Crystal structure of human endothelin ET(B) receptor in complex with peptide inverse agonist IRL2500

Endothelin receptors (ET(A) and ET(B)) are G-protein-coupled receptors activated by endothelin-1 and are involved in blood pressure regulation. IRL2500 is a peptide-mimetic of the C-terminal tripeptide of endothelin-1, and has been characterized as a potent ET(B)-selective antagonist, which has preventive effects against brain edema. Here, we report the crystal structure of the human ET(B) receptor in complex with IRL2500 at 2.7 Å-resolution. The structure revealed the different binding modes between IRL2500 and endothelin-1, and provides structural insights into its ET(B)-selectivity. Notably, the biphenyl group of IRL2500 penetrates into the transmembrane core proximal to D(2.50), thus stabilizing the inactive conformation. Using the newly-established constitutively active mutant, we clearly demonstrate that IRL2500 functions as an inverse agonist for the ET(B) receptor. The current findings will expand the chemical space of ETR antagonists and facilitate the design of inverse agonists for other class A GPCRs.