Selective binding of anchorin CII (annexin V) to type II and X collagen and to chondrocalcin (C-propeptide of type II collagen). Implications for anchoring function between matrix vesicles and matrix proteins.

Anchorin CII is a collagen binding protein of the annexin family associated with plasma membranes of chondrocytes, osteoblasts, and many other cells. As a major constituent of cartilage-derived matrix vesicles it has been shown to bind to native type II and X collagen. In accordance with this observation, here we show the localization of anchorin CII in the extracellular matrix of calcifying cartilage in the fetal human growth plate, and that it was restricted to the chondrocyte surface in proliferating and resting cartilage. Furthermore, we present evidence, using a slot blot assay, that anchorin CII not only binds to native type II and X collagen, but also to chondrocalcin, the carboxy-terminal extension of type II procollagen, in a calcium-independent manner. Pepsin digestion of type II collagen results in loss of anchorin CII binding, confirming our previous notion that the telopeptide region of type II collagen carries anchorin CII binding sites.