PAR1 is an unusual GPCR. The PAR1 structure (blue) is superimposed on the structure of the ß2 adrenergic receptor (pink) or the M2 muscarinic receptor (yellow). The ligand-binding pocket is substantially shallower in PAR1, as demonstrated by the binding of vorapaxar (green) on the surface of PAR1. By comparison, binding of the inverse agonist carazolol (magenta) on the ß2 adrenergic receptor or the antagonist QNB (orange) on the M2 muscarinic receptor occurs in the deep ligand binding pockets of these GPCRs.Adapted by permission from Macmillan Publishers Ltd: Nature (Zhang et al. Nature. 492:387- 392), Copyright 2012.