Thrombin complexed with receptor, molecular model. Protease-activated receptor 1 (PAR1, white-pink) is the prototypical member of a family of G-protein-coupled receptors that mediate cellular responses to thrombin (pink) and related proteases. Thrombin irreversibly activates PAR1 by cleaving the amino-terminal exodomain of the receptor, which exposes a tethered peptide ligand that binds the heptahelical bundle of the receptor to affect G-protein activation. PAR1 is a key part of re-myelination and neuron repair processes.