To isolate collagen-binding cell surface proteins, detergent extracts of surface-iodinated MG-63 human osteosarcoma cells were chromatographed on affinity matrices of either type I collagen-Sepharose or Sepharose carrying a collagen-like triple-helical peptide. The peptide was designed to be triple helical and to contain the sequence Arg-Gly-Asp, which has been implicated as the cell attachment site of fibronectin, vitronectin, fibrinogen, and von Willebrand factor, and is also present in type I collagen. Three radioactive polypeptides having apparent molecular masses of 250 kD, 70 kD, and 30 kD were distinguishable in that they showed affinity toward the collagen and collagen-like peptide affinity columns, and could be specifically eluted from these columns with a solution of an Arg-Gly-Asp-containing peptide, Gly-Arg-Gly-Asp-Thr-Pro. These collagen-binding polypeptides associated with phosphatidylcholine liposomes, and the resulting liposomes bound specifically to type I collagen or the collagen-like peptide but not to fibronectin or vitronectin or heat-denatured collagen. The binding of these liposomes to type I collagen could be inhibited with the peptide Gly-Arg-Gly-Asp-Thr-Pro and with EDTA, but not with a variant peptide Gly-Arg-Gly-Glu-Ser-Pro. We conclude from these data that these three polypeptides are membrane molecules that behave as a cell surface receptor (or receptor complex) for type I collagen by interacting with it through the Arg-Gly-Asp tripeptide adhesion signal. The lack of binding to denatured collagen suggests that the conformation of the Arg-Gly-Asp sequence is important in the recognition of collagen by the receptor complex.

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