Crystallization and preliminary crystallographic study of the pentamerizing domain from cartilage oligomeric matrix protein: a five-stranded alpha-helical bundle.

Cartilage oligomeric matrix protein (COMP) is a pentameric glycoprotein of the thrombospondin family found in cartilage and tendon. Self-association of COMP is achieved through the formation of a five-stranded alpha-helical bundle that involves 64 N-terminal residues (from 20 to 83). The complex is further stabilized by the interchain disulfide bonds between cysteines 68 and 71. We have prepared, by expression in Escherichia coli, several peptides of different lengths from the N-terminal region of COMP and studied their amenability to crystallization. Crystals of the best quality were obtained with a peptide spanning COMP residues 28-72. This peptide forms disulfide linked pentamers with 87% of alpha-helical structure. Crystals were grown by the hanging drop vapor diffusion method, using polyethylene glycol 1500 as a precipitant. The crystals belong to space group P2(1) with unit cell dimensions a = 38.47 angstroms, b = 49.47 angstroms, c = 54.98 angstroms, beta = 103.84 degrees and contain one pentamer per asymmetric unit. They diffract strongly to at least 1.8 angstrom resolution.