Immunochemical studies of the purified human platelet receptor for the alpha 1(I)-chain of chick skin collagen.

The membrane receptor of human platelets that binds the alpha 1(I)-chain of chick skin collagen was purified to homogeneity by molecular sieve chromatography, affinity chromatography, and preparative gel-electrophoresis. Rabbits that were immunized with the purified receptor emulsified in complete Freund's adjuvant produced antibody, as measured by an enzyme-linked immunosorbent assay. The antiserum was shown to be highly receptor-specific by immunoprecipitation of solubilized platelet membrane protein that had been labeled with (gamma-32P)ATP and protein kinase. Platelet aggregation induced by alpha 1(I) as well as native chick skin collagen was inhibited by both the purified receptor and antibody against the receptor in a dose-dependent fashion. In contrast, neither the receptor nor the antiserum inhibited ADP-induced aggregation. These studies provide the most definitive evidence that alpha 1(I) and native collagen interact specifically with a cell surface receptor on human platelets to induce aggregation.