Collagen-induced platelet aggregation: involement of an active glycopeptide fragment (alpha1-CB5).

It is widely held that the tertiary structure of collagen is essential for induction of platelet aggregation. However, we have found that the purified alpha1 chain prepared from denatured chick skin collagen aggregates platelets. This activity appears to be confined to a distinct region of the molecule representing less than 4 percent of the length of the alpha1 chain. Of all of the cyanogen bromide peptides of the alpha1 chain tested, only one (alpha1-CB5) was active. This glycopeptide, devoid of any ordered tertiary structure, contains only 36 amino acids and one residue of O-alpha-D-glucopyranosyl-(1 --> 2)-O-beta-D-galactopyranosyloxy-(1 --> 5)-lysine (Glc-Gal-Hyl). Blocking experiments strongly suggest that the Glc-Gal-Hyl is one of the structural determinants involved in collagen-induced platelet aggregation.