Structure of endothelin ET_B receptor-G_i complex in a conformation stabilized by unique NPxxL motif

Endothelin type B receptor (ET_BR) plays a crucial role in regulating blood pressure and humoral homeostasis, making it an important therapeutic target for related diseases. ET_BR activation by the endogenous peptide hormones endothelin (ET)-1-3 stimulates several signaling pathways, including G_s, G_i/o, G_q/11, G_12/13, and β-arrestin. Although the conserved NPxxY motif in transmembrane helix 7 (TM7) is important during GPCR activation, ET_BR possesses the lesser known NPxxL motif. In this study, we present the cryo-EM structure of the ET_BR-G_i complex, complemented by MD simulations and functional studies. These investigations reveal an unusual movement of TM7 to the intracellular side during ET_BR activation and the essential roles of the diverse NPxxL motif in stabilizing the active conformation of ET_BR and organizing the assembly of the binding pocket for the α5 helix of G_i protein. These findings enhance our understanding of the interactions between GPCRs and G proteins, thereby advancing the development of therapeutic strategies.