ROLE OF THE GAMMA-CHAIN ALA-GLY-ASP-VAL AND A-ALPHA-CHAIN ARG-GLY-ASP-SER SITES OF FIBRINOGEN IN COAGGREGATION OF PLATELETS AND FIBRINOGEN-COATED BEADS

Fibrinogen (Fg) mediates platelet aggregation and adhesion to artifici al surfaces. The carboxyl terminus of the gamma chain of Fg (residues AGDV at gamma 408-411) is known to play an exclusive role in platelet aggregation, while there is no known role for the consensus RGD sites in the A a chain. In this study, we used flow cytometry to measure the coaggregation (CA) of platelets with Fg-coated beads, and investigate d which domains in surface-immobilized Fg support platelet adhesion. C A of platelets with Fg-beads was nearly abolished in the presence of 4 A5, a monoclonal antibody (mAb) whose epitope includes AGDV, while 269 /8, a mAb that also binds to the gamma chain carboxyl terminus but doe s not cover AGDV, had little effect. When beads were coated with recom binant Fg (rFg) lacking AGDV, CA was similarly abolished. In contrast, beads coated with Fg that lacked the RGDS site, supported platelet CA as did intact Fg. These results were confirmed in experiments that me asured the binding of activated soluble glycoprotein IIb and IIIa (GPI lbma), the platelet membrane glycoprotein complex known to be the Fg r eceptor, to immobilized Fg. This binding was inhibited by mAb 4A5, but not by mAb 269/8. Binding was totally retained when beads were coated with Fg lacking RGDS, but was completely lost when beads were coated with Fg lacking AGDV. These results demonstrated that the AGDV sequenc e on the carboxyl terminus of the gamma chain of Fg plays an exclusive role in platelet adhesion to surface-immobilized Fg, while the carbox yl terminus of the A alpha chain, including a consensus RGD site, is n ot required. (C) 1998 Elsevier Science B.V. All rights reserved.