AFFINITY MODULATION IN PLATELET ALPHA-2-BETA-1 FOLLOWING LIGAND-BINDING

In order to test for ligand-induced change in the affinity of platelet alpha 2 beta 1 to collagen we passaged labeled viable platelets throu gh a column of fibrillar collagen and used stringent lysis conditions to remove all low-affinity receptors. A high affinity fraction left on the collagen could be eluted with DTT and 2% SDS. Antibodies raised a gainst it Western-blotted alpha 2 beta 1. Functional tests performed w ith the antibodies confirmed the involvement of the high affinity prot eins in platelet-collagen interactions attributed to alpha 2 beta 1: i nhibition of collagen-specific platelet adhesion and aggregation. EDTA , chaotropic agents or low pH did not elute the high affinity fraction of cuapl. However, DTT followed by acetic acid did. Our data suggest that 1) ligand binding induces the formation of a new disulfide bond i n a fraction of alpha 2 beta 1, 2) that this bond is intrareceptor and 3) that this change increases the affinity of the receptor to its lig and. (C) 1997 Academic Press.