Interaction of a 59-kDa connective tissue matrix protein with collagen I and collagen II

We have studied binding to collagen of the 59-kDa protein present in most connective tissues. Collagen fibril formation, measured as increasing turbidity, was markedly retarded and reduced by the presence of small amounts of this protein. This was true for both collagen I and collagen II. The effect was also observed when pepsin-treated collagens were used, indicating that interaction with the telopeptides is not involved. The proportion of collagen precipitated in the assay was not or only marginally reduced. Thus, the altered optical properties indicate that structurally different fibrils are formed in the presence of the 59-kDa protein. The 59-kDa protein bound to collagen I or collagen II that had been insolubilized on polystyrene 96-well microtiter plates, as measured by enzyme-linked immunosorbent assay. Analogously, binding to the collagens was demonstrated for the PG-S2 low Mr proteoglycan, previously shown only to inhibit collagen fibrillogenesis. The two matrix components showed similar strength of binding, i.e. Kd 35 nM for the 59-kDa protein and 16 nM for PG-S2 at 20 degrees C. The results do not reveal if the collagen interaction site of the 59-kDa protein is different from that of PG-S2. Our observations do, however, suggest that the 59-kDa protein, as well as PG-S2, have functions related to the regulation of collagen organization in tissues.