PAR1 and PAR4 cleavage sites. Proteases cleave PAR1 and PAR4 at different sites on their N terminus. The residues in green denote the canonical tethered ligand generated by thrombin. (A) Model of PAR activation mechanism via proteolysis of the N terminus. (B) The amino acid sequence of the N terminus of PAR1 or PAR4. The cleavage sites for thrombin, MMP1, MMP2, APC, and cathepsin G are inidicated. CatG, cathepsin G.