PAR peptides (TRAP peptides and thrombin receptor-like peptides) activate the proteinase-activated receptors PAR-1 to PAR-4.
The peptide T1, MSRPACPNDKYE, is based on the sequence of the thrombin receptor domain that functions as a tethered ligand for the receptor itself. T1 has been selected from a phage peptide library as an inhibitor of thrombin triggered platelet aggregation, serotonin release and tyrosine phosphorylation. Its anti-aggregatory activity was about ten-fold higher than that of the previously reported peptide antagonists of the thrombin receptor. MSRPACPNDKYE has served as model peptide in protein modification and MS studies.