Development of a high-throughput screening system for the compounds that inhibit collagen-protein interactions

A Transparent and Injectable Biomaterial Prepared by Mixing Collagen and Anti-Cancer Platinum Derivatives

This study presents the synthesis of a cross-linked collagen material, named platinum-containing collagen gel (PCG), which is achieved by simply mixing collagen and derivatives of an anti-cancer platinum complex. The cross-linking reagents are derivatives of cisplatin or transplatin, generated through a ligand exchange with dimethyl sulfoxide. PCG exhibits superior physical strength and transparency compared with the native collagen gel formed through spontaneous fibril formation. The versatility of PCG as a cell culture scaffold, applicable to both 2D and 3D models, with low cytotoxicity is demonstrated. Furthermore, PCG exhibits pH-responsive gel-forming properties. This enables the removal of free cross-linker by dialysis in an acidic solution and subsequent gel formation upon neutralization. This material holds promise for application in cell culture scaffolds and medical injections.

Identification of HSP47 Binding Site on Native Collagen and Its Implications for the Development of HSP47 Inhibitors

HSP47 (heat shock protein 47) is a collagen-specific molecular chaperone that is essential for procollagen folding and function. Previous studies have shown that HSP47 binding requires a critical Arg residue at the Y position of the (Gly-Xaa-Yaa) repeats of collagen; however, the exact binding sites of HSP47 on native collagens are not fully defined. To address this, we mapped the HSP47 binding sites on collagens through an ELISA binding assay using collagen toolkits, synthetic collagen peptides covering the entire amino acid sequences of collagen types II and III assembled in triple-helical conformation. Our results showed that HSP47 binds to only a few of the GXR motifs in collagen, with most of the HSP47 binding sites identified located near the N-terminal part of the triple-helical region. Molecular modelling and binding energy calculation indicated that residues flanking the key Arg in the collagen sequence also play an important role in defining the high-affinity HSP47 binding site of collagen. Based on this binding mode of HSP47 to collagen, virtual screening targeting both the Arg binding site and its neighboring area on the HSP47 surface, and a subsequent bioassay, we identified two novel compounds with blocking activity towards HSP47 binding of collagen. Overall, our study revealed the native HSP47 binding sites on collagen and provided novel information for the design of small-molecule inhibitors of HSP47.

Screening of Inhibitors Targeting Heat Shock Protein 47 Involved in the Development of Idiopathic Pulmonary Fibrosis

Heat shock protein 47 (HSP47), a collagen-specific molecular chaperone, is causally related to fibrotic diseases, including idiopathic pulmonary fibrosis. The identification of Compounds that interfere with the HSP47-collagen interaction is essential for the development of relevant therapeutics. Herein, we prepared human HSP47 as a soluble fusion protein expressed in E. coli and established an assay system for HSP47 inhibitor screening. We screened a natural and synthetic Compound library established at Nagasaki University. Among 1023 Compounds, 13 exhibited inhibitory activity against human HSP47, of which three inhibited its function in a dose-dependent manner. Epigallocatechin-3-O-gallate, one of these three Compounds, is a typical polyphenol Compound derived from tea leaves. Structurally related Compounds were synthesized and examined for their activity, revealing a hydroxyl group at A-ring position 5 as important for its activity. The present findings provide valuable insight for the development of natural product-derived therapeutics for fibrotic diseases, including idiopathic pulmonary fibrosis.

COMP and TSP-4 interact specifically with the novel GXKGHR motif only found in fibrillar collagens

COMP (cartilage oligomeric matrix protein) is a member of the thrombospondin family and forms homopentamers as well as mixed heterooligomers with its closely related family member TSP-4. COMP is long known to bind to collagens and to influence collagen fibril formation. Recent work indicates that already intracellular interaction with collagen is important for collagen secretion. However, the exact binding site of COMP on the collagen triple helix has not been described up to now. In this study we have identified a GXKGHR motif on the collagen II helix to bind to COMP, using a recombinantly expressed collagen II peptide library. This binding sequence is conserved throughout evolution and we demonstrate that TSP-4 binds to the same sequence. The identified binding motif overlaps with the recognition sites of many other collagen-binding partners (e.g. PEDF, Heparin) and also spans the lysine residues, which form collagen cross-links. COMP might thereby protect collagen helices from premature modification and cross-linking. Interestingly, this motif is only found in classical fibrillar collagens, although COMP is known to also bind other types. This might indicate that COMP has a unique interface for fibrillar collagens, thus making it an interesting target for the development of antifibrotic drugs.

Ca2+ -induced orientation of tandem collagen binding domains from clostridial collagenase ColG permits two opposing functions of collagen fibril formation and retardation

To penetrate host tissues, histotoxic clostridia secrete virulence factors including enzymes to hydrolyze extracellular matrix. Clostridium histolyticum, recently renamed as Hathewaya histolytica, produces two classes of collagenase (ColG and ColH). The high-speed AFM study showed that ColG collagenase moves unidirectionally to plane collagen fibril and rebundles fibril when stalled . The structural explanation of the roles for the tandem collagen-binding segment (CBDs) is illuminated by its calcium-bound crystal structure at 1.9 Å resolution (R_work = 15.0%; R_free = 19.6%). Activation may involve calcium-dependent domain rearrangement supported by both small-angle X-ray scattering and size exclusion chromatography. At pCa ≥ 5 (pCa = -log[Ca²⁺ ]), the tandem CBD adopts an extended conformation that may facilitate secretion from the bacterium. At pCa ≤ 4, the compact structure seen in the crystal structure is adopted. This arrangement positions the two binding surfaces ~ 55 Å apart, and possibly ushers ColG along tropocollagen molecules that allow for unidirectional movement. A sequential binding mode where tighter binding CBD2 binds first could aid in processivity as well. Switch from processive collagenolysis to fibril rearrangement could be concentration dependent. Collagen fibril formation is retarded at 1 : 1 molar ratio of tandem CBD to collagen. Tandem CBD may help isolate a tropocollagen molecule from a fibril at this ratio. At 0.1 : 1 to 0.5 : 1 molar ratios fibril self-assembly was accelerated. Gain of function as a result of gene duplication of CBD for the M9B enzymes is speculated. The binding and activation modes described here will aid in drug delivery design.

ACCESSION CODES

The full atomic coordinates of the tandem CBD and its corresponding structure factor amplitudes have been deposited in the Protein Data Bank (PDB accession code 5IKU). Small-angle X-ray scattering data and corresponding ab initio models have been submitted to the Small Angle Scattering Biological Data Bank (SASBDB). Accession codes CL2, collagenase module 2, CN2, CP2 are assigned to envelopes for tandem CBD at -log[Ca²⁺ ] (pCa) 3, 4, 5, and 6, respectively. Accession code DC64 was assigned to the complex of polycystic kidney disease-CBD1-CBD2 with mini-collagen.

A High-Throughput Assay for Collagen Secretion Suggests an Unanticipated Role for Hsp90 in Collagen Production

Collagen overproduction is a feature of fibrosis and cancer, while insufficient deposition of functional collagen molecules and/or the secretion of malformed collagen is common in genetic disorders like osteogenesis imperfecta. Collagen secretion is an appealing therapeutic target in these and other diseases, as secretion directly connects intracellular biosynthesis to collagen deposition and biological function in the extracellular matrix. However, small molecule and biological methods to tune collagen secretion are severely lacking. Their discovery could prove useful not only in the treatment of disease, but also in providing tools for better elucidating mechanisms of collagen biosynthesis. We developed a cell-based, high-throughput luminescent assay of collagen type I secretion and used it to screen for small molecules that selectively enhance or inhibit that process. Among several validated hits, the Hsp90 inhibitor 17-allylaminogeldanamycin (17-AAG) robustly decreases the secretion of collagen-I by our model cell line and by human primary cells. In these systems, 17-AAG and other pan-isoform Hsp90 inhibitors reduce collagen-I secretion post-translationally and are not global inhibitors of protein secretion. Surprisingly, the consequences of Hsp90 inhibitors cannot be attributed to inhibition of the endoplasmic reticulum's Hsp90 isoform, Grp94. Instead, collagen-I secretion likely depends on the activity of cytosolic Hsp90 chaperones, even though such chaperones cannot directly engage nascent collagen molecules. Our results highlight the value of a cell-based high-throughput screen for selective modulators of collagen secretion and suggest an unanticipated role for cytosolic Hsp90 in collagen secretion.

A cisplatin derivative that inhibits collagen fibril-formation in vitro

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.

Direct in vitro and in vivo evidence for interaction between Hsp47 protein and collagen triple helix

Hsp47 (heat shock protein 47), a collagen-specific molecular chaperone, is essential for the maturation of various types of procollagens. Previous studies have suggested that Hsp47 may preferentially recognize the triple-helix form of procollagen rather than unfolded procollagen chains in the endoplasmic reticulum. However, the underlying mechanism has remained unclear because of limitations in the available methods for detecting in vitro and in vivo interactions between Hsp47 and collagen. In this study, we established novel methods for this purpose by adopting a time-resolved FRET technique in vitro and a bimolecular fluorescence complementation technique in vivo. Using these methods, we provide direct evidence that Hsp47 binds to collagen triple helices but not to the monomer form in vitro. We also demonstrate that Hsp47 binds a collagen model peptide in the trimer conformation in vivo. Hsp47 did not bind collagen peptides that had been modified to block their ability to form triple helices in vivo. These results conclusively indicate that Hsp47 recognizes the triple-helix form of procollagen in vitro and in vivo.

Pigment epithelium-derived factor (PEDF) shares binding sites in collagen with heparin/heparan sulfate proteoglycans

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 α1(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 KGXRGFXGL 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.