Collagen II containing a Cys substitution for Arg-alpha 1-519: Abnormal interactions of the mutated molecules with collagen IX

Single amino acid Substitutions in collagen II cause heterogeneous cartilag e disorders including some chondrodysplasias and certain forms of heritable osteoarthritis. III this study, we examined molecular interactions between normal collagen II and colla,,en IX. and the effect, of a Cys substitution for Arg-alpha1-519 in collagen II on these interactions. Binding assays sh owed that the association equilibrium constant of collagen IX-collagen II i nteraction is 15 x 10(6) M-1. Specificity of the interaction was analyzed b y the binding of collagen IX to recombinant collagen II variants lacking fr agments of 234 amino acids corresponding to particular D-periods. The resul ts indicated that the C-terminal half of collagen II, which includes the D3 and D4 periods, has a high affinity for collagen IX, and that tile nontrip le helical telopeptides of collagen H are not essential for the specific bi nding of collagen IX. Computer analysis of the surface the mutated collagen II and binding assays showed that a Cys substitution for Arg-alpha1-519 ch anges electrostatic properties around the mutation site, increases the affi nity of mutant collagen II for collagen IX. and possibly alters the specifi city of the interaction, Thus, the results indicate that interactions betwe en collagen II and collagen IX are site specific and that single amino acid substitutions in collagen II may change the molecular interactions with co llagen IX that could destabilize the cartilaginous matrix.