The partial degradation of osteonectin by a bone-derived metalloprotease enhances binding to type I collagen.

Cultured neonatal rat calvaria produce latent metalloproteases capable of degrading collagen, gelatin, and osteonectin. The osteonectin-degrading activity was further characterized and found to be optimally active between pH 6 and 8 and inhibited with EDTA and 1, 10-phenanthroline but not phenylmethylsulfonyl fluoride. Analysis of the degradation products of osteonectin by SDS-PAGE in the presence of dithiothreitol showed the generation of a somewhat stable 32,000 mw cleavage product. Comparison of the binding properties of this cleavage product with intact osteonectin indicated that the fragment retained its ability to bind hydroxyapatite in the presence of high salt (2 M NaCl). Importantly, the binding of osteonectin to type I collagen fibrils was enhanced by limited proteolysis.