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J Biol Chem. 1998 Aug 7;273(32):20397-403.

Cartilage oligomeric matrix protein shows high affinity zinc-dependent interaction with triple helical collagen.

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Department of Cell and Molecular Biology, Section of Connective Tissue Biology, Lund University, S-221 00 Lund, Sweden.


Cartilage and tendon extracellular matrices are composed of collagens, proteoglycans, and a number of noncollagenous proteins. Cartilage oligomeric matrix protein (COMP) is a prominent such protein, structurally related to the thrombospondins. We found that native COMP binds to collagen I/II and procollagen I/II and that the interaction is dependent on the divalent cations Zn2+ or Ni2+, whereas Ca2+, Mg2+, and Mn2+ did not promote binding. Using a solid phase assay, Scatchard analysis identified one class of binding site with a dissociation constant (Kd) close to 1.5 nM in the presence of Zn2+. The results were confirmed by studies using surface plasmon resonance. Furthermore, metal chelate chromatography demonstrated that COMP bound Zn2+ and Ni2+. Electron microscopy showed that the interaction occurred at four defined sites on the 300-nm collagen and procollagen molecules. Two were located close to each end, and two at 126 and 206 nm, respectively, from the C-terminal. COMP interacted via its C-terminal globular domain and significantly only in the presence of Zn2+.

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