Affinity of Fibrinogen Binding to Platelet Membrane Glycoprotein IIb/IIIa Increases with RGDS and gamma Chain Fibrinogen Peptide Hybrid.

Arg-Gly-Asp (RGD)-containing peptides and the peptide unique to fibrinogen in the C-terminal domain of the gamma chain are important for fibrinogen binding to platelet membrane glycoprotein (GP) II b/III a. We synthesized a unique hybrid peptide of YRGDSPLGGAKQAGDV encompassing the RGD sequence (RGDS) with the gamma chain peptide (LGGAKQAGDV). Maximum binding to thrombin-stimulated platelets was achieved within 40 minutes with the YRGDS peptide and within 20 minutes with the hybrid peptide and native fibrinogen. The platelet binding sites were 58,600 molecules with the hybrid peptide and 52,400 molecules with YRGDS. These peptides inhibited fibrinogen binding to thrombin-stimulated platelets in a dose-dependent manner. The order of inhibitory potency of these peptides was as follows: fibrinogen models R: hybrid peptide > YRGDS > GQQHHLGGAKQAGDV (G15). The RGES peptide had no inhibitory activity. These three peptides inhibited binding of the anti-GP II b/III a monoclonal antibody (LJ-CP8) to platelets. The hybrid peptide showed the most potent inhibitory activity, with an IC50 of 48 µM. These results suggest that the linear combined RGDS and gamma chain peptide created with proline increases the affinity of binding to activated platelets.