G protein ß4 as a structural determinant of enhanced nucleotide exchange in the A2AAR-Gs complex.

ABSTRACT

Adenosine A2A receptors (A2AAR) evoke pleiotropic intracellular signaling events via activation of the stimulatory heterotrimeric G protein, Gs. Here, we used cryoEM to solve the agonist-bound structure of A2AAR in a complex with full-length Gs α and Gß4γ2 (A2AAR-Gs αß4γ2). The orthosteric binding site of A2AAR-Gs αß4γ2 was similar to other structures of agonist-bound A2AAR, with or without Gs. Unexpectedly, the solvent accessible surface area within the interior of the complex was substantially larger for the complex with Gß4 versus the closest analog, A2AAR-miniGs αß1γ2. Consequently, there are fewer interactions between the switch II in Gs α and the Gß4 torus. In reconstitution experiments Gß4γ2 displayed a ten-fold higher efficiency over Gß1γ2 in catalyzing A2AAR dependent GTPγS binding to Gs α. We propose that the less constrained switch II in A2AAR-Gs αß4γ2 accounts for this increased efficiency. These results suggest that Gß4 functions as a positive allosteric enhancer versus Gß1.