Collagen-binding proteins in collagenase-released matrix vesicles from cartilage. Interaction between matrix vesicle...

Recent evidence indicates that matrix vesicles (MV) interact with cartilage-specific collagens and other matrix proteins. Both type II and X collagens bind to and cosediment with MV. Our companion study shows that MV also are tightly coupled to proteoglycan link proteins (LP) and hyaluronic acid-binding region (HABR) in cartilage matrix. Here we sought to identify proteins responsible for the nexus between MV and matrix collagens using affinity chromatography with types I, II, and X collagen-Sepharose columns. Elution with NaCl step-gradients in the presence of nonionic detergent was used to assess the affinity between the MV proteins and the covalently attached collagens. Several MV proteins were found to bind to native type I, II, and X collagens but none bound to denatured type I collagen. Alkaline phosphatase, proteoglycan LP and HABR, and the 33- and 67-kDa annexins, bound with varying affinities to the native type I, II and X columns. In particular, LP and HABR, the 67-kDa annexin, and alkaline phosphatase bound with high affinity to the cartilage-specific collagens, although LP, HABR, and a 37-kDa protein also bound less tightly to native type I collagen. Thus, several MV proteins bind specifically to native type II and X collagens and should promote interaction between MV and the extracellular matrix. Such interactions may be important in MV formation, or in MV-mediated mineralization.