Structural basis and mechanism of activation of two different families of G proteins by the same GPCR

The β 1 -adrenergic receptor (β 1 -AR) can activate two families of G proteins. When coupled to Gs, β 1 -AR increases cardiac output, and coupling to Gi leads to decreased responsiveness in myocardial infarction. By comparative structural analysis of turkey β 1 -AR complexed with either Gi or Gs, we investigate how a single G-protein-coupled receptor simultaneously signals through two G proteins. We find that, although the critical receptor-interacting C-terminal α5-helices on Gα i and Gα s interact similarly with β 1 -AR, the overall interacting modes between β 1 -AR and G proteins vary substantially. Functional studies reveal the importance of the differing interactions and provide evidence that the activation efficacy of G proteins by β 1 -AR is determined by the entire three-dimensional interaction surface, including intracellular loops 2 and 4 (ICL2 and ICL4).