The alpha 2 beta 1 integrin binds to the CB4 peptide of the alpha 2(I) collagen chain

The adhesion of platelets and other cells to type I collagen is mediated by the alpha 2 beta 1 integrin. A binding site for the alpha 2 beta 1 integrin within the alpha 1(I) collagen chain has previously been localized to the cyanogen bromide fragment alpha 1(I)-CB3. We noe show by use of inhibitory monoclonal antibodies against the alpha 2 beta 1 integrin, that platelets also adhere to purified alpha 2(I) collagen chains by a mechanism mediated by the alpha 2 beta 1 integrin. Moreover, following isolation of cyanogen bromide fragments of the alpha 2(I) collagen chain by HPLC, we demonstrate that alpha 2 beta 1 integrin-mediated adhesion is restricted to the CB4 fragment of the alpha 2(I) collagen polypeptide. These findings indicate the presence of at least two spatially distinct binding sites for the alpha 2 beta 1 integrin on the native type I collagen triple helix.