TRIFLAVIN, AN ANTIPLATELET ARG-GLY-ASP-CONTAINING PEPTIDE, IS A SPECIFIC ANTAGONIST OF PLATELET MEMBRANE GLYCOPROTEIN IIB-IIIA COMPLEX

Triflavin, an antiplatelet peptide containing Arg-Gly-Asp, purified from Trimeresurus flavoviridis venom, inhibits aggregation of human platelets stimulated by a variety of agonists. It blocks aggregation through interference with fibrinogen binding to its specific receptor on the platelet surface membrane in a competitive manner, but it has no apparent effect on intracellular events, such as thromboxane B2 formation, phosphoinositides breakdown and intracellular Ca2+ mobilization of thrombin-activated platelets. In this study, we determined the complete sequence of triflavin, which is composed of a single polypeptide chain of 70 amino acids. Its sequence is rich in cysteine and contains Arg-Gly-Asp at residues 49-51 in the carboxy-terminal domain. Triflavin shows about 68% identity of amino acid sequence with trigramin, which is a specific antagonist of the fibrinogen receptor associated with glycoprotein IIb/IIIa complex. [I-125] Triflavin binds to unstimulated and ADP-stimulated platelets in a saturable manner and its K(d) values are estimated to be 76 and 74 nM, respectively; the corresponding numbers of binding sites are 31,029 and 34,863 per platelet, respectively. [I-125]Triflavin binding is blocked by Gly-Arg-Gly-Asp-Ser in a competitive manner. EDTA, the Arg-Gly-Asp-containing peptides (including naturally occurring polypeptides, trigramin and rhodostomin), and monoclonal antibody, 7E3, raised against GP IIb/IIIa complex, inhibit [I-125]triflavin binding to unstimulated and ADP-stimulated human platelets. In conclusion, triflavin specifically binds to fibrinogen receptor associated with GP IIb/IIIa complex binds to fibrinogen receptor associated with GP IIb/IIIa complex and its binding site is located at or near GP IIb/IIIa complex, overlapping with those of 7E3 and another Arg-Gly-Asp-containing polypeptide, rhodostomin. The Arg-Gly-Asp sequence of triflavin plays an important role in mediating the binding of triflavin towards GP IIb/IIIa complex.