Structural basis of collagen recognition by human osteoclast-associated receptor and design of osteoclastogenesis inhibitors

Abstract

Human osteoclast-associated receptor (OSCAR) is an immunoglobulin (Ig)-like collagen receptor that is up-regulated on osteoclasts during osteoclastogenesis and is expressed in a range of myeloid cells. As a member of the leukocyte receptor complex family of proteins, OSCAR shares a high degree of sequence and structural homology with other collagen receptors of this family, including glycoprotein VI, leukocyte-associated Ig-like receptor-1, and leukocyte Ig-like receptor B4, but recognizes a unique collagen sequence. Here, we present the crystal structures of OSCAR in its free form and in complex with a triple-helical collagen-like peptide (CLP). These structures reveal that the CLP peptide binds only one of the two Ig-like domains, the membrane-proximal domain (domain 2) of OSCAR, with the middle and trailing chain burying a total of 661 Å 2 of solvent-accessible collagen surface. This binding mode is facilitated by the unusual topography of the OSCAR protein, which displays an obtuse interdomain angle and a rotation of domain 2 relative to the membrane-distal domain 1. Moreover, the binding of the CLP to OSCAR appears to be mediated largely by tyrosine residues and conformational changes at a shallow Phe pocket. Furthermore, we investigated CLP peptides as inhibitors of osteoclastogenesis and found that a peptide length of 40 amino acids is required to ensure adequate inhibition of osteoclastogenesis in vitro. These findings provide valuable structural insights into the mode of collagen recognition by OSCAR and into the use of synthetic peptide matrikines for osteoclastogenesis inhibition.C ollagen is a highly versatile family of proteins consisting of more than 28 members that achieve a high degree of complexity through association of different collagen types, the use of multiple transcription initiation sites, alternative splicing patterns, posttranslational modifications, and a wide range of expression patterns (1). Despite this heterogeneity, studies of collagen over the past 60 y have revealed that collagens are commonly found as large fibrillar structures consisting of varying lengths of righthanded triple-helical structures that are formed by association of three left-handed polyproline type II helices with a one-residue stagger (2, 3). Crucial to the formation of these triple helical structures are the repetitive amino acid triplet sequences G-X-Y, of which the most frequently observed triplet is G-P-O, with O representing 4-hydroxyproline (4). In these structures the obligate glycine of the triplet is buried toward the center of the helix and is solvent inaccessible, whereas the X and Y residues are solvent accessible with the latter providing crucial stability to collagen fibrils through interchain hydrogen bonding (3). The diversity of imino and amino acids within these X and Y repetitive sequences are thought to result in changes in the helical parameters of collagen, which vary from a tight left-handed 7 2 to a looser 10 3 helical symmetry, and could provide a more flexible and accessible motif fo...

Collagen Type I as a Ligand for Receptor-Mediated Signaling

“…Of interest, collagen has been recently demonstrated to act as a ligand for a number of stimulatory and inhibitory receptors in this family, including osteoclast associated receptor (OSCAR), GPVI, and LAIR-1 [21][22][23]. The structural basis for collagen recognition by the immune receptors has been investigated in a number of studies [24][25][26][27], however some controversy regarding the alignment of collagen-recognition sites among different receptors exists.…”

“…OSCAR is particularly important for osteoclast differentiation, as it acts as a critical co-stimulatory receptor for osteoclast formation and function [23,[26][27][28]. GPVI is mainly found in platelets and binds to collagen during the process of blood coagulation [21].…”

“…We can speculate that LAIR-1 is present on early precursors, and that its role is to prohibit osteoclast differentiation on immature matrix, while OSCAR is expressed later during osteoclastogenesis and is engaged by the matrix-incorporated collagen to support osteoclast formation on the correct substrate. While extensive studies on the role of OSCAR during osteoclast formation have been performed [23,26,28], much less is known about the temporal and spatial aspects of regulation of osteoclastogenesis by LAIR-1. In diseases associated with abnormal collagen synthesis, such as OI, as well as abnormal mineralization, for example osteomalacia due to calcium and phosphate deficiency, the structure of the mature tissue matrix is altered, which may potentially result in changes in receptor-ligand binding for collagen receptors, contributing to the pathophysiology of these disorders.…”

Calcio como agente terapéutico en osteoporosis

“…Se puede concluir afi rmando que el papel del calcio como elemento mineral es muy importante para el tejido óseo, Nosotros caminamos literalmente sobre nuestras reservas del calcio y este en conjunto con la Vitamina D sirve para edifi car el hueso de tal manera que, si bien es cierto que estos agentes se vienen cuestionando en algunos aspectos como seguridad cardiovascular entre otros, existen nuevos conceptos, especialmente para la Vitamina D que le dan nuevos aires posicionándola más como una hormona que como una vitamina y con acción pleiotró-pica por la multiplicidad de receptores celulares en los diferentes tejidos (387)(388)(389)(390), y que defi nitivamente tanto el calcio como la Vitamina D no son los elementos más potentes en el arsenal terapéutico contra la enfermedad, pero sus défi cits son los más sencillos de identifi car y los más fáciles de corregir. …”

Adapting extracellular matrix proteomics for clinical studies on cardiac remodeling post-myocardial infarction

“…We took this observation and showed that a fragment was generated by MMP-2 and MMP-9, with MMP-9 further degrading it. ECM fragments that are generated by proteolysis or other processing and have biological activity in addition to or distinct from the parent ECM protein are termed matrikines or matricryptins [ 42 ]. To test whether the collagen matrikine had signaling activity, a peptide 20 amino acids downstream of the cleavage site was generated and tested for in vitro and in vivo activity.…”