CONFORMATION-DEPENDENT PLATELET-ADHESION TO COLLAGEN INVOLVING INTEGRIN ALPHA-2-BETA-1-MEDIATED AND OTHER MECHANISMS - MULTIPLE ALPHA-2-BETA-1-RECOGNITION SITES IN COLLAGEN TYPE-I

Platelet adhesion has been measured to type-I monomeric collagen, coll agen fibres, alpha 1(I) and alpha 2(I) chains and the chain fragments alpha 1(I)CB3, alpha 1(I)CB6, alpha 1(I)CB7 and alpha 1(I)CB8, and alp ha 2(I)CB3,5 and alpha 2(I)CB4. Little if any adhesion occurred to any denatured species at 37 degrees C, demonstrating the importance of th e collagen helix. However, on coating at 4 degrees C to promote helix formation, and assaying at room temperature to avoid denaturation, adh esion was observed to both a-chain types and all fragments, the exact level of which depended on the identity of the species in question. Ad hesion was strongly Mg2+-dependent. Antibodies against the integrin al pha 2 beta 1 partially inhibited adhesion to alpha-chains and all frag ments except alpha 1(I)CB6, indicating a wide distribution of alpha 2 beta 1-binding sites in the collagen molecule. 'Activation-dependent' adhesion to monomeric collagen, totally