Thrombin signaling of platelets is mediated by a G protein-coupled protease-activated receptor (PAR). The PAR is activated after thrombin binding and subsequent cleavage of the amino terminal end of the receptor. This new amino terminus acts as a tethered ligand and binds intramolecularly to the body of the PAR, resulting in a transmembrane signal. A synthetic thrombin receptor agonist peptide (TRP) of 6 residues (SFLLRN) corresponding to aa42-47 of the thrombin receptor was found to be as effective as thrombin for Ca2+ mobilization. TRAP can be used instead of thrombin to trigger platelet aggregation and clot retraction.Human: H-Ser-Phe-Leu-Leu-Arg-Asn-Pro-Asn-Asp-Lys-Tyr-Glu-Pro-Phe-OH or H-SFLLRNPNDKYEPF-OH