Structural insights into G protein activation by D1 dopamine receptor

Abstract

G protein-coupled receptors (GPCRs) comprise the largest family of membrane receptors and are the most important drug targets. An agonist-bound GPCR engages heterotrimeric G proteins and triggers the exchange of GDP with GTP to promote G proteins activation. A complete understanding of the molecular mechanisms of G proteins activation has been hindered by a lack of structural information of GPCR-G protein complex in nucleotide-bound states. Here, we present the cryoelectron microscopy (cryo-EM) structures of D1 dopamine receptor (D1R)-Gs in the nucleotide-free state, the GDP-bound state and the GTP-bound state with endogenous ligand dopamine. These structures reveal important conformational changes accounting for the release of GDP and the GTP-dependent dissociation of G from G{beta}{gamma} subunits. Combining mutagenesis functional studies, we also identified an important sequence motif in D1R that determines its G protein selectivity. Taken together, these results shed light into the molecular basis of G protein selectivity and the entire molecular signaling events of GPCR-mediated G protein activation.