Synthetic peptides demonstrate RGD-independent platelet glycoprotein IIb/IIIa recognition site in cell binding domain of human fibronectin.

Fibronectin binds to platelet membrane glycoprotein (GP) IIb/IIIa in both an Arg-Gly-Asp (RGD)-dependent and -independent manner. The identification of an RGD-independent binding domain(s) that interacts with GPIIb/IIIa may be the key to understand the mechanism of thrombus formation. A recombinant fibronectin fragment containing the residues from Ile1359 to Ser1436 (lacking the RGD sequence) had been shown to bind to GPIIb/IIIa in a divalent cation- and activation-dependent manner. To identify a minimal peptide ligand that participates in the recognition of GPIIb/IIIa, we synthesized peptides extending this region, which consist of 12 amino acid residues in length and overlapping by six amino acids. We obtained evidence that two 12-residue peptide sequences from this region (residues 1371-1382 and 1377-1388) inhibit fibronectin binding to GPIIb/IIIa by interacting directly with this receptor, with IC50s of 95 +/- 16 and 104 +/- 19 microM, respectively. These peptides inhibited the binding of fibrinogen to GPIIb/IIIa, as well as ADP-induced platelet aggregation. These results indicate that an RGD-independent GPIIb/IIIa binding site in the cell binding domain of fibronectin was localized within the residues His1377-Ile1382.