes. This artificial pathway consists of a coenzyme-independent decarboxylase and a coenzyme-independent oxygenase. When Escherichia coli cells harboring the decarboxylase/oxygenase cascade were incubated with ferulic acid, the cells efficiently synthesized vanillin (8.0 mM, 1.2 g L(-1) ) via 4-vinylguaiacol in one pot, without the generation of any detectable aromatic by-products. The efficient method described here might be applicable to the synthesis of other high-value chemicals from plant-derived aromatics.

:We evaluated the substrate specificities of four proline cis-selective hydroxylases toward the efficient synthesis of proline derivatives. In an initial evaluation, 15 proline-related compounds were investigated as substrates. In addition to l-proline and l-pipecolinic acid, we found that 3,4-dehydro-l-proline, l-azetidine-2-carboxylic acid, cis-3-hydroxy-l-proline, and l-thioproline were also oxygenated. Subsequently, the product structures were determined, revealing cis-3,4-epoxy-l-proline, cis-3-hydroxy-l-azetidine-2-carboxylic acid, and 2,3-cis-3,4-cis-3,4-dihydroxy-l-proline.

:Microbial hydroxylases were screened for the capacity to effect direct hydroxylation of proline and pipecolinic acid, based on genomic information. Of the eight candidates screened, 2-oxoglutarate-dependent hydroxylase from Streptosporangium roseum NBRC 3776(T) and aspartyl/asparaginyl β-hydroxylase from Catenulispora acidiphila NBRC 102108(T) showed both proline and pipecolinic acid hydroxylation activities. In the case of l-proline hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-l-proline and cis-4-hydroxy-l-proline, and cis-4-hydroxy-l-proline was preferentially produced. In the case of l-pipecolinic acid hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-l-pipecolinic acid and cis-5-hydroxy-l-pipecolinic acid. While the former enzyme preferentially produced cis-3-hydroxy-l-pipecolinic acid, the latter enzyme preferentially produced cis-5-hydroxy-l-pipecolinic acid.

:4-Hydroxyphenylacetate 3-hydroxylases (HPAHs) of the two-component flavin-dependent monooxygenase family are attractive enzymes that possess the catalytic potential to synthesize valuable ortho-diphenol compounds from simple monophenol compounds. In this study, we investigated the catalytic activity of HPAH from Pseudomonas aeruginosa strain PAO1 toward cinnamic acid derivatives. We prepared Escherichia coli cells expressing the hpaB gene encoding the monooxygenase component and the hpaC gene encoding the oxidoreductase component. E. coli cells expressing HpaBC exhibited no or very low oxidation activity toward cinnamic acid, o-coumaric acid, and m-coumaric acid, whereas they rapidly oxidized p-coumaric acid to caffeic acid. Interestingly, after p-coumaric acid was almost completely consumed, the resulting caffeic acid was further oxidized to 3,4,5-trihydroxycinnamic acid. In addition, HpaBC exhibited oxidation activity toward 3-(4-hydroxyphenyl)propanoic acid, ferulic acid, and coniferaldehyde to produce the corresponding ortho-diphenols. We also investigated a flask-scale production of caffeic acid from p-coumaric acid as the model reaction for HpaBC-catalyzed syntheses of hydroxycinnamic acids. Since the initial concentrations of the substrate p-coumaric acid higher than 40 mM markedly inhibited its HpaBC-catalyzed oxidation, the reaction was carried out by repeatedly adding 20 mM of this substrate to the reaction mixture. Furthermore, by using the HpaBC whole-cell catalyst in the presence of glycerol, our experimental setup achieved the high-yield production of caffeic acid, i.e., 56.6 mM (10.2 g/L) within 24 h. These catalytic activities of HpaBC will provide an easy and environment-friendly synthetic approach to hydroxycinnamic acids.

Bacterial binuclear iron monooxygenases play numerous physiological roles in oxidative metabolism. Monooxygenases of this type found in actinomycetes also catalyze various useful reactions and have attracted much attention as oxidation biocatalysts. However, difficulties in expressing these multicomponent monooxygenases in heterologous hosts, particularly in Escherichia coli, have hampered the development of engineered oxidation biocatalysts. Here, we describe a strategy to functionally express the mycobacterial binuclear iron monooxygenase MimABCD in Escherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the mimABCD gene expression in E. coli revealed that the oxygenase components MimA and MimC were insoluble. Furthermore, although the reductase MimB was expressed at a low level in the soluble fraction of E. coli cells, a band corresponding to the coupling protein MimD was not evident. This situation rendered the transformed E. coli cells inactive. We found that the following factors are important for functional expression of MimABCD in E. coli: coexpression of the specific chaperonin MimG, which caused MimA and MimC to be soluble in E. coli cells, and the optimization of the mimD nucleotide sequence, which led to efficient expression of this gene product. These two remedies enabled this multicomponent monooxygenase to be actively expressed in E. coli. The strategy described here should be generally applicable to the E. coli expression of other actinomycetous binuclear iron monooxygenases and related enzymes and will accelerate the development of engineered oxidation biocatalysts for industrial processes.

Functional peptides are expected to be beneficial compounds that improve our quality of life. To address the growing need for functional peptides, we have examined peptide synthesis by using microbial enzymes. L-Amino acid ligase (Lal) catalyzes the condensation of unprotected amino acids in an ATP-dependent manner and is applicable to fermentative production. Hence, Lal is a promising enzyme to achieve cost-effective synthesis. To obtain a Lal with novel substrate specificity, we focused on the putative Lal involved in the biosynthesis of the dipeptidic phytotoxin designated tabtoxin. The tabS gene was cloned from Pseudomonas syringae NBRC14081 and overexpressed in Escherichia coli cells. The recombinant TabS protein produced showed the broadest substrate specificity of any known Lal; it detected 136 of 231 combinations of amino acid substrates when dipeptide synthesis was examined. In addition, some new substrate specificities were identified and unusual amino acids, e.g., L-pipecolic acid, hydroxy-L-proline, and beta-alanine, were found to be acceptable substrates. Furthermore, kinetic analysis and monitoring of the reactions over a short time revealed that TabS showed distinct substrate selectivity at the N and C termini, which made it possible to specifically synthesize a peptide without by-products such as homopeptides and heteropeptides with the reverse sequence. TabS specifically synthesized the following functional peptides, including their precursors: L-arginyl-L-phenylalanine (antihypertensive effect; yield, 62%), L-leucyl-L-isoleucine (antidepressive effect; yield, 77%), L-glutaminyl-L-tryptophan (precursor of L-glutamyl-L-tryptophan, which has antiangiogenic activity; yield, 54%), L-leucyl-L-serine (enhances saltiness; yield, 83%), and L-glutaminyl-L-threonine (precursor of L-glutamyl-L-threonine, which enhances saltiness; yield, 96%). Furthermore, our results also provide new insights into tabtoxin biosynthesis.

The proton motive force (PMF) is bio-energetically important for various cellular reactions to occur. We developed PMF-photogenerating mitochondria in cultured mammalian cells. An archaebacterial rhodopsin, delta-rhodopsin, which is a light-driven proton pump derived from Haloterrigena turkmenica, was expressed in the mitochondria of CHO-K1 cells. The constructed stable CHO-K1 cell lines showed suppression of cell death induced by rotenone, a pesticide that inhibits mitochondrial complex I activity involved in PMF generation through the electron transport chain. Delta-rhodopsin was also introduced into the mitochondria of human neuroblastoma SH-SY5Y cells. The constructed stable SH-SY5Y cell lines showed suppression of dopaminergic neuronal cell death induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an inducer of Parkinson's disease models, which acts through inhibition of complex I activity. These results suggest that the light-activated proton pump functioned as a PMF generator in the mitochondria of mammalian cells, and suppressed cell death induced by inhibition of respiratory PMF generation.

Dipeptides exhibit unique physiological functions and physical properties, e.g., L-aspartyl-L-phenylalanine-methyl. ester (Asp-Phe-OMe, aspartame) as an artificial sweetener, and functional studies of peptides have been carried out in various fields. Therefore, to establish a manufacturing process for the useful dipeptides, we investigated its enzymatic synthesis by utilizing an L-amino acid ligase (Lal), which catalyzes dipeptide synthesis in an ATP-dependent manner. Many Lals were obtained, but the Lals recognizing acidic amino acids as N-terminal substrates have not been identified. To increase the variety of dipeptides that are enzymatically synthesized, we proposed a two-step synthesis: Asn-Xaa and Gln-Xaa (Asn, L-asparagine; Gln, L-glutamine; and Xaa, arbitrary amino acids) synthesized by Lals were continuously deamidated by a novel amidase, yielding Asp-Xaa and Glu-Xaa (Asp, L-aspartic add; and Glu, L-glutamic acid). We searched for amidases that specifically deamidate the N-terminus of Asn or Gln in dipeptides since none have been previously reported. We focused on the protein N-terminal amidase from Saccharomyces cerevisiae (NTA1), and assayed its activity toward dipeptides. Our findings showed that NTA1 deamidated L-asparaginyl-L-valine (Asn-Val) and L-glutaminyl-glycine (Gln-Gly), but did not deamidate L-valyl-L-asparagine and L-alanyl-L-glutamine, suggesting that this deamidation activity is N-terminus specific. The specific activity toward Asn-Val and Gln-Gly were 190 +/- 30 nmol min(-1) mg(-1) protein and 136 +/- 6 nmol min(-1) mg(-1) protein. Additionally, we examined some characteristics of NTA1. Acidic dipeptide synthesis was examined by a combination of Lals and NTA1, resulting in the synthesis of 12 kinds of Asp-Xaa, including Asp-Phe, a precursor of aspartame, and 11 kinds of Glu-Xaa. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

The mimABCD gene clusters in Mycobacterium smegmatis strain mc2155 and Mycobacterium goodii strain 12523 encode binuclear iron monooxygenases that oxidize propane and phenol. In this study, we attempted to express each mimABCD gene cluster in a heterologous host. The actinomycetous strain Rhodococcus opacus B-4, which is phylogenetically close to Mycobacterium, was selected as the host. Each mimABCD gene cluster was cloned into the RhodococcusEscherichia coli shuttle vector, pTip-QC2, and then introduced into R. opacus cells. Although whole-cell assays were performed with phenol as a substrate, the transformed R. opacus cells did not oxidize this substrate. SDS/PAGE analysis revealed that the oxygenase large subunit MimA was expressed in the insoluble fraction of R. opacus cells. We found that a gene designated mimG, which lies downstream of mimABCD, exhibits similarity in the amino acid sequence of its product with the products of genes encoding the chaperonin GroEL. When the mimG gene was cloned and coexpressed with each mimABCD gene cluster in R. opacus strain B-4, this host successfully acquired oxidation activity towards phenol. SDS/PAGE and western blotting analyses demonstrated that MimA was clearly soluble when in the presence of MimG. These results indicated that MimG played essential roles in the productive folding of MimA, and that the resulting soluble MimA protein led to the active expression of MimABCD.

:5-Hydroxy-l-tryptophan (5-HTP) is a naturally occurring aromatic amino acid present in the seeds of the African plant Griffonia simplicifolia. Although 5-HTP has therapeutic effects in various symptoms, efficient method of producing 5-HTP has not been established. In this study, we developed a novel cofactor regeneration process to achieve enhanced synthesis of 5-HTP by using modified l-phenylalanine 4-hydroxylase of Chromobacterium violaceum. For the synthesis of 5-HTP using Escherichia coli whole cell bioconversion, l-tryptophan and 5-HTP degradation by E. coli endogenous catabolic enzymes should be considered. The tryptophanase gene was disrupted using the λ red recombination system, since tryptophanase is postulated as an initial enzyme for the degradation of l-tryptophan and 5-HTP in E. coli. For regeneration of the cofactor pterin, we screened and investigated several key enzymes, including dihydropteridine reductase from E. coli, glucose dehydrogenase from Bacillus subtilis, and pterin-4α-carbinolamine dehydratase from Pseudomonas syringae. Genes encoding these three enzymes were overexpressed in an E. coli tryptophanase-deficient host, resulting in the synthesis of 0.74 mM 5-HTP in the presence of 0.1 mM pterin and the synthesis of 0.07 mM 5-HTP in the absence of regeneration of pterin. These results clearly indicated the successful regeneration of pterin. Following optimization of the reaction conditions, 2.5 mM 5-HTP was synthesized with cofactor regeneration, while 0.8 mM 5-HTP was recovered without cofactor regeneration under the same reaction conditions, suggesting that the principle described here provides a new method for cofactor regeneration.

:Bacterial binuclear iron monooxygenases play numerous physiological roles in oxidative metabolism. Monooxygenases of this type found in actinomycetes also catalyze various useful reactions and have attracted much attention as oxidation biocatalysts. However, difficulties in expressing these multicomponent monooxygenases in heterologous hosts, particularly in Escherichia coli, have hampered the development of engineered oxidation biocatalysts. Here, we describe a strategy to functionally express the mycobacterial binuclear iron monooxygenase MimABCD in Escherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the mimABCD gene expression in E. coli revealed that the oxygenase components MimA and MimC were insoluble. Furthermore, although the reductase MimB was expressed at a low level in the soluble fraction of E. coli cells, a band corresponding to the coupling protein MimD was not evident. This situation rendered the transformed E. coli cells inactive. We found that the following factors are important for functional expression of MimABCD in E. coli: coexpression of the specific chaperonin MimG, which caused MimA and MimC to be soluble in E. coli cells, and the optimization of the mimD nucleotide sequence, which led to efficient expression of this gene product. These two remedies enabled this multicomponent monooxygenase to be actively expressed in E. coli. The strategy described here should be generally applicable to the E. coli expression of other actinomycetous binuclear iron monooxygenases and related enzymes and will accelerate the development of engineered oxidation biocatalysts for industrial processes.

:Functional peptides are expected to be beneficial compounds that improve our quality of life. To address the growing need for functional peptides, we have examined peptide synthesis by using microbial enzymes. l-Amino acid ligase (Lal) catalyzes the condensation of unprotected amino acids in an ATP-dependent manner and is applicable to fermentative production. Hence, Lal is a promising enzyme to achieve cost-effective synthesis. To obtain a Lal with novel substrate specificity, we focused on the putative Lal involved in the biosynthesis of the dipeptidic phytotoxin designated tabtoxin. The tabS gene was cloned from Pseudomonas syringae NBRC14081 and overexpressed in Escherichia coli cells. The recombinant TabS protein produced showed the broadest substrate specificity of any known Lal; it detected 136 of 231 combinations of amino acid substrates when dipeptide synthesis was examined. In addition, some new substrate specificities were identified and unusual amino acids, e.g., l-pipecolic acid, hydroxy-l-proline, and β-alanine, were found to be acceptable substrates. Furthermore, kinetic analysis and monitoring of the reactions over a short time revealed that TabS showed distinct substrate selectivity at the N and C termini, which made it possible to specifically synthesize a peptide without by-products such as homopeptides and heteropeptides with the reverse sequence. TabS specifically synthesized the following functional peptides, including their precursors: l-arginyl-l-phenylalanine (antihypertensive effect; yield, 62%), l-leucyl-l-isoleucine (antidepressive effect; yield, 77%), l-glutaminyl-l-tryptophan (precursor of l-glutamyl-l-tryptophan, which has antiangiogenic activity; yield, 54%), l-leucyl-l-serine (enhances saltiness; yield, 83%), and l-glutaminyl-l-threonine (precursor of l-glutamyl-l-threonine, which enhances saltiness; yield, 96%). Furthermore, our results also provide new insights into tabtoxin biosynthesis.

:Dipeptides exhibit unique physiological functions and physical properties, e.g., l-aspartyl-l-phenylalanine-methyl ester (Asp-Phe-OMe, aspartame) as an artificial sweetener, and functional studies of peptides have been carried out in various fields. Therefore, to establish a manufacturing process for the useful dipeptides, we investigated its enzymatic synthesis by utilizing an l-amino acid ligase (Lal), which catalyzes dipeptide synthesis in an ATP-dependent manner. Many Lals were obtained, but the Lals recognizing acidic amino acids as N-terminal substrates have not been identified. To increase the variety of dipeptides that are enzymatically synthesized, we proposed a two-step synthesis: Asn-Xaa and Gln-Xaa (Asn, l-asparagine; Gln, l-glutamine; and Xaa, arbitrary amino acids) synthesized by Lals were continuously deamidated by a novel amidase, yielding Asp-Xaa and Glu-Xaa (Asp, l-aspartic acid; and Glu, l-glutamic acid). We searched for amidases that specifically deamidate the N-terminus of Asn or Gln in dipeptides since none have been previously reported. We focused on the protein N-terminal amidase from Saccharomyces cerevisiae (NTA1), and assayed its activity toward dipeptides. Our findings showed that NTA1 deamidated l-asparaginyl-l-valine (Asn-Val) and l-glutaminyl-glycine (Gln-Gly), but did not deamidate l-valyl-l-asparagine and l-alanyl-l-glutamine, suggesting that this deamidation activity is N-terminus specific. The specific activity toward Asn-Val and Gln-Gly were 190 ± 30 nmol min(-1) mg(-1)·protein and 136 ± 6 nmol min(-1) mg(-1)·protein. Additionally, we examined some characteristics of NTA1. Acidic dipeptide synthesis was examined by a combination of Lals and NTA1, resulting in the synthesis of 12 kinds of Asp-Xaa, including Asp-Phe, a precursor of aspartame, and 11 kinds of Glu-Xaa.

:The mimABCD gene clusters in Mycobacterium smegmatis strain mc(2) 155 and Mycobacterium goodii strain 12523 encode binuclear iron monooxygenases that oxidize propane and phenol. In this study, we attempted to express each mimABCD gene cluster in a heterologous host. The actinomycetous strain Rhodococcus opacus B-4, which is phylogenetically close to Mycobacterium, was selected as the host. Each mimABCD gene cluster was cloned into the Rhodococcus-Escherichia coli shuttle vector, pTip-QC2, and then introduced into R. opacus cells. Although whole-cell assays were performed with phenol as a substrate, the transformed R. opacus cells did not oxidize this substrate. SDS/PAGE analysis revealed that the oxygenase large subunit MimA was expressed in the insoluble fraction of R. opacus cells. We found that a gene designated mimG, which lies downstream of mimABCD, exhibits similarity in the amino acid sequence of its product with the products of genes encoding the chaperonin GroEL. When the mimG gene was cloned and coexpressed with each mimABCD gene cluster in R. opacus strain B-4, this host successfully acquired oxidation activity towards phenol. SDS/PAGE and western blotting analyses demonstrated that MimA was clearly soluble when in the presence of MimG. These results indicated that MimG played essential roles in the productive folding of MimA, and that the resulting soluble MimA protein led to the active expression of MimABCD.

5-Hydroxy-2-adamantanone is a versatile starting material for the synthesis of various adamantane derivatives. In this study, we investigated the biocatalytic production of 5-hydroxy-2-adamantanone using P450cam monooxygenase coupled with NADH regeneration. We constructed Escherichia coli cells that expressed P450cam and its redox partners, putidaredoxin and putidaredoxin reductase, and cells that co-expressed this P450cam multicomponent system with a glucose dehydrogenase (Gdh) to regenerate NADH using glucose. Two types of cells - wet cells that did not receive any treatment after washing with glycerol-containing buffer, and freeze-dried cells that were lyophilized after the washing - were prepared as whole-cell catalysts. When wet cells were reacted with 2-adamantanone, E. coli cells expressing only the P450cam multicomponent system efficiently produced 5-hydroxy-2-adamantanone in the presence of glucose. However, the co-expression of this P450cam system with Gdh did not further enhance the amount of this product. These results indicate that enough amounts of NADH for P450cam catalysis would be supplied by endogenous glucose metabolism in the E. coli host. In contrast, when freeze-dried cells were used, only the cells co-expressing the P450cam multicomponent system with Gdh efficiently catalyzed the oxidation in the presence of glucose. These results suggest that the exogenous Gdh compensated loss of NADH regeneration by the endogenous glucose metabolism that would be damaged by the lyophilization process. Furthermore, we attempted to produce 5-hydroxy-2-adamantanone with repeated additions of the substrate using wet cells expressing only the P450cam multicomponent system and freeze-dried cells co-expressing this P450cam system with Gdh. These whole-cell catalysts attained high-yield production
the wet cells and the freeze-dried cells produced 36 mM (5.9 g/l) and 21 mM (3.5 g/l) of 5-hydroxy-2-adamantanone, respectively. © 2013 Elsevier B.V.

Microorganisms are capable of producing a wide variety of biopolymers. Homopoly(amino acid)s and homooligo(amino acid)s, which are made up of only a single type of amino acid, are relatively rare; in fact, only two homopoly(amino acid)s have been known to occur in nature: poly(epsilon-L-lysine) (epsilon-PL) and poly(gamma-glutamic acid) (gamma-PGA). Bacterial enzymes that produce homooligo(amino acid)s, such as L-beta-lysine-, L-valine-, L-leucine-, L-isoleucine-, L-methionine-, and L-glutamic acid-oligopeptides and poly(alpha-L-glutamic acid) (alpha-PGA) have recently been identified, as well as epsilon-PL synthetase and gamma-PGA synthetase. This article reviews the current knowledge about these unique enzymes producing homopoly(amino acid)s and homooligo(amino acid)s.

The proline analogue cis-4-hydroxy-l-proline (CHOP), which inhibits the biosynthesis of collagen, has been clinically evaluated as an anticancer drug, but its water solubility and low molecular weight limits its therapeutic potential since it is rapidly excreted. In addition, CHOP is too toxic to be practical as an anticancer drug, due primarily to its systematic effects on noncollagen proteins. To promote CHOP's retention in blood and/or to decrease its toxicity, N-acetylation of CHOP might be a novel approach as a prodrug. The present study was designed to achieve the microbial production of N-acetyl CHOP from l-proline by coexpression of l-proline cis-4-hydroxylases converting l-proline into CHOP (SmP4H) from the Rhizobium Sinorhizobium meliloti and N-acetyltransferase converting CHOP into N-acetyl CHOP (Mpr1) from the yeast Saccharomyces cerevisiae. We constructed a coexpression plasmid harboring both the SmP4H and Mpr1 genes and introduced it into Escherichia coli BL21(DE3) or its l-proline oxidase gene-disrupted (ΔputA) strain. M9 medium containing l-proline produced more N-acetyl CHOP than LB medium containing l-proline. E. coli ΔputA cells accumulated l-proline (by approximately 2-fold) compared to that in wild-type cells, but there was no significant difference in CHOP production between wild-type and ΔputA cells. The addition of NaCl and l-ascorbate resulted in a 2-fold increase in N-acetyl CHOP production in the l-proline-containing M9 medium. The highest yield of N-acetyl CHOP was achieved at 42 h cultivation in the optimized medium. Five unknown compounds were detected in the total protein reaction, probably due to the degradation of N-acetyl CHOP. Our results suggest that weakening of the degradation or deacetylation pathway improves the productivity of N-acetyl CHOP. © 2012 Springer-Verlag.

5-Hydroxy-L-tryptophan (5-HTP) is a naturally occurring aromatic amino acid present in the seeds of the African plant Griffonia simplicifolia. Although 5-HTP has therapeutic effects in various symptoms, efficient method of producing 5-HTP has not been established. In this study, we developed a novel cofactor regeneration process to achieve enhanced synthesis of 5-HTP by using modified L-phenylalanine 4-hydroxylase of Chromobacterium violaceum. For the synthesis of 5-HTP using Escherichia coli whole cell bioconversion, L-tryptophan and 5-HTP degradation by E. coli endogenous catabolic enzymes should be considered. The tryptophanase gene was disrupted using the λ red recombination system, since tryptophanase is postulated as an initial enzyme for the degradation of L-tryptophan and 5-HTP in E. coli. For regeneration of the cofactor pterin, we screened and investigated several key enzymes, including dihydropteridine reductase from E. coli, glucose dehydrogenase from Bacillus subtilis, and pterin-4α-carbinolamine dehydratase from Pseudomonas syringae. Genes encoding these three enzymes were overexpressed in an E. coli tryptophanase-deficient host, resulting in the synthesis of 0.74 mM 5-HTP in the presence of 0.1 mM pterin and the synthesis of 0.07 mM 5-HTP in the absence of regeneration of pterin. These results clearly indicated the successful regeneration of pterin. Following optimization of the reaction conditions, 2.5 mM 5-HTP was synthesized with cofactor regeneration, while 0.8 mM 5-HTP was recovered without cofactor regeneration under the same reaction conditions, suggesting that the principle described here provides a new method for cofactor regeneration. © 2013 Hara and Kino.

L -Amino-acid ligases (LALs) are enzymes which catalyze the formation of dipeptides by linking two l-amino acids. Although many dipeptides are known and expected to have medical and nutritional benefits, their practical use has been limited owing to their low availability and high expense. LALs are potentially desirable tools for the efficient production of dipeptides; however, the molecular basis of substrate recognition by LAL has not yet been sufficiently elucidated for the design of ideal LALs for the desired dipeptides. This report presents the crystal structure of the LAL BL00235 derived from Bacillus licheniformis NBRC 12200 determined at 1.9 angstrom resolution using the multi-wavelength anomalous dispersion method. The overall structure of BL00235 is fairly similar to that of YwfE, the only LAL with a known structure, but the structure around the catalytic site contains some significant differences. Detailed structural comparison of BL00235 with YwfE sheds some light on the molecular basis of the substrate specificities.

Scope We found that a dipeptide, Arg-Phe (RF), had vasorelaxing activity in mesenteric artery isolated from spontaneously hypertensive rats (SHRs) (EC50 = 580 nM). We then investigated its mechanism of action, and elucidated its physiological functions. Methods and results Vasorelaxing activities of RF-related peptides were tested. The retro-sequence dipeptide FR was inactive, suggesting that the RF sequence is important for a potent vasorelaxing effect. RA and AF were also inactive. RF-nh2 had vasorelaxing activity, implying that the C-terminal amidation of RF is tolerated. Nitric oxide (NO) and prostaglandins (PGs) are known to be vasorelaxing factors; however, the vasorelaxing activity of RF was inhibited by neither NG-nitro-l-arginine methyl ester (l-NAME), an NO synthase inhibitor, nor indomethacin, a COX inhibitor. Interestingly, the activity was blocked by lorglumide, an antagonist of the cholecystokinin (CCK)1 receptor; however, RF had no affinity for CCK receptors, suggesting that RF stimulates CCK release. Orally administered RF decreased blood pressure in SHRs, and this antihypertensive activity was also blocked by a CCK1 antagonist. RF had CCK-like suppressive effects on food intake and gastrointestinal transit. RF increased intracellular Ca2+ flux and CCK release in enteroendocrine STC-1 cells. Conclusion A novel CCK-dependent vasorelaxing RF decreases both blood pressure and food intake.

Caffeic acid is a biologically active molecule that has various beneficial properties, including antioxidant, anticancer, and anti-inflammatory activities. In this study, we explored the catalytic potential of a bacterial cytochrome P450, CYP199A2, for the biotechnological production of caffeic acid. When the CYP199A2 enzyme was reacted with p-coumaric acid, it stoichiometrically produced caffeic acid. The crystal structure of CYP199A2 shows that Phe at position 185 is situated directly above, and only 6.35 angstrom from, the heme iron. This F185 residue was replaced with hydrophobic or hydroxylated amino acids using site-directed mutagenesis to create mutants with novel and improved catalytic properties. In whole-cell assays with the known substrate of CYP199A2, 2-naphthoic acid, only the wild-type enzyme hydroxylated 2-naphthoic acid at the C-7 and C-8 positions, whereas all of the active F185 mutants exhibited a preference for C-5 hydroxylation. Interestingly, several F185 mutants (F185V, F185L, F1851, F185G, and F185A mutants) also acquired the ability to hydroxylate cinnamic acid, which was not hydroxylated by the wild-type enzyme. These results demonstrate that F185 is an important residue that controls the regioselectivity and the substrate specificity of CYP199A2. Furthermore, Escherichia coli cells expressing the F185L mutant exhibited 5.5 times higher hydroxylation activity for p-coumaric acid than those expressing the wild-type enzyme. By using the F185L whole-cell catalyst, the production of caffeic acid reached 15 mM (2.8 g/liter), which is the highest level so far attained in biotechnological production of this compound.

The alpha-glucosyl transfer enzyme (XgtA), a novel type alpha-glucosidase produced by Xanthomonas campestris WU-9701, was purified from the cell-free extract and characterized. The molecular weight of XgtA is estimated to be 57 kDa by SOS-PAGE and 60 kDa by gel filtration, indicating that XgtA is a monomeric enzyme. Kinetic properties of XgtA were determined for alpha-glucosyl transfer and maltose-hydrolyzing activities using maltose as the alpha-glucosyl donor, and if necessary, hydroquinone as the acceptor. The V-max value for alpha-glucosyl transfer activity was 1.3 x 10(-2) (mM/s); this value was 3.9-fold as much as that for maltose-hydrolyzing activity. XgtA neither produced maltooligosaccharides nor hydrolyzed sucrose. The gene encoding XgtA that contained a 1614-bp open reading frame was cloned, identified, and highly expressed in Escherichia coli JM109 as the host. Site-directed mutagenesis identified Asp201,Glu270, and Asp331 as the catalytic sites of XgtA, indicating that XgtA belongs to the glycoside hydrolase family 13. (C) 2012 Elsevier B.V. All rights reserved.

:Caffeic acid is a biologically active molecule that has various beneficial properties, including antioxidant, anticancer, and anti-inflammatory activities. In this study, we explored the catalytic potential of a bacterial cytochrome P450, CYP199A2, for the biotechnological production of caffeic acid. When the CYP199A2 enzyme was reacted with p-coumaric acid, it stoichiometrically produced caffeic acid. The crystal structure of CYP199A2 shows that Phe at position 185 is situated directly above, and only 6.35 Å from, the heme iron. This F185 residue was replaced with hydrophobic or hydroxylated amino acids using site-directed mutagenesis to create mutants with novel and improved catalytic properties. In whole-cell assays with the known substrate of CYP199A2, 2-naphthoic acid, only the wild-type enzyme hydroxylated 2-naphthoic acid at the C-7 and C-8 positions, whereas all of the active F185 mutants exhibited a preference for C-5 hydroxylation. Interestingly, several F185 mutants (F185V, F185L, F185I, F185G, and F185A mutants) also acquired the ability to hydroxylate cinnamic acid, which was not hydroxylated by the wild-type enzyme. These results demonstrate that F185 is an important residue that controls the regioselectivity and the substrate specificity of CYP199A2. Furthermore, Escherichia coli cells expressing the F185L mutant exhibited 5.5 times higher hydroxylation activity for p-coumaric acid than those expressing the wild-type enzyme. By using the F185L whole-cell catalyst, the production of caffeic acid reached 15 mM (2.8 g/liter), which is the highest level so far attained in biotechnological production of this compound.

The mimABCD gene cluster encodes the binuclear iron monooxygenase that oxidizes propane and phenol in Mycobacterium smegmatis strain MC2 155 and Mycobacterium goodii strain 12523. Interestingly, expression of the mimABCD gene cluster is induced by acetone. In this study, we investigated the regulator gene responsible for this acetone-responsive expression. In the genome sequence of M. smegmatis strain MC2 155, the mimABCD gene cluster is preceded by a gene designated mimR, which is divergently transcribed. Sequence analysis revealed that MimR exhibits amino acid similarity with the NtrC family of transcriptional activators, including AcxR and AcoR, which are involved in acetone and acetoin metabolism, respectively. Unexpectedly, many homologs of the mimR gene were also found in the sequenced genomes of actinomycetes. A plasmid carrying a transcriptional fusion of the intergenic region between the mimR and mimA genes with a promoterless green fluorescent protein (GFP) gene was constructed and introduced into M. smegmatis strain MC2 155. Using a GFP reporter system, we confirmed by deletion and complementation analyses that the mimR gene product is the positive regulator of the mimABCD gene cluster expression that is responsive to acetone. M. goodii strain 12523 also utilized the same regulatory system as M. smegmatis strain MC2 155. Although transcriptional activators of the NtrC family generally control transcription using the sigma(54) factor, a gene encoding the sigma(54) factor was absent from the genome sequence of M. smegmatis strain MC2 155. These results suggest the presence of a novel regulatory system in actinomycetes, including mycobacteria.

We prepared ATP photosynthetic vesicles from inside-out membranes of Escherichia coli cells that express delta-rhodopsin (a novel light-driven H ? transporter) and TF(0)F(1)-ATP synthase (a thermostable ATP synthase). These vesicles showed light-dependent ATP synthesis. Furthermore, coupling the ATP photosynthetic vesicles with an ATP-hydrolyzing hexokinase enabled light-dependent glucose consumption. The ATP photosynthetic vesicles indicate their potential to applied to light-driven ATP-regenerating bioprocess for various ATP-hydrolyzing bioproductions.

Depsipeptides are peptide-like polymers consisting of amino acids and hydroxy acids, and are expected to be new functional materials for drug-delivery systems and polymer science. In our previous study, D-alanyl-D-lactate, a type of depsipeptide, was enzymatically synthesized using D-alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) by Y207F substitution. Thereafter, in this study, further mutagenesis was introduced, based on structural comparison between TmDdl and a well-characterized D-alanine-D-alanine ligase from Escherichia coli. The S137A/Y207F mutant showed higher n-alanyl-D-lactate and lower D-alanyl-D-alanine synthesizing activity than the Y207F mutant. This suggests that substitution at the S137 residue contributes to product selectivity. Saturated mutagenesis on S137 revealed that the S137G/Y207F mutant showed the highest D-alanyl-D-lactate synthesizing activity. Moreover, the mutant showed broad substrate specificity toward D-amino acid and recognized D-lactate and D,L-isoserine as substrates. On the basis of these characteristics, various depsipeptides can be produced using S137G/Y207F-replaced TmDdl.

Poly-L-alpha-amino acids have various applications because of their biodegradable properties and biocompatibility. Microorganisms contain several enzymes that catalyze the polymerization of L-amino acids in an ATP-dependent manner, but the products from these reactions contain amide linkages at the side residues of amino acids: e.g., poly-gamma-glutamic acid, poly-epsilon-lysine, and cyanophycin. In this study, we found a novel catalytic activity of RimK, a ribosomal protein S6-modifying enzyme derived from Escherichia coli K-12. This enzyme catalyzed poly-alpha-glutamic acid synthesis from unprotected L-glutamic acid (Glu) by hydrolyzing ATP to ADP and phosphate. RimK synthesized poly-alpha-glutamic acid of various lengths; matrix-assisted laser desorption ionization-time of flight-mass spectrometry showed that a 46-mer of Glu (maximum length) was synthesized at pH 9. Interestingly, the lengths of polymers changed with changing pH. RimK also exhibited 86% activity after incubation at 55 degrees C for 15 min, thus showing thermal stability. Furthermore, peptide elongation seemed to be catalyzed at the C terminus in a stepwise manner. Although RimK showed strict substrate specificity toward Glu, it also used, to a small extent, other amino acids as C-terminal substrates and synthesized heteropeptides. In addition, RimK-catalyzed modification of ribosomal protein S6 was confirmed. The number of Glu residues added to the protein varied with pH and was largest at pH 9.5.

Mycobacterium goodii strain 12523 is an actinomycete that is able to oxidize phenol regioselectively at the para position to produce hydroquinone. In this study, we investigated the genes responsible for this unique regioselective oxidation. On the basis of the fact that the oxidation activity of M. goodii strain 12523 toward phenol is induced in the presence of acetone, we first identified acetone-induced proteins in this microorganism by two-dimensional electrophoretic analysis. The N-terminal amino acid sequence of one of these acetone-induced proteins shares 100% identity with that of the protein encoded by the open reading frame Msmeg_1971 in Mycobacterium smegmatis strain mc(2)155, whose genome sequence has been determined. Since Msmeg_1971, Msmeg_1972, Msmeg_1973, and Msmeg_1974 constitute a putative binuclear iron monooxygenase gene cluster, we cloned this gene cluster of M. smegmatis strain mc(2)155 and its homologous gene cluster found in M. goodii strain 12523. Sequence analysis of these binuclear iron monooxygenase gene clusters revealed the presence of four genes designated mimABCD, which encode an oxygenase large subunit, a reductase, an oxygenase small subunit, and a coupling protein, respectively. When the mimA gene (Msmeg_1971) of M. smegmatis strain mc(2)155, which was also found to be able to oxidize phenol to hydroquinone, was deleted, this mutant lost the oxidation ability. This ability was restored by introduction of the mimA gene of M. smegmatis strain mc(2)155 or of M. goodii strain 12523 into this mutant. Interestingly, we found that these gene clusters also play essential roles in propane and acetone metabolism in these mycobacteria.

:The mimABCD gene cluster encodes the binuclear iron monooxygenase that oxidizes propane and phenol in Mycobacterium smegmatis strain MC2 155 and Mycobacterium goodii strain 12523. Interestingly, expression of the mimABCD gene cluster is induced by acetone. In this study, we investigated the regulator gene responsible for this acetone-responsive expression. In the genome sequence of M. smegmatis strain MC2 155, the mimABCD gene cluster is preceded by a gene designated mimR, which is divergently transcribed. Sequence analysis revealed that MimR exhibits amino acid similarity with the NtrC family of transcriptional activators, including AcxR and AcoR, which are involved in acetone and acetoin metabolism, respectively. Unexpectedly, many homologs of the mimR gene were also found in the sequenced genomes of actinomycetes. A plasmid carrying a transcriptional fusion of the intergenic region between the mimR and mimA genes with a promoterless green fluorescent protein (GFP) gene was constructed and introduced into M. smegmatis strain MC2 155. Using a GFP reporter system, we confirmed by deletion and complementation analyses that the mimR gene product is the positive regulator of the mimABCD gene cluster expression that is responsive to acetone. M. goodii strain 12523 also utilized the same regulatory system as M. smegmatis strain MC2 155. Although transcriptional activators of the NtrC family generally control transcription using the σ(54) factor, a gene encoding the σ(54) factor was absent from the genome sequence of M. smegmatis strain MC2 155. These results suggest the presence of a novel regulatory system in actinomycetes, including mycobacteria.

:Depsipeptides are peptide-like polymers consisting of amino acids and hydroxy acids, and are expected to be new functional materials for drug-delivery systems and polymer science. In our previous study, D-alanyl-D-lactate, a type of depsipeptide, was enzymatically synthesized using D-alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) by Y207F substitution. Thereafter, in this study, further mutagenesis was introduced, based on structural comparison between TmDdl and a well-characterized D-alanine-D-alanine ligase from Escherichia coli. The S137A/Y207F mutant showed higher D-alanyl-D-lactate and lower D-alanyl-D-alanine synthesizing activity than the Y207F mutant. This suggests that substitution at the S137 residue contributes to product selectivity. Saturated mutagenesis on S137 revealed that the S137G/Y207F mutant showed the highest D-alanyl-D-lactate synthesizing activity. Moreover, the mutant showed broad substrate specificity toward D-amino acid and recognized D-lactate and D,L-isoserine as substrates. On the basis of these characteristics, various depsipeptides can be produced using S137G/Y207F-replaced TmDdl.

:Mycobacterium goodii strain 12523 is an actinomycete that is able to oxidize phenol regioselectively at the para position to produce hydroquinone. In this study, we investigated the genes responsible for this unique regioselective oxidation. On the basis of the fact that the oxidation activity of M. goodii strain 12523 toward phenol is induced in the presence of acetone, we first identified acetone-induced proteins in this microorganism by two-dimensional electrophoretic analysis. The N-terminal amino acid sequence of one of these acetone-induced proteins shares 100% identity with that of the protein encoded by the open reading frame Msmeg_1971 in Mycobacterium smegmatis strain mc(2)155, whose genome sequence has been determined. Since Msmeg_1971, Msmeg_1972, Msmeg_1973, and Msmeg_1974 constitute a putative binuclear iron monooxygenase gene cluster, we cloned this gene cluster of M. smegmatis strain mc(2)155 and its homologous gene cluster found in M. goodii strain 12523. Sequence analysis of these binuclear iron monooxygenase gene clusters revealed the presence of four genes designated mimABCD, which encode an oxygenase large subunit, a reductase, an oxygenase small subunit, and a coupling protein, respectively. When the mimA gene (Msmeg_1971) of M. smegmatis strain mc(2)155, which was also found to be able to oxidize phenol to hydroquinone, was deleted, this mutant lost the oxidation ability. This ability was restored by introduction of the mimA gene of M. smegmatis strain mc(2)155 or of M. goodii strain 12523 into this mutant. Interestingly, we found that these gene clusters also play essential roles in propane and acetone metabolism in these mycobacteria.

L-Amino acid ligase synthesizes various peptides from unprotected L-amino acids in an ATP-dependent manner. Known L-amino acid ligases catalyze only dipeptide synthesis, but recently we found that RizB of Bacillus subtilis NBRC 3134 catalyzes oligopeptide synthesis. In the present study, we searched for new members of the L-amino acid ligase group that catalyze oligopeptide synthesis. Several hypothetical proteins possessing the ATP-grasp motif were selected by in silico analysis. These recombinant proteins were assayed for L-amino acid ligase activity. We obtained five L-amino acid ligases showing oligopeptide synthesis activities. These proteins showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacterium adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones. We also examined some of their characteristics.

L-Amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We recently identified a new member of L-amino acid ligase, the plu1440 protein, from Photorhabdus luminescens subsp. laumondii TT01 by in silico analysis. This protein was found to synthesize dipeptides containing L-asparagine at the N-terminus, which is a novel substrate specificity. (C) 2009, The Society for Biotechnology, japan. All rights reserved.

A novel metabolic pathway was found in the yeast Trichosporon moniliiforme WU-0401 for salicylate degradation via phenol as the key intermediate. When 20 mM salicylate was used as the sole carbon source for the growth of strain WU-0401, phenol was detected as a distinct metabolite in the culture broth. Analysis of the products derived from salicylate or phenol through reactions with resting cells and a cell-free extract of strain WU-0401 indicated that salicylate is initially decarboxylated to phenol and then oxidized to catechol, followed by aromatic ring cleavage to form cis-cis muconate.

Cytochrome P450 enzymes (P450s) are able to regioselectively and stereoselectively introduce oxygen into organic compounds under mild reaction conditions. These monooxygenases in particular easily catalyze the insertion of oxygen into less reactive carbon-hydrogen bonds. Hence, P450s are of considerable interest as oxidation biocatalysts. To date, although several P450s have been discovered through screening of microorganisms and have been further genetically engineered, the substrate range of these biocatalysts is still limited to fulfill the requirements for a large number of oxidation processes. On the other hand, the recent rapid expansion in the number of reported microbial genome sequences has revealed the presence of an unexpectedly vast number of P450 genes. This large pool of naturally evolved P450s has attracted much attention as a resource for new oxidation biocatalysts. In this review, we focus on aspects of the genome mining approach that are relevant for the discovery of novel P450 biocatalysts. This approach opens up possibilities for exploitation of the catalytic potential of P450s for the preparation of a large choice of oxidation biocatalysts with a variety of substrate specificities.

CYP199A2, a bacterial P450 monooxygenase from Rhodopseudomonas palustris, was previously reported to oxidize 2-naphthoic acid and 4-ethylbenzoic acid. In this study, we examined the substrate specificity and regioselectivity of CYP199A2 towards indole- and quinolinecarboxylic acids. The CYP199A2 gene was coexpressed with palustrisredoxin gene from R. palustris and putidaredoxin reductase gene from Pseudomonas putida to provide the redox partners of CYP199A2 in Escherichia coli. Following whole-cell assays, reaction products were identified by mass spectrometry and NMR spectroscopy. CYP199A2 did not exhibit any activity towards indole and indole-3-carboxylic acid, whereas this enzyme oxidized indole-2-carboxylic acid, indole-5-carboxylic acid, and indole-6-carboxylic acid. Indole-2-carboxylic acid was converted to 5- and 6-hydroxyindole-2-carboxylic acids at a ratio of 59:41. In contrast, the indole-6-carboxylic acid oxidation generated only one product, 2-indolinone-6-carboxylic acid, at a rate of 130 mol (mol P450)(-1) min(-1). Furthermore, CYP199A2 also oxidized quinoline-6-carboxylic acid, although this enzyme did not exhibit any activity towards quinoline and its derivatives with a carboxyl group at the C-2, C-3, or C-4 positions. The oxidation product of quinoline-6-carboxylic acid was identified to be 3-hydroxyquinoline-6-carboxylic acid, which was a novel compound. These results suggest that CYP199A2 may be a valuable biocatalyst for the regioselective oxidation of various aromatic carboxylic acids.

:L-Amino acid ligase (EC 6.3.2.28) is a microbial enzyme catalyzing formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner. The YwfE protein from Bacillus subtilis 168 was the first reported L-amino acid ligase, and it synthesizes various dipeptides. Thereafter, several L-amino acid ligases were newly obtained by in silico analysis using the ATP-grasp motif. But these L-amino acid ligases synthesize only dipeptide and no longer peptide. A novel L-amino acid ligase capable of catalyzing oligopeptide synthesis is required to increase the variety of peptides. We have previously found a new member of L-amino acid ligase, RizA, from B. subtilis NBRC3134, a microorganism that produces the peptide-antibiotic rhizocticin. We newly found that a gene at approximately 9 kbp upstream of rizA encoded a novel L-amino acid ligase RizB. Recombinant RizB synthesized homo-oligomers of branched-chain amino acids consisting of 2 to 5 amino acids, and also synthesized various heteropeptides. RizB is the first reported L-amino acid ligase that catalyzes oligopeptide synthesis. In addition, we obtained L-amino acid ligases showing oligopeptide synthesis activities by in silico analysis using BLAST, which is a set of similarity search programs. These L-amino acid ligases showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacteria adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones.

:L-Amino acid ligase synthesizes various peptides from unprotected L-amino acids in an ATP-dependent manner. Known L-amino acid ligases catalyze only dipeptide synthesis, but recently we found that RizB of Bacillus subtilis NBRC 3134 catalyzes oligopeptide synthesis. In the present study, we searched for new members of the L-amino acid ligase group that catalyze oligopeptide synthesis. Several hypothetical proteins possessing the ATP-grasp motif were selected by in silico analysis. These recombinant proteins were assayed for L-amino acid ligase activity. We obtained five L-amino acid ligases showing oligopeptide synthesis activities. These proteins showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacterium adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones. We also examined some of their characteristics.

:L-amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We recently identified a new member of L-amino acid ligase, the plu1440 protein, from Photorhabdus luminescens subsp. laumondii TT01 by in silico analysis. This protein was found to synthesize dipeptides containing L-asparagine at the N-terminus, which is a novel substrate specificity.

:Cytochrome P450 enzymes (P450s) are able to regioselectively and stereoselectively introduce oxygen into organic compounds under mild reaction conditions. These monooxygenases in particular easily catalyze the insertion of oxygen into less reactive carbon-hydrogen bonds. Hence, P450s are of considerable interest as oxidation biocatalysts. To date, although several P450s have been discovered through screening of microorganisms and have been further genetically engineered, the substrate range of these biocatalysts is still limited to fulfill the requirements for a large number of oxidation processes. On the other hand, the recent rapid expansion in the number of reported microbial genome sequences has revealed the presence of an unexpectedly vast number of P450 genes. This large pool of naturally evolved P450s has attracted much attention as a resource for new oxidation biocatalysts. In this review, we focus on aspects of the genome mining approach that are relevant for the discovery of novel P450 biocatalysts. This approach opens up possibilities for exploitation of the catalytic potential of P450s for the preparation of a large choice of oxidation biocatalysts with a variety of substrate specificities.

:CYP199A2, a bacterial P450 monooxygenase from Rhodopseudomonas palustris, was previously reported to oxidize 2-naphthoic acid and 4-ethylbenzoic acid. In this study, we examined the substrate specificity and regioselectivity of CYP199A2 towards indole- and quinolinecarboxylic acids. The CYP199A2 gene was coexpressed with palustrisredoxin gene from R. palustris and putidaredoxin reductase gene from Pseudomonas putida to provide the redox partners of CYP199A2 in Escherichia coli. Following whole-cell assays, reaction products were identified by mass spectrometry and NMR spectroscopy.CYP199A2 did not exhibit any activity towards indole and indole-3-carboxylic acid, whereas this enzyme oxidized indole-2-carboxylic acid, indole-5-carboxylic acid, and indole-6-carboxylic acid. Indole-2-carboxylic acid was converted to 5- and 6-hydroxyindole-2-carboxylic acids at a ratio of 59:41. In contrast, the indole-6-carboxylic acid oxidation generated only one product, 2-indolinone-6-carboxylic acid,at a rate of 130 mol (mol P450)(-1) min(-1). Furthermore,CYP199A2 also oxidized quinoline-6-carboxylic acid,although this enzyme did not exhibit any activity towards quinoline and its derivatives with a carboxyl group at the C-2,C-3, or C-4 positions. The oxidation product of quinoline-6-carboxylic acid was identified to be 3-hydroxyquinoline-6-carboxylic acid, which was a novel compound. These results suggest that CYP199A2 may be a valuable biocatalyst for the regioselective oxidation of various aromatic carboxylic acids.

:L-Amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We have purified a new L-amino acid ligase, RizA, which synthesizes dipeptides whose N-terminus is Arg, from Bacillus subtilis NBRC3134, a microorganism that produces a rhizocticin peptide antibiotic. It was suggested that RizA is probably involved in rhizocticin biosynthesis. In this study, we performed sequence analysis of unknown regions around rizA, and newly identified a gene that encodes a protein that possesses an ATP-grasp motif upstream of rizA. This gene was designated rizB, and its recombinant protein was prepared. Recombinant RizB synthesized homo-oligomers of branched-chain L-amino acids and L-methionine consisting of two to five amino acids in an ATP-dependent manner. RizB also synthesized various heteropeptides. Further examination showed that RizB might elongate a peptide chain at the N-terminus. This is the first report on an L-amino acid ligase catalyzing oligopeptide synthesis.

:A novel metabolic pathway was found in the yeast Trichosporon moniliiforme WU-0401 for salicylate degradation via phenol as the key intermediate. When 20 mM salicylate was used as the sole carbon source for the growth of strain WU-0401, phenol was detected as a distinct metabolite in the culture broth. Analysis of the products derived from salicylate or phenol through reactions with resting cells and a cell-free extract of strain WU-0401 indicated that salicylate is initially decarboxylated to phenol and then oxidized to catechol, followed by aromatic ring cleavage to form cis-cis muconate.

L-Amino acid ligase (EC 6.3.2.28) is a microbial enzyme catalyzing formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner. The YwfE protein from Bacillus subtilis 168 was the first reported L-amino acid ligase, and it synthesizes various dipeptides. Thereafter, several L-amino acid ligases were newly obtained by in silico analysis using the ATP-grasp motif. But these L-amino acid ligases synthesize only dipeptide and no longer peptide. A novel L-amino acid ligase capable of catalyzing oligopeptide synthesis is required to increase the variety of peptides. We have previously found a new member of L-amino acid ligase, RizA, from B. subtilis NBRC3134, a microorganism that produces the peptide-antibiotic rhizocticin. We newly found that a gene at approximately 9 kbp upstream of rizA encoded a novel L-amino acid ligase RizB. Recombinant RizB synthesized homo-oligomers of branched-chain amino acids consisting of 2 to 5 amino acids, and also synthesized various heteropeptides. RizB is the first reported L-amino acid ligase that catalyzes oligopeptide synthesis. In addition, we obtained L-amino acid ligases showing oligopeptide synthesis activities by in silico analysis using BLAST, which is a set of similarity search programs. These L-amino acid ligases showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacteria adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones.

L-Amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We have purified a new L-amino acid ligase, RizA, which synthesizes dipeptides whose N-terminus is Arg, from Bacillus subtilis NBRC3134, a microorganism that produces a rhizocticin peptide antibiotic. It was suggested that RizA is probably involved in rhizocticin biosynthesis. In this study, we performed sequence analysis of unknown regions around rizA, and newly identified a gene that encodes a protein that possesses an ATP-grasp motif upstream of rizA. This gene was designated rizB, and its recombinant protein was prepared. Recombinant RizB synthesized homo-oligomers of branched-chain L-amino acids and L-methionine consisting of two to five amino acids in an ATP-dependent manner. RizB also synthesized various heteropeptides. Further examination showed that RizB might elongate a peptide chain at the N-terminus. This is the first report on an L-amino acid ligase catalyzing oligopeptide synthesis.

The moderately thermophilic bacterium Bacillus subtilis WU-S2B desulfurized dibenzothiophene (DBT) at 50 degrees C through the selective cleavage of carbon-sulfur bonds. In this study, three enzymes involved in the microbial DBT desulfurization were purified and characterized. The first two enzymes, DBT monooxygenase (BdsC) and DBT sulfone monooxygenase (BdsA), were purified from the wild-type strain, and the last one, 2'-hydroxybiphenyl 2-sulfinic acid desulfinase (13613), was purified from the recombinant Escherichia coli overexpressing the gene, bdsB, with chaperonin genes, groEL/ES. The genes of BdsC and BdsA were also overexpressed. The molecular weights of BdsC and BdsA were determined to be 200 and 174 kDa, respectively, by gel filtration chromatography, suggesting that both enzymes had four identical subunits. BdsB had a monomeric structure of 40 kDa. The three enzymes were characterized and compared with the corresponding enzymes (DszC, DszA, and DszB) of mesophilic desulfurization bacteria. The specific activities of BdsC, BdsA, and BdsB were 84.2, 855, and 280 units/mg, respectively, and the latter two activities were higher than those of DszA and DszB. The heat stability and optimum temperature of BdsC, BdsA, and BdsB were higher than those of DszC, DszA, and DszB. Other enzymatic properties were investigated in detail.

The moderately thermophilic bacterium Bacillus subtilis WU-S2B desulfurized dibenzothiophene (DBT) at 50 degrees C through the selective cleavage of carbon-sulfur bonds. In this study, three enzymes involved in the microbial DBT desulfurization were purified and characterized. The first two enzymes, DBT monooxygenase (BdsC) and DBT sulfone monooxygenase (BdsA), were purified from the wild-type strain, and the last one, 2'-hydroxybiphenyl 2-sulfinic acid desulfinase (13613), was purified from the recombinant Escherichia coli overexpressing the gene, bdsB, with chaperonin genes, groEL/ES. The genes of BdsC and BdsA were also overexpressed. The molecular weights of BdsC and BdsA were determined to be 200 and 174 kDa, respectively, by gel filtration chromatography, suggesting that both enzymes had four identical subunits. BdsB had a monomeric structure of 40 kDa. The three enzymes were characterized and compared with the corresponding enzymes (DszC, DszA, and DszB) of mesophilic desulfurization bacteria. The specific activities of BdsC, BdsA, and BdsB were 84.2, 855, and 280 units/mg, respectively, and the latter two activities were higher than those of DszA and DszB. The heat stability and optimum temperature of BdsC, BdsA, and BdsB were higher than those of DszC, DszA, and DszB. Other enzymatic properties were investigated in detail.

Mycobacterium phlei WU-F1 possesses the ability to convert dibenzothiophene (DBT) to 2-hydroxybiphenyl with the release of inorganic sulfur over a wide temperature range from 20 degrees C to 50 degrees C. The conversion is initiated by consecutive sulfur atom-specific oxidations by two mono-oxygenases, and a flavin reductase is essential in combination with these flavin-dependent monooxygenases. The flavin reductase gene (frm) of M. phlei WU-F1, which encodes a protein of 162 amino acid residues with a molecular weight of 17,177, was cloned and the deduced amino acid sequence shares approximately 30% identity with those of several flavin reductases in two protein-component monooxygenases. It was confirmed that the coexpression of frm with the DBT-desulfurization genes (bdsABC) from M. phlei WU-F1 was critical for high DBT-desulfurizing ability over a wide temperature range from 20 degrees C to 55 degrees C. The frm gene was overexpressed in Escherichia coli cells, and the enzyme (Frm) was purified to homogeneity from the recombinant cells. The purified Frm was found to be a 34-kDa homodimeric protein with a monomeric molecular mass of 17 kDa. Frm exhibited high flavin reductase activity over a wide temperature range, and in particular, the turnover rate for FMN reduction with NADH as the electron donor reached 564 s(-1) at 50 degrees C, which is one of the highest activities among all of the flavin reductases previously reported. Intriguingly, Frm also exhibited a high ferric reductase activity.

Mycobacterium phlei WU-F1 possesses the ability to convert dibenzothiophene (DBT) to 2-hydroxybiphenyl with the release of inorganic sulfur over a wide temperature range from 20 degrees C to 50 degrees C. The conversion is initiated by consecutive sulfur atom-specific oxidations by two mono-oxygenases, and a flavin reductase is essential in combination with these flavin-dependent monooxygenases. The flavin reductase gene (frm) of M. phlei WU-F1, which encodes a protein of 162 amino acid residues with a molecular weight of 17,177, was cloned and the deduced amino acid sequence shares approximately 30% identity with those of several flavin reductases in two protein-component monooxygenases. It was confirmed that the coexpression of frm with the DBT-desulfurization genes (bdsABC) from M. phlei WU-F1 was critical for high DBT-desulfurizing ability over a wide temperature range from 20 degrees C to 55 degrees C. The frm gene was overexpressed in Escherichia coli cells, and the enzyme (Frm) was purified to homogeneity from the recombinant cells. The purified Frm was found to be a 34-kDa homodimeric protein with a monomeric molecular mass of 17 kDa. Frm exhibited high flavin reductase activity over a wide temperature range, and in particular, the turnover rate for FMN reduction with NADH as the electron donor reached 564 s(-1) at 50 degrees C, which is one of the highest activities among all of the flavin reductases previously reported. Intriguingly, Frm also exhibited a high ferric reductase activity.

Various heterocyclic sulfur compounds such as naphtho[2,1-b]thiophene (NTH) and benzo[b]thiophene (BTH) derivatives can be detected in diesel oil, in addition to dibenzothiophene (DBT) derivatives. Mycobacterium phlei WU-0103 was newly isolated as a bacterial strain capable of growing in a medium with NTH as the sulfur source at 50degreesC. M. phlei WU-0103 could degrade various heterocyclic sulfur compounds, not only NTH and its derivatives but also DBT, BTH, and their derivatives at 45degreesC. When M. phlei WU-0103 was cultivated with the heterocyclic sulfur compounds such as NTH, NTH 3,3-dioxide, DBT, BTH, and 4,6-dialkylDBTs as sulfur sources, monohydroxy compounds and sulfone compounds corresponding to starting heterocyclic sulfur compounds were detected by gas chromatography-mass spectrometry analysis, suggesting the sulfur-specific desulfurization pathways for heterocyclic sulfur compounds. Moreover, total sulfur content in 12-fold-diluted crude straight-run light gas oil fraction was reduced from 1000 to 475 ppm S, with 52% reduction, by the biodesulfurization treatment at 45degreesC with growing cells of M. phlei WU-0103. Gas chromatography analysis with a flame photometric detector revealed that most of the resolvable peaks, such as those corresponding to alkylated derivatives of NTH, DBT, and BTH, disappeared after the biodesulfurization treatment. These results indicated that M. phlei WU-0103 may have a good potential as a biocatalyst for practical biodesulfurization of diesel oil.

Various heterocyclic sulfur compounds such as naphtho[2,1-b]thiophene (NTH) and benzo[b]thiophene (BTH) derivatives can be detected in diesel oil, in addition to dibenzothiophene (DBT) derivatives. Mycobacterium phlei WU-0103 was newly isolated as a bacterial strain capable of growing in a medium with NTH as the sulfur source at 50degreesC. M. phlei WU-0103 could degrade various heterocyclic sulfur compounds, not only NTH and its derivatives but also DBT, BTH, and their derivatives at 45degreesC. When M. phlei WU-0103 was cultivated with the heterocyclic sulfur compounds such as NTH, NTH 3,3-dioxide, DBT, BTH, and 4,6-dialkylDBTs as sulfur sources, monohydroxy compounds and sulfone compounds corresponding to starting heterocyclic sulfur compounds were detected by gas chromatography-mass spectrometry analysis, suggesting the sulfur-specific desulfurization pathways for heterocyclic sulfur compounds. Moreover, total sulfur content in 12-fold-diluted crude straight-run light gas oil fraction was reduced from 1000 to 475 ppm S, with 52% reduction, by the biodesulfurization treatment at 45degreesC with growing cells of M. phlei WU-0103. Gas chromatography analysis with a flame photometric detector revealed that most of the resolvable peaks, such as those corresponding to alkylated derivatives of NTH, DBT, and BTH, disappeared after the biodesulfurization treatment. These results indicated that M. phlei WU-0103 may have a good potential as a biocatalyst for practical biodesulfurization of diesel oil.

We found a gamma-resorcylic acid (gamma-RA, 2,6-dihydroxybenzoic acid) decarboxylase, as a novel enzyme applicable to carboxylation of resorcinol (RE, 1,3-dihydroxybenzene) to form gamma-RA, in a bacterial strain Rhizobium radiobacter WU-0108 isolated through the screening of gamma-RA degrading microorganisms. The activities for carboxylation of RE and decarboxylation of gamma-RA were detected in the cell-free extracts of R. radiobacter WU-0108 grown aerobically with gamma-RA. The enzyme, gamma-RA decarboxylase, was purified to homogeneity on SDS-PAGE through the steps of one ion-exchange chromatography and two kinds of hydrophobic chromatography. The molecular weight of the enzyme was estimated to be 130 kDa by gel-filtration, and that of the subunit was determined to be 34 kDa by SDS-PAGE, suggesting that the enzyme is a homotetrameric structure. The enzyme catalyzed the decarboxylation of gamma-RA, but not alpha-RA or beta-RA. Without addition of any cofactors, the enzyme catalyzed the regio-selective carboxylation of RE to form gamma-RA, without formation of alpha-RA and P-RA, and of catechol to 2,3-dihydroxybenzoic acid. In the presence of oxygen, this gamma-RA decarboxylase showed no decrease in both of the activities as for decarboxylation of gamma-RA and carboxylation of RE, different from other decarboxylases reported so far. The gene, rdc, encoding the gamma-RA decarboxylase was cloned into Escherichia coli, sequenced, and subjected to over-expression. The deduced amino acid sequence of the rdc gene consists of 327 amino acid residues corresponding to 34 kDa protein, and shows 42% and 30% identity to those of a 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus niger and a 5- carboxyvanillate decarboxylase from Splingomonas paucimobilis SYK-6. A site-directed mutagenesis study revealed the two histidine residues at positions of 164 and 2 18 in Rdc to be essential for the catalytic activities of decarboxylation of gamma-RA and carboxylation of RE. (C) 2004 Elsevier Inc. All rights reserved.

Thermophilic bacteria Bacillus subtilis WU-S2B and Mycobacterium phlei WU-F1 desulfurize dibenzothiophene (DBT) and alkylated DBTs through specific cleavage of the carbon-sulfur bonds over a temperature range up to 52 degreesC. In order to identify and functionally analyze the DBT-desulfurization genes, the gene cluster containing bdsA, bdsB, and bdsC was cloned from B. subtilis WU-S2B. The nucleotide and amino acid sequences of bdsABC show homologies to those of the other known DBT-desulfurization genes and enzymes; e. g. a nucleotide sequence homology of 61.0% to dszABC of the mesophilic bacterium Rhodococcus sp. IGTS8 and 57.8% to tdsABC of the thermophilic bacterium Paenibacillus sp. A11-2. Deletion and subcloning analysis of bdsABC revealed that the gene products of bdsC, bdsA and bdsB oxidized DBT to DBT sulfone (DBTO2), converted DBTO2 to 2'-hydroxybiphenyl-2-sulfinate (HBPSi), and desulfurized HBPSi to 2-hydroxybiphenyl (2-HBP), respectively. Resting cells of a recombinant Escherichia coli JM109 harboring bdsABC converted DBT to 2-HBP over a temperature range of 30 - 52 degreesC, indicating that the gene products of bdsABC were functional in the recombinant. The activities of DBT degradation at 50 degreesC and DBT desulfurization (2-HBP production) at 40 degreesC in resting cells of the recombinant were approximately five times and twice, respectively, as high as those in B. subtilis WU-S2B. The recombinant E. coli cells also degraded alkylated DBTs, such as 2,8-dimethylDBT and 4,6-dimethylDBT. The nucleotide sequences of B. subtilis WU-S2B bdsABC and the corresponding genes from M. phlei WU-F1 were found to be completely identical to each other although the strains are genetically different.

Thermophilic bacteria Bacillus subtilis WU-S2B and Mycobacterium phlei WU-F1 desulfurize dibenzothiophene (DBT) and alkylated DBTs through specific cleavage of the carbon-sulfur bonds over a temperature range up to 52 degreesC. In order to identify and functionally analyze the DBT-desulfurization genes, the gene cluster containing bdsA, bdsB, and bdsC was cloned from B. subtilis WU-S2B. The nucleotide and amino acid sequences of bdsABC show homologies to those of the other known DBT-desulfurization genes and enzymes; e. g. a nucleotide sequence homology of 61.0% to dszABC of the mesophilic bacterium Rhodococcus sp. IGTS8 and 57.8% to tdsABC of the thermophilic bacterium Paenibacillus sp. A11-2. Deletion and subcloning analysis of bdsABC revealed that the gene products of bdsC, bdsA and bdsB oxidized DBT to DBT sulfone (DBTO2), converted DBTO2 to 2'-hydroxybiphenyl-2-sulfinate (HBPSi), and desulfurized HBPSi to 2-hydroxybiphenyl (2-HBP), respectively. Resting cells of a recombinant Escherichia coli JM109 harboring bdsABC converted DBT to 2-HBP over a temperature range of 30 - 52 degreesC, indicating that the gene products of bdsABC were functional in the recombinant. The activities of DBT degradation at 50 degreesC and DBT desulfurization (2-HBP production) at 40 degreesC in resting cells of the recombinant were approximately five times and twice, respectively, as high as those in B. subtilis WU-S2B. The recombinant E. coli cells also degraded alkylated DBTs, such as 2,8-dimethylDBT and 4,6-dimethylDBT. The nucleotide sequences of B. subtilis WU-S2B bdsABC and the corresponding genes from M. phlei WU-F1 were found to be completely identical to each other although the strains are genetically different.

We found a gamma-resorcylic acid (gamma-RA, 2,6-dihydroxybenzoic acid) decarboxylase, as a novel enzyme applicable to carboxylation of resorcinol (RE, 1,3-dihydroxybenzene) to form gamma-RA, in a bacterial strain Rhizobium radiobacter WU-0108 isolated through the screening of gamma-RA degrading microorganisms. The activities for carboxylation of RE and decarboxylation of gamma-RA were detected in the cell-free extracts of R. radiobacter WU-0108 grown aerobically with gamma-RA. The enzyme, gamma-RA decarboxylase, was purified to homogeneity on SDS-PAGE through the steps of one ion-exchange chromatography and two kinds of hydrophobic chromatography. The molecular weight of the enzyme was estimated to be 130 kDa by gel-filtration, and that of the subunit was determined to be 34 kDa by SDS-PAGE, suggesting that the enzyme is a homotetrameric structure. The enzyme catalyzed the decarboxylation of gamma-RA, but not alpha-RA or beta-RA. Without addition of any cofactors, the enzyme catalyzed the regio-selective carboxylation of RE to form gamma-RA, without formation of alpha-RA and P-RA, and of catechol to 2,3-dihydroxybenzoic acid. In the presence of oxygen, this gamma-RA decarboxylase showed no decrease in both of the activities as for decarboxylation of gamma-RA and carboxylation of RE, different from other decarboxylases reported so far. The gene, rdc, encoding the gamma-RA decarboxylase was cloned into Escherichia coli, sequenced, and subjected to over-expression. The deduced amino acid sequence of the rdc gene consists of 327 amino acid residues corresponding to 34 kDa protein, and shows 42% and 30% identity to those of a 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus niger and a 5- carboxyvanillate decarboxylase from Splingomonas paucimobilis SYK-6. A site-directed mutagenesis study revealed the two histidine residues at positions of 164 and 2 18 in Rdc to be essential for the catalytic activities of decarboxylation of gamma-RA and carboxylation of RE. (C) 2004 Elsevier Inc. All rights reserved.

We found a gamma-resorcylic acid (gamma-RA, 2,6-dihydroxybenzoic acid) decarboxylase, as a novel enzyme applicable to carboxylation of resorcinol (RE, 1,3-dihydroxybenzene) to form gamma-RA, in a bacterial strain Rhizobium radiobacter WU-0108 isolated through the screening of gamma-RA degrading microorganisms. The activities for carboxylation of RE and decarboxylation of gamma-RA were detected in the cell-free extracts of R. radiobacter WU-0108 grown aerobically with gamma-RA. The enzyme, gamma-RA decarboxylase, was purified to homogeneity on SDS-PAGE through the steps of one ion-exchange chromatography and two kinds of hydrophobic chromatography. The molecular weight of the enzyme was estimated to be 130 kDa by gel-filtration, and that of the subunit was determined to be 34 kDa by SDS-PAGE, suggesting that the enzyme is a homotetrameric structure. The enzyme catalyzed the decarboxylation of gamma-RA, but not alpha-RA or beta-RA. Without addition of any cofactors, the enzyme catalyzed the regio-selective carboxylation of RE to form gamma-RA, without formation of alpha-RA and P-RA, and of catechol to 2,3-dihydroxybenzoic acid. In the presence of oxygen, this gamma-RA decarboxylase showed no decrease in both of the activities as for decarboxylation of gamma-RA and carboxylation of RE, different from other decarboxylases reported so far. The gene, rdc, encoding the gamma-RA decarboxylase was cloned into Escherichia coli, sequenced, and subjected to over-expression. The deduced amino acid sequence of the rdc gene consists of 327 amino acid residues corresponding to 34 kDa protein, and shows 42% and 30% identity to those of a 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus niger and a 5- carboxyvanillate decarboxylase from Splingomonas paucimobilis SYK-6. A site-directed mutagenesis study revealed the two histidine residues at positions of 164 and 2 18 in Rdc to be essential for the catalytic activities of decarboxylation of gamma-RA and carboxylation of RE. (C) 2004 Elsevier Inc. All rights reserved.

With the objective of developing an odorless biodegradation process for dimethyl sulfoxide (DMSO), Hyphomicrobium sp. WU-OM3 was isolated. During the cultivation of strain WU-OM3 cells with 20 mM dimethyl sulfone (DMSO2) as the sole carbon source, DMSO2 was completely consumed within 48 h and sulfate ion accumulated in the culture broth. Methanesulfonate was also detected as an intermediate of DMSO2 degradation. By combining the DMSO-oxidizing microorganism and strain WU-OM3 cells, 0.64 mM (50 mg/l) DMSO was degraded to sulfate ion with 80% molar conversion ratio.

The thermophilic dibenzothiophene (DBT)-desulfurizing bacterium, Bacillus subtilis WU-S2B, possesses the ability to convert DBT to 2-hydroxybiphenyl with the release of inorganic sulfur over a wide temperature range up to 50degreesC. The conversion is initiated by consecutive sulfur atom-specific oxidations by two monooxygenases, and flavin reductase is essential in combination with these flavin-dependent monooxygenases. The recombinant Escherichia coli cells expressing the DBT monooxygenase gene (bdsC) from B. subtilis WU-S2B also oxidize indole to blue pigment indigo in the presence of a heterologous flavin reductase. Thus, to clone a gene encoding flavin reductase from B. subtilis WU-S2B, indigo production by coexpression of the gene with bdsC in E coli was used as a selection. Using this method, the corresponding gene (frb) was obtained from a recombinant strain forming a blue colony due to indigo production on a nutrient agar plate, and it was confirmed that this gene product Frb exhibited flavin reductase activity. The deduced amino acid sequence of frb consists of 174 amino acid residues and shares 61% identity with that of nitroreductase (YwrO) of Bacillus amyloliquefaciens. In addition, coexpression of frb with the DBT-desulfurization genes (bdsABC) from B. subtilis WU-S2B was critical for high DBT-desulfurizing ability over a wide temperature range of 20-55degreesC. This coexpression screening using indigo production as selective indication may be widely applicable for cloning novel genes encoding either component of flavin reductase or flavin-dependent monooxygenase which efficiently couples with the other component in two-component monooxygenases. (C) 2003 Elsevier Inc. All rights reserved.

The thermophilic dibenzothiophene (DBT)-desulfurizing bacterium, Bacillus subtilis WU-S2B, possesses the ability to convert DBT to 2-hydroxybiphenyl with the release of inorganic sulfur over a wide temperature range up to 50degreesC. The conversion is initiated by consecutive sulfur atom-specific oxidations by two monooxygenases, and flavin reductase is essential in combination with these flavin-dependent monooxygenases. The recombinant Escherichia coli cells expressing the DBT monooxygenase gene (bdsC) from B. subtilis WU-S2B also oxidize indole to blue pigment indigo in the presence of a heterologous flavin reductase. Thus, to clone a gene encoding flavin reductase from B. subtilis WU-S2B, indigo production by coexpression of the gene with bdsC in E coli was used as a selection. Using this method, the corresponding gene (frb) was obtained from a recombinant strain forming a blue colony due to indigo production on a nutrient agar plate, and it was confirmed that this gene product Frb exhibited flavin reductase activity. The deduced amino acid sequence of frb consists of 174 amino acid residues and shares 61% identity with that of nitroreductase (YwrO) of Bacillus amyloliquefaciens. In addition, coexpression of frb with the DBT-desulfurization genes (bdsABC) from B. subtilis WU-S2B was critical for high DBT-desulfurizing ability over a wide temperature range of 20-55degreesC. This coexpression screening using indigo production as selective indication may be widely applicable for cloning novel genes encoding either component of flavin reductase or flavin-dependent monooxygenase which efficiently couples with the other component in two-component monooxygenases. (C) 2003 Elsevier Inc. All rights reserved.

With the objective of developing an odorless biodegradation process for dimethyl sulfoxide (DMSO), Hyphomicrobium sp. WU-OM3 was isolated. During the cultivation of strain WU-OM3 cells with 20 mM dimethyl sulfone (DMSO2) as the sole carbon source, DMSO2 was completely consumed within 48 h and sulfate ion accumulated in the culture broth. Methanesulfonate was also detected as an intermediate of DMSO2 degradation. By combining the DMSO-oxidizing microorganism and strain WU-OM3 cells, 0.64 mM (50 mg/l) DMSO was degraded to sulfate ion with 80% molar conversion ratio.

Dimethyl sulfoxide (DMSO)-degrading ability of Hyphomicrobium denitrificans WU-K217 immobilized by entrapment with calcium-alginate gel was examined. The immobilized cells with the cell density of 0.46 mg-dry weight ml(-1) degraded 0.64 mM (50 mg l(-1)) DMSO within 180 min at a temperature range from 20 to 35 degreesC, similarly to the freely- suspended cells. At 40 degreesC, the immobilized cells completely degraded 0.64 mM DMSO within 240 min, although the freely-suspended cells could not degrade it under the same condition. The half-life of DMSO-degradation activity for the immobilized cells stored at 30 degreesC was 96 h and it was extended to more than 240 h by the storage at 4 degreesC. However, in the case of the freely-suspended cells, the half-life was shorter than 48 h even by the storage at 4 degreesC. These results indicated that the immobilized WU-K217 cells had high thermostability and storage stability compared to those of the freely- suspended cells. Considering these characteristics, we performed the repeated DMSO degradation by reuse of the immobilized cells. As a result, even at the tenth reaction, the immobilized cells maintained 90% of DMSO-degradation rate of that at the first reaction. These results suggested that the immobilized cells of WU-K217 might be applicable to a wastewater-treatment system for the removal of DMSO. (C) 2003 Elsevier Science B.V. All rights reserved.

Dimethyl sulfoxide (DMSO)-degrading ability of Hyphomicrobium denitrificans WU-K217 immobilized by entrapment with calcium-alginate gel was examined. The immobilized cells with the cell density of 0.46 mg-dry weight ml(-1) degraded 0.64 mM (50 mg l(-1)) DMSO within 180 min at a temperature range from 20 to 35 degreesC, similarly to the freely- suspended cells. At 40 degreesC, the immobilized cells completely degraded 0.64 mM DMSO within 240 min, although the freely-suspended cells could not degrade it under the same condition. The half-life of DMSO-degradation activity for the immobilized cells stored at 30 degreesC was 96 h and it was extended to more than 240 h by the storage at 4 degreesC. However, in the case of the freely-suspended cells, the half-life was shorter than 48 h even by the storage at 4 degreesC. These results indicated that the immobilized WU-K217 cells had high thermostability and storage stability compared to those of the freely- suspended cells. Considering these characteristics, we performed the repeated DMSO degradation by reuse of the immobilized cells. As a result, even at the tenth reaction, the immobilized cells maintained 90% of DMSO-degradation rate of that at the first reaction. These results suggested that the immobilized cells of WU-K217 might be applicable to a wastewater-treatment system for the removal of DMSO. (C) 2003 Elsevier Science B.V. All rights reserved.

Recalcitrant organosulfur compounds such as dibenzothiophene (DBT) derivatives in light gas oil (LGO) cannot be removed by conventional hydrodesulfurization (HDS) treatment using metallic catalysts. The thermophilic DBT-desulfurizing bacterium Mycobacterium phlei WU-F1 grew in a medium with hydrodesulfurized LGO as the sole source of sulfur, and exhibited high desulfurizing ability toward LGO between 30 and 50degreesC. When WU-F1 was cultivated at 45degreesC with B-LGO (390 ppm S), F-LGO (120 ppm S) or X-LGO (34 ppm S) as the sole source of sulfur, biodesulfurization resulted in around 60-70% reduction of sulfur content for all three types of hydrodesulfurized LGOs. In addition, when resting cells were incubated at 45degreesC with hydrodesulfurized LGOs in the reaction mixtures containing 50% (v/v) oils, biodesulfurization reduced the sulfur content from 390 to 100 ppm S (B-LGO), from 120 to 42 ppm S (F-LGO) and from 34 to 15 ppm S (X-LGO). Gas chromatography analysis with an atomic emission detector revealed that the peaks of alkylated DBTs including 4-methyl-DBT, 4,6-dimethyl-DBT and 3,4,6-trimethyl-DBT significantly decreased after biodesulfurization. Therefore, thermophilic M. phlei WU-F1, which could effectively desulfurize HDS-treated LGOs over a wide temperature range up to 50 C, may be a promising biocatalyst for practical biodesulfurization of diesel oil. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Recalcitrant organosulfur compounds such as dibenzothiophene (DBT) derivatives in light gas oil (LGO) cannot be removed by conventional hydrodesulfurization (HDS) treatment using metallic catalysts. The thermophilic DBT-desulfurizing bacterium Mycobacterium phlei WU-F1 grew in a medium with hydrodesulfurized LGO as the sole source of sulfur, and exhibited high desulfurizing ability toward LGO between 30 and 50degreesC. When WU-F1 was cultivated at 45degreesC with B-LGO (390 ppm S), F-LGO (120 ppm S) or X-LGO (34 ppm S) as the sole source of sulfur, biodesulfurization resulted in around 60-70% reduction of sulfur content for all three types of hydrodesulfurized LGOs. In addition, when resting cells were incubated at 45degreesC with hydrodesulfurized LGOs in the reaction mixtures containing 50% (v/v) oils, biodesulfurization reduced the sulfur content from 390 to 100 ppm S (B-LGO), from 120 to 42 ppm S (F-LGO) and from 34 to 15 ppm S (X-LGO). Gas chromatography analysis with an atomic emission detector revealed that the peaks of alkylated DBTs including 4-methyl-DBT, 4,6-dimethyl-DBT and 3,4,6-trimethyl-DBT significantly decreased after biodesulfurization. Therefore, thermophilic M. phlei WU-F1, which could effectively desulfurize HDS-treated LGOs over a wide temperature range up to 50 C, may be a promising biocatalyst for practical biodesulfurization of diesel oil. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

A dimethyl sulfoxide (DMSO)-degrading yeast strain Cryptococcus humicolus WU-2 was isolated and characterized. When 0.64 mM (50 mg/l) DMSO was added as the sole source of sulfur, DMSO was completely consumed by WU-2 in 48 h and oxidized to dimethyl sulfone with a molar conversion ratio of 83%. WU-2 also oxidized alkyl sulfides such as dimethyl sulfide, ethyl methyl sulfide and diethyl sulfide into the corresponding sulfones, which are odorless compounds.

A dimethyl sulfoxide (DMSO)-degrading yeast strain Cryptococcus humicolus WU-2 was isolated and characterized. When 0.64 mM (50 mg/l) DMSO was added as the sole source of sulfur, DMSO was completely consumed by WU-2 in 48 h and oxidized to dimethyl sulfone with a molar conversion ratio of 83%. WU-2 also oxidized alkyl sulfides such as dimethyl sulfide, ethyl methyl sulfide and diethyl sulfide into the corresponding sulfones, which are odorless compounds.

l-Menthyl alpha-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranosid(alpha-MenG(2)), a novel glycoside of l- menthol, was synthesized enzymatically, and its physicochemical properties were characterized. Production of alpha-MenG(2) from l-menthyl alpha-D-glucopyranoside (alpha-MenG) was attempted since we had already succeeded in the high-yield production of alpha-MenG using a Xanthomonas campestris enzyme (Nakagawa, H., et al., J. Biosci. Bioeng., 89, 138-1441. 2000). Through production tests on enzymes, it was confirmed that cyclodextrin glucanotransferase (CGTase) from Bacillus macerans produced l-menthyl alpha-D-maltooligosides (alpha-MenG(n)), containing alpha-MenG(2), from alpha-MenG and soluble starch. When 10 ml of a 10 mM citrate-10 mM phosphate buffer (pH 6.0) containing 150 mg of alpha-MenG, 3 g of soluble starch and CGTase was shaken at 70degreesC for 24 h, a total of 81.8% alpha-MenG was reacted. The molar conversion yields of alpha-MenG(2) and alpha-MenG(n) with alpha-glucose degrees of polymerization of 3-18, based on the amount of alpha-WenG supplied, reached 16.1% and 65.7%, respectively. For efficient production of alpha-MenG(2), the reaction mixture was treated with a-amylase of Aspergillus oryzae, and alpha-MenG(n) were mainly converted into alpha-MenG: finally, the molar conversion yield of alpha-MenG(2) reached 74.2% based on the amount of alpha-MenG supplied. alpha-MenG(2) was purified and its molecular structure was confirmed by C-13-NMR, H-1-NMR and two-dimensional HMBC (heteronuclear multiple-bond coherence).alpha-MenG(2) and its aqueous solution tasted bitter and a little sweet at first, but in a few minutes, a refreshing flavor and sweetness spread. At 20degreesC the solubility of alpha-MenG(2) in pure water was 29.6 g/100 ml, approximately 1570-fold that of alpha-MenG.

Naphtho[2,1-b]thiophene (NTH) is an asymmetric structural isomer of dibenzothiophene (DBT), and in addition to DBT derivatives, NTH derivatives can also be detected in diesel oil following hydrodesulfurization treatment. Rhodococcus sp. strain WU-K2R was newly isolated from soil for its ability to grow in a medium with NTH as the sole source of sulfur, and growing cells of WU-K2R degraded 0.27 mM NTH within 7 days. WUK2R could also grow in the medium with NTH sulfone, benzothiophene (BTH), 3-methyl-BTH, or 5-methyl-BTH as the sole source of sulfur but could not utilize DBT, DBT sulfone, or 4,6-dimethyl-DBT. On the other hand, WU-K2R did not utilize NTH or BTH as the sole source of carbon. By gas chromatography-mass spectrometry analysis, desulfurized NTH metabolites were identified as NTH sulfone, 2'-hydroxynaphthylethene, and naphtho[2,1-b]furan. Moreover, since desulfurized BTH metabolites were identified as BTH sulfone, benzo[c] [1,2]oxathiin S-oxide, benzo[c] [1,2]oxathiin S,S-dioxide, o-hydroxystyrene, 2-(2'-hydroxyphenyl) ethan-1-al, and benzofuran, it was concluded that WU-K2R desulfurized NTH and BTH through the sulfur-specific degradation pathways with the selective cleavage of carbon-sulfur bonds. Therefore, Rhodococcus sp. strain WU-K2R, which could preferentially desulfurize asymmetric heterocyclic sulfur compounds such as NTH and BTH through the sulfur-specific degradation pathways, is a unique desulfurizing biocatalyst showing properties different from those of DBT-desulfurizing bacteria.

Naphtho[2,1-b]thiophene (NTH) is an asymmetric structural isomer of dibenzothiophene (DBT), and in addition to DBT derivatives, NTH derivatives can also be detected in diesel oil following hydrodesulfurization treatment. Rhodococcus sp. strain WU-K2R was newly isolated from soil for its ability to grow in a medium with NTH as the sole source of sulfur, and growing cells of WU-K2R degraded 0.27 mM NTH within 7 days. WUK2R could also grow in the medium with NTH sulfone, benzothiophene (BTH), 3-methyl-BTH, or 5-methyl-BTH as the sole source of sulfur but could not utilize DBT, DBT sulfone, or 4,6-dimethyl-DBT. On the other hand, WU-K2R did not utilize NTH or BTH as the sole source of carbon. By gas chromatography-mass spectrometry analysis, desulfurized NTH metabolites were identified as NTH sulfone, 2'-hydroxynaphthylethene, and naphtho[2,1-b]furan. Moreover, since desulfurized BTH metabolites were identified as BTH sulfone, benzo[c] [1,2]oxathiin S-oxide, benzo[c] [1,2]oxathiin S,S-dioxide, o-hydroxystyrene, 2-(2'-hydroxyphenyl) ethan-1-al, and benzofuran, it was concluded that WU-K2R desulfurized NTH and BTH through the sulfur-specific degradation pathways with the selective cleavage of carbon-sulfur bonds. Therefore, Rhodococcus sp. strain WU-K2R, which could preferentially desulfurize asymmetric heterocyclic sulfur compounds such as NTH and BTH through the sulfur-specific degradation pathways, is a unique desulfurizing biocatalyst showing properties different from those of DBT-desulfurizing bacteria.

l-Menthyl alpha-D-glucopyranosyl-(1-->4)-alpha-D-glucopyranosid(alpha-MenG(2)), a novel glycoside of l- menthol, was synthesized enzymatically, and its physicochemical properties were characterized. Production of alpha-MenG(2) from l-menthyl alpha-D-glucopyranoside (alpha-MenG) was attempted since we had already succeeded in the high-yield production of alpha-MenG using a Xanthomonas campestris enzyme (Nakagawa, H., et al., J. Biosci. Bioeng., 89, 138-1441. 2000). Through production tests on enzymes, it was confirmed that cyclodextrin glucanotransferase (CGTase) from Bacillus macerans produced l-menthyl alpha-D-maltooligosides (alpha-MenG(n)), containing alpha-MenG(2), from alpha-MenG and soluble starch. When 10 ml of a 10 mM citrate-10 mM phosphate buffer (pH 6.0) containing 150 mg of alpha-MenG, 3 g of soluble starch and CGTase was shaken at 70degreesC for 24 h, a total of 81.8% alpha-MenG was reacted. The molar conversion yields of alpha-MenG(2) and alpha-MenG(n) with alpha-glucose degrees of polymerization of 3-18, based on the amount of alpha-WenG supplied, reached 16.1% and 65.7%, respectively. For efficient production of alpha-MenG(2), the reaction mixture was treated with a-amylase of Aspergillus oryzae, and alpha-MenG(n) were mainly converted into alpha-MenG: finally, the molar conversion yield of alpha-MenG(2) reached 74.2% based on the amount of alpha-MenG supplied. alpha-MenG(2) was purified and its molecular structure was confirmed by C-13-NMR, H-1-NMR and two-dimensional HMBC (heteronuclear multiple-bond coherence).alpha-MenG(2) and its aqueous solution tasted bitter and a little sweet at first, but in a few minutes, a refreshing flavor and sweetness spread. At 20degreesC the solubility of alpha-MenG(2) in pure water was 29.6 g/100 ml, approximately 1570-fold that of alpha-MenG.

With the objective of removing dimethyl sulfoxide (DMSO) contained in wastewater from semiconductor or liquid crystal display factories, biodegradation of DMSO, particularly at a low concentration, was examined. Through the screening of DMSO-degrading microorganisms, Hyphomicrobium denitrificans WU-K217 utilizing DMSO as the sole source of carbon was isolated from soil. DMSO at less than 20 mM was degraded to sulfate ion by WU-K217 with 100% molar conversion ratio based on DMSO added during 60-h cultivation at 30degreesC under aerobic conditions. Even in the presence of 116 mM or 225 mM DMSO, WU-K217 showed growth although the amount of DMSO degraded was only 33 mM or 10 mM, respectively. Similar to the growing cells, the resting cells of WU-K217 degraded DMSO at over a wide range of temperature, 20-40degreesC. The highest DMSO-degradation activity was obtained at 30degreesC, and 0.64 mM (50 mg/l) DMSO was completely degraded to sulfate ion with 100% molar conversion ratio within only 15 min. Furthermore, to examine whether WU-K217 would be useful for the removal of DMSO contained in wastewater exhausted in large amounts, continuous degradation of DMSO was examined. When 0.64 mM DMSO was added to the resting cells periodically at 15-min intervals, DMSO was completely degraded to sulfate ion without any decrease of the degradation activity at least during the twelve times of DMSO addition.

With the objective of removing dimethyl sulfoxide (DMSO) contained in wastewater from semiconductor or liquid crystal display factories, biodegradation of DMSO, particularly at a low concentration, was examined. Through the screening of DMSO-degrading microorganisms, Hyphomicrobium denitrificans WU-K217 utilizing DMSO as the sole source of carbon was isolated from soil. DMSO at less than 20 mM was degraded to sulfate ion by WU-K217 with 100% molar conversion ratio based on DMSO added during 60-h cultivation at 30degreesC under aerobic conditions. Even in the presence of 116 mM or 225 mM DMSO, WU-K217 showed growth although the amount of DMSO degraded was only 33 mM or 10 mM, respectively. Similar to the growing cells, the resting cells of WU-K217 degraded DMSO at over a wide range of temperature, 20-40degreesC. The highest DMSO-degradation activity was obtained at 30degreesC, and 0.64 mM (50 mg/l) DMSO was completely degraded to sulfate ion with 100% molar conversion ratio within only 15 min. Furthermore, to examine whether WU-K217 would be useful for the removal of DMSO contained in wastewater exhausted in large amounts, continuous degradation of DMSO was examined. When 0.64 mM DMSO was added to the resting cells periodically at 15-min intervals, DMSO was completely degraded to sulfate ion without any decrease of the degradation activity at least during the twelve times of DMSO addition.

Carbazole (CA) is a heterocyclic nitrogen compound contained in the crude petroleum oil and recalcitrant to removal through the refinery processes. For development of the efficient CA-degradation bioprocess, conditions for the recycle use of Sphingomonas sp. CDH-7 resting cells were examined. When the resting cells (O.D.(660) 3.3) were shaken in 50 mM K2HPO4-KH2PO4 buffer (pH 7.0) containing CA 1000 mg/L, CA 880 mg/L was degraded within 3 h, but thereafter the activity decreased markedly. However, the activity was found to be restored to the initial level after the shaking treatment for 3 h in CA-free medium solution or in the buffer containing 20 mM MgCl2. Although the CA-degradation activity of CDH-7 resting cells was lost after 3 h of shaking in the buffer containing 100 mM EDTA, it was restored through the shaking treatment for 3 h in the buffer containing 20 mM MgCl2. When CA was periodically added eight times at a concentration of 100 mg/L (0.599 mM) to the reaction mixture containing the resting cells, CA 778 mg/L (4.66 mM) was continuously degraded within 35 h by the recycle use of resting cells, with the restoration treatment after each CA-degradation reaction by the resting cells.

Carbazole (CA) is a heterocyclic nitrogen compound contained in the crude petroleum oil and recalcitrant to removal through the refinery processes. For development of the efficient CA-degradation bioprocess, conditions for the recycle use of Sphingomonas sp. CDH-7 resting cells were examined. When the resting cells (O.D.(660) 3.3) were shaken in 50 mM K2HPO4-KH2PO4 buffer (pH 7.0) containing CA 1000 mg/L, CA 880 mg/L was degraded within 3 h, but thereafter the activity decreased markedly. However, the activity was found to be restored to the initial level after the shaking treatment for 3 h in CA-free medium solution or in the buffer containing 20 mM MgCl2. Although the CA-degradation activity of CDH-7 resting cells was lost after 3 h of shaking in the buffer containing 100 mM EDTA, it was restored through the shaking treatment for 3 h in the buffer containing 20 mM MgCl2. When CA was periodically added eight times at a concentration of 100 mg/L (0.599 mM) to the reaction mixture containing the resting cells, CA 778 mg/L (4.66 mM) was continuously degraded within 35 h by the recycle use of resting cells, with the restoration treatment after each CA-degradation reaction by the resting cells.

alpha-Arbutin, a useful cosmetic ingredient, was selectively synthesized by alpha-anomer-selective glucosylation of hydroquinone with maltose as a glucosyl donor using lyophilized cells of Xanthomonas campestris WU-9701 as a biocatalyst. When 45 mM hydroquinone and 120 mg of lyophilized cells showing 11 nkat of alpha-glucosyl transfer activity were shaken in 2 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 7.5) containing 1.2 M maltose at 40degreesC, only one form of hydroquinone glucoside was selectively obtained as a product and identified as hydroquinone 1-O-alpha-D-glucopyranoside (alpha-arbutin) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. Although hydroquinone has two phenolic -OH groups at the para position in its structure, only one -OH group, but not both -OHs, was glucosylated and no other glucosylated products such as maltotriose were detected in the reaction mixture. The reaction at 40degreesC for 36 h under optimum conditions yielded 42 mM alpha-arbutin, and the maximum molar conversion yield based on the amount of hydroquinone supplied reached 93%.

alpha-Arbutin, a useful cosmetic ingredient, was selectively synthesized by alpha-anomer-selective glucosylation of hydroquinone with maltose as a glucosyl donor using lyophilized cells of Xanthomonas campestris WU-9701 as a biocatalyst. When 45 mM hydroquinone and 120 mg of lyophilized cells showing 11 nkat of alpha-glucosyl transfer activity were shaken in 2 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 7.5) containing 1.2 M maltose at 40degreesC, only one form of hydroquinone glucoside was selectively obtained as a product and identified as hydroquinone 1-O-alpha-D-glucopyranoside (alpha-arbutin) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. Although hydroquinone has two phenolic -OH groups at the para position in its structure, only one -OH group, but not both -OHs, was glucosylated and no other glucosylated products such as maltotriose were detected in the reaction mixture. The reaction at 40degreesC for 36 h under optimum conditions yielded 42 mM alpha-arbutin, and the maximum molar conversion yield based on the amount of hydroquinone supplied reached 93%.

Dibenzothiophene (DBT) derivatives can be detected in diesel oil following hydrodesulfurization treatment, and they are widely recognized as target compounds for more efficient desulfurization. The moderately thermophilic bacterium Mycobacterium phlei WU-F1 was isolated for its ability to grow at 50 degreesC in a medium with DBT as the sole source of sulfur. At 50 degreesC, resting cells of WU-F1 degraded 0.81 mM DBT within only 90 min to produce 2-hydroxybiphenyl as a desulfurized metabolite through the selective cleavage of carbon-sulfur bonds,, and also degraded 0.81 mM of derivatives such as 2,8-dimethylDBT, 4,6-dimethylDBT and 3,4-benzoDBT within 8 h. In addition, the resting cells exhibited high DBT-desulfurizing ability over a wide temperature range from 20 to 50 degreesC. Because M. phlei WU-F1 possesses higher desulfurizing ability toward DBT and the derivatives over a wider temperature range than any other microorganisms previously reported, it may have useful practical applications for biodesulfurization. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Dibenzothiophene (DBT) derivatives can be detected in diesel oil following hydrodesulfurization treatment, and they are widely recognized as target compounds for more efficient desulfurization. The moderately thermophilic bacterium Mycobacterium phlei WU-F1 was isolated for its ability to grow at 50 degreesC in a medium with DBT as the sole source of sulfur. At 50 degreesC, resting cells of WU-F1 degraded 0.81 mM DBT within only 90 min to produce 2-hydroxybiphenyl as a desulfurized metabolite through the selective cleavage of carbon-sulfur bonds,, and also degraded 0.81 mM of derivatives such as 2,8-dimethylDBT, 4,6-dimethylDBT and 3,4-benzoDBT within 8 h. In addition, the resting cells exhibited high DBT-desulfurizing ability over a wide temperature range from 20 to 50 degreesC. Because M. phlei WU-F1 possesses higher desulfurizing ability toward DBT and the derivatives over a wider temperature range than any other microorganisms previously reported, it may have useful practical applications for biodesulfurization. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Heterocyclic organosulfur compounds such as dibenzothiophene (DBT) in petroleum cannot be completely removed by hydrodesulfurization using chemical catalysts. A moderately thermophilic bacterium Bacillus subtilis WU-S2B, which could desulfurize DBT at 50 degreesC through the selective cleavage of carbon-sulfur (C-S) bonds, was newly isolated. At 50 degreesC, growing tells of WU-S2B could degrade 0.54 mM DBT within 120 h to produce 2-hydroxybiphenyl, and the resting cells could also degrade 0.81 mM DBT within 12 h, The DBT-desulfurizing ability of WU-S2B is high over a wide temperature range from 30 to 50 degreesC, and highest at 50 degreesC for both the growing and resting cells, and this is an extremely advantageous property for the practical biodesulfurization. In addition, WU-S2B could also desulfurize DBT derivatives such as 2,8-dimethylDBT, 4,6-dimethylDBT and 3,4-benzoDBT, Therefore, S. subtilis WU-S2B is considered to have more beneficial properties than other desulfurizing bacteria such as Rhodococcus strains previously reported, particularly from the viewpoint of its capacity for thermophilic desulfurization through the C-S bond cleavage.

Heterocyclic organosulfur compounds such as dibenzothiophene (DBT) in petroleum cannot be completely removed by hydrodesulfurization using chemical catalysts. A moderately thermophilic bacterium Bacillus subtilis WU-S2B, which could desulfurize DBT at 50 degreesC through the selective cleavage of carbon-sulfur (C-S) bonds, was newly isolated. At 50 degreesC, growing tells of WU-S2B could degrade 0.54 mM DBT within 120 h to produce 2-hydroxybiphenyl, and the resting cells could also degrade 0.81 mM DBT within 12 h, The DBT-desulfurizing ability of WU-S2B is high over a wide temperature range from 30 to 50 degreesC, and highest at 50 degreesC for both the growing and resting cells, and this is an extremely advantageous property for the practical biodesulfurization. In addition, WU-S2B could also desulfurize DBT derivatives such as 2,8-dimethylDBT, 4,6-dimethylDBT and 3,4-benzoDBT, Therefore, S. subtilis WU-S2B is considered to have more beneficial properties than other desulfurizing bacteria such as Rhodococcus strains previously reported, particularly from the viewpoint of its capacity for thermophilic desulfurization through the C-S bond cleavage.

alpha -Anomer-selective glucosylation of(+)-catechin was carried out using the crude enzyme, showing a-glucose transferring activity, of Xanthomonas campestris WU-9701 with maltose as a glucosyl donor. When 60 mg of (+)-catechin and 50 mg of the enzyme (5.25 units as maltose hydrolysing activity) were incubated in 10 mi of 10 mM citrate-Na2HPO4 buffer (pH 6.5) containing 1.2 M maltose at 45 degreesC, only one (+)-catechin glucoside was selectively obtained as a product. The (+)-catechin glucoside was identified as (+)-catechin 3'-O-alpha -D-glucopyranoside (alpha -C-G) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. The reaction at 45 degreesC for 36 h under the optimum conditions gave 12 mM alpha -C-G, 5.4 mg/ml in the reaction mixture, and the maximum molar conversion yield based on the amount of (+)-catechin supplied reached 57.1%. At 20 degreesC, the solubility in pure water of alpha -C-G, of 450 mg/ml, was approximately 100 fold higher than that of(+)-catechin, of 4.6 mg/ml. Since alpha -C-G has no bitter taste and a slight sweet taste compared with (+)-catechin which has a very bitter taste, alpha -C-G may be a desirable additive for foods, particularly sweet foods.

alpha -Anomer-selective glucosylation of(+)-catechin was carried out using the crude enzyme, showing a-glucose transferring activity, of Xanthomonas campestris WU-9701 with maltose as a glucosyl donor. When 60 mg of (+)-catechin and 50 mg of the enzyme (5.25 units as maltose hydrolysing activity) were incubated in 10 mi of 10 mM citrate-Na2HPO4 buffer (pH 6.5) containing 1.2 M maltose at 45 degreesC, only one (+)-catechin glucoside was selectively obtained as a product. The (+)-catechin glucoside was identified as (+)-catechin 3'-O-alpha -D-glucopyranoside (alpha -C-G) by C-13-NMR, H-1-NMR and two-dimensional HMBC analysis. The reaction at 45 degreesC for 36 h under the optimum conditions gave 12 mM alpha -C-G, 5.4 mg/ml in the reaction mixture, and the maximum molar conversion yield based on the amount of (+)-catechin supplied reached 57.1%. At 20 degreesC, the solubility in pure water of alpha -C-G, of 450 mg/ml, was approximately 100 fold higher than that of(+)-catechin, of 4.6 mg/ml. Since alpha -C-G has no bitter taste and a slight sweet taste compared with (+)-catechin which has a very bitter taste, alpha -C-G may be a desirable additive for foods, particularly sweet foods.

l-Menthyl alpha-D-glucopyranoside (alpha-MenG) is a desirable derivative of l-menthol with useful properties for the production of new flavors and novel food additives, Bacteria were screened for alpha-anomer-selective glucosglation activity toward l-menthol, resulting in the isolation of two strains, Xanthomonas campestris WU-9701 and Stenotrophomonas maltophilia WU-9702, from independent soil samples, Since the safety of X, campestris for use in the food industry is well established, WU-9701 was selected as the more suitable strain for further study, When 50 mg X. campestris WU-9701 lyophilized cells as a biocatalyst were incubated with 1.0 M maltose and 100 mg l-menthol in 10 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 8.0) at 40 degrees C, alpha-MenG was accumulated, mainly in a crystalline form, through the anomer-selective synthesis reaction without any by-product formation. Under the optimal conditions, 202 mg alpha-MenG was obtained over 48 h with a highest conversion yield of 99.1% based on the supplied l-menthol. Crude alpha-MenG formed through tills "crystal accumulation reaction" was easily collected from the reaction mixture by separation on filter paper. Plank-like crystals of purified alpha-MenG were subsequently obtained by recrystallization in ethyl acetate solution.

l-Menthyl alpha-D-glucopyranoside (alpha-MenG) is a desirable derivative of l-menthol with useful properties for the production of new flavors and novel food additives, Bacteria were screened for alpha-anomer-selective glucosglation activity toward l-menthol, resulting in the isolation of two strains, Xanthomonas campestris WU-9701 and Stenotrophomonas maltophilia WU-9702, from independent soil samples, Since the safety of X, campestris for use in the food industry is well established, WU-9701 was selected as the more suitable strain for further study, When 50 mg X. campestris WU-9701 lyophilized cells as a biocatalyst were incubated with 1.0 M maltose and 100 mg l-menthol in 10 ml of 10 mM H3BO3-NaOH-KCl buffer (pH 8.0) at 40 degrees C, alpha-MenG was accumulated, mainly in a crystalline form, through the anomer-selective synthesis reaction without any by-product formation. Under the optimal conditions, 202 mg alpha-MenG was obtained over 48 h with a highest conversion yield of 99.1% based on the supplied l-menthol. Crude alpha-MenG formed through tills "crystal accumulation reaction" was easily collected from the reaction mixture by separation on filter paper. Plank-like crystals of purified alpha-MenG were subsequently obtained by recrystallization in ethyl acetate solution.

An efficient production strain for L-threonine fermentation was derived from Escherichia coli by multiple rounds of mutation programs that aimed at deregulation of the L-threonine biosynthetic pathway and blocking of L-threonine degradation pathways. When the optimum amount of DL-methionine was added, this strain KY10935, an L-methionine auxotroph, gave 100 g/liter L-threonine after 77 h cultivation. In this strain, key enzymes in the L-threonine biosynthetic pathway were highly derepressed, but some were inhibited by lower concentrations of L-threonine than the accumulated level. Such incomplete deregulation of the pathway was accounted for by the intracellular concentration of L-threonine being lower than the extracellular level. In an assessment of L-threonine transport in terms of phenotypic growth responses to the amino acid, L-threonine-auxotrophic mutants with a lesion in the L-threonine operon were derived from strain KY10935 by selection for auxotrophy for dipeptide L-alanyl-L-threonine or glycyl-L-threonine, the transport systems of which were different from those of L-threonine. All three independent mutants isolated needed an extraordinarily high concentration (10mg/ml) of L-threonine, but grew in the presence of a low concentration (10 mu g/ml) of either dipeptide, indicating that strain KY10935 had impaired L-threonine uptake. These results suggested that the strain had an unusual mechanism of L-threonine hyperproduction: the inability to take up L-threonine that had accumulated extracellularly decreased the steady-state level of intracellular L-threonine, freeing the remaining regulatory steps of feedback inhibition.

An efficient production strain for L-threonine fermentation was derived from Escherichia coli by multiple rounds of mutation programs that aimed at deregulation of the L-threonine biosynthetic pathway and blocking of L-threonine degradation pathways. When the optimum amount of DL-methionine was added, this strain KY10935, an L-methionine auxotroph, gave 100 g/liter L-threonine after 77 h cultivation. In this strain, key enzymes in the L-threonine biosynthetic pathway were highly derepressed, but some were inhibited by lower concentrations of L-threonine than the accumulated level. Such incomplete deregulation of the pathway was accounted for by the intracellular concentration of L-threonine being lower than the extracellular level. In an assessment of L-threonine transport in terms of phenotypic growth responses to the amino acid, L-threonine-auxotrophic mutants with a lesion in the L-threonine operon were derived from strain KY10935 by selection for auxotrophy for dipeptide L-alanyl-L-threonine or glycyl-L-threonine, the transport systems of which were different from those of L-threonine. All three independent mutants isolated needed an extraordinarily high concentration (10mg/ml) of L-threonine, but grew in the presence of a low concentration (10 mu g/ml) of either dipeptide, indicating that strain KY10935 had impaired L-threonine uptake. These results suggested that the strain had an unusual mechanism of L-threonine hyperproduction: the inability to take up L-threonine that had accumulated extracellularly decreased the steady-state level of intracellular L-threonine, freeing the remaining regulatory steps of feedback inhibition.

Introduction of plasmid pKW99, which coexpresses the deregulated 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase and tryptophan-biosynthetic enzymes, into tryptophan-producing Corynebacterium glutamicum KY10894 resulted in a marked increase (54%) in yield of tryptophan production (43 g/liter), but incurred two problems. One was a decline in sugar consumption at the late stage of fermentation, and the other the loss of the plasmid in the absence of selective pressure. The retarded sugar assimilation was found to be attributed to the death of cells that arose from the detrimental action of indole, the last intermediate in the tryptophan pathway, accumulated as a by-product. A chain of these events simultaneously disappeared when serine, the other substrate of the final reaction by tryptophan synthase, was added. These results indicated that a limiting supply of serine was the cause of the decline in the sugar consumption. Thus, to increase carbon flux into serine, the gene for 3-phosphoglycerate dehydrogenase (PGD), the first enzyme in the serine pathway, was cloned from wild-type C.glutamicum ATCC 31833 and joined onto pKW99 to generate pKW9901. Strain KY10894 transformed with pKW9901 favorably consumed sugar through fermentation with accumulating little indole. Furthermore, on the basis of the observation that serine in the medium was consumed rapidly by the recombinant cells, we developed a unique plasmid stabilization system composed of KY9218 (a PGD-deficient serine-requiring strain of KY10894) and pKW9901: In its combination, cells lacking the plasmid should not proliferate in the fermentation medium which does not contain serine. Even if selective pressure was not applied, the modified strain KY9218 with pKW9901 stably maintained the plasmid during fermentation and produced 50 g/liter of tryptophan in a 61% increased yield relative to strain KY10894.

Introduction of plasmid pKW99, which coexpresses the deregulated 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase and tryptophan-biosynthetic enzymes, into tryptophan-producing Corynebacterium glutamicum KY10894 resulted in a marked increase (54%) in yield of tryptophan production (43 g/liter), but incurred two problems. One was a decline in sugar consumption at the late stage of fermentation, and the other the loss of the plasmid in the absence of selective pressure. The retarded sugar assimilation was found to be attributed to the death of cells that arose from the detrimental action of indole, the last intermediate in the tryptophan pathway, accumulated as a by-product. A chain of these events simultaneously disappeared when serine, the other substrate of the final reaction by tryptophan synthase, was added. These results indicated that a limiting supply of serine was the cause of the decline in the sugar consumption. Thus, to increase carbon flux into serine, the gene for 3-phosphoglycerate dehydrogenase (PGD), the first enzyme in the serine pathway, was cloned from wild-type C.glutamicum ATCC 31833 and joined onto pKW99 to generate pKW9901. Strain KY10894 transformed with pKW9901 favorably consumed sugar through fermentation with accumulating little indole. Furthermore, on the basis of the observation that serine in the medium was consumed rapidly by the recombinant cells, we developed a unique plasmid stabilization system composed of KY9218 (a PGD-deficient serine-requiring strain of KY10894) and pKW9901: In its combination, cells lacking the plasmid should not proliferate in the fermentation medium which does not contain serine. Even if selective pressure was not applied, the modified strain KY9218 with pKW9901 stably maintained the plasmid during fermentation and produced 50 g/liter of tryptophan in a 61% increased yield relative to strain KY10894.

In the aconitase superfamily, which includes the archetypical aconitase, homoaconitase, and isopropylmalate isomerase, only aconitase X is not functionally annotated. The corresponding gene (LhpI) was often located within the bacterial gene cluster involved in L-hydroxyproline metabolism. Screening of a library of (hydroxy) proline analogues revealed that this protein catalyzes the dehydration of cis-3-hydroxy-L-proline to Delta(1)-pyrroline-2-carboxylate. Furthermore, electron paramagnetic resonance and site-directed mutagenic analyses suggests the presence of a mononuclear Fe(III) center, which may be coordinated with one glutamate and two cysteine residues. These properties were significantly different from those of other aconitase members, which catalyze the isomerization of alpha-to beta-hydroxy acids, and have a [4Fe-4S] cluster-binding site composed of three cysteine residues. Bacteria with the LhpI gene could degrade cis-3-hydroxy-L-proline as the sole carbon source, and LhpI transcription was up-regulated not only by cis-3-hydroxy-L-proline, but also by several isomeric 3-and 4-hydroxyprolines.

L-Amino acid ligase (Lal) catalyzes dipeptide synthesis from unprotected L-amino acids by hydrolysis ATP to ADP. Each Lal displays unique substrate specificity, and many different dipeptides can be synthesized by selecting suitable Lal. We have already successfully synthesized Met-Gly selectively by replacing the Pro85 residues of Lal from Bacillus licheniformis (BL00235). From these results, we deduced that the amino acid residue at position 85 had a key role in enzyme activity, and applied these findings to other Lals. When Pro and Gly were used as substrates, TabS from Pseudomonas syringae, synthesized the salt taste enhancing dipeptide Pro Gly and other three dipeptides (Gly-Pro, Pro-Pro, and Gly-Gly) was hardly synthesized from its substrate specificity. However, the amount of Pro Gly was low. Therefore, to alter the substrate specificity and increase the amount of Pro Gly, we selected amino acid residues that might affect the enzyme activity, Ser85 corresponding to Pro85 of BL00235, and His294 on the results from previous studies and the predicted structure of TabS. These residues were replaced with 20 proteogenic amino acids, and Pro Gly synthesizing reactions were conducted. The S85T and the H294D mutants synthesized more Pro Gly than wild-type. Furthermore, the S85T/H294D double mutant synthesized considerably more Pro Gly than the single mutant did. These results showed that the amino acid position 85 of TabS affect the enzyme activity similarly to BL00235. In addition, replacing the amino acid residue positioning around the N-terminal substrate and constructing the double mutant led to increase the amount of Pro-Gly. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.

HpaBC monooxygenase was previously reported to hydroxylate resveratrol to piceatannol. In this article, we report a novel catalytic activity of HpaBC for the synthesis of a pentahydroxylated stilbene. When Escherichia coli cells expressing HpaBC were incubated with resveratrol, the resulting piceatannol was further converted to a new product. This product was identified by mass spectrometry and NMR spectroscopy as a 5-hydroxylated piceatannol, 3,4,5,3,5-pentahydroxy-trans-stilbene (PHS), which is a reportedly valuable biologically active stilbene derivative. We attempted to produce PHS from piceatannol on a flask scale. After examining the effects of detergents and buffers on PHS production, E. coli cells expressing HpaBC efficiently hydroxylated piceatannol to PHS in a reaction mixture containing 1.5% (v/v) Tween 80 and 100mM 3-morpholinopropanesulfonic acid-NaOH buffer at pH 7.5. Under the optimized conditions, the whole cells regioselectively hydroxylated piceatannol, and the production of PHS reached 6.9mM (1.8g L-1) in 48h.

Naturally occurring l-hydroxyproline in its four regio- and stereoisomeric forms has been explored as a possible precursor for pharmaceutical agents, yet the selective synthesis of trans-3-hydroxy-l-proline has not been achieved. Our aim was to develop a novel biocatalytic asymmetric method for the synthesis of trans-3-hydroxy-l-proline. So far, we focused on the rhizobial arginine catabolic pathway: arginase and ornithine cyclodeaminase are involved in l-arginine degradation to l-proline via l-ornithine. We hypothesized that trans-3-hydroxy-l-proline should be synthesized if arginase and ornithine cyclodeaminase act on (2S,3S)-3-hydroxyarginine and (2S,3S)-3-hydroxyornithine, respectively. To test this hypothesis, we cloned the genes of l-arginine 3-hydroxylase, arginase, and ornithine cyclodeaminase and overexpressed them in Escherichia coli, with subsequent enzyme purification. After characterization and optimization of each enzyme, a three-step procedure involving l-arginine 3-hydroxylase, arginase, and ornithine cyclodeaminase (in this order) was performed using l-arginine as a starting substrate. At the second step of the procedure, putative hydroxyornithine was formed quantitatively by arginase from (2S,3S)-3-hydroxyarginine. Nuclear magnetic resonance and chiral high-performance liquid chromatography analyses revealed that the absolute configuration of this compound was (2S,3S)-3-hydroxyornithine. In the last step of the procedure, trans-3-hydroxy-l-proline was synthesized selectively by ornithine cyclodeaminase from (2S,3S)-3-hydroxyornithine. Thus, we successfully developed a novel synthetic route, comprised of three reactions, to convert l-arginine to trans-3-hydroxy-l-proline. The excellent selectivity makes this procedure simpler and more efficient than conventional chemical synthesis.

We examined 66 aromatics for carboxylation by the gamma-resorcylic acid decarboxylase from Rhizobium radiobacter WU-0108 under reverse reaction conditions. The enzyme carboxylated resorcinol, catechol, 5-methylresorcinol and three hydroxystilbenes (resveratrol, gnetol, and piceatannol) with high yields. Except for catechol, the structures of these substrates include a 1,3-dihydroxybenzene moiety. Other compounds gave no reaction products. The reaction products from resveratrol and gnetol were 2,6-dihydroxy-4-[(E)-2-(4-hydroxyphenyl)ethenyl]benzoic acid and 2,6-dihydroxy-4-[(E)-2-(2,6-dihydroxyphenyl)ethenyl]benzoic acid, respectively, as determined by mass spectrometry and nuclear magnetic resonance analyses. Kinetic analyses of the carboxylation reactions indicated that resveratrol and gnetol are better substrates than resorcinol or catechol. (C) 2015 Elsevier B.V. All rights reserved.

Mycobacteria such as Mycobacterium smegmatis strain mc(2)155 and Mycobacterium goodii strain 12523 are able to grow on acetone and use it as a source of carbon and energy. We previously demonstrated by gene deletion analysis that the mimABCD gene cluster, which encodes a binuclear iron monooxygenase, plays an essential role in acetone metabolism in these mycobacteria. In the present study, we determined the catalytic function of MimABCD in acetone metabolism. Whole-cell assays were performed using Escherichia coli cells expressing the MimABCD complex. When the recombinant E. coli cells were incubated with acetone, a product was detected by gas chromatography (GC) analysis. Based on the retention time and the gas chromatography-mass spectrometry (GC-MS) spectrum, the reaction product was identified as acetol (hydroxyacetone). The recombinant E. coli cells produced 1.02 mM of acetol from acetone within 24 h. Furthermore, we demonstrated that MimABCD also was able to convert methylethylketone (2-butanone) to 1-hydroxy-2-butanone. Although it has long been known that microorganisms such as mycobacteria metabolize acetone via acetol, this study provides the first biochemical evidence for the existence of a microbial enzyme that catalyses the conversion of acetone to acetol.

RizA is an L-amino-acid ligase from Bacillus subtilis that participates in the biosynthesis of rhizocticin, an oligopeptide antibiotic. The substrate-free form of RizA has been crystallized and the structure was solved at 2.8 angstrom resolution. The amino-acid-binding site appears to be capable of accommodating multiple amino acids, consistent with previous biochemical studies.

Vanillin is one of the world's most important flavor and fragrance compounds in foods and cosmetics. Recently, we demonstrated that vanillin could be produced from ferulic acid via 4-vinylguaiacol in a coenzyme-independent manner using the decarboxylase Fdc and the oxygenase Cso2. In this study, we investigated a new two-pot bioprocess for vanillin production using the whole-cell catalyst of Escherichia coli expressing Fdc in the first stage and that of E. coli expressing Cso2 in the second stage. We first optimized the second-step Cso2 reaction from 4-vinylguaiacol to vanillin, a rate-determining step for the production of vanillin. Addition of FeCl2 to the cultivation medium enhanced the activity of the resulting E. coli cells expressing Cso2, an iron protein belonging to the carotenoid cleavage oxygenase family. Furthermore, a butyl acetate-water biphasic system was effective in improving the production of vanillin. Under the optimized conditions, we attempted to produce vanillin from ferulic acid by a two-pot bioprocess on a flask scale. In the first stage, E. coli cells expressing Fdc rapidly decarboxylated ferulic acid and completely converted 75 mM of this substrate to 4-vinylguaiacol within 2 h at pH 9.0. After the first-stage reaction, cells were removed from the reaction mixture by centrifugation, and the pH of the resulting supernatant was adjusted to 10.5, the optimal pH for Cso2. This solution was subjected to the second-stage reaction. In the second stage, E. coli cells expressing Cso2 efficiently oxidized 4-vinylguaiacol to vanillin. The concentration of vanillin reached 52 mM (7.8 g L-1) in 24 h, which is the highest level attained to date for the biotechnological production of vanillin using recombinant cells.

We demonstrated the usefulness of a hydroxamate-based colorimetric assay for predicting amide bond formation (through an aminoacyl-AMP intermediate) by the adenylation domain of nonribosomal peptide synthetases. By using a typical adenylation domain of tyrocidine synthetase (involved in tyrocidine biosynthesis), we confirmed the correlation between the absorbance at 490 nm of the L-Trp-hydroxamate-Fe3+ complex and the formation of L-Trp-L-Pro, where L-Pro was used instead of hydroxylamine. Furthermore, this assay was adapted to the adenylation domains of surfactin synthetase (involved in surfactin biosynthesis) and bacitracin synthetase (involved in bacitracin biosynthesis). Consequently, the formation of various aminoacyl L-Pro formations was observed. (C) 2015 Elsevier Inc. All rights reserved.

Enzymatic regio- and stereoselective hydroxylation are valuable for the production of hydroxylated chiral ingredients. Pro line hydroxylases are representative members of the nonheme Fe2+/alpha-ketoglutarate-dependent dioxygenase family. These enzymes catalyze the conversion of L-proline into hydroxy-L-prolines (Hyps). L-Proline cis-4-hydroxylases (cis-P4Hs) from Sinorhizobium rneliloti and Mesorhizobium loti catalyze the hydroxylation of L-proline, generating cis-4-hydroxy-L-proline, as well as the hydroxylation of L-pipecolic acid (L-Pip), generating two regioisomers, cis-5-Hypip and cis-3-Hypip. To selectively produce cis-5-Hypip without simultaneous production of two isomers, protein engineering of cis-P4Hs is required. We therefore carried out protein engineering of cis-P4H to facilitate the conversion of the majority of L-Pip into the cis-5-Hypip isomer. We first solved the X-ray crystal structure of cis-P4H in complex with each of L-Pro and L-Pip. Then, we conducted three rounds of directed evolution and successfully created a cis-P4H triple mutant, V97F/V95W/E114G, demonstrating the desired regioselectivity toward cis-5-Hypip.

We developed a novel process for efficient synthesis of L-threo-3-hydroxyaspartic acid (L-THA) using microbial hydroxylase and hydrolase. A well-characterized mutant of asparagine hydroxylase (AsnO-D241N) and its homologous enzyme (SCO2693- D246N) were adaptable to the direct hydroxylation of L-aspartic acid
however, the yields were strictly low. Therefore, the highly stable and efficient wild-type asparagine hydroxylases AsnO and SCO2693 were employed to synthesize L-THA. By using these recombinant enzymes, L-THA was obtained by L-asparagine hydroxylation by AsnO followed by amide hydrolysis by asparaginase via 3-hydroxyasparagine. Subsequently, the two-step reaction was adapted to one-pot bioconversion in a test tube. L-THA was obtained in a small amount with a molar yield of 0.076% by using intact Escherichia coli expressing the asnO gene, and thus, two asparaginase-deficient mutants of E. coli were investigated. A remarkably increased L-THA yield of 8.2% was obtained with the asparaginase I-deficient mutant. When the expression level of the asnO gene was enhanced by using the T7 promoter in E. coli instead of the lac promoter, the L-THA yield was significantly increased to 92%. By using a combination of the E. coli asparaginase I-deficient mutant and the T7 expression system, a whole-cell reaction in a jar fermentor was conducted, and consequently, L-THA was successfully obtained from L-asparagine with a maximum yield of 96% in less time than with test tube-scale production. These results indicate that asparagine hydroxylation followed by hydrolysis would be applicable to the efficient production of L-THA.

Dipeptides have unique physiological functions. This study focused on the salt-taste-enhancing dipeptide Met-Gly. BL00235, an L-amino acid ligase from Bacillus licheniformis NBRC12200, synthesizes Met-Gly as a major product as well as Met-Met as a by-product. To alter the substrate specificity of BL00235 and synthesize Met-Gly selectively, we chose to alter Pro85 residue based on the BL00235 crystal structure. We predicted that Met might be not recognized as a C-terminal substrate by occupying the space around C-terminal substrate. Pro85 was replaced with Phe, Tyr, and Trp, which have bulky aromatic side chains, by site-directed mutagenesis. These mutants lost the capacity to synthesize Met-Met, during the synthesis of Met-Gly. Furthermore, they did not synthesize Met-Met, even when methionine was used as a substrate. These results show that the amino acid residue at position 85 has a key role in C-terminal substrate specificity.

CYP199A2, a member of the cytochrome P450 family, is a monooxygenase that specializes in the oxidation of aromatic carboxylic acids. The crystal structure of CYP199A2 determined by Bell et al. (J. Mol. Biol., 383, 561-574, 2008) suggested that the S97 and S247 residues conferred the substrate specificity on this enzyme through interaction between the hydroxy side chains of these Ser residues and the carboxy group of the substrates. In this study, we attempted to design and construct CYP199A2 mutants that recognize hydroxy aromatic compounds as substrates by protein engineering. We speculated that substitution of the S97 and 5247 residues with acidic amino acids Asp and Glu, which have carboxy side chains, would provide CYP199A2 mutants that recognize hydroxy aromatic compounds instead of aromatic carboxylic acids. The S97 and S247 residues were substituted with Asp and Glu using site-directed mutagenesis. In whole-cell assays with p-methylbenzylalcohol and phenol as hydroxy aromatic substrates, the S247D mutant regioselectively oxidized these compounds to 1,4-benzenedimethanol and hydroquinone, respectively, although the wild-type enzyme exhibited no oxidation activity for these compounds. Furthermore, the S97D, S247D, and S247E mutants acquired oxidation activity for p-cresol. Especially, the S247D mutant rapidly oxidized p-cresol; the whole cells expressing the S247D mutant completely converted 1 HIM p-cresol to p-hydroxybenzylalcohol in only 30 min. These results also clearly demonstrate that S97 and S247 are important residues that control the substrate specificity of CYP199A2. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.

Many dipeptides have unique physiological functions such as antihypertensive effects and taste enhancing effects. In this study, we focused on the taste of dipeptides and conducted screening for dipeptides as salt taste enhancers. Dipeptides were synthesized using TabS, an L-amino acid ligase (Lal) from Pseudomonas syringae NBRC14081. Six kinds of amino acids, which were easily released by the hydrolysis of proteins or peptides, reacted with 20 proteogenic amino acids, and the reaction mixtures were evaluated using sensory evaluation. In the first screening, the reaction mixture or L-Leu-L-Ser, a known salt taste enhancing dipeptide, was added to a salt solution containing ATP and panelists judged the salt taste intensities. In the second screening, the reaction mixture or residual substrate amino acids was added to a salt solution containing ATP and subjected to sensory evaluation. L-Met-Gly was identified as a candidate salt taste enhancer. In addition to sensory evaluation, the salt taste enhancing effect of L-Met-Gly was evaluated using a taste sensor. Taste sensor analysis showed that L-Met-Gly had a salt taste enhancing effect, and the relative sensor response for L-Met-Gly was equal to or higher than that for L-Leu-L-Ser. This is the first report that L-Met-Gly is a salt taste enhancing dipeptide. Furthermore, we propose that the screening method using reaction mixtures of Lal is applicable for the taste evaluation of other dipeptides.

Peptides are expected to be one of the most promising compounds that are beneficial for improving our quality of life. Research on functional peptides has been carried out in various fields, including food science, medicine, and cosmetics
new findings are frequently reported. Oligopeptides such as dipeptides or tripeptides also have unique physiological functions and physical properties that cannot be found in the constitutive amino acids. However, only a few dipeptides, such as l-aspartyl-l-phenylalanine methyl ester (Asp-Phe-OMe, aspartame), as an artificial sweetener and l-alanyl-l-glutamine (Ala-Gln), as a patient infusion, are commercially used, which can be attributed to the lack of an efficient process for production of these oligopeptides. Therefore, the development of an oligopeptide manufacturing process is important for addressing the growing needs of functional peptides. Recently, bacterial enzymes that produce various dipeptides, oligopeptides, or homopoly(oligo) amino acids have been found. l-Amino acid α-ligase (Lal, EC 6.3.2.28) belongs to the ATP-dependent (ADP-forming) carboxylate-amine/thiol ligase superfamily that catalyzes the condensation of unprotected amino acids and is applicable to fermentative production. In this group, ATP and Mg2+ are generally required for peptide synthesis, and aminoacyl phosphate is synthesized as the reaction intermediate. Various Lals have been newly identified by in silico searches using a BLAST program and by different approaches including purification of putative Lal from microorganisms producing peptide antibiotics as secondary metabolites. Furthermore, using only an adenylation domain (A-domain) of nonribosomal peptide synthetase (NRPS), various aminoacyl prolines, which are dipeptides containing a proline residue at the C-terminus, or various amide compounds can be synthesized from unprotected amino acids and proline without any additional process. This chapter reviews the current knowledge about these unique enzymes and novel enzymatic production methods of designed peptides.

Vanillin is one of the most widely used flavor compounds in the world as well as a promising versatile building block. The biotechnological production of vanillin from plant-derived ferulic acid has attracted much attention as a new alternative to chemical synthesis. One limitation of the known metabolic pathway to vanillin is its requirement for expensive coenzymes. Here, we developed a novel route to vanillin from ferulic acid that does not require any coenzymes. This artificial pathway consists of a coenzyme-independent decarboxylase and a coenzyme-independent oxygenase. When Escherichia coli cells harboring the decarboxylase/oxygenase cascade were incubated with ferulic acid, the cells efficiently synthesized vanillin (8.0 mM, 1.2 gL(-1)) via 4-vinylguaiacol in one pot, without the generation of any detectable aromatic by-products. The efficient method described here might be applicable to the synthesis of other high-value chemicals from plant-derived aromatics.

We evaluated the substrate specificities of four proline cis-selective hydroxylases toward the efficient synthesis of proline derivatives. In an initial evaluation, 15 proline-related compounds were investigated as substrates. In addition to L-proline and L-pipecolinic acid, we found that 3,4-dehydro-L-proline, L-azetidine-2-carboxylic acid, cis-3-hydroxy-L-proline, and L-thioproline were also oxygenated. Subsequently, the product structures were determined, revealing cis-3,4-epoxy-L-proline, cis-3-hydroxy-L-azetidine-2-carboxylic acid, and 2,3-cis-3,4-cis-3,4-dihydroxy-L-proline.

Piceatannol, a valuable biologically active stilbene derivative, was efficiently synthesized from resveratrol. Whole-cell catalysis with HpaBC monooxygenase enabled the regioselective hydroxylation of resveratrol to produce 23 mM (5.2 g L-1) of piceatannol. (C) 2014 Elsevier Ltd. All rights reserved.

Microbial hydroxylases were screened for the capacity to effect direct hydroxylation of proline and pipecolinic acid, based on genomic information. Of the eight candidates screened, 2-oxoglutaratedependent hydroxylase from Streptosporangium roseum NBRC 3776T and aspartyl/asparaginyl p-hydroxylase from Catenulispora acidiphila NBRC 102108T showed both proline and pipecolinic acid hydroxylation activities. In the case of L-proline hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-L-proline and cis-4-hydroxy-L-proline, and cis-4-hydroxy-L-proline was preferentially produced. In the case of L-pipecolinic acid hydroxylation, both enzymes catalyzed the simultaneous formation of cis-3-hydroxy-L-pipecolinic acid and cis-5-hydroxy-L-pipecolinic acid. While the former enzyme preferentially produced cis-3-hydroxy-L-pipecolinic acid, the latter enzyme preferentially produced cis-5-hydroxy-L-pipecolinic acid. (C) 2013 Elsevier B.V. All rights reserved.

4-Hydroxyphenylacetate 3-hydroxylases (HPAHs) of the two-component flavin-dependent monooxygenase family are attractive enzymes that possess the catalytic potential to synthesize valuable ortho-diphenol compounds from simple monophenol compounds. In this study, we investigated the catalytic activity of HPAH from Pseudomonas aeruginosa strain PAO1 toward cinnamic acid derivatives. We prepared Escherichia coli cells expressing the hpaB gene encoding the monooxygenase component and the hpaC gene encoding the oxidoreductase component. E coli cells expressing HpaBC exhibited no or very low oxidation activity toward cinnamic acid, o-coumaric acid, and m-coumaric acid, whereas they rapidly oxidized p-coumaric acid to caffeic acid. Interestingly, after p-coumaric acid was almost completely consumed, the resulting caffeic acid was further oxidized to 3,4,5-trihydroxycinnamic acid. In addition, HpaBC exhibited oxidation activity toward 3-(4-hydroxyphenyl)propanoic acid, ferulic acid, and coniferaldehyde to produce the corresponding ortho-diphenols. We also investigated a flask-scale production of caffeic acid from p-coumaric acid as the model reaction for HpaBC-catalyzed syntheses of hydroxycinnamic acids. Since the initial concentrations of the substrate p-coumaric acid higher than 40 mM markedly inhibited its HpaBC-catalyzed oxidation, the reaction was carried out by repeatedly adding 20 mM of this substrate to the reaction mixture. Furthermore, by using the HpaBC whole-cell catalyst in the presence of glycerol, our experimental setup achieved the high-yield production of caffeic acid, i.e., 56.6 mM (10.2 g/L) within 24 h. These catalytic activities of HpaBC will provide an easy and environment-friendly synthetic approach to hydroxycinnamic acids. © 2013 Springer-Verlag Berlin Heidelberg.

Bacterial binuclear iron monooxygenases play numerous physiological roles in oxidative metabolism. Monooxygenases of this type found in actinomycetes also catalyze various useful reactions and have attracted much attention as oxidation biocatalysts. However, difficulties in expressing these multicomponent monooxygenases in heterologous hosts, particularly in Escherichia coli, have hampered the development of engineered oxidation biocatalysts. Here, we describe a strategy to functionally express the mycobacterial binuclear iron monooxygenase MimABCD in Escherichia coli. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the mimABCD gene expression in E. coli revealed that the oxygenase components MimA and MimC were insoluble. Furthermore, although the reductase MimB was expressed at a low level in the soluble fraction of E. coli cells, a band corresponding to the coupling protein MimD was not evident. This situation rendered the transformed E. coli cells inactive. We found that the following factors are important for functional expression of MimABCD in E. coli: coexpression of the specific chaperonin MimG, which caused MimA and MimC to be soluble in E. coli cells, and the optimization of the mimD nucleotide sequence, which led to efficient expression of this gene product. These two remedies enabled this multicomponent monooxygenase to be actively expressed in E. coli. The strategy described here should be generally applicable to the E. coli expression of other actinomycetous binuclear iron monooxygenases and related enzymes and will accelerate the development of engineered oxidation biocatalysts for industrial processes.

Functional peptides are expected to be beneficial compounds that improve our quality of life. To address the growing need for functional peptides, we have examined peptide synthesis by using microbial enzymes. L-Amino acid ligase (Lal) catalyzes the condensation of unprotected amino acids in an ATP-dependent manner and is applicable to fermentative production. Hence, Lal is a promising enzyme to achieve cost-effective synthesis. To obtain a Lal with novel substrate specificity, we focused on the putative Lal involved in the biosynthesis of the dipeptidic phytotoxin designated tabtoxin. The tabS gene was cloned from Pseudomonas syringae NBRC14081 and overexpressed in Escherichia coli cells. The recombinant TabS protein produced showed the broadest substrate specificity of any known Lal; it detected 136 of 231 combinations of amino acid substrates when dipeptide synthesis was examined. In addition, some new substrate specificities were identified and unusual amino acids, e.g., L-pipecolic acid, hydroxy-L-proline, and beta-alanine, were found to be acceptable substrates. Furthermore, kinetic analysis and monitoring of the reactions over a short time revealed that TabS showed distinct substrate selectivity at the N and C termini, which made it possible to specifically synthesize a peptide without by-products such as homopeptides and heteropeptides with the reverse sequence. TabS specifically synthesized the following functional peptides, including their precursors: L-arginyl-L-phenylalanine (antihypertensive effect; yield, 62%), L-leucyl-L-isoleucine (antidepressive effect; yield, 77%), L-glutaminyl-L-tryptophan (precursor of L-glutamyl-L-tryptophan, which has antiangiogenic activity; yield, 54%), L-leucyl-L-serine (enhances saltiness; yield, 83%), and L-glutaminyl-L-threonine (precursor of L-glutamyl-L-threonine, which enhances saltiness; yield, 96%). Furthermore, our results also provide new insights into tabtoxin biosynthesis.

The proton motive force (PMF) is bio-energetically important for various cellular reactions to occur. We developed PMF-photogenerating mitochondria in cultured mammalian cells. An archaebacterial rhodopsin, delta-rhodopsin, which is a light-driven proton pump derived from Haloterrigena turkmenica, was expressed in the mitochondria of CHO-K1 cells. The constructed stable CHO-K1 cell lines showed suppression of cell death induced by rotenone, a pesticide that inhibits mitochondrial complex I activity involved in PMF generation through the electron transport chain. Delta-rhodopsin was also introduced into the mitochondria of human neuroblastoma SH-SY5Y cells. The constructed stable SH-SY5Y cell lines showed suppression of dopaminergic neuronal cell death induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an inducer of Parkinson's disease models, which acts through inhibition of complex I activity. These results suggest that the light-activated proton pump functioned as a PMF generator in the mitochondria of mammalian cells, and suppressed cell death induced by inhibition of respiratory PMF generation.

Dipeptides exhibit unique physiological functions and physical properties, e.g., L-aspartyl-L-phenylalanine-methyl. ester (Asp-Phe-OMe, aspartame) as an artificial sweetener, and functional studies of peptides have been carried out in various fields. Therefore, to establish a manufacturing process for the useful dipeptides, we investigated its enzymatic synthesis by utilizing an L-amino acid ligase (Lal), which catalyzes dipeptide synthesis in an ATP-dependent manner. Many Lals were obtained, but the Lals recognizing acidic amino acids as N-terminal substrates have not been identified. To increase the variety of dipeptides that are enzymatically synthesized, we proposed a two-step synthesis: Asn-Xaa and Gln-Xaa (Asn, L-asparagine; Gln, L-glutamine; and Xaa, arbitrary amino acids) synthesized by Lals were continuously deamidated by a novel amidase, yielding Asp-Xaa and Glu-Xaa (Asp, L-aspartic add; and Glu, L-glutamic acid). We searched for amidases that specifically deamidate the N-terminus of Asn or Gln in dipeptides since none have been previously reported. We focused on the protein N-terminal amidase from Saccharomyces cerevisiae (NTA1), and assayed its activity toward dipeptides. Our findings showed that NTA1 deamidated L-asparaginyl-L-valine (Asn-Val) and L-glutaminyl-glycine (Gln-Gly), but did not deamidate L-valyl-L-asparagine and L-alanyl-L-glutamine, suggesting that this deamidation activity is N-terminus specific. The specific activity toward Asn-Val and Gln-Gly were 190 +/- 30 nmol min(-1) mg(-1) protein and 136 +/- 6 nmol min(-1) mg(-1) protein. Additionally, we examined some characteristics of NTA1. Acidic dipeptide synthesis was examined by a combination of Lals and NTA1, resulting in the synthesis of 12 kinds of Asp-Xaa, including Asp-Phe, a precursor of aspartame, and 11 kinds of Glu-Xaa. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.

The mimABCD gene clusters in Mycobacterium smegmatis strain mc2155 and Mycobacterium goodii strain 12523 encode binuclear iron monooxygenases that oxidize propane and phenol. In this study, we attempted to express each mimABCD gene cluster in a heterologous host. The actinomycetous strain Rhodococcus opacus B-4, which is phylogenetically close to Mycobacterium, was selected as the host. Each mimABCD gene cluster was cloned into the RhodococcusEscherichia coli shuttle vector, pTip-QC2, and then introduced into R. opacus cells. Although whole-cell assays were performed with phenol as a substrate, the transformed R. opacus cells did not oxidize this substrate. SDS/PAGE analysis revealed that the oxygenase large subunit MimA was expressed in the insoluble fraction of R. opacus cells. We found that a gene designated mimG, which lies downstream of mimABCD, exhibits similarity in the amino acid sequence of its product with the products of genes encoding the chaperonin GroEL. When the mimG gene was cloned and coexpressed with each mimABCD gene cluster in R. opacus strain B-4, this host successfully acquired oxidation activity towards phenol. SDS/PAGE and western blotting analyses demonstrated that MimA was clearly soluble when in the presence of MimG. These results indicated that MimG played essential roles in the productive folding of MimA, and that the resulting soluble MimA protein led to the active expression of MimABCD.

5-Hydroxy-L-tryptophan (5-HTP) is a naturally occurring aromatic amino acid present in the seeds of the African plant Griffonia simplicifolia. Although 5-HTP has therapeutic effects in various symptoms, efficient method of producing 5-HTP has not been established. In this study, we developed a novel cofactor regeneration process to achieve enhanced synthesis of 5-HTP by using modified L-phenylalanine 4-hydroxylase of Chromobacterium violaceum. For the synthesis of 5-HTP using Escherichia coli whole cell bioconversion, L-tryptophan and 5-HTP degradation by E. coli endogenous catabolic enzymes should be considered. The tryptophanase gene was disrupted using the. red recombination system, since tryptophanase is postulated as an initial enzyme for the degradation of L-tryptophan and 5-HTP in E. coli. For regeneration of the cofactor pterin, we screened and investigated several key enzymes, including dihydropteridine reductase from E. coli, glucose dehydrogenase from Bacillus subtilis, and pterin-4a-carbinolamine dehydratase from Pseudomonas syringae. Genes encoding these three enzymes were overexpressed in an E. coli tryptophanase-deficient host, resulting in the synthesis of 0.74 mM 5-HTP in the presence of 0.1 mM pterin and the synthesis of 0.07 mM 5-HTP in the absence of regeneration of pterin. These results clearly indicated the successful regeneration of pterin. Following optimization of the reaction conditions, 2.5 mM 5-HTP was synthesized with cofactor regeneration, while 0.8 mM 5-HTP was recovered without cofactor regeneration under the same reaction conditions, suggesting that the principle described here provides a new method for cofactor regeneration.

5-Hydroxy-2-adamantanone is a versatile starting material for the synthesis of various adamantane derivatives. In this study, we investigated the biocatalytic production of 5-hydroxy-2-adamantanone using P450cam monooxygenase coupled with NADH regeneration. We constructed Escherichia coli cells that expressed P450cam and its redox partners, putidaredoxin and putidaredoxin reductase, and cells that co-expressed this P450cam multicomponent system with a glucose dehydrogenase (Gdh) to regenerate NADH using glucose. Two types of cells - wet cells that did not receive any treatment after washing with glycerol-containing buffer, and freeze-dried cells that were lyophilized after the washing - were prepared as whole-cell catalysts. When wet cells were reacted with 2-adamantanone, E. coli cells expressing only the P450cam multicomponent system efficiently produced 5-hydroxy-2-adamantanone in the presence of glucose. However, the co-expression of this P450cam system with Gdh did not further enhance the amount of this product. These results indicate that enough amounts of NADH for P450cam catalysis would be supplied by endogenous glucose metabolism in the E. coli host. In contrast, when freeze-dried cells were used, only the cells co-expressing the P450cam multicomponent system with Gdh efficiently catalyzed the oxidation in the presence of glucose. These results suggest that the exogenous Gdh compensated loss of NADH regeneration by the endogenous glucose metabolism that would be damaged by the lyophilization process. Furthermore, we attempted to produce 5-hydroxy-2-adamantanone with repeated additions of the substrate using wet cells expressing only the P450cam multicomponent system and freeze-dried cells co-expressing this P450cam system with Gdh. These whole-cell catalysts attained high-yield production
the wet cells and the freeze-dried cells produced 36 mM (5.9 g/l) and 21 mM (3.5 g/l) of 5-hydroxy-2-adamantanone, respectively. © 2013 Elsevier B.V.

The proline analogue cis-4-hydroxy-l-proline (CHOP), which inhibits the biosynthesis of collagen, has been clinically evaluated as an anticancer drug, but its water solubility and low molecular weight limits its therapeutic potential since it is rapidly excreted. In addition, CHOP is too toxic to be practical as an anticancer drug, due primarily to its systematic effects on noncollagen proteins. To promote CHOP's retention in blood and/or to decrease its toxicity, N-acetylation of CHOP might be a novel approach as a prodrug. The present study was designed to achieve the microbial production of N-acetyl CHOP from l-proline by coexpression of l-proline cis-4-hydroxylases converting l-proline into CHOP (SmP4H) from the Rhizobium Sinorhizobium meliloti and N-acetyltransferase converting CHOP into N-acetyl CHOP (Mpr1) from the yeast Saccharomyces cerevisiae. We constructed a coexpression plasmid harboring both the SmP4H and Mpr1 genes and introduced it into Escherichia coli BL21(DE3) or its l-proline oxidase gene-disrupted (ΔputA) strain. M9 medium containing l-proline produced more N-acetyl CHOP than LB medium containing l-proline. E. coli ΔputA cells accumulated l-proline (by approximately 2-fold) compared to that in wild-type cells, but there was no significant difference in CHOP production between wild-type and ΔputA cells. The addition of NaCl and l-ascorbate resulted in a 2-fold increase in N-acetyl CHOP production in the l-proline-containing M9 medium. The highest yield of N-acetyl CHOP was achieved at 42 h cultivation in the optimized medium. Five unknown compounds were detected in the total protein reaction, probably due to the degradation of N-acetyl CHOP. Our results suggest that weakening of the degradation or deacetylation pathway improves the productivity of N-acetyl CHOP. © 2012 Springer-Verlag.

Microorganisms are capable of producing a wide variety of biopolymers. Homopoly(amino acid)s and homooligo(amino acid)s, which are made up of only a single type of amino acid, are relatively rare; in fact, only two homopoly(amino acid)s have been known to occur in nature: poly(epsilon-L-lysine) (epsilon-PL) and poly(gamma-glutamic acid) (gamma-PGA). Bacterial enzymes that produce homooligo(amino acid)s, such as L-beta-lysine-, L-valine-, L-leucine-, L-isoleucine-, L-methionine-, and L-glutamic acid-oligopeptides and poly(alpha-L-glutamic acid) (alpha-PGA) have recently been identified, as well as epsilon-PL synthetase and gamma-PGA synthetase. This article reviews the current knowledge about these unique enzymes producing homopoly(amino acid)s and homooligo(amino acid)s.

L -Amino-acid ligases (LALs) are enzymes which catalyze the formation of dipeptides by linking two l-amino acids. Although many dipeptides are known and expected to have medical and nutritional benefits, their practical use has been limited owing to their low availability and high expense. LALs are potentially desirable tools for the efficient production of dipeptides; however, the molecular basis of substrate recognition by LAL has not yet been sufficiently elucidated for the design of ideal LALs for the desired dipeptides. This report presents the crystal structure of the LAL BL00235 derived from Bacillus licheniformis NBRC 12200 determined at 1.9 angstrom resolution using the multi-wavelength anomalous dispersion method. The overall structure of BL00235 is fairly similar to that of YwfE, the only LAL with a known structure, but the structure around the catalytic site contains some significant differences. Detailed structural comparison of BL00235 with YwfE sheds some light on the molecular basis of the substrate specificities.

Scope We found that a dipeptide, Arg-Phe (RF), had vasorelaxing activity in mesenteric artery isolated from spontaneously hypertensive rats (SHRs) (EC50 = 580 nM). We then investigated its mechanism of action, and elucidated its physiological functions. Methods and results Vasorelaxing activities of RF-related peptides were tested. The retro-sequence dipeptide FR was inactive, suggesting that the RF sequence is important for a potent vasorelaxing effect. RA and AF were also inactive. RF-nh2 had vasorelaxing activity, implying that the C-terminal amidation of RF is tolerated. Nitric oxide (NO) and prostaglandins (PGs) are known to be vasorelaxing factors; however, the vasorelaxing activity of RF was inhibited by neither NG-nitro-l-arginine methyl ester (l-NAME), an NO synthase inhibitor, nor indomethacin, a COX inhibitor. Interestingly, the activity was blocked by lorglumide, an antagonist of the cholecystokinin (CCK)1 receptor; however, RF had no affinity for CCK receptors, suggesting that RF stimulates CCK release. Orally administered RF decreased blood pressure in SHRs, and this antihypertensive activity was also blocked by a CCK1 antagonist. RF had CCK-like suppressive effects on food intake and gastrointestinal transit. RF increased intracellular Ca2+ flux and CCK release in enteroendocrine STC-1 cells. Conclusion A novel CCK-dependent vasorelaxing RF decreases both blood pressure and food intake.

Caffeic acid is a biologically active molecule that has various beneficial properties, including antioxidant, anticancer, and anti-inflammatory activities. In this study, we explored the catalytic potential of a bacterial cytochrome P450, CYP199A2, for the biotechnological production of caffeic acid. When the CYP199A2 enzyme was reacted with p-coumaric acid, it stoichiometrically produced caffeic acid. The crystal structure of CYP199A2 shows that Phe at position 185 is situated directly above, and only 6.35 angstrom from, the heme iron. This F185 residue was replaced with hydrophobic or hydroxylated amino acids using site-directed mutagenesis to create mutants with novel and improved catalytic properties. In whole-cell assays with the known substrate of CYP199A2, 2-naphthoic acid, only the wild-type enzyme hydroxylated 2-naphthoic acid at the C-7 and C-8 positions, whereas all of the active F185 mutants exhibited a preference for C-5 hydroxylation. Interestingly, several F185 mutants (F185V, F185L, F1851, F185G, and F185A mutants) also acquired the ability to hydroxylate cinnamic acid, which was not hydroxylated by the wild-type enzyme. These results demonstrate that F185 is an important residue that controls the regioselectivity and the substrate specificity of CYP199A2. Furthermore, Escherichia coli cells expressing the F185L mutant exhibited 5.5 times higher hydroxylation activity for p-coumaric acid than those expressing the wild-type enzyme. By using the F185L whole-cell catalyst, the production of caffeic acid reached 15 mM (2.8 g/liter), which is the highest level so far attained in biotechnological production of this compound.

The alpha-glucosyl transfer enzyme (XgtA), a novel type alpha-glucosidase produced by Xanthomonas campestris WU-9701, was purified from the cell-free extract and characterized. The molecular weight of XgtA is estimated to be 57 kDa by SOS-PAGE and 60 kDa by gel filtration, indicating that XgtA is a monomeric enzyme. Kinetic properties of XgtA were determined for alpha-glucosyl transfer and maltose-hydrolyzing activities using maltose as the alpha-glucosyl donor, and if necessary, hydroquinone as the acceptor. The V-max value for alpha-glucosyl transfer activity was 1.3 x 10(-2) (mM/s); this value was 3.9-fold as much as that for maltose-hydrolyzing activity. XgtA neither produced maltooligosaccharides nor hydrolyzed sucrose. The gene encoding XgtA that contained a 1614-bp open reading frame was cloned, identified, and highly expressed in Escherichia coli JM109 as the host. Site-directed mutagenesis identified Asp201,Glu270, and Asp331 as the catalytic sites of XgtA, indicating that XgtA belongs to the glycoside hydrolase family 13. (C) 2012 Elsevier B.V. All rights reserved.

The mimABCD gene cluster encodes the binuclear iron monooxygenase that oxidizes propane and phenol in Mycobacterium smegmatis strain MC2 155 and Mycobacterium goodii strain 12523. Interestingly, expression of the mimABCD gene cluster is induced by acetone. In this study, we investigated the regulator gene responsible for this acetone-responsive expression. In the genome sequence of M. smegmatis strain MC2 155, the mimABCD gene cluster is preceded by a gene designated mimR, which is divergently transcribed. Sequence analysis revealed that MimR exhibits amino acid similarity with the NtrC family of transcriptional activators, including AcxR and AcoR, which are involved in acetone and acetoin metabolism, respectively. Unexpectedly, many homologs of the mimR gene were also found in the sequenced genomes of actinomycetes. A plasmid carrying a transcriptional fusion of the intergenic region between the mimR and mimA genes with a promoterless green fluorescent protein (GFP) gene was constructed and introduced into M. smegmatis strain MC2 155. Using a GFP reporter system, we confirmed by deletion and complementation analyses that the mimR gene product is the positive regulator of the mimABCD gene cluster expression that is responsive to acetone. M. goodii strain 12523 also utilized the same regulatory system as M. smegmatis strain MC2 155. Although transcriptional activators of the NtrC family generally control transcription using the sigma(54) factor, a gene encoding the sigma(54) factor was absent from the genome sequence of M. smegmatis strain MC2 155. These results suggest the presence of a novel regulatory system in actinomycetes, including mycobacteria.

We prepared ATP photosynthetic vesicles from inside-out membranes of Escherichia coli cells that express delta-rhodopsin (a novel light-driven H ? transporter) and TF(0)F(1)-ATP synthase (a thermostable ATP synthase). These vesicles showed light-dependent ATP synthesis. Furthermore, coupling the ATP photosynthetic vesicles with an ATP-hydrolyzing hexokinase enabled light-dependent glucose consumption. The ATP photosynthetic vesicles indicate their potential to applied to light-driven ATP-regenerating bioprocess for various ATP-hydrolyzing bioproductions.

Depsipeptides are peptide-like polymers consisting of amino acids and hydroxy acids, and are expected to be new functional materials for drug-delivery systems and polymer science. In our previous study, D-alanyl-D-lactate, a type of depsipeptide, was enzymatically synthesized using D-alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) by Y207F substitution. Thereafter, in this study, further mutagenesis was introduced, based on structural comparison between TmDdl and a well-characterized D-alanine-D-alanine ligase from Escherichia coli. The S137A/Y207F mutant showed higher n-alanyl-D-lactate and lower D-alanyl-D-alanine synthesizing activity than the Y207F mutant. This suggests that substitution at the S137 residue contributes to product selectivity. Saturated mutagenesis on S137 revealed that the S137G/Y207F mutant showed the highest D-alanyl-D-lactate synthesizing activity. Moreover, the mutant showed broad substrate specificity toward D-amino acid and recognized D-lactate and D,L-isoserine as substrates. On the basis of these characteristics, various depsipeptides can be produced using S137G/Y207F-replaced TmDdl.

Poly-L-alpha-amino acids have various applications because of their biodegradable properties and biocompatibility. Microorganisms contain several enzymes that catalyze the polymerization of L-amino acids in an ATP-dependent manner, but the products from these reactions contain amide linkages at the side residues of amino acids: e.g., poly-gamma-glutamic acid, poly-epsilon-lysine, and cyanophycin. In this study, we found a novel catalytic activity of RimK, a ribosomal protein S6-modifying enzyme derived from Escherichia coli K-12. This enzyme catalyzed poly-alpha-glutamic acid synthesis from unprotected L-glutamic acid (Glu) by hydrolyzing ATP to ADP and phosphate. RimK synthesized poly-alpha-glutamic acid of various lengths; matrix-assisted laser desorption ionization-time of flight-mass spectrometry showed that a 46-mer of Glu (maximum length) was synthesized at pH 9. Interestingly, the lengths of polymers changed with changing pH. RimK also exhibited 86% activity after incubation at 55 degrees C for 15 min, thus showing thermal stability. Furthermore, peptide elongation seemed to be catalyzed at the C terminus in a stepwise manner. Although RimK showed strict substrate specificity toward Glu, it also used, to a small extent, other amino acids as C-terminal substrates and synthesized heteropeptides. In addition, RimK-catalyzed modification of ribosomal protein S6 was confirmed. The number of Glu residues added to the protein varied with pH and was largest at pH 9.5.

Mycobacterium goodii strain 12523 is an actinomycete that is able to oxidize phenol regioselectively at the para position to produce hydroquinone. In this study, we investigated the genes responsible for this unique regioselective oxidation. On the basis of the fact that the oxidation activity of M. goodii strain 12523 toward phenol is induced in the presence of acetone, we first identified acetone-induced proteins in this microorganism by two-dimensional electrophoretic analysis. The N-terminal amino acid sequence of one of these acetone-induced proteins shares 100% identity with that of the protein encoded by the open reading frame Msmeg_1971 in Mycobacterium smegmatis strain mc(2)155, whose genome sequence has been determined. Since Msmeg_1971, Msmeg_1972, Msmeg_1973, and Msmeg_1974 constitute a putative binuclear iron monooxygenase gene cluster, we cloned this gene cluster of M. smegmatis strain mc(2)155 and its homologous gene cluster found in M. goodii strain 12523. Sequence analysis of these binuclear iron monooxygenase gene clusters revealed the presence of four genes designated mimABCD, which encode an oxygenase large subunit, a reductase, an oxygenase small subunit, and a coupling protein, respectively. When the mimA gene (Msmeg_1971) of M. smegmatis strain mc(2)155, which was also found to be able to oxidize phenol to hydroquinone, was deleted, this mutant lost the oxidation ability. This ability was restored by introduction of the mimA gene of M. smegmatis strain mc(2)155 or of M. goodii strain 12523 into this mutant. Interestingly, we found that these gene clusters also play essential roles in propane and acetone metabolism in these mycobacteria.

L-Amino acid ligase (EC 6.3.2.28) is a microbial enzyme catalyzing formation of an alpha-peptide bond from unprotected L-amino acids in an ATP-dependent manner. The YwfE protein from Bacillus subtilis 168 was the first reported L-amino acid ligase, and it synthesizes various dipeptides. Thereafter, several L-amino acid ligases were newly obtained by in silico analysis using the ATP-grasp motif. But these L-amino acid ligases synthesize only dipeptide and no longer peptide. A novel L-amino acid ligase capable of catalyzing oligopeptide synthesis is required to increase the variety of peptides. We have previously found a new member of L-amino acid ligase, RizA, from B. subtilis NBRC3134, a microorganism that produces the peptide-antibiotic rhizocticin. We newly found that a gene at approximately 9 kbp upstream of rizA encoded a novel L-amino acid ligase RizB. Recombinant RizB synthesized homo-oligomers of branched-chain amino acids consisting of 2 to 5 amino acids, and also synthesized various heteropeptides. RizB is the first reported L-amino acid ligase that catalyzes oligopeptide synthesis. In addition, we obtained L-amino acid ligases showing oligopeptide synthesis activities by in silico analysis using BLAST, which is a set of similarity search programs. These L-amino acid ligases showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD-1200 protein of Bifidobacteria adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones. © 2010 The Pharmaceutical Society of Japan.

L-Amino acid ligase synthesizes various peptides from unprotected L-amino acids in an ATP-dependent manner. Known L-amino acid ligases catalyze only dipeptide synthesis, but recently we found that RizB of Bacillus subtilis NBRC 3134 catalyzes oligopeptide synthesis. In the present study, we searched for new members of the L-amino acid ligase group that catalyze oligopeptide synthesis. Several hypothetical proteins possessing the ATP-grasp motif were selected by in silico analysis. These recombinant proteins were assayed for L-amino acid ligase activity. We obtained five L-amino acid ligases showing oligopeptide synthesis activities. These proteins showed low similarity in amino acid sequence, but commonly used branched-chain amino acids, such as RizB, as substrates. Furthermore, the spr0969 protein of Streptococcus pneumoniae synthesized longer peptides than those synthesized by RizB, and the BAD_1200 protein of Bifidobacterium adolescentis showed higher activity toward aromatic amino acids than toward branched-chain ones. We also examined some of their characteristics.

L-Amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We recently identified a new member of L-amino acid ligase, the plu1440 protein, from Photorhabdus luminescens subsp. laumondii TT01 by in silico analysis. This protein was found to synthesize dipeptides containing L-asparagine at the N-terminus, which is a novel substrate specificity. (C) 2009, The Society for Biotechnology, japan. All rights reserved.

A novel metabolic pathway was found in the yeast Trichosporon moniliiforme WU-0401 for salicylate degradation via phenol as the key intermediate. When 20 mM salicylate was used as the sole carbon source for the growth of strain WU-0401, phenol was detected as a distinct metabolite in the culture broth. Analysis of the products derived from salicylate or phenol through reactions with resting cells and a cell-free extract of strain WU-0401 indicated that salicylate is initially decarboxylated to phenol and then oxidized to catechol, followed by aromatic ring cleavage to form cis-cis muconate.

Cytochrome P450 enzymes (P450s) are able to regioselectively and stereoselectively introduce oxygen into organic compounds under mild reaction conditions. These monooxygenases in particular easily catalyze the insertion of oxygen into less reactive carbon-hydrogen bonds. Hence, P450s are of considerable interest as oxidation biocatalysts. To date, although several P450s have been discovered through screening of microorganisms and have been further genetically engineered, the substrate range of these biocatalysts is still limited to fulfill the requirements for a large number of oxidation processes. On the other hand, the recent rapid expansion in the number of reported microbial genome sequences has revealed the presence of an unexpectedly vast number of P450 genes. This large pool of naturally evolved P450s has attracted much attention as a resource for new oxidation biocatalysts. In this review, we focus on aspects of the genome mining approach that are relevant for the discovery of novel P450 biocatalysts. This approach opens up possibilities for exploitation of the catalytic potential of P450s for the preparation of a large choice of oxidation biocatalysts with a variety of substrate specificities.

CYP199A2, a bacterial P450 monooxygenase from Rhodopseudomonas palustris, was previously reported to oxidize 2-naphthoic acid and 4-ethylbenzoic acid. In this study, we examined the substrate specificity and regioselectivity of CYP199A2 towards indole- and quinolinecarboxylic acids. The CYP199A2 gene was coexpressed with palustrisredoxin gene from R. palustris and putidaredoxin reductase gene from Pseudomonas putida to provide the redox partners of CYP199A2 in Escherichia coli. Following whole-cell assays, reaction products were identified by mass spectrometry and NMR spectroscopy. CYP199A2 did not exhibit any activity towards indole and indole-3-carboxylic acid, whereas this enzyme oxidized indole-2-carboxylic acid, indole-5-carboxylic acid, and indole-6-carboxylic acid. Indole-2-carboxylic acid was converted to 5- and 6-hydroxyindole-2-carboxylic acids at a ratio of 59:41. In contrast, the indole-6-carboxylic acid oxidation generated only one product, 2-indolinone-6-carboxylic acid, at a rate of 130 mol (mol P450)-1 min-1. Furthermore, CYP199A2 also oxidized quinoline-6-carboxylic acid, although this enzyme did not exhibit any activity towards quinoline and its derivatives with a carboxyl group at the C-2, C-3, or C-4 positions. The oxidation product of quinoline-6-carboxylic acid was identified to be 3-hydroxyquinoline-6-carboxylic acid, which was a novel compound. These results suggest that CYP199A2 may be a valuable biocatalyst for the regioselective oxidation of various aromatic carboxylic acids. © 2009 Springer-Verlag.

L-Amino acid ligase catalyzes dipeptide synthesis from unprotected L-amino acids in an ATP-dependent manner. We have purified a new L-amino acid ligase, RizA, which synthesizes dipeptides whose N-terminus is Arg, from Bacillus subtilis NBRC3134, a microorganism that produces a rhizocticin peptide antibiotic. It was suggested that RizA is probably involved in rhizocticin biosynthesis. In this study, we performed sequence analysis of unknown regions around rizA, and newly identified a gene that encodes a protein that possesses an ATP-grasp motif upstream of rizA. This gene was designated rizB, and its recombinant protein was prepared. Recombinant RizB synthesized homo-oligomers of branched-chain L-amino acids and L-methionine consisting of two to five amino acids in an ATP-dependent manner. RizB also synthesized various heteropeptides. Further examination showed that RizB might elongate a peptide chain at the N-terminus. This is the first report on an L-amino acid ligase catalyzing oligopeptide synthesis.

CYP199A2, a bacterial P450 monooxygenase from Rhodopseudomonas palustris, was found to exhibit oxidation activity towards three hydroxynaphthoic acids. Whole cells of the recombinant Escherichia coli strain expressing CYP199A2 efficiently catalyzed the regioselective oxidation of 1-, 3-, and 6-hydroxy-2-naphthoic acids to produce 1,7-, 3,7-, and 6,7-dihydroxynaphthoic acid respectively. These results suggest that CYP199A2 might be a useful oxidation biocatalyst for the synthesis of dihydroxynaphthoic acids.

Cytochrome P450 (P450) open reading frames (ORFs) identified in genome sequences of Bacillus species are potential resources for new oxidation biocatalysts. Phylogenetic analysis of 29 Bacillus P450 ORFs revealed that the P450s consist of a limited number of P450 families, CYP102, CYP106, CYP107 CYP109, CYP134, CYP152, and CYP197. Previously, we identified the catalytic activities of three P450s of Bacillus subtilis towards steroids by rapid substrate screening using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Here, we further applied this method to evaluate the activity of Bacillus cereus P450s towards steroids. Five P450 genes were cloned from B. cereus ATCC 10987 based on its genomic sequence and were expressed in Escherichia coli. These P450s were reacted with a mixture of 30 compounds that mainly included steroids, and the reaction mixtures were analyzed using FT-ICR/MS. We found that BCE_2659 (CYP106) catalyzed the monooxygenation of methyltestosterone, progesterone, 11-ketoprogesterone, medroxyprogesterone acetate, and chlormadinone acetate. BCE-2654 (CYP107) monooxygenated testosterone enanthate, and BCE_3250 (CYP109) monooxygenated testosterone and compactin. Based on the phylogenetic relationship and the known substrate specificities including ones identified in this study, we discuss the catalytic potential of Bacillus P450s towards steroids. (C) 2009 Elsevier Inc. All rights reserved.

The objective of this study was to enhance L-tryptophan hydroxylation activity of L-phenylalanine 4-hydroxylase. It had been known that L-phenylalanine 4-hydroxylase from Chromobacterium violaceum could convert L-tryptophan to 5-hydroxy-L-tryptophan and L-phenylalanine to L-tyrosine; however, the activity for L-tryptophan was extremely low compared to L-phenylalanine activity levels. We used the information on the crystal structures of aromatic amino acid hydroxylases to generate C. violaceum L-phenylalanine 4-hydroxylase with high L-tryptophan hydroxylating activity. In silico structural modeling analysis suggested that hydrophobic and/or stacking interactions with the substrate and cofactor at L701 and W180 in C. violaceum L-phenylalanine 4-hydroxylase would increase hydroxylation activity. Based on this hypothesis, we introduced a saturation mutagenesis towards these sites followed by the evaluation of 5-hydroxy-L-tryptophan productivity using a modified Gibbs assay. Three and nine positive mutants were obtained from the L701 and W180 mutant libraries, respectively. Among the mutants, L101Y and W180F showed the highest L-tryptophan hydroxylation activity at the respective residues. Steady-state kinetic analysis revealed that k(cat) values for L-tryptophan hydroxylation were increased from 0.40 (wild-type) to 1.02 (L101Y) and 0.51 s(-1) (W180F). In addition, the double mutant (L101Y-W180F) displayed higher L-tryptophan hydroxlylation activity than the wild-type and the W180F and L101Y mutants. The k(cat), value of L101Y-W180F increased to 2.08 s(-1), showing a 5.2-fold increase compared to wild-type enzyme levels. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.

Dibenzothiophene monooxygenase (BdsC) from Bacillus subtilis WU-S2B utilized aromatic compounds not having sulfur atoms as substrates. It acted on indole and its derivatives to form indigoid pigments, and also utilized indoline and phenoxazine. In addition, BdsC exhibited activity toward benzothiophene (BT) derivatives but not BT, suggesting that it shows wide reactivity toward aromatic compounds.

The citric acid-producing fungus Aspergillus niger WU-2223L possesses a cyanide-insensitive respiratory pathway catalyzed by alternative oxidase. The regulation of the alternative oxidase under the conditions of citric acid production was determined from the transcription level of the alternative oxidase gene (aox1). PCR and Southern blot analyses revealed that there is only one copy of aox1 on the chromosome of WU-2223L and no homologous gene of aox1. To confirm the regulation stage of alternative oxidase, alternative oxidase activities and aox1 transcription levels were measured under several cultivation conditions, including those for citric acid production. On each cultivation day, the changes in the specific activity of the alternative oxidase were found to be comparable to those in the transcription level of aox1. These results indicate that the activity of the alternative oxidase encoded by aox1 is regulated at the transcription stage under the conditions tested for A. niger WU-2223L.

L-Amino acid ligase catalyzes the formation of an alpha-peptide bond from unprotected L-amino acids in ail ATP-dependent manner, and this enzyme is very useful in efficient peptide production. We performed enzyme purification to obtain a novel L-amino acid ligase from Bacillus subtilis NBRC3134, a microorganism producing peptide-antibiotic rhizocticin. Rhizocticins are dipeptide or tripeptide antibiotics and commonly possess L-arginyl-L2-amino-5-phosphono-3-cis-pentenoic acid. The purification was carried out by detecting L-arginine hydroxamate synthesis activity, and a target enzyme was finally purified 1,280-fold with 0.8% yield. The corresponding gene was then cloned and designated rizA. rizA was 1,242bp and coded for 413 amino acid residues. Recombinant RizA was prepared, and it was found that the recombinant RizA synthesized dipeptides whose N-terminus was L-arginine in an ATP-dependent manner. RizA had strict substrate specificity toward L-arginine as the N-terminal substrate; on the other hand, the substrate specificity at the C-terminus was relaxed.

Hydroxyprolines are valuable chiral building blocks for organic synthesis of pharmaceuticals. Several microorganisms producing L-proline trans-4- and cis-3-hydroxylase were discovered and these enzymes were applied to the industrial production of trans-4- and cis-3-hydroxy-L-proline, respectively. Meanwhile, other hydroxyproline isomers, cis-4- and trans-3-hydroxy-L-proline, were not easily available because the corresponding hydroxylase have not been discovered. Herein we report novel L-proline cis-4-hydroxylases converting free L-proline to cis-4-hydroxy-L-proline. Two genes encoding uncharacterized proteins from Mesorhizobium loti and Sinorhizobium meliloti were cloned and overexpressed in Escherichia coli, respectively. The functions of purified proteins were investigated in detail, and consequently we detected L-proline cis-4-hydroxylase activity in both proteins. Likewise L-proline trans-4-, cis-3-hydroxylase and prolyl hydroxylase, these enzymes belonged to a 2-oxoglutarate dependent dioxygenase family and required a non-heme ferrous ion. Although their reaction mechanisms were similar to other hydroxylases, the amino acid sequence homology was not observed (less than 40%). (C) 2008 Elsevier Inc. All rights reserved.

Bacillus subtilis WU-S2B is a thermophilic dibenzothiophene (DBT)-desulfurizing bacterium and produces a flavin reductase (Frb) that couples with DBT and DBT sulfone monooxygenases. The recombinant Frb was purified from Escherichia coli cells expressing the frb gene and was characterized. The purified Frb exhibited high stability over wide temperature and pH ranges of 20-55 degrees C and 2-12, respectively. Frb contained FMN and exhibited both flavin reductase and nitroreductase activities. (C) 2008, The Society for Biotechnology, Japan. All rights reserved.

The large pool of cytochrome P450 (P450) open-reading frames identified in genome sequences has attracted much attention as a resource for new oxidation biocatalysts. P450 genes were cloned from genome-sequenced bacteria and coexpressed with putidaredoxin and its reductase genes to provide the redox partners of P450 in Escherichia coli. Whole-cell assays were performed with 2-napthoic acid as a substrate. Hydroxylated naphthoic acid products were rapidly detected with two reagents showing different colors in the presence of the products. Two P450s, CYP199A1 and CYP199A2 were found to hydroxylate the substrate to 7- and 8-hydroxy-2-naphthoic acids. The CYP199A1 whole-cell biocatalyst converted 1 mM 2-napthoic acid to 0.27 mM 7-hydroxy-2-naphthoic acid and 0.53 mM 8-hydroxy-2-naphthoic acid CYP199A2 exhibited similar regioselectivity to CYP199A1. Furthermore, we found that 8-hydroxy-2-naphthoic acid emits near-white fluorescence when exposed to UV light. These P450s will provide a facile and environmentally friendly synthetic approach to the hydroxynaphthoic acids.

For the determination of substrate specificities of thermophilic alpha-aminotransferases (AATs), a novel high-throughput assay method was developed. In this method, a thermophilic omega-aminotransferase (OAT) and a thermophilic aldehyde dehydrogenase (ALDH) are coupled to the AAT reaction. Glutamic acid is used as an amino group donor for the AAT reaction yielding 2-oxoglutalic acid. 2-Oxoglutalic acid produced by the AAT reaction is used as an amino group acceptor in the OAT reaction regenerating glutamic acid. The amino group donor of the OAT reaction is 5-aminopentanoic acid yielding pentanedioic acid semialdehyde which is oxidized by ALDH to pentanedioic acid with concomitant reduction of NADP+ to NADPH. NADPH thus produced then reduces colorless tetrazolium salt into colored formazan. To construct such a reaction system, the genes for a thermophilic AAT, a thermophilic OAT and a thermophilic ALDH were cloned and expressed in Escherichia coli. These enzymes were subsequently purified and used to determine the activities of AAT for the synthesis of unnatural amino acids. This method allowed the clear detection of the AAT activities as it measures the increase in the absorbance on a low background absorbance reading. (C) 2007 Published by Elsevier B.V.

A maltose phosphorylase (EC 2.4.1.8; MPase) showed novel acceptor specificity and transferred the glucosyl moiety of maltose not only to sugars but also to various acceptors having alcoholic OH groups. Salicyl alcohol acted as acceptor for MPase from Enterococcus hirae, and the product, salicyl-O-alpha-D-glucopyranoside (alpha-SalGlc) was identified. The yield based on supplied salicyl alcohol was 86% (mol/mol).

A recombinant Escherichia coli, expressing the rdc gene, which encodes a gamma-resorcylic acid decarboxylase (Rdc) reversibly catalyzing regioselective carboxylation of resorcinol derived from Rhizobium radiobacter WU-0108, converted 20 mM resorcinol to gamma-resorcylic acid with a 44% (mol/mol) yield at 30 degrees C for 7 h. The recombinant E. coli cells were recyclable at least five times for use as biocatalysts.

D-Alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) was a useful biocatalyst for synthesizing D-amino acid dipeptides. TmDdl showed a broad substrate specificity at a high temperature; however, ATP was required for its reaction. One of the methods for an effective ATP supply was the coupling reaction with an ATP regeneration system. However, ATP regeneration systems consisted of enzymes from mesophiles and were difficult to operate at high temperatures. Therefore, an ATP regeneration system that could be used at high temperatures was desired to utilize TmDdl for the effective production Of D-amino acid dipeptides. To establish a thermostable ATP regeneration system, polyphosphate kinase from a thermophile, Thermosynechococcus elongatus BP-1 (TePpk), was characterized. TePpk showed thermostability up to 70 degrees C; therefore, it was considered that a thermostable ATP regeneration system could be established using TePpk. In the coupling reaction with purified TmDdl and TePpk at 60 degrees C, the amount of ATP required for D-alanyl-D-alanine synthesis could be reduced to 1% of the theoretical amount required when there was no ATP regeneration. When the coupling reaction was applied to a resting cell reaction, ATP was regenerated from an adenosine scaffold in the cell, and D-alanyl-D-alanine was successfully synthesized in the maximum yield of 80% (mol/mol) without the addition of ATP. Thus, an effective synthesis of D-amino acid dipepitides was achieved using the thermostable ATP regeneration system.

Broad specificity amino acid racemase (E.C. 5.1.1.10) from Pseudomonas putida IFO 12996 (BAR) is a unique racemase because of its broad substrate specificity. BAR has been considered as a possible catalyst which directly converts inexpensive L-amino acids to DL-amino acid racemates. The gene encoding BAR was cloned to utilize BAR for the synthesis of D-amino acids, especially D-Trp which is an important intermediate of pharmaceuticals. The substrate specificity of cloned BAR covered all of the standard amino acids; however, the activity toward Trp was low. Then, we performed random mutagenesis on bar to obtain mutant BAR derivatives with high activity for Trp. Five positive mutants were isolated after the two-step screening of the randomly mutated BAR. After the determination of the amino acid substitutions in these mutants, it was suggested that the substitutions at Y396 and I384 increased the Trp specific racemization activity and the racemization activity for overall amino acids, respectively. Among the positive mutants, I384M mutant BAR showed the highest activity for Trp. L-Trp (20 mM) was successfully racemized, and the proportion of D-Trp was reached 43% using I384M mutant BAR, while wild-type BAR racemized only 6% of initial L-Trp.

Glutathione (GSH) is synthesized by gamma-glutamylcysteine synthetase (gamma-GCS) and glutathione synthetase (GS) in living organisms. Recently, bifunctional fusion protein, termed gamma-GCS-GS catalyzing both gamma-GCS and GS reactions from gram-positive firmicutes Streptococcus agalactiae has been reported. We revealed that in the gamma-GCS activity, S. agalactiae gamma-GCS-GS had different substrate specificities from those of Escherichia coli gamma-GCS. Furthermore, S. agalactiae gamma-GCS-GS synthesized several kinds of gamma-glutamyltripeptide gamma-Glu-X-aa-Gly from free three amino acids. In Clostridium acetobutylicum, the genes encoding gamma-GCS and putative GS were found to be immediately adjacent by BLAST search, and had amino acid sequence homology with S. agalactiae gamma-GCS-GS, respectively. We confirmed that the proteins expressed from each gene showed gamma-GCS and GS activity, respectively. C. acetobutylicum GS had broad substrate specificities and synthesized several kinds of gamma-glutamyltripeptide, gamma-Glu-Cys-X-aa. Whereas the substrate specificities of gamma-GCS domain protein and GS domain protein of S. agalactiae gamma-GCS-GS were the same as those of S. agalacticie gamma-GCS-GS. (c) 2006 Elsevier Inc. All rights reserved.

Twenty-nine aminotransferase genes from Pyrococcus horikoshii, Aeropyrum pernix, and Sulfolobus tokodaii were cloned and expressed in Escherichia coli. The expression of several of the genes at 15, 25, or 37 degrees C resulted in the formation of insoluble protein aggregates. Therefore, we developed a simple method to express these genes into soluble proteins, by cultivating E. coli clones at a higher temperature. Thus, four genes could be expressed efficiently into soluble and active enzymes by cultivating the respective E. coli clones at 46 degrees C. Subsequently, the method was applied to the expression into soluble proteins of other aminotransferase genes that were derived from nine species of thermophilic microorganisms.

D-Alanine-D-alanine ligase (Ddl) and its mutants maintain the biosynthesis of peptidoglycan, and the substrate specificity of Ddls partially affects the resistance mechanism of vancomycin-resistant enterococci. Through investigation of Ddls, Ddl from Thermotoga, maritima ATCC 43589 showed novel characteristics, vis. thermostability up to 90 degrees C and broad substrate specificity toward 15 D-amino acids, particularly D-alanine, p-cysteine, and D-serine, in that order.

In a citric acid-producing filamentous fungus Aspergillus niger WU-2223L, a cyanide- and antimycin A-insensitive and salicylhydroxamic acid-sensitive respiratory pathway functions in the mitochondria besides the cytochrome pathway and is catalyzed by alternative oxidase (AOX). We constructed an A. niger transformant strain AOXEGFP-1 expressing a fusion gene, aox1-egfp, encoding AOX and enhanced green fluorescent protein (EGFP) to visually analyze the expression levels of aox1 without disruption of mycelia. In strain AOXEGFP-1, the localization of the fusion protein AOX-EGFP in the mitochondria was clearly confirmed because the sites of the green fluorescence by AOX-EGFP were in agreement with those of the red fluorescence of the mitochondria stained with MitoTracker Red CMXRos. When strain AOXEGFP-1 was cultivated with antimycin A, which inhibits the cytochrome pathway at the level of cytochrome bc(1) to cytochrome c and increases the expression level of aox1, EGFP fluorescence intensity increased with an increase in AOX activity measured as duroquinol oxidase activity. Moreover, EGFP fluorescence was detected in strain AOXEGFP-1 regardless of the glucose concentration in the cultivation media: for example, when cultivations were performed with 10, 30, 60 and 120 g/l glucose, EGFP fluorescence was usually detected in the mitochondria. These results indicate that aox1 was constitutively expressed regardless of the glucose concentration in A. niger.

This work attempts to clarify the influence of carbon black (CB) addition on the microstructure of injection-molded high-density polyethylene (HDPE)/polypropylone (PP) blends and effect of shear-induced polymer deformation on the conductive network structure. We observed that HDPE molecules are strongly interacted with carbon surfaces and CB particles are selectively located in HDPE domains. Morphology of the injection-molded specimen consists of three parts, namely, CB-HDPE complex domain, free HDPE domain and PP domain. The volume and microstructure of the free HDPE domain are significantly influenced by HDPE and CB concentration, CB structure, and PP viscosity. We also confirmed that the CB particles are capable of self-assembly to form random conductive networks even under high shear rate within very short time. The morphological changes were finally correlated to the variation of electrical conductivity. (c) 2006 Elsevier Ltd. All rights reserved.

With the objective of developing an odorless biodegradation process for dimethyl sulfoxide (DMSO), Hyphomicrobium sp. WU-OM3 was isolated. During the cultivation of strain WU-OM3 cells with 20 mM dimethyl sulfone (DMSO2) as the sole carbon source, DMSO2 was completely consumed within 48 h and sulfate ion accumulated in the culture broth. Methanesulfonate was also detected as an intermediate of DMSO2 degradation. By combining the DMSO-oxidizing microorganism and strain WU-OM3 cells, 0.64 mM (50 mg/l) DMSO was degraded to sulfate ion with 80% molar conversion ratio.

The complementary DNA (cDNA) and chromosomal DNA (icdA) encoding the NADP+-specific isocitrate dehydrogenase (EC 1.1.1.42) of Aspergillus niger WU-2223L, a citric acid-producing strain, were cloned. Two cDNA clones (cDNA-1, 2.0 kb
cDNA-2, 1.5 kb) were obtained and sequenced, and an ORF of 1494 base pairs (bp) encoding a protein of 498 amino acids (aa) was identified in cDNA-1. The predicted amino acid sequence showed 73% and 67% sequence identities with those of the mitochondrial NADP+-ICDHs from Saccharomyces cerevisiae and pig, respectively. The sequence analysis of cDNA-1 and -2 revealed that the cDNA-2 lacks a 500-bp fragment from cDNA-1 which contains a mitochondrial targeting motif. A peroxisomal targeting motif at the C-terminus was found on the aa sequences of cDNA-1 and cDNA-2, but the cDNA-2 product seemed to be localized in the cytoplasm since the peroxisomes were not found in the mycelia of WU-2223L cultivated under the conditions of citric acid production. The expression of both cDNAs in Escherichia coli DEK2004, an isocitrate dehydrogenase-deficient mutant, revealed that both cDNAs complemented the glutamate-requiring phenotype, and that the transformants retained NADP+-ICDH activities. Therefore, it was clarified that both of the cDNA-1 and -2 products are fully functional. The chromosomal DNA, icdA, was cloned to correspond to cDNA-1, and its nucleotide sequence revealed that it contains seven introns. Southern hybridization using cDNA-1 and cDNA-2 indicated that there is only one copy of icdA on the chromosomes of A. niger WU-2223L. Northern hybridization analysis as for total RNA of WU-2223L revealed that two mRNAs of different sizes, 2.0 kb and 1.5 kb, were hybridized to the ORF of cDNA-1 used as a probe. Therefore, it was found that approximately 1500-nt and 2000-nt mRNAs were transcribed from only one icdA chromosomal gene in A. niger. Sucha transcription has not been observed for ICDH, which is one of the key regulatory enzymes in TCA cycle, in any other organisms.

Introduction of plasmid pKW99, which coexpresses the deregulated 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase and tryptophan-biosynthetic enzymes, into tryptophan-producing Corynebacterium glutamicum KY10894 resulted in a marked increase (54%) in yield of tryptophan production (43 g/liter), but incurred two problems. One was a decline in sugar consumption at the late stage of fermentation, and the other the loss of the plasmid in the absence of selective pressure. The retarded sugar assimilation was found to be attributed to the death of cells that arose from the detrimental action of indole, the last intermediate in the tryptophan pathway, accumulated as a by-product. A chain of these events simultaneously disappeared when serine, the other substrate of the final reaction by tryptophan synthase, was added. These results indicated that a limiting supply of serine was the cause of the decline in the sugar consumption. Thus, to increase carbon flux into serine, the gene for 3-phosphoglycerate dehydrogenase (PGD), the first enzyme in the serine pathway, was cloned from wild-type C. glutamicum ATCC 31833 and joined onto pKW99 to generate pKW9901. Strain KY10894 transformed with pKW9901 favorably consumed sugar through fermentation with accumulating little indole. Furthermore, on the basis of the observation that serine in the medium was consumed rapidly by the recombinant cells, we developed a unique plasmid stabilization system composed of KY9218 (a PGD-deficient serine-requiring strain of KY10894) and pKW9901: In its combination, cells lacking the plasmid should not proliferate in the fermentation medium which does not contain serine. Even if selective pressure was not applied, the modified strain KY9218 with pKW9901 stably maintained the plasmid during fermentation and produced 50 g/liter of tryptophan in a 61% increased yield relative to strain KY10894. © 1994 Taylor &amp
Francis Group LLC.

Ferric reduction by Thiobacillus ferrooxidans and Thiobacillus thiooxidans when grown on an elemental sulfur medium was studied. Ferric iron served as an oxidant for elemental sulfur oxidation, but not as an electron acceptor for respiration. The reduction was a nonenzymatic process, although ferric iron reduction was parallel to the cell growth during elemental sulfur oxidation. It is suggested that reduction is mainly dependent on some reducing substrates produced during the growth period.

Recalcitrant organosulfur compounds such as dibenzothiophene (DBT) derivatives in light gas oil (LGO) cannot be removed by hydrodesulfurization using metallic catalysts. The thermophilic bacteria, Bacillus subtilis WU-S2B and Mycobacterium phlei WU-F1, were isolated for its ability to grow on DBT as the sole source of sulfur at 50℃. In addition to DBT, WU-S2B and WU-F1 also could desulfurize alkylated DBTs such as 4, 6-dimethyl DBT through a sulfur-specific degradation pathway with the selective cleavage of carbon-sulfur bonds. Moreover, when resting cells of WU-F1 were incubated at 45℃ with two types of hydrodesulfurized LGOs in the reaction mixtures containing 50%(v/v)oils, the biodesulfurization reduced the sulfur contents from 120 to 50 ppm S (F-LGO) and from 34 to 15 ppm S (X-LGO), respectively. Gas chromatography analysis with an atomic emission detector revealed that the peaks of alkylated DBTs including 4-methyl DBT, 4, 6-dimethyl DBT, and 3, 4, 6-trimethyl DBT significantly decreased after the biodesulfurization. The DBT-desulfurization genes, bdsABC, were cloned from these two bacteria, and the flavin reductase genes, frb and frm, were also cloned from WU-S2B and Wu-F1, respectively. The recombinant WU-F1 carrying one more set of bdsABC and frm was constructed, and the desulfurizing activity of the recombinant strain was 2. 2-fold higher than that of the wild type strain WU-F1.

In this study, the novel method of the glucoside production using microbial enzymes was investigated. Xanthomonas campestris WU-9701 produces a novel enzyme catalyzing α-anomer-selective glucosylation. Using this enzyme, α-anomer-selective glucosylation of alcoholic and phenolic -OH groups was performed. Moreover, it was identified that the enzyme has also an activity of α-anomer-selective glucosylation of -SH group. This enzyme was purified and characterized, and the properties of this enzyme were clarified. The gene (xgtA) encoding the enzyme catalyzing α-anomer-selective glucosylation was cloned. The nucleotide sequence of xgtA shows homologies to those of several glucosidases. In addition, the 3D structure of XgtA was predicted. The gene xgtA was highly expressed in Escherichia coli, and the recombinant enzyme produced in E. coli was utilized to the production of α-arbutin, a useful glucoside. The synthesis of a glucoside by condensing was investigated. In the case of commercial enzymes, α-arbutin was synthesized by α-glucosidase of Aspergillus niger from hydroquinone and glucose. It was cleared that maltose was synthesized using glucose, and α-arbutin was synthesized by glucosetranslation from this maltose. Arbutin was similarly synthesized by β-glucosidase of A. niger from hydroquinone and glucose. Through the screening, strain (YS003) was obtained. A glucose condensing activity was not confirmed, but YS003 produced an enzyme catalyzing β-anomer-selective glucosylation of hydroquinone. On the other hand, it was identified that a commercial maltose phosphorylase (EC 2.4.1.8, MPase) has an activity of the production of α-glucoside using maltose as a glucosyl donor. It was confirmed that the glucosylation of an alcoholic -OH group by MPase.

酵素タンパク質に対する新規改変手法の方法論の構築を目的に、制限酵素BamHIの耐熱性向上をモデルとして研究を実施。
Bacillus amyloliquefaciensH株の染色体DNAを抽出し、制限酵素BamHI遺伝子(bamHIR)と対応する修飾酵素遺伝子(bamHIM)を含むDNA断片を取得したが、大腸菌において一段階でクローニングすることは不可能であった。そこでbamHIMとbamHIRの個別クローニングを検討した。PCRによりbamHIMを含む約1.8kbHindIIIのDNA断片を取得し、これをpUC19に連結してプラスミドpUBMCを構築した。次に本プラスミドをE.coliDH5αMCR株に導入して得られた形質転換株を宿主としてbamHIRのクローニングを行った。PCRにより得たbamHIRを含む約1.4kbHindIIIのDNA断片を低コピーベクターpSTV28に連結し、プラスミドpSBRCを構築した。このpUBMCとpSBRCの2種のプラスミドを保有するE.coliBRの菌体内抽出液には制限酵素BamHI活性が検出され、目的遺伝子のクローニングと大腸菌での発現に成功した。しかし、粗酵素の見かけ上の熱安定性はクローンごとにまちまちであり、また希釈して活性を測定したところ限界希釈濃度に差が認められたため、クローンごとに発現強度の異なることが示唆された。以上より、変異を導入した制限酵素BamHIの解析や正確な評価、ならびにその生産を考慮すると精製ステップを新たに組み入れる必要性のあることが明らかになった。
部位特異的変異の導入個所は、報告されている野生型BamHIの三次構造から算出した溶媒露出表面積やB-factor値よりアミノ酸の立体構造上の位置と揺らぎを計算し、二次構造・活性中心を加味して8ヶ所決定した。さらにその候補部位に対して、一般的にタンパク質を安定化すると考えられているアミノ酸の置換をシミュレーションして有効な置換アミノ酸を決定した。

ペプチド、ポリマーなどの有用化合物を合成するうえで、アミド結合形成反応の実用的なプロセスが求められている。ペプチド合成において一般的に利用される固相合成法は、多量の縮合剤を必要とし、かつ煩雑な工程を繰り返す必要があり、実験室用途に限定される。近年、Boronic acid誘導体を触媒とするアミド合成が報告されているが（Nature, 480, 471-479, 2011）汎用的ではない。リボゾームを介したタンパク質合成システムはアミノ酸同士の結合に限定され、コモディティーケミカルの実生産において問題があるなど、現在、汎用性のあるアミド化合物合成法は確立されていない。我々は新規アミノ酸リガーゼによる革新的な短鎖ペプチド合成法の開発に成功しているが（Biosci. Biotech. Biochem., 74(1), 129-134, 2010, 他）、任意のペプチド合成には至っていない。一方、非リボソーム型ペプチド合成酵素（NRPS）はチオテンプレート機構によりリボソームとは独立してペプチド性二次代謝産物の生合成を行う巨大酵素複合体で、その反応特性と組織化された構造から、構成モジュールの組み合せによって任意のペプチド合成が可能であるが、合成収量が少なく工業的利用は困難であるとされている。我々は、NRPSのモジュールであるTycAを単独利用した場合、C末端にプロリンを配する直鎖状ジペプチドを高収量で合成できることを明らかにした。ジペプチドの生成量はプロリン濃度に依存して増大し、D-体を含むプロリン誘導体に対してもジペプチドが生成することなどから、TycAによりチオエステル化したアミノ酸に対してプロリンのような求核活性を有する化合物が化学的に作用してジペプチドが合成されるものと推察している。そこで、工業的な利用を目指し、化学反応と連動した酵素的アミド結合形成反応プロセスの開発検討を行った。① TycAモジュールを利用した各種アミド合成TycAモジュールによりL-トリプトファンをチオエステル化し、プロリン誘導体（L-アゼチジン-2-カルボン酸、cis-4-ヒドロキシ-L-プロリン、L-プロリンアミド）およびアミン類（メチルアミン、ジメチルアミン、アゼチジン）を求核剤として反応させた結果、全ての反応においてアミド化合物が生成していることを確認した。② TycAにおけるアデニル化ドメインを利用した各種アミド合成TycAモジュールはアデニル化、チオエステル化、エピメリ化の各ドメイン構造から形成される。ここで、アデニル化ドメインのみでも基質アミノ酸の活性化が可能であり、モジュールを利用した場合と同様に、アミン類を作用させることで求核置換反応が可能であると推察した。本仮説に基づき、TycAにおけるアデニル化ドメインのみを用いて①の反応を行った結果、同様に各種アミド化合物の合成が可能であった。　本研究から、アミノ酸を酵素的にチオエステル化またはアデニル化できれば、アミン類による求核置換（化学反応）によってアミド結合形成が可能であることが強く示唆された。

アミド結合を有する化合物には機能性の高い有用物質が多いが、化学合成法では工程が煩雑で多量の縮合剤を必要と課題が多い。我々は無保護のアミノ酸を直接連結（アミド結合）してジペプチドを合成するアミノ酸リガーゼを数種類見出しているが、合成可能なジペプチドの種類に限度がある。とくにプロリンをC末端に配置するジペプチドやトリペプチドには血圧上昇抑制作用など有用な生理機能を有するものが多いが、従来のアミノ酸リガーゼでは合成困難なペプチドであった。Non Ribosomal Peptide Synthetase (NRPS)は、放線菌や糸状菌でリボソームとは独立してペプチド性二次代謝産物の生合成を行う巨大酵素複合体で、ペプチド合成量が少なく工業的利用は困難であるとされている。最近、我々はペプチド抗生物質チロシジンの合成を担うNRPSのモジュールの一つであるTycAを単独利用した場合、C末端にプロリンを配する直鎖状ジペプチドXaa-L-Proを高収量(～g/L)で合成できることを明らかにした。ジペプチドの生成量はプロリン濃度に依存して増大し、D-体を含むプロリン誘導体に対してもジペプチド生成が可能であることから、TycAによりチオエステル化したアミノ酸に対してプロリンのような求核活性を有する化合物が化学的に作用してジペプチドが合成されるものと推察した。実際に、TycAによってチオエステル化されたアミノ酸に対して、求核剤としてはプロリンのようなアミノ酸に限定されず、メチルアミン、ジメチルアミン、4員環から8員環までの環状アミン、さらにβ-アミノ酸やγ-アミノ酸各種アミンともアミド結合を形成することを見出した。また、求核剤となるアミノ酸のキラリティーはそのまま維持され、かつ多くのアナログ（ヒドロキシプロリン等）も取り込まれ、対応する酸アミド（ジペプチドあるいはトリペプチド）の合成も可能であることを明らかにした。基質アミノ酸活性化の観点からアデニル化に着目し、A-domain（TycA_A）のみを用いた場合にも種々のアミンを求核剤として用いることでアミド結合の形成が可能であると予想した。予想通り、ほぼ同様にアミド化合物合成が可能であった。この場合、T-domainによるチオエステル化によるホロ酵素化が必要ないため、ホスホパンテテイン転移酵素およびCoenzyme Aを必要としない簡便な合成プロセスの構築が可能で、工業的にも有用であることが示された。また、起源の異なるNRPS由来のA-domainを利用して当該反応機構の一般性を検証した。L-アスパラギン酸(L-Asp)をアデニル化するBacitracin合成酵素由来のAドメイン(BacC4_A)を用いて反応を実施した。BacC4_Aの基質をL-Aspとして、求核剤をL-Proとする反応を行ったところL-Asp-L-Proの生成を確認できた。以上の結果から、NRPSのAドメインによる基質アミノ酸のアデニル化とそれに続く求核剤の求核置換反応によりアミド結合形成が可能であることが示され、化学反応と連携した革新的かつ汎用性の高いアミド化合物合成プロセスの開発可能性を確実にした。

近年、ペプチドの持つ有用な物性や機能性に着目した開発研究が医薬品・食品・化粧品などの様々な分野で展開されている。我々はこれまで、微生物由来酵素であるL-アミノ酸リガーゼ（Lal）を利用したペプチド合成研究を展開してきた。Lalは保護基を持たない遊離のアミノ酸を基質としてATPの加水分解反応と共役してペプチドを生成するため、発酵法などの環境負荷低減型合成プロセスへの応用展開が可能であり、物質生産において非常に優位性の高い酵素であると言える。他の研究グループの成果も含めると、様々な微生物から約20種類のLalが取得されているが、結晶構造を解くことに成功しているLalは、現在までに2例のみである。そのため各酵素に特有な基質特異性や合成されるペプチド鎖長を制御する機構を解明するためには、さらなる立体構造情報の取得が不可欠である。本研究では、複数種類のLal立体構造を明らかとし、これらの情報からLalの構造と機能との相関を考察することで上記課題を解決することを目的とした。1.1.Bacillus subtilis NBRC3134由来RizAの結晶構造解析構造解析の研究対象として、Bacillus subtilis由来のRizAおよびRizBと命名した2種類のLalを選択した。両酵素ともB. subtilisにおいてRhizocticinと呼ばれるペプチド性抗生物質の合成に関わる酵素であり、RizAはアルギニン（Arg）をN末端に配したジペプチドを特異的に合成し、一方でRizBはバリン（Val）やロイシン（Leu）などの分岐鎖アミノ酸を中心としてオリゴペプチドを合成するLalである。RizAに関しては、これまでにネイティブ酵素の単結晶から2.0Åの良好なX線回折像を得ることに成功しており、さらには多波長異常分散法による位相決定を目的としてSe-Met置換型RizAの精製工程の確立ならびに単結晶の取得にも成功している。そこで、取得したSe-Met置換型RizAの単結晶を大型放射光施設Photon factory（つくば）にてX線解析試験を行った。その結果、最大解像度2.8Åの反射を得ることに成功し、先のネイティブ酵素のデータと併せて解析することで位相の決定ならびに構造計算からRizA立体構造を解くことに成功した。RizAの全体的な構造は既に取得されている2種類のLal（YwfE:PDB ID 3VMM, BL00235:PDB ID 3VOT）の立体構造と類似しており、構造を重ね合わせた結果では、特に活性中心付近での重なりが良好であった。また、活性中心においてはRizAのN末端基質Argに対する基質特異性を決定する因子として、適切な位置に酸性アミノ酸が位置することを確認した。したがって、これらの間に電荷による相互作用が働くことで塩基性アミノ酸Argが強く認識されている可能性が示唆された。一方、RizAのC末端側のアミノ酸基質に対する特異性は低く、様々なアミノ酸が取り込まれることが確認されている。RizA構造において、C末端のアミノ酸が配すると推定される基質ポケットが空間的に広くなっており、側鎖の小さなアミノ酸から大きなアミノ酸まで許容されることが示唆された。1.2.B.subtilis NBRC3134由来RizBの結晶構造解析RizBに対してはこれまでにネイティブ酵素の精製工程を確立している。そこで精製RizBの結晶化スクリーニングを実施した。しかしながら、種々の条件を検討したが単結晶を得ることはできなかったことから、検討対象を変更し、RizBと同様の活性を示すBacillus licheniformis NBRC12200由来BL02410（一次配列相同性：約60％）について検討を行うこととした。晶析条件を見直したところ、期待通り単結晶を取得することに成功した。続いて行ったX線回折試験では、最大解像度3.0Åの反射を得ることに成功した。

近年、二酸化炭素排出削減に向けてカーボンニュートラルの観点からバイオ燃料が注目を集めているが、限りある化石資源に依存した産業構造から脱却するためには燃料のみならず化学品もその原料を石油からバイオマスに転換することが重要である。また、石油化学工業では物質変換に大量のエネルギー消費、二酸化炭素排出を伴うため、バイオマス由来の原料を出発物質として、温和な条件下での反応を実現する生体触媒により様々な化学品を生産できれば理想的である。植物バイオマス中にはケイ皮酸類が二次代謝産物の前駆体や中間体として広く存在し、またエステルやリグニンなどの誘導体としても多く存在する。そこで申請者らは、ケイ皮酸類をバイオマス由来のモデル原料とし、これらの出発物質から生体触媒を利用して様々な有用物質を生産するための技術開発に取り組んでいる。カフェ酸は、ケイ皮酸に水酸基が2つ結合した化合物であり、非常に高い抗酸化活性を有する。さらに抗癌活性や抗炎症活性、抗ウイルス活性も有しており、医薬中間体やポリマー原料として応用する試みも近年多数報告されている。これまでに申請者らは、ゲノム情報を利用した探索により2-ナフトエ酸に水酸基を導入するRhodopseudomonas palustris由来シトクロムP450モノオキシゲナーゼCYP199A2を見出しており、さらに本酵素の立体構造に基づいて活性中心近傍のアミノ酸に変異を導入することにより、ケイ皮酸をカフェ酸に変換する酵素の創製にも成功している。そこで本研究では、変異酵素の詳細な機能解析とカフェ酸生産への応用を中心に検討を行った。活性中心近傍に存在する185位のフェニルアラニン残基を他の9種類のアミノ酸残基に置換した。その結果、ロイシンに置換した酵素Phe185Leuではp-クマル酸に対する水酸化活性が向上し、野生型酵素の5.5倍の活性を示した。また、ロイシン、グリシン、アラニンに置換した酵素は、2段階の水酸化反応を触媒して、ケイ皮酸からm-クマル酸、p-クマル酸を経てカフェ酸を合成することが可能になった。さらに変異酵素Phe185Leuを用いてフラスコレベルでのカフェ酸生産試験を検討したところ、リッターあたりグラムスケールでの生産を達成した。

アミノ酸リガーゼは保護基を持たない遊離のアミノ酸同士を直接縮合することが可能な有用酵素である。我々は、とくにL-アミノ酸リガーゼ（Lal）に着目し、これを用いた効率的かつ汎用的なペプチド合成システムの構築を最終目標として、まずは結晶構造解析により触媒残基や反応機構の詳細を解明することを検討した。Lalとしては既にBacillus licheniformis由来BL00235が結晶構造の取得に成功しているが、ここで明らかにされた情報からだけでは基質特異性などに関わる残基の特定には至らなかった。そこで、我々は新たにBacillus subtilis由来のRizA, RizBという二種類のLalについて結晶構造解析を行うこととした。RizAにおいては各種クロマトカラムを用いることで組換え酵素を高濃度（10 mg/ml）かつ高純度で精製することに成功した。さらに、蒸気拡散法による結晶化スクリーニングを検討して単結晶を得ることに成功し、X線結晶構造解析によって2.7Åの回折像を得た。分子置換法による位相決定には至らなかったが、結晶系が斜方晶系であることを明らかとすることに成功している。また、RizBに関しては組換え酵素の精製を検討中であり、完了次第結晶化条件のスクリーニングに移行する予定である。次に、既に結晶構造が解かれたBL00235について、構造情報を利用した酵素の耐熱化を検討した。酵素の耐熱性は工業レベルでの安定利用に不可欠な要素である。まず、B-FITTERと呼ばれるB-value計算プログラムを用いて構造の揺らぎを推定した。そしてBL00235において最もB-valueの高かった148位のAspを19種類のタンパク質構成性アミノ酸に置換した結果、Cysへの置換によって野生型のBL00235よりも変異型BL00235では加熱安定性が3℃ほど向上していた。

我々は、ペプチドの効率的な生産法確立を目的として、ATPの加水分解反応と共役して遊離アミノ酸同士の連結反応を触媒するアミノ酸リガーゼに着目した研究を進めている。特にL-アミノ酸リガーゼを用いた短鎖ペプチド合成研究において、これまで目覚しい成果をあげてきたが、オリゴならびにポリペプチド合成への新たな展開を考え、報告例のないオリゴペプチドを合成可能な新規L-アミノ酸リガーゼを探索するとともに、他のペプチド合成酵素としてNRPS(Non-Ribosomal Peptide Synthesis)や新規ポリアミノ酸合成酵素など新領域での酵素探索も推進した。微生物の生産するトリペプチド性の二次代謝産物に着目し、これら生産菌からの合成酵素の探索を検討した。その結果、トリペプチド以上のオリゴペプチドの合成活性を有するジペプチド合成酵素RizAの取得に成功した。リゾクチシン生産菌からは、精製酵素のN末端配列を決定して得た新規アミノ酸配列の酵素を取得した。さらに、当該酵素遺伝子の周辺領域の解析によって、トリペプチド以上のオリゴペプチド合成を可能とする初めてのリガーゼ酵素RizBの発見にも成功した。また、遺伝子クラスターの解析を進め、抗生物質リゾクチシンの生合成経路を推定することもできた。さらに、オリゴペプチド合成を可能とするRizBのアミノ酸配列情報を基にin silicoスクリーニングを実施し、新たに6種類のオリゴペプチド合成反応を触媒する酵素を見出すことにも成功した。現在、取得した多様なジペプチドならびにオリゴペプチド合成酵素を組み合わせ、任意のオリゴペプチド合成システムの開発を目指し検討を行っている。これまでに固定化酵素を用いた基本プロセスの構築に成功しており、具体例として血圧上昇抑制効果のある有用トリペプチドの生産も可能となった。

我々は、ペプチドの効率的な生産法確立を目的として、ATPの加水分解反応と共役して遊離アミノ酸同士の連結反応を触媒するアミノ酸リガーゼに着目した研究を進めている。特にL-アミノ酸リガーゼを用いた短鎖ペプチド合成研究において、これまで目覚しい成果をあげてきたが、オリゴならびにポリペプチド合成への新たな展開を考え、オリゴペプチドを合成可能な新規L-アミノ酸リガーゼを探索するとともに、他のリガーゼ酵素としてCyanophycin合成酵素に着目し、構造-活性相関に基づくCyanophycin合成酵素からの新規なポリペプチド合成酵素の創製を検討している。我々は、遊離アミノ酸を原料としてCyanophycinを直接合成できるプライマー非依存的な新規酵素の取得に成功している。本酵素は2つの活性ドメインを有している。そこで、酵素の構造-活性相関に関する情報を取得するためにD-Ala-D-AlaリガーゼやMurリガーゼなどとの一次配列の比較からATPとの結合に関わる活性残基を推定し、Alaに置換した変異酵素をいくつか作製した。これらの中でK261AならびにK497A変異酵素において活性の消失を確認し、活性に関わる残基の一部を特定することに成功した。また、一方で新規L-アミノ酸リガーゼの探索を目的として、微生物の生産するトリペプチド性の二次代謝産物（ファゼオロトキシン、リゾクチシン）に着目し、これらの合成酵素を探索した。その結果、いずれの検討においてもトリペプチド構成要素となるジペプチドの合成活性を有する酵素の取得に成功した。今後、これら近傍の遺伝子領域を解析することでトリペプチド合成を可能とする新規酵素が取得されることが期待されるとともに、Cyanophycin合成酵素との比較によって、構造-活性相関に関する知見を蓄積し、新規ペプチド合成酵素の創製へとつなげていくことを予定している。

我々は、多様な生理活性機能を有するペプチドの効率的な供給を目的として、ATPの加水分解反応を介し遊離アミノ酸同士の連結反応を触媒するアミノ酸リガーゼに着目し、特性の異なる新規アミノ酸リガーゼの探索や発現、当該酵素を利用した短鎖ペプチド合成プロセスの開発研究を実施してきた。一方、オリゴペプチドへの新たな展開を考え、その効率的な合成法を可能にする酵素としてCyanophycin合成酵素に着目した。本研究では、短鎖ペプチド合成酵素研究での知見を踏まえ、分子設計を中心としたタンパク質工学的な手法によるCyanophycin合成酵素からの新規なオリゴペプチド合成酵素の創製を目的とした。Cyanophycinは、シアノバクテリア（藍藻類）が菌体内に蓄積するポリペプチド（分子量：25～100 kDa）で、Aspが-ペプチド結合をした骨格にArgがAspの-カルボキシル基でペプチド結合した構造を有している。この独特な構造に着目し、遊離のAspとArgからのCyanophycin合成、さらには遊離アミノ酸からの任意オリゴペプチド合成を可能とする酵素の存在可能性を推定した。そこで、ゲノム情報を活用し、種々のシアノバクテリアからCyanophycin合成酵素を取得し、活性評価を行った。その結果、Thermosynechococcus elongatus BP-1由来のCyanophycin合成酵素において期待する活性を見出すことに成功した。さらに、本酵素の基質特異性は、極めて厳密であることもわかった。また、本酵素が2つの活性ドメインを有することから、酵素の構造-活性相関に関する情報を得るために各機能ドメインでの分割を試みたが、いずれのタンパク質もペプチド合成活性を示さなかった。今後、本酵素特性の詳細な解析やドメインの分割位置の最適化を検討し、基質特異性等の機能改変へと展開していく予定である。

【低基質特異性アミノ酸ラセマーゼの機能改変と解析】　Pseudomonas putida IFO 12996が生産する低基質特異性アミノ酸ラセマーゼは中性、塩基性アミノ酸に対し広範なラセミ化活性を示すユニークな酵素である。当該酵素を利用して、安価なL-アミノ酸を出発原料としたD-アミノ酸生産プロセスを検討しているが、酵素工学的な見地からの基質認識機構は未解明のままである。そこで基質特異性の変化した改変酵素を取得し、遺伝子配列、タンパク質レベルの比較解析を行うことで当該酵素の基質認識機構を解明することを検討した。さらに、広範な基質特異性を示す高機能アミノ酸ラセマーゼを用いた工業的なD-アミノ酸生産法の開発研究も行った。　これまでに低基質特異性アミノ酸ラセマーゼ遺伝子へのランダム変異導入を行い、トリプトファンに対して顕著な活性を示す改変酵素を5種類取得した。これらの改変酵素の変異部位の解析から、384位のイソロイシン残基、396位のチロシン残基が当該酵素の全体的な活性の向上とトリプトファン特異的な活性向上に寄与していることが示唆された。そこで、両残基をタンパク質を構成する20種類のアミノ酸すべてで置換した変異体を作成したところ、384位では疎水的な脂肪族アミノ酸への置換が、396位では側鎖に水酸基、チオール基を有するアミノ酸への置換が当該酵素の活性を向上させることを明らかにした。現在は反応速度論的解析や分光学的解析に加えタンパク質立体構造モデリングによる解析も含めた両残基でのアミノ酸置換による活性向上のメカニズムを検討中である。【D-アラニン-D-アラニンリガーゼによるD-アミノ酸ジペプチド合成】D-アミノ酸含有ペプチド（D-アミノ酸ペプチド）は天然のペプチドとは異なる機能を示し，医薬原料，機能性食品としての用途開発が期待される。本研究では、細菌の細胞膜生合成の過程で機能するEscherichia coli K-12由来のD-アラニン-D-アラニンリガーゼ（Ddl）が反応機構、基質特異性の点でD-アミノ酸ジペプチド合成に有用な酵素であることを明らかにしてきた。Ddlは多くの細菌の生育に必須な酵素であり、類縁酵素はその遺伝子配列も含めてゲノムデータベースより容易に取得可能である。そこで、遺伝子配列が既知の好熱性細菌Thermotoga maritimaに着目し、当該菌のDdlホモログ（TmDdl）の耐熱性と高温反応における基質特異性を検討することで、より多様なD-アミノ酸ジペプチド合成法の確立を検討した。これまでに、TmDdlがDdl活性を示し、常温での反応でもD-アラニン、D-セリン、D-スレオニン、D-システイン、グリシンを基質とする基質特異性の広いDdlであることを明らかにしてきた。そこで、当該酵素の耐熱性を測定したところ、TmDdlは10ºCから90ºCの範囲において熱安定性を示し、その反応速度は温度の上昇に伴って顕著に増大した。さらに60ºCの高温条件下ではTmDdlの基質特異性が拡張し，常温反応では合成が困難であったD-メチオニン、D-フェニルアラニンなどを含有する数種類のD-アミノ酸ジペプチドの合成にも成功した。さらにTmDdlが反応に必要とする微量のMg2+イオンを他の2価のカチオンで置換することで基質特異性が変化することを示唆する結果も得た。このようにTmDdlは高い安定性と広範な基質特異性を示す新規なDdlであり、効率的なD-アミノ酸ジペプチド合成法の開発に大きく寄与できるものと考えられる。

【アミノ酸ラセマーゼの機能改変と解析】公開されているゲノム情報を利用して低基質特異性のPseudomonas putida IFO12996由来のアミノ酸ラセマーゼ遺伝子をクローニングし、error-prone PCRによる遺伝子のランダム変異導入を実施した。L-トリプトファン要求性の大腸菌を用いて変異クローンライブラリーを構築し、D-トリプトファンで要求性が相補される変異クローンを取得して活性を評価した。その結果、期待通り活性の増大した変異クローンを取得できた。本クローンは芳香族アミノ酸であるフェニルアラニンに対する活性も増大しており、他のポジティブクローンと併せ詳細検討中。また、変異部位も特定しており、ネイティブ酵素遺伝子に対して部位特異的変異導入によって、取得変異クローンの活性変化の検証を進めている。【D-アミノ酸リガーゼの解析とD-アミノ酸ジペプチド合成法の開発】E. coli K 12由来のD-アラニン-D-アラニンリガーゼ（Ddl）をゲノム情報をもとにクローニングし、His-Tag融合酵素として大腸菌で発現させた。D-Alaに加え，D-Ser，D-Thr，D-Cys，Glyを基質とした場合にも活性に差はあるものの、それぞれ対応するD-アミノ酸からD-アミノ酸ホモジペプチドが生成していることを確認した。バンコマイシン耐性腸球菌（VRE）の変異型DdlがC末端側にD-AlaではなくD-Serを連結することは既に報告されているが、VRE以外の微生物のDdlがD-Ala 以外のアミノ酸も基質にすることに加え、C末端側だけではなくN末端側にもD-Ser，D-Thr，D-Cys，Glyが挿入される基質特異性のあることを明らかにしたのは本研究が初めてとなる。D-アラニル-D-アラニン，D-セリル-D-セリン，D-スレオニル-D-スレオニン，D-システイニル-D-システイン，グリシル-グリシンは収率にして71，71，2，60，77%での合成に成功し、Ddlを利用したD-アミノ酸ジペプチド合成プロセスの有効性を示した。【アミノ酸ラセマーゼ/D-アミノ酸リガーゼ共役系によるL-アミノ酸からD-アミノ酸ジペプチド合成法の開発】　E. coli K 12由来のDdlは立体特異性が厳密なため、D-アミノ酸だけでなくラセミ体混合基質からも目的のD-アミノ酸ジペプチドを生成する。この時、アミノ酸ラセマーゼを作用させることでラセミ体中のL-アミノ酸も基質として利用できるようになり、さらには安価に供給できるL-アミノ酸のみからのD-アミノ酸ジペプチド合成も可能となる。　上述の低基質特異性のPseudomonas putida IFO12996由来のアミノ酸ラセマーゼとDdlを共役させてL-アミノ酸からのD-アミノ酸ジペプチド合成を検討した。L-Ala、L-Ser、L-Cysから反応7時間で対応するD-アミノ酸ジペプチドをそれぞれ収率44%、36%、9%で合成することができた。D-アミノ酸を原料とする場合に比べ収率は低いものの、L-アミノ酸ジペプチドの副生は予想通り認められず、本プロセスではL-アミノ酸のラセミ化とD-アミノ酸ジペプチドの合成を一段階の反応で行うことができる。

【工業用微生物の生育制御システムの開発】　発酵生産菌の生育を自由に制御することができれば，発酵時間の短縮や目的産物の発酵収率を高めることが可能となる．実際，工業生産では栄養要求性変異を付与した微生物が用いられているが，こうした変異株の取得はネガティブ選択であり，また添加する栄養要求物質によってはコスト高，あるいは精製に影響を及ぼす場合もある．メチオニンは安価で，その要求株は安定な生産実績を示すことが知られている．我々は，鋭意検討した結果，メチオニンの少量存在下で取得した大腸菌のDL-エチオニン耐性株の中から高頻度にメチオニン要求株が得られることを見出し（取得頻度：３７％），従来法に比較するとその取得効率は８００倍以上であった．遺伝子解析の結果，いずれもmetBかつmetJ変異株であり，メチオニン要求性とDL-エチオニン耐性変異が検証され，また取得温度との関係も見出された．現在，metBとmetJへの部位特異的二重変異導入頻度の高い理由を解析中．【エネルギー代謝酵素を利用した発酵生産収率の向上と形質転換系の構築】　クエン酸生産菌である糸状菌Aspergillus nigerには，ミトコンドリア内に通常のチトクロム鎖とは別に酸化的リン酸化を伴わない呼吸系バイパス酵素alternative oxidase (AOX) が存在し，クエン酸生産とAOX活性がリンクしていることを見出している．A. niger WU-2223L由来のAOXをコードする全長2856bpの染色体遺伝子aox1の一部を欠失させ，相同組換え手法によりaox1破壊株を取得し，特性解析を実施した．サザンハイブリダイゼーションとPCR増幅によってaox1破壊を確認できた形質転換株A. niger⊿aox1-1は，AOX活性の特徴であるシアン非感受性呼吸が消失しており，糖代謝活性ならびにクエン酸生産活性の低下が認められた．また，形質転換マーカーとして重要なpyrG破壊用プラスミドを作成．【有用酵素の機能改変と大腸菌における高発現化】　遺伝子操作ツールとして重要な制限酵素BamHIの耐熱化をコンピュータシミュレーションと部位特異的変異の導入により達成．当該酵素の高発現はBamHIの制限系と修飾系酵素遺伝子の同時発現が必須であるが，大腸菌においては修飾系酵素遺伝子の発現が律速であることを明らかにした．解析の結果，転写には問題はなくレアコドンの影響で翻訳効率が低くなっていることが判明し，アルギニンに対応するtRNA遺伝子dnaYの共発現によって高発現を達成．

　L-ヒスチジン(HIS)は胃潰瘍、貧血の治療薬など医薬品としてのほか、食品添加物や化学品としてもその用途は広く、世界で約４００T/年が生産されている。そのほとんどを供給している協和発酵では、糖蜜を主炭素源としコリネ型グルタミン酸生産菌の変異株を用いた発酵法により生産しているが、本生産菌では生産されるHISと等モルのグリシン(Gly)を副生するため、大幅な成績向上が期待できず、またGlyの生理的特性から生産菌活性の低下が余儀なくされている。一方、糖蜜産出国における精糖技術の向上とグルタミン酸発酵工業の隆盛等によって、我国など諸外国へ輸出される糖蜜の価格上昇や品質の低下は著しく、発酵成績の低下や製品品質への影響が問題となっている。さらに発酵廃液処理に関わる環境対策も解決すべき大きな課題である。こうした状況を踏まえ、我々は大腸菌を生産菌株として選定し、従来の知見も生かしつつ変異育種にて効率的に生合成制御の解除を図り、生産性の高い実用菌株の造成に成功した。（特許出願）