Collagen II containing a Cys substitution for Arg-alpha 1-519. Analysis byatomic force microscopy demonstrates that mutated monomers alter the topography of the surface of collagen II fibrils

A recombinant human procollagen II was prepared that contained a substituti on of Cys for Arg at alpha 1-519 and that was found in five families with e arly onset generalized osteoarthritis with or without features of a mild ch ondrodysplasia. Previously, the presence of mutated monomers in mixtures wi th wildtype collagen II was shown to increase the lag period for fibril ass embly. Also, the fibrils were more loosely packed and some thick fibrils la cked a D-periodic banding pattern. Here we re-examined the fibrils using a combination of transmission electron microscopy and atomic force microscopy . The presence of the mutated monomers increased the diameter of the thin f ilaments that were consistently formed in association with the thick fibril s of collagen II. In addition, the presence of the mutated monomers increas ed the depth of the gap regions in all fibrils with a distinct D-periodic b anding pattern. The results, therefore, may indicate that the mutated monom ers formed two or three additional outer layers of monomers in 0D-period st aggers on the surface of the fibrils. Apparently, the mutated monomers were bound on the surface through intermolecular disulfide bonds. (C) 1999 Else vier Science B.V./International Society of Matrix Biology. All rights reser ved.