Molecular mechanism of the endothelin receptor type B interactions with Gs, Gi, and Gq

The endothelin receptor type B (ETB) exhibits promiscuous coupling with various G protein subtypes including Gs, Gi/o, Gq/11, and G12/13, leading to multi-modal signal transduction. Recent fluorescence and structural studies have raised questions regarding the coupling efficiencies and determinants of these G protein subtypes. Herein, by utilizing an integrative approach, combining hydrogen/deuterium exchange mass spectrometry and NanoLuc Binary Technology-based cellular systems, we investigated conformational changes of Gs, Gi and Gq triggered by ETB activation. ETB coupled to Gi and Gq but not with Gs. We underscored the critical roles of specific regions, including the C-terminus of Gα and intracellular loop 2 (ICL2) of ETB in ETB-Gi1 or ETB-Gq coupling. Although The C-terminus of Gα is essential for ETB-Gi1 and ETB-Gq coupling, ETB ICL2 influences Gq-coupling but not Gi1-coupling. Our results suggest a differential coupling efficiency of ETB with Gs, Gi1, and Gq, accompanied by distinct conformational changes in G proteins upon ETB-induced activation.