Mechanism of PAR-1 activation. The N-terminus of PAR-1, a seven transmembrane domain G protein–coupled receptor, contains a protease cleavage site that, once cleaved by thrombin, results in a new N-terminus. The new N-terminal sequence, SFLLRN, acts as a tethered ligand and binds intramolecularly to the heptahelical body of the receptor to effect transmembrane signaling and G protein activation.