Dynamic remodeling of the extracellular matrix affects many cellular processes, either directly or indirectly, through the regulation of soluble ligands; however, the mechanistic details of this process remain largely unknown. Here we propose that type I collagen remodeling regulates the receptor-binding activity of pigment epithelium-derived factor (PEDF), a widely expressed secreted glycoprotein that has multiple important biological functions in tissue and organ homeostasis. We determined the crystal structure of PEDF in complex with a disulfide cross-linked heterotrimeric collagen peptide, in which the α(I) chain segments-each containing the respective PEDF-binding region (residues 930 to 938)-are assembled with an α2α1α1 staggered configuration. The complex structure revealed that PEDF specifically interacts with a unique amphiphilic sequence, KGHRGFSGL, of the type I collagen α1 chain, with its proposed receptor-binding sites buried extensively. Molecular docking demonstrated that the PEDF-binding surface of type I collagen contains the cross-link-susceptible Lys930 residue of the α1 chain and provides a good foothold for stable docking with the α1(I) N-telopeptide of an adjacent triple helix in the fibril. Therefore, the binding surface is completely inaccessible if intermolecular crosslinking between two crosslink-susceptible lysyl residues, Lys9 in the N-telopeptide and Lys930, is present. These structural analyses demonstrate that PEDF molecules, once sequestered around newly synthesized pericellular collagen fibrils, are gradually liberated as collagen crosslinking increases, making them accessible for interaction with their target cell surface receptors in a spatiotemporally regulated manner.

<p>Collagen-like peptides containing Gly-Ser <italic>O</italic>-acyl isopeptide units without self-assembling propensity serve as precursors for collagen-detecting agents.</p>

Heat shock protein 47 (HSP47) is an endoplasmic reticulum (ER)-resident molecular chaperone that specifically recognizes triple helical portions of procollagens. The chaperone function of HSP47 is indispensable in mammals, and hsp47-null mice show an embryonic lethal phenotype accompanied by severe abnormalities in collagen-based tissue structures. Two leading hypotheses are currently accepted for the molecular function of HSP47 as a procollagen-specific chaperone. One is facilitation of procollagen folding by stabilizing thermally unstable triple helical folding intermediates, and the other is inhibition of procollagen aggregation or lateral association in the ER. The aim of this study was to elucidate the functional essence of this unique chaperone using fibroblasts established from hsp47-/- mouse embryos. When the cells were cultured at 37 °C, various defects in procollagen biosynthesis were observed, such as accumulation in the ER, over-modifications including prolyl hydroxylation, lysyl hydroxylation, and further glycosylation, and unusual secretion of type I collagen homotrimer. All defects were corrected by culturing the cells at a lower temperature of 33 °C. These results indicated that lowering the culture temperature compensated for the loss of HSP47. This study elucidated that HSP47 stabilizes the elongating triple helix of procollagens, which is otherwise unstable at the body temperature of mammals.

Collagen is the most abundant protein in the animal kingdom and has a unique triple-helical structure. It not only provides mechanical strength to tissues, but also performs specific biological functions as a multifaceted signaling molecule. Animal-derived collagen is therefore widely used as a biocompatible material in vitro and in vivo. In this study, we developed a novel peptide-based material that mimicked both the polymeric properties and a selected biological function of native collagen. This material was prepared by end-to-end multiple disulfide cross-linking of chemically synthesized triple-helical peptides. The peptide polymer showed a gel-forming property, and receptor-specific cell binding was observed in vitro by incorporating a peptide harboring an integrin α2β1-binding sequence. Furthermore, cell signaling activity and biodegradability were tunable according to the polymer contents. The results demonstrated the potential of this material as a designer collagen. STATEMENT OF SIGNIFICANCE: Collagen is a useful biomaterial with the gel-forming property. It also exhibits various biological activities through the interaction of specific amino acid sequences displayed on the triple helix with functional biomacromolecules. Here we report a novel synthetic material, artificial collagen, by end-to-end cross-linking of chemically synthesized collagen-like triple-helical peptides. The material allows independent regulation of polymer properties, i.e. gel stiffness, and sequence-specific bioactivities by altering peptide compositions. This material can also be variously shaped, for example, thin films with high transparency. In addition, it has low inflamatogenic properties and tunable biodegradability in vivo.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim We report here a new class of collagen-binding peptides, cyclic collagen-mimetic peptides (cCMPs), that efficiently hybridize with the triple-helix-forming portions of collagen. cCMPs are composed of two parallel collagen-like (Xaa-Yaa-Gly)n strands with both termini tethered by covalent linkages. Enzyme-linked immunosorbent assays and western blotting analysis showed that cCMPs exhibit more potent affinity toward collagen than reported collagen-binding peptides and can specifically detect different collagen polypeptides in a mixture of proteins. Collagen secreted from cultured cells was detected by confocal microscopy with fluorescein-labeled cCMP. The cCMP is also shown to detect sensitively folding intermediates in the endoplasmic reticulum, something that was difficult to visualize with conventional collagen detectors. Molecular-dynamics simulations suggested that a cCMP forms a more stably hybridized product than its single-chain counterpart; this could explain why cCMP has higher affinity toward denatured collagen. These results indicate the usefulness of cCMPs as tools for detecting denatured collagen.

Aim: The development of a platinum anticancer agent that has improved efficacy by efficient delivery to a tumor and that suppresses side effects has been investigated. Arginine-rich triple-helical peptides are promising drug carriers because of their stability in body fluids and cell-penetrating activity. Results: We synthesized a carboplatin derivative conjugated with an arginine-rich triple-helical peptide. This derivative released platinum under acidic conditions or in the presence Cl- ions. Administration of this derivative to P388 tumor-bearing mice showed comparable survival rates to twice the dose of carboplatin, which was attributed to a longer mean residence time by pharmacokinetics analysis. Conclusion: The collagen-like triple-helical peptide was an efficient carrier of a platinum anticancer agent because of a modification to its pharmacokinetic profile.

Vibrio alginolyticus is an opportunistic pathogen in both humans and marine animals. Collagenase encoded by colA is considered to be one of the virulence factors. Expression of colA is regulated by multiple environmental factors, e.g., temperature, growth phase, and substrate. To elucidate the mechanism of regulation of colA expression, transposon mutagenesis was performed. VarS, a sensor histidine kinase of the two-component regulatory system, was demonstrated to regulate the expression of colA. VarA, a cognate response regulator of VarS, was also identified and shown to be involved in the regulation of colA expression. In vitro phosphorylation assays showed that phosphorylated VarS acted as a phosphoryl group donor to VarA. A site-directed mutagenesis study showed that the His300, Asp718 and His874 residues in VarS were essential for the phosphorylation of VarS, and the Asp54 residue in VarA was likely to receive the phosphoryl group from VarS. The results demonstrate that the VarS/VarA two-component regulatory system regulates the expression of collagenase in V. alginolyticus.

Basic fibroblast growth factor 2 (bFGF) accelerates bone formation during fracture healing. Because the efficacy of bFGF decreases rapidly following its diffusion from fracture sites, however, repeated dosing is required to ensure a sustained therapeutic effect. We previously developed a fusion protein comprising bFGF, a polycystic kidney disease domain (PKD
s2b), and collagen-binding domain (CBD
s3) sourced from the Clostridium histolyticum class II collagenase, ColH, and reported that the combination of this fusion protein with a collagen-like peptide, poly(Pro-Hyp-Gly)10, induced mesenchymal cell proliferation and callus formation at fracture sites. In addition, C. histolyticum produces class I collagenase (ColG) with tandem CBDs (s3a and s3b) at the C-terminus. We therefore hypothesized that a bFGF fusion protein containing ColG-derived tandem CBDs (s3a and s3b) would show enhanced collagen-binding activity, leading to improved bone formation. Here, we examined the binding affinity of four collagen anchors derived from the two clostridial collagenases to H-Gly-Pro-Arg-Gly-(Pro-Hyp-Gly)12-NH2, a collagenous peptide, by surface plasmon resonance and found that tandem CBDs (s3a-s3b) have the highest affinity for the collagenous peptide. We also constructed four fusion proteins consisting of bFGF and s3 (bFGF-s3), s2b-s3b (bFGF-s2b-s3), s3b (bFGF-s3b), and s3a-s3b (bFGF-s3a-s3b) and compared their biological activities to those of a previous fusion construct (bFGF-s2b-s3) using a cell proliferation assay in vitro and a mouse femoral fracture model in vivo. Among these CB-bFGFs, bFGF-s3a-s3b showed the highest capacity to induce mesenchymal cell proliferation and callus formation in the mice fracture model. The poly(Pro-Hyp-Gly)10/bFGF-s3a-s3b construct may therefore have the potential to promote bone formation in clinical settings.

An antimicrobial triple-helical peptide, R3, was previously obtained from a collagen-like combinatorial peptide library. In this research, based on structure-activity relationship studies of R3, a more potent peptide, RR4, with increased positive net charge and charge density relative to R3, was developed. RR4 exhibited antimicrobial activity against both Gram-negative and Gram-positive bacterial strains, including multidrug-resistant strains. Its action could be attributed to entry into cells and interactions with intercellular molecules such as DNA/RNA that inhibited cell division rather than increasing bacterial membrane permeability. Furthermore, RR4 exhibited remarkable stability in serum and low cytotoxicity.

Combinatorial library composed of rigid rod-like peptides with a triple-helical scaffold was constructed. The component peptides were designed to have various combinations of basic and neutral (or hydrophobic) amino acid residues based on collagen-like (Gly-Pro-Yaa)-repeating sequences, inspired from the basic and amphiphilic nature of naturally occurring antimicrobial peptides. Screening of the peptide pools resulted in identification of antimicrobial peptides. A structure-activity relationship study revealed that the position of Arg-cluster at N-terminus and cystine knots at C-terminus in the triple helix significantly contributed to the antimicrobial activity. The most potent peptide RO-A showed activity against Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. In addition, Escherichia coli exposed to RO-A resulted in abnormal elongation of the cells. RO-A was also shown to have remarkable stability in human serum and low cytotoxicity to mammalian cells. (C) 2016 Wiley Periodicals, Inc.

Cell-penetrating peptides (CPPs) are attractive tools for delivering macromolecules that have poor membrane permeability, such as antibodies, into cells. However, the major drawback of conventional CPPs is their instability in bodily fluids. We previously reported a novel CPP employing a collagen-like triple-helical structure that exhibited remarkable resistance against serum proteases. Herein, we report the delivery of full-length immunoglobulin G (IgG) antibody into cells using a triple-helical CPP. The CPP was conjugated to IgG via a one-pot reaction using 2-iminothiolane as a crosslinking reagent. The triple-helical CPP was less prone to being aggregated and neutralized by serum than was octaarginine, a conventional CPP. However, most of the conjugates were found to be entrapped in endosomes.

Orally ingested peptides are generally digested in the gastrointestinal (GI) tract and absorbed in the form of oligopeptides. We previously reported that intravenously administered collagen-like triple-helical peptides circulated in the bloodstream and were excreted in their intact forms in urine nearly quantitatively. In the present study, we investigated the fates of orally administered collagen-like peptides in rats. (Pro-Hyp-Gly)10 (Hyp: 4-hydroxyproline), which formed a stable triple-helical structure, was stable in the GI tract, and 72.3±13.0% of the peptide was excreted in the feces. Its recovery ratio was similar to that of all-D-(Pro-Pro-Gly)10 (75.1±15.7%), the indigestible control. In contrast, (Pro-Hyp-Gly)5 and (Pro-Pro-Gly)10, the random coil conformations of which were dominant at body temperature, were not detected in fecal samples, indicating that they were digested by proteases. The high stability of the triple-helical conformation in mammalian bodies suggests the potential use of collagen-like peptides as novel scaffolds of peptide drugs.

Using an in vitro random screening of small-molecule compounds, we discovered cis-diamminedichloroplatinum(II) (cisplatin), an anticancer agent, as a potential inhibitor of collagen fibril-formation. The inhibitory effect was found only when cisplatin was dissolved in dimethylsulphoxide (DMSO), indicating that the active species were cisplatin derivatives formed in the DMSO solution. The cisplatin derivatives inhibited the formation of collagen fibrils in vitro without affecting the triple-helical conformation of the collagen molecules. Incubation with the cisplatin solution in DMSO also inhibited in situ deposition of collagen fibrils in a human umbilical vein endothelial cell (HUVEC) culture. In addition, the derivatization of cisplatin in DMSO abolished the cytotoxicity of the original compound. The platinum complex was further revealed to interact with specific sites on the collagen triple helix, and the binding sites were suggested to contain His and/or Met residues. Mass spectrometry analysis of the cisplatin solution in DMSO and a structure-activity relationship study strongly suggested that the active compound is [Pt(NH3)(2)(Cl)(DMSO)](+). This platinum complex will be useful for investigating molecular mechanisms of collagen self-assembly and for drug development for the treatment of fibrotic diseases.

Collagen family proteins are the predominant components of extracellular matrices existing in all multicellular animals. They provide mechanical strength to tissues, and maintain structural integrity of organs. Also, collagens regulate various biological events, including cell attachment, migration, tissue regeneration and animal development. The specific functions of collagens are generally elicited by interactions of collagen-binding molecules (membrane receptors, soluble factors and other matrix components) with certain amino acid sequences displayed on the collagen triple helices. To date, numbers of functional sequences have been identified from the triple helical domains. Collagen is also acknowledged as one of useful biomaterials in regenerative medicine and tissue engineering. In this review, I summarize challenges made for the development of safer and highly-functional collagen surrogates by means of self-assembly of synthetic collagen-like peptides. I also describe other possible applications of collagen-like peptides in drug delivery focusing on the particular biophysical properties of the triple helical structure. © 2013 The Pharmaceutical Society of Japan.

Collagen-model peptides composed of (X-Y-Gly)n sequences were used to study the triple helical structure of collagen. We report the stability of these collagen-like peptides in biological fluids, and their pharmacokinetics including distribution, metabolism, and excretion in animals. A typical collagen-model peptide, H-(Pro-Hyp-Gly)10-OH, was found to be extremely stable in the plasma and distributed mainly in the vascular blood space, and was eliminated through glomerular filtration in the kidneys. Triple helical peptides of (X-Y-Gly)n sequences were quantitatively recovered from the urine of rats after intravenous injection regardless of the differences in peptide net charge between -3 and +6 per triple helix. In contrast, the renal clearance became less efficient when the number of triplet repeats (n) was 12 or more. We also demonstrated the application of a collagen-like triple helical peptide as a novel drug carrier in the blood with a high urinary excretion profile. We further demonstrated that a collagen-like triple helical peptide conjugated to a spin probe, PROXYL, has the potential to evaluate the redox status of oxidative stress-induced animals in vivo. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci).

Clostridium histolyticum collagenase causes extensive degradation of collagen in connective tissue that results in gas gangrene. The C-terminal collagen-binding domain (CBD) of these enzymes is the minimal segment required to bind to a collagen fibril. CBD binds unidirectionally to the undertwisted C-terminus of triple helical collagen. Here, we examine whether CBD could also target undertwisted regions even in the middle of the triple helix. Collageneous peptides with an additional undertwisted region were synthesized by introducing a Gly ? Ala substitution [(POG)xPOA(POG)y]3, where x + y = 9 and x &gt; 3). 1H15N heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) titration studies with 15N-labeled CBD demonstrated that the minicollagen binds to a 10 angstrom wide 25 angstrom long cleft. Six collagenous peptides each labeled with a nitroxide radical were then titrated with 15N-labeled CBD. CBD binds to either the Gly ? Ala substitution site or to the C-terminus of each minicollagen. Small-angle X-ray scattering measurements revealed that CBD prefers to bind the Gly ? Ala site to the C-terminus. The HSQC NMR spectra of 15N-labeled minicollagen and minicollagen with undertwisted regions were unaffected by the titration of unlabeled CBD. The results imply that CBD binds to the undertwisted region of the minicollagen but does not actively unwind the triple helix.

Heat shock protein 47 (Hsp47) acts as a client-specific chaperone for collagen and plays a vital role in collagen maturation and the consequent embryonic development. In addition, this protein can be a potential target for the treatment of fibrosis. Despite its physiological and pathological importance, little is currently known about the collagen-binding mode of Hsp47 from a structural aspect. Here, we describe an NMR study that was conducted to identify the collagen-binding site of Hsp47. We used chicken Hsp47, which has higher solubility than its human counterpart, and applied a selective N-15-labeling method targeting its tryptophan and histidine residues. Spectral assignments were made based on site-directed mutagenesis of the individual residues. By inspecting the spectral changes that were observed upon interaction with a trimeric collagen peptide and the mutational data, we successfully mapped the collagen-binding site in the B/C beta-barrel domain and a nearby loop in a 3D-homology model based upon a serpin fold. This conclusion was confirmed by mutational analysis. Our findings provide a molecular basis for the design of compounds that target the interaction between Hsp47 and procollagen as therapeutics for fibrotic diseases.

Square-millimeter-sized free-floating translucent films are formed in physiological buffer by multiway connections between biotinylated collagen-like triple-helical peptides and avidin. Although the compositions of the films are almost constant, regardless of the ratios of the components loaded, their thicknesses can be controlled by the concentrations of the components. The film surfaces can be further modified by taking advantage of exposed biotin (or avidin) functionalities. The self-assembled films could serve as novel materials in biomedical and biosensing applications.

Safer heparin-neutralizing agents are currently required to replace protamine, the use of which causes adverse effects such as anaphylaxia. Low-molecular-weight (LMW) heparin mimetics that potentiate antithrombin III (AT) action are also valuable as anti-thrombotics. This paper describes a high-throughput assay for both heparin-neutralizing agents and LMW heparin mimetics without the use of blood preparations. The assay is based on turbidimetric measurement of a solution of collagen, heparin, and a test compound. Native collagen molecules spontaneously form insoluble fibrils when transferred to a physiological buffer, and this process is inhibited by heparin. In the presence of a heparin-neutralizing agent or an LMW heparin mimetic, the inhibitory effect of heparin is canceled and turbidity increase is retrieved. We demonstrated that this assay is effective in detecting potential agents with high reliability (Z' factor=0.9). The screening of a chemical library (34400 compounds) was further performed in a 384-well format, and led to the identification of a novel heparin-neutralizing agent. Since this assay protocol is feasible for an automated high-throughput screening (HTS) system, it could enhance the lead seeking process for drugs related to heparin/heparan sulfate (HS) functions.

Pigment epithelium-derived factor (PEDF) is a collagen-binding protein that is abundantly distributed in various tissues, including the eye. It exhibits various biological functions, such as anti-angiogenic, neurotrophic, and neuroprotective activities. PEDF also interacts with extracellular matrix components such as collagen, heparan sulfate proteoglycans (HSPGs), and hyaluronan. The collagen-binding property has been elucidated to be important for the anti-angiogenic activity in vivo (Hosomichi, J., Yasui, N., Koide, T., Soma, K., and Morita, I. (2005) Biochem. Biophys. Res. Commun. 335, 756-761). Here, we investigated the collagen recognition mechanism by PEDF. We first narrowed down candidate PEDF-binding sequences by taking advantage of previously reported structural requirements in collagen. Subsequent searches for PEDF-binding sequences employing synthetic collagen-like peptides resulted in the identification of one of the critical binding sites for PEDF, human alpha 1(I)(929-938) (IKGHRGFSGL). Further analysis revealed that the collagen recognition by PEDF is sequence-and conformation-specific, and the high affinity binding motif is KGXRG-FXGL in the triple helix. The PEDF-binding motif significantly overlapped with the heparin/HSPG-binding motif, KGHRG(F/Y). The interaction of PEDF with collagen I was specifically competed with by heparin but not by chondroitin sulfate-C or hyaluronan. The binding sequences for PEDF and heparin/HSPG also overlapped with the covalent cross-linking sites between collagen molecules. These findings imply a functional relationship between PEDF and HSPGs during angiogenesis, and the interaction of these molecules is regulated by collagen modifications.

Heat-shock protein 47 (HSP47) is a chaperone that facilitates the proper folding of procollagen. Our previous studies showed that the high-affinity HSP47-binding motif in the collagen triple helix is Xaa-(Thr/Pro)-Gly-Xaa-Arg-Gly. In this study, we further investigated structural requirements for the HSP47-binding motif, using synthetic triple-helical collagen-model peptides with systematic amino acid substitutions at either the Thr/Pro (=Yaa(-3)) or the Arg(=Yaa(0)) position. Results obtained from in vitro binding assays indicated that HSP47 detects the side-chain structure of Arg at the Yaa(0)-position, while the Yaa(-3) amino acid serves as the secondary recognition site that affects affinity to HSP47. (C) 2010 Elsevier Ltd. All rights reserved.

Collagen is an abundantly distributed extracellular matrix protein in mammalian bodies that maintains structural integrity of the organs and tissues. Besides its function as a structural protein, collagen has various biological functions which regulate cell adhesion, migration and differentiation. In order to develop totally synthetic collagen-surrogates, we recently reported a basic concept for preparing collagen-like triple helical supramolecules based on the self-assembly of staggered trimeric peptides with self-complementary shapes. In this paper, we add one of the specific cellular functions of the native collagen to the collagen-mimetic supramolecule. We synthesized a self-assembling peptide unit containing the integrin-binding sequence Gly-Phe-Hyp-Gly-Glu-Arg. The supramolecule carrying the sequence exhibited significant binding activity to human dermal fibroblasts. The supramolecular structure was found to be essential for function in in vitro cell culture. Cell adhesion was shown to be comparable to that of native collagen, and was further demonstrated to be mediated solely by integrin alpha 2 beta 1. Well-grown focal contacts and stress fibers were observed in cells spread on the supramolecular collagen-mimetic. The results demonstrate the potential of pepticle-based artificial collagen as a biomaterial for regulating specific cellular function and fate. (C) 2009 Elsevier Ltd. All rights reserved.

Collagen-binding proteins (CBPs) play important roles in various physiological events. Some CBPs are regarded as targets for drug development; for example, platelet glycoprotein VI (GPVI) and heat shock protein 47 (HSP47) are promising targets for the development of novel antiplatelet and antifibrotic drugs, respectively. However, no systematic screening method to search compounds that inhibit collagen-CBP interactions have been developed, and only a few CBP inhibitors have been reported to date. In this study, a facile turbidimetric multiwell plate assay was developed to evaluate inhibitors of CBPs. The assay is based on the finding that CBPs retard spontaneous collagen fibril formation in vitro and that fibril formation is restored in the presence of compounds that interfere with the collagen-CBP interactions. Using the same platform, the assay was performed in various combinations of fibril-forming collagen types and CBPs. This homogeneous assay is simple, convenient, and suitable as an automated high-throughput screening system. (C) 2009 Elsevier Inc. All rights reserved.

Histotoxic clostridia produce collagenases responsible for extensive tissue destruction in gas gangrene. The C-terminal collagen-binding domain (CBD) of these enzymes is the minimal segment required to bind to collagen fibril. Collagen binding efficiency of CBD is more pronounced in the presence of Ca(2+). We have shown that CBD can be functional to anchor growth factors in local tissue. A (1)H-(15)N HSQC NMR titration study with three different tropocollagen analogues ((POG)(10))(3), ((GPOG)(7)PRG)(3), and (GPRG(POG)(7)C-carbamidomethyl)(3), mapped a saddle-like binding cleft on CBD. NMR titrations with three nitroxide spin-labeled analogues of collagenous peptide, (PROXYL-G(POG)(7)PRG)(3), (PROXYL-G(POG)(7))(3), and (GPRG(POG)(7)C-PROXYL)(3) (where PROXYL represents 2,2,5,5-tetramethyl-L-pyrrolidinyloxy), unambiguously demonstrated unidirectional binding of CBD to the tropocollagen analogues. Small angle x-rays cattering data revealed that CBD binds closer to a terminus for each of the five different tropocollagen analogues, which in conjunction with NMR titration studies, implies a binding mode where CBD binds to the C terminus of the triple helix.

Development of artificial collagens to replace the animal-derived collagens presents a challenge in the formation of safer and functional biomaterials. We report here the development of collagen-like gels by means of the self-assembly of chemically synthesized peptides. The peptides are disulfide-linked trimers of collagenous Gly-X-Y triplet repeats with self-complementary shapes. Upon cooling the peptide solutions, hydrogels of peptide supramolecules are formed by spontaneous intermolecular triple helix formation. The thermal gel-sol transition appeared to be reversible and the transition temperatures were found to be tunable by the design of the peptides. Our systems for the formation of artificial collagen-like gels will offer possibilities for novel types of biomaterials. (C) 2008 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 90: 816-823, 2008.

Collagens, characterized by a unique triple-helical structure, are the predominant component of extracellular matrices (ECMs) existing in all multicellular animals. Collagens not only maintain structural integrity of tissues and organs, but also regulate a number of biological events, including cell attachment, migration and differentiation, tissue regeneration and animal development. The specific functions of collagens are generally triggered by specific interactions of collagen-binding molecules (membrane receptors, soluble factors and other ECM components) with certain structures displayed on the collagen triple helices. Thus, synthetic triple-helical peptides that mimic the structure of native collagens have been used to investigate the individual collagen-protein interactions, as well as collagen structure and stability. The first part of this article illustrates the design of various collagen-mimetic peptides and their recent applications in matrix biology. Collagen is also acknowledged as one of the most promising biornaterials in regenerative medicine and tissue engineering. However, the use of animal-derived collagens in human could put the recipients at risks of pathogen transmission or allergic reactions. Hence, the production of safe artificial collagen surrogates is currently of considerable interest. The latter part of this article reviews recent attempts to develop artificial collagens as novel biomaterials.

The endoplasmic reticulum-resident chaperone heat-shock protein 47 (HSP47) plays an essential role in procollagen biosynthesis. The function of HSP47 relies on its specific interaction with correctly folded triple-helical regions comprised of Gly-Xaa-Yaa repeats, and Arg residues at Yaa positions have been shown to be important for this interaction. The amino acid at the Yaa position (Yaa(-3)) in the N-terminal-adjoining triplet containing the critical Arg ( defined as Arg(0)) was also suggested to be directly recognized by HSP47 (Koide, T., Asada, S., Takahara, Y., Nishikawa, Y., Nagata, K., and Kitagawa, K. ( 2006) J. Biol. Chem. 281, 3432 - 3438). Based on this finding, we examined the relationship between the structure of Yaa(-3) and HSP47 binding using synthetic collagenous peptides. The results obtained indicated that the structure of Yaa(-3) determined the binding affinity for HSP47. Maximal binding was observed when Yaa(-3) was Thr. Moreover, the required relative spatial arrangement of these key residues in the triple helix was analyzed by taking advantage of heterotrimeric collagen-model peptides, each of which contains one Thr(-3) and one Arg(0). The results revealed that HSP47 recognizes the Yaa(-3) and Arg(0) residues only when they are on the same peptide strand. Taken together, the data obtained led us to define the HSP47-binding structural epitope in the collagen triple helix and also define the HSP47-binding motif in the primary structure. A motif search against human protein database predicted candidate clients for this molecular chaperone. The search result indicated that not all collagen family proteins require the chaperoning by HSP47.

The unique folding of procollagens in the endoplasmic reticulum is achieved with the assistance of procollagen-specific molecular chaperones. Heat-shock protein 47 (HSP47) is an endoplasmic reticulum-resident chaperone that plays an essential role in normal procollagen folding, although its molecular function has not yet been clarified. Recent advances in studies on the binding specificity of HSP47 have revealed that Arg residues at Yaa positions in collagenous Gly-Xaa-Yaa repeats are critical for its interactions (Koide, T., Takahara, Y., Asada, S., and Nagata, K. (2002) J. Biol. Chem. 277, 6178-6182
Tasab, M., Jenkinson, L., and Bulleid, N. J. (2002) J. Biol. Chem. 277, 35007-35012). In the present study, we further examined the client recognition mechanism of HSP47 by taking advantage of systems employing engineered collagen model peptides. First, in vitro binding studies using conformationally constrained collagen-like peptides revealed that HSP47 only recognized correctly folded triple helices and that the interaction with the corresponding single-chain polypeptides was negligible. Second, a binding study using heterotrimeric model clients for HSP47 demonstrated aminimal requirement for the number of Arg residues in the triple helix. Finally, a cross-linking study using photoreactive collagenous peptides provided information about the spatial orientation of an HSP47 molecule in the chaperone-collagen complex. The obtained results led to the development of a new model of HSP47-collagen complexes that differs completely from the previously proposed "flying capstan model" (Dafforn, T. R., Della, M., and Miller, A. D. (2001) J. Biol. Chem. 276, 49310-49319). © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.

Collagen is acknowledged as one of the most prominent biomaterials on account of its high biocompatibility and biostability. The development of artificial collagens to replace the animal-derived collagens presents a challenge in the formation of safer and highly functionalized biomaterials. Here, a novel peptide-based system for obtaining collagen-like supramolecules via a spontaneous self-assembling process is described. The designed collagen-like peptides are self-complementary trimers in which each of the 24-mer peptide strands is tethered by two cystine knots forming a staggered arrangement. Their self-assembling ability in aqueous solution was analyzed by circular dichroism, ultrafiltration, and laser diffraction particle size estimation. The obtained results indicate that the staggered trimers form large supramolecular architectures through intermolecular triple helix-formation. (c) 2005 Elsevier Ltd. All rights reserved.

Pigment epithelium-derived factor (PEDF) is the most potent endogenous inhibitor of angiogenesis in age-related macular degeneration and tumors. However, the molecular mechanism of the anti-angiogenic activity of PEDF is poorly understood. PEDF interacts with the extracellular matrix (ECM) in vitro. Here, we investigated the possible involvement of the motif for ECM interaction in the anti-angiogenic activity of PEDF. The growth rates of HeLa cells in culture were not affected by transfection of PEDF, indicating that PEDF did not suppress tumor cell growth directly. In tumor xenografts, the overexpression of wild-type PEDF significantly suppressed tumor growth, whereas a mutant of the collagen I-binding site of PEDF (Col-mut PEDF) did not inhibit tumor growth. A mutant of the heparin-binding site of PEDF (Hep-mut PEDF) suppressed tumor growth. Histological analysis showed that the density and area of microvasculatures in either PEDF or Hep-mut PEDF were suppressed when compared with those in either vector or Col-mut PEDF. Our data indicate that PEDF inhibits tumor growth via its anti-angiogenic activity, and the collagen I-binding motif of PEDF is involved in the biological activity. (C) 2005 Elsevier Inc. All rights reserved.

Collagen, a large insoluble protein with a characteristic triple helical structure, is found as the most prominent component of extracellular matrix. The functions of collagen are not limited to providing mechanical strength to various tissues and organs as a structural protein, as it has been pointed out that collagen exhibits various biological functions through specific interactions with other macromolecules. However, the use of native triple helical collagen is often troublesome because of its insolubility and gelating properties. Instead, triple helical collagen-like peptides have been designed and are used as collagen surrogates in studies on collagen structure, stability, and biological functions including binding to other proteins and cultured cells. This article reviews recent progress in peptide design, synthesis, and the applications of collagen-like peptides in current matrix biology, while emphasizing the advantages of the peptide-based strategy.

Collagen is synthesized in the endoplasmic reticulum (ER) as pro collagen, which is the precursor protein that bears propeptide domains at either end of the triple helical domain. The processes by which procollagen is synthesized in the lumen of the ER include unique steps that are not found in the biosynthesis of globular proteins. First, each polypeptide chain of procollagen (pro alpha-chains) finds its correct partners, which enables the formation of the distinct types of procollagen. Second, triple helix-formation of long Gly-X-Y repeats starts at a defined region, which results in the formation of a correctly aligned triple helix and thereby prevents mis-staggering. The most characteristic step is the formation of the triple helix. This step involves specific post-translational modifications, in particular, the prolyl 4-hydroxylation of the Upsilon-position amino acids that stabilizes the triple helical conformation. The formation of the triple helix is a slow process compared to the folding of globular proteins, including cis-trans isomerization of the many prolyl and hydroxyprolyl peptide bonds. Recent advances have indicated that these processes are assisted by a set of the ER-resident molecular chaperones, such as protein disulfide isomerase (PDI), peptidyl prolyl cis-trans isomerases (PPIases), heat-shock protein (Hsp)47, and prolyl 4-hydroxylase (P4-H). The intracellular trafficking of procollagen molecules has also been shown to involve a pathway distinct from that utilized by small secretory proteins.

An Arg residue incorporated into the Y-position of collagenous host-guest peptide Ac-(Gly-Pro-Hyp)(3)-Gly-Pro-Y-(Gly-Pro-Hyp)(4)-Gly-Gly-NH2 is reported to stabilize the triple helical structure as well as a 4(R)-hydroxyproline (Hyp) residue. Here, we synthesized heterotrimeric collagen models containing Arg in Y-positions utilizing the cystine knot strategy. Analysis of their thermal transition temperatures using circular dichroism spectrometry demonstrated unexpected decrease in the triple helical stability as the number of Arg increased. The obtained results indicated that an Arg residue in a Y-position is not always an equivalent of a Hyp residue, and that it possesses a potential helix destabilizing effect. (C) 2003 Elsevier Ltd. All rights reserved.

Pigment epithelium-derived factor (PEDF), a member of the serine protease inhibitor (serpin) superfamily, possesses anti-angiogenic and neurotrophic activities. PEDF has been reported to bind to extracellular matrix (ECM) components such as collagens and glycosaminoglycans (GAGs). In this study, to determine the binding sites for collagens and GAGs, we analyzed the interaction of recombinant mouse PEDF (rPEDF) with collagen I and heparin. By utilizing residue-specific chemical modification and site-directed mutagenesis techniques, we revealed that the acidic amino acid residues on PEDF (Asp(255), Asp(257), and Asp(299)) are critical to collagen binding, and three clustered basic amino acid residues (Arg(145). Lys(146), and Arg(148)) are necessary for heparin binding. Mapping of these residues on the crystal structure of human PEDF (Simonovic, M., Gettins, P. G. W., and Volz, K. (2001) Proc. Natl. Acad. Sci. U.S.A. 98, 11131-11135) demonstrated that the collagen-binding site is oriented toward the opposite side of the highly basic surface where the heparin-binding site is localized. These results indicate that PEDF possesses dual binding sites for different ECM components, and this unique localization of ECM-binding sites implies that the binding to ECM components could regulate PEDF activities.

HSP47 is an essential procollagen-specific molecular chaperone that resides in the endoplasmic reticulum of procollagen-producing cells. Recent advances have revealed that HSP47 recognizes the (Pro-Pro-Gly)(n) sequence but not (Pro-Hyp-Gly)(n) and that HSP47 recognizes the triple-helical conformation. In this study, to better understand the substrate recognition by HSP47, we synthesized various collagen model peptides and examined their interaction with HSP47 in vitro. We found that the Pro-Arg-Gly triplet forms an HSP47-binding site. The HSP47 binding was observed only when Arg residues were incorporated in the Xaa positions of the Xaa-Yaa-Gly triplets. Amino acids in the Xaa position did not largely affect the interaction. The recognition of the Arg residue by HSP47 was specific to its side-chain structure because replacement of the Arg residue by other basic amino acids decreased the affinity to HSP47. The significance of Arg residues in HSP47 binding was further confirmed by using residue-specific chemical modification of types I and III collagen. Our results demonstrate that Xaa-Arg-Gly sequences in the triple-helical procollagen molecule are dominant binding sites for HSP47 and enable us to predict HSP47-binding sites in homotrimeric procollagen molecules.

Clostridium histolyticum type I collagenase (ColG) has a segmental structure, S1+S2+S3a+S3b. S3a and S3b bound to insoluble collagen, but S2 did not, thus indicating that S3 forms a collagen-binding domain (CBD). Because S3a+S3b showed the most efficient binding to substrate, cooperative binding by both domains was suggested for the enzyme. Monomeric (S3b) and tandem (S3a+S3b) CBDs bound to atelocollagen, which contains only the collagenous region. However, they did not bind to telopeptides immobilized on Sepharose beads. These results suggested that the binding site(s) for the CBD is(are) present in the collagenous region. The CBD bound to immobilized collagenous peptides, (Pro-Hyp-Gly)(n) and (Pro-Pro-Gly)(n), only when n is large enough to allow the peptides to have a triple-helical conformation. They did not bind to various peptides with similar amino acid sequences or to gelatin, which lacks a triple-helical conformation, The CBD did not bind to immobilized Glc-Gal disaccharide, which is attached to the side chains of hydroxylysine residues in the collagenous region. These observations suggested that the CBD specifically recognizes the triple helical conformation made by three polypeptide chains in the collagenous region.

To identify proteins that interact with HSP47, an endoplasmic reticulum (ER)-resident molecular chaperone, a yeast two-hybrid screening was performed using mouse full-length HSP47 including an N-terminal signal sequence as a bait. Analysis of several positive clones led to the identification and cloning of a novel gene, ubin, encoding a ubiquitin-like protein. Unlike other ubiquitin-like proteins, UBIN was shown to interact with signal sequences of various secretory and ER-luminal proteins, including HSP47, but not interact with signal sequences of mitochondrial targeting in two-hybrid system. The possible function of UBIN will be discussed with regards to novel characteristics of binding to signal sequences for ER targeting. (C) 2001 Academic Press.

The collagen binding chaperone HSP47 interacts with procollagen in the endoplasmic reticulum and plays a crucial role in the biosynthesis of collagen. We recently demonstrated that typical collagen model peptides, (Pro-Pro-Gly)(n), possess sufficient structural information for interaction with HSP47 (Koide, T., Asada, S., and Nagata, K. (1999) J. Biol. Chem. 274, 34523-34526). Here we show that binding of (Gly-Pro-Pro), peptides to HSP47 can be detected using the two-hybrid system in yeast if a trimerizing domain is fused to the C termini of the peptides. Some peptides interacted with HSP47 at a lowered assay temperature at 24 degrees C but not at 30 degrees C, indicating the importance of conformational change of the substrate peptides, To analyze the spectrum of HSP47 substrate sequences, we performed two-hybrid screening of collagen-like peptides in designed random peptide libraries using HSP47 as a bait. In selected peptides, the enrichment ratio calculated for each amino acid residue correlated strongly with the contribution of the residue to triple-helix stability independently determined using synthetic collagen model peptides. Taken together, our results suggest that HSP47 preferentially recognizes collagenous Gly-X-Y repeats in triple-helical conformation. We also demonstrated that screening of combinatorial peptide libraries is a powerful strategy to determine conformational requirements as web as the elucidation of binding motifs in primary structure.

Prior to secretion, procollagen molecules are correctly folded to triple helices in the endoplasmic reticulum (ER). HSP47 specifically associates with procollagen in the ER during its folding and/or modification processes and is thought to function as a collagen-specific molecular chaperone (Nagata, K, (1996) Trends Bio chem. Sci, 21, 23-26), However, structural requirements for substrate recognition and regulation of the binding have not yet been elucidated. Here, we show that a typical collagen model sequence, (Pro-Pro-Gly)(n), possesses sufficient structural information required for recognition by HSP47. A structure-activity relationship study using synthetic analogs of (Pro-Pro-Gly)(n) has revealed the requirements in both chain length and primary structure for the interaction. The substrate recognition of HSP47 has also been shown to be similar but distinct from that of prolyl 4-hydroxylase, an ER resident enzyme, Further, it has shown that the interaction of HSP47 with the substrate peptides is abolished by prolyl 4-hydroxylation of the second Pro residues in Pro-Pro-Gly triplets and that the fully prolyl 4-hydroxylated peptide, (Pro-Hyp-Gly)(n), does not interact with HSP47, We thus have proposed a model in which HSP47 dissociates from procollagen during the process of prolyl 4-hydroxylation in the ER.

Prolyl 4-hydroxylation, the most important post-translational modification in collagen biosynthesis, is catalyzed by prolyl 4-hydroxylase, an endoplasmic reticulum-resident enzyme. HSP47 is a collagen-binding stress protein which also resides in the endoplasmic reticulum (Nagata, K. and Yamada, K.M. (1986) J. Biol. Chem., 261, 7531-7536). Both prolyl 4-hydroxylase and HSP47 interact with procollagen alpha-chains during their folding and/or modification in the endoplasmic reticulum. Recent study has revealed that a simple collagen model peptide, (Pro-Pro-Gly)(n), is recognized by HSP47 as well as by prolyl 4-hydroxylase in vitro (Koide et al., manuscript submitted). In the present study, we investigated the effect of HSP47 on the prolyl 4-hydroxylation of such collagen model peptides. To monitor the enzymatic hydroxylation of the peptides, we developed a non-RI assay system based on reversed-phase HPLC. When HSP47 was added to the reaction mixture, substrate and less-hydroxylated materials accumulated. This effect depended on the peptide-binding activity of HSP47, because a mutant HSP47 without collagen-binding activity did not show any inhibitory effect on prolyl 4-hydroxylation. Kinetic analysis and other biochemical analyses suggest that HSP47 retards the enzymatic reaction competing for the substrate peptide.

Cystine-containing peptides are obtained in a one-pot manner by treatment of protected peptidyl resins with trimethylsilyl chloride (TMSCl)-dimethyl sulfoxide (DMSO)-trifluoroacetic acid (TFA), The TMSCl-DMSO-TFA system simultaneously cleaves peptides from the resins, with deprotection of all side chain protecting groups and disulfide bond formation.

Disulfide bond formation in S-acetamidomethyl (Acm) cysteine-containing peptides by successive treatments with silver trifluoromethanesulfonate (AgOTf) and dimethyl sulfoxide (DMSO)/aqueous HCl is described. An S-Acm cysteine was found to be quantitatively converted into cystine by deprotection of the Acm group with AgOTf followed by DMSO/aqueous HCl treatment. Under these reaction conditions, no significant side reactions were observed with oxidation-sensitive amino acids such as Met, Tyr and Trp. Oxytocin and a Trp-containing peptide, urotensin II, were prepared by this method. Furthermore, regioselective two disulfide bond formation was found to be feasible by the combination of air oxidation and the AgOTf-DMSO/HCl system. This strategy has been successfully applied to the syntheses of tachyplesin I and endothelin I, which have two disulfide bonds and a Trp residue in the molecule. (C) Munksgaard 1995.

A 47-kDa heat shock protein (HSP47) is a collagen-binding stress protein which is localized in the endoplasmic reticulum (ER) of collagen secreting cells. Recent studies have shown that HSP47 transiently binds to newly synthesized procollagens and that conformationally abnormal procollagen is also bound by HSP47 for a much longer time in the ER (Nakai, A, Satoh, M., Hirayoshi, K., and Nagata, K. (1992) J. Cell Biol. 117, 903-914). HSP47 is thus suggested to have a collagen-specific molecular chaperone-like function. In this report, we analyzed the interaction of HSP47 and types I to V collagen using BIAcore(TM) system, an optical biosensor based on the principles of surface plasmon resonance. Types I-V collagen were purified from porcine skin, porcine articular cartilage, bovine lens capsule, and porcine placenta and immobilized on sensorchips of the BIAcore(TM) system at a surface concentration of 10-15 ng/mm(2). Purified recombinant mouse HSP47 (rmHSP47) expressed in Escherichia coli was passed over the sensorchips at a now rate of 2 mu l/min and binding curves of rmHSP47 to collagens were monitored. Using this approach, accurate association and dissociation rate constants were determined in addition to dissociation constants. rmHSP47 was found to bind to types I-V collagen with similar dissociation constants of the order of 10(-7) M. This relatively low dissociation constant resulted from the rapid dissociation rate constant (k(diss) &gt; 10(-2) s(-1)) and considerably high (k(ass) approximate to 2 x 10(4) m(-1) s(-1)) association rate constant. These kinetic parameters may reflect a transient interaction between HSP47 and procollagen in vivo.

T22 ([Tyr5,12, Lys7]-polyphemusin II) was found to exhibit strong anti-human immunodeficiency virus (HIV) activity and exert its effects on a virus-cell fusion process. In the present study, the all-D enantiomer of T22 and its related compounds were synthesized to examine the molecular parameters required for the interaction of T22 with membrane components of cells or viruses in order to exert this anti-HIV activity. The anti-HIV activity of these analogs was investigated in comparison with their membrane permeability with aspect to large unilamellar vesicles (LUVs). The all-D enantiomer of T22 exhibited a 20-fold lower anti-HIV activity compared with T22, whereas they both showed the same membrane permeability. No positive correlation between anti-HIV activity and membrane permeability was observed. These results suggest that the anti-HIV activity of T22 is mediated through the interaction with chiral component(s) of the cell or virus. © 1994, The Pharmaceutical Society of Japan. All rights reserved.

S-Acetamidomethyl (Acm) cysteine was found to be converted quantitatively to cystine by deprotection of the Acm group with silver trifluoromethanesulfonate (AgOTf) followed by dimethylsulfoxide (DMSO) / aqueous hydrochloric acid (HCI) treatment. No significant side reactions were observed with oxidation-sensitive amino acids such as Met, Tyr, and Trp under these reaction conditions. This method has been applied successfully to the syntheses of oxytocin and a Trp-containing peptide, urotensin II.

a-Rat atrial natriuretic peptide (7—28) (rANP (7—28)) and a series of its analogs in which half cystine residue(s) were substituted with half selenocystine residue(s) were synthesized by using the Fmoc-based solid-phase method followed by cyclization by means of dimethylsulfoxide (DMSO)-trifluoroacetic acid (TFA) oxidation. These analogs possess comparable activities in both receptor binding and cGMP accumulation in rat vascular smooth muscle cells to those of rAMP (7—28). © 1993, The Pharmaceutical Society of Japan. All rights reserved.

N-9-Fluorenylmethoxycarbonyl-Se-4-methoxybenzylselenocysteine [Fmoc-Sec(MBzl)-OH] was synthesized from selenocystine and successfully applied to Fmoc-based solid-phase peptide synthesis. The stability and the deprotection conditions of the Se-MBzl group were examined. The diselenide bond of a peptide was directly and effectively established between Sec(MBzl) residues by treatment with iodine or the dimethyl sulfoxide-trifluoroacetic acid system. Reduction kinetics of diselenide and disulfide in model peptides by reduced glutathione were also studied comparatively. © 1993, The Pharmaceutical Society of Japan. All rights reserved.

Disulfide bonds of peptides were effectively established between S-protected cysteine residues as well as free cysteine residues by the action of dimethylsulfoxide in trifluoroacetic acid. Oxytocin and a-human calcitonin gene-related peptide were synthesized using this oxidation system. The feasibility of this method for the formation of two disulfide bridges of apamin was also examined. © 1993, The Pharmaceutical Society of Japan. All rights reserved.

S-protected cysteine derivatives [Cys(Trt), Cys(MBzl), Cys(Dbs), Cys(Bzh)] as well as cysteine were converted to cystine by the action of DMSO/TFA; as examples, two model peptides, oxytocin and an alpha-human calcitonin gene-related peptide (alpha-hCGRP), were prepared by this reaction.

The properties of S-benzyloxymethylcysteine, Cys(Bom), were examined. The S-Bom group is stable to trifluoroacetic acid (TFA), but is easily cleaved by treatment with silver trifluoromethanesulfonate (AgOTf)/TFA or 1 M trimethylsilyl trifluoromethanesulfonate (TMSOTf)-thioanisole/TFA. Cys(Bom) can be converted to cystine by treatment with thallium(lll) triffuoroacetate. Cys(Bom) was successfully applied to the Fmoc-based solid phase synthesis of porcine brain natriuretic peptide (pBNP), a 26-residue peptide with one disulfide bond [Fmoc.9-fluorenylmethytoxycarbonyl]. In the final step, the peptide-resin was first treated with AgOTf/TFA, then with 1 M trimethylsilyl bromide-thioanisole/TFA. After dithiothreitol treatment and subsequent air-oxidation, a homogeneous pBNP was obtained in 17% yield, based on the first amino acid loaded on the resin. The result was compared with those produced by other alternative deprotecting procedures. © 1989, The Pharmaceutical Society of Japan. All rights reserved.