G protein β 4 as a structural determinant of enhanced nucleotide exchange in the A 2A AR-Gs complex.

Adenosine A _2A receptors (A _2A AR) 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 A _2A AR in a complex with full-length Gs α and Gβ ₄ γ ₂ (A _2A AR-Gs α:β ₄ γ ₂ ). The orthosteric binding site of A _2A AR-Gs α:β ₄ γ ₂ was similar to other structures of agonist-bound A _2A AR, with or without Gs. Unexpectedly, the solvent accessible surface area within the interior of the complex was substantially larger for the complex with Gβ ₄ versus the closest analog, A _2A AR-miniGs α:β ₁ γ ₂ . Consequently, there are fewer interactions between the switch II in Gs α and the Gβ ₄ torus. In reconstitution experiments Gβ ₄ γ ₂ displayed a ten-fold higher efficiency over Gβ ₁ γ ₂ in catalyzing A _2A AR dependent GTPγS binding to Gs α. We propose that the less constrained switch II in A _2A AR-Gs α:β ₄ γ ₂ accounts for this increased efficiency. These results suggest that Gβ ₄ functions as a positive allosteric enhancer versus Gβ ₁ .
Competing Interests: Additional Declarations: There is NO Competing Interest.