The peptide Glu-His-Ile-Pro-Ala binds fibrinogen and inhibits platelet aggregation and adhesion to fibrinogen and vitronectin.

Antiplatelet agents are clinically useful as antithrombotic entities. The importance of antiplatelet agents led us to design, synthesize, and characterize a new antiplatelet peptide. This peptide is a presumptive mimic of a ligand binding site on the platelet fibrinogen receptor. Unlike peptides related to Arg-Gly-Asp-Ser and His-His-Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val that bind to the fibrinogen receptor, this peptide binds to fibrinogen. The anticomplementarity hypothesis was used to design this presumptive peptide mimic of the vitronectin binding site on the fibrinogen receptor, glycoprotein IIb/IIIa complexes. The resulting peptide (Glu-His-Ile-Pro-Ala) has the characteristics of a fibrinogen binding site mimic: It binds fibrinogen and inhibits both the adhesion of platelets to fibrinogen and platelet aggregation. The peptide also inhibits the adhesion of platelets to vitronectin. The antiplatelet activity of this mimic peptide was dependent on its amino acid sequence, since closely related analogues were either inactive or less active inhibitors of platelet function than the original peptide. These results demonstrate that the peptide Glu-His-Ile-Pro-Ala has the characteristics expected of a mimic of a glycoprotein IIb/IIIa ligand binding site.