G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the Gα subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound G_s protein (G_s·GDP; hereafter G_s^GDP) upon coupling to the β₂-adrenergic receptor (β₂AR) in atomic detail. The binding of G_s^GDP to the β₂AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of α1-αF helices, the displacement of the αG helix and the opening of the α-helical domain. Signal propagation to the G_s occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this β₂AR–G_s^GDP intermediate, G_s undergoes an in-plane rotation along the receptor axis to approach the β₂AR–G_s^empty state. The simulations shed light on how the structural elements at the receptor–G-protein interface may interact to transmit the signal over 30 Å to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.

G 蛋白偶联受体 (GPCR) 通过促进鸟嘌呤核苷酸交换来激活异三聚体 G 蛋白。在这里，我们研究了 G 蛋白与 GPCR 的偶联，并描述了最终导致 GDP 从 Gα 亚基中的结合口袋中弹出的事件，这是 G 蛋白激活过程中的限速步骤。利用分子动力学模拟，我们研究了 GDP 结合 G _s蛋白（G _s ·GDP；以下简称 G _s ^GDP ）在与 β _{2 -}肾上腺素能受体（β ₂ AR）偶联后的原子细节结构重排的时间进程。 G _s ^GDP与 β ₂ AR 结合后会产生长程变构效应，显着降低 GDP 释放所需的能量：α1-αF 螺旋的打开、αG 螺旋的位移和 α- 的打开螺旋域。信号传播到 G _s是通过一个扩展的受体界面发生的，包括在扭结的跨膜螺旋 6 的细胞内末端富含赖氨酸的基序，这已通过定点诱变和功能测定得到证实。从这个 β ₂ AR–G _s ^GDP中间体，G _s沿着受体轴进行面内旋转以接近 β ₂ AR–G _s^空态。模拟揭示了受体-G 蛋白界面的结构元件如何相互作用，将超过 30 Å 的信号传输到核苷酸结合位点。 我们的分析扩展了目前无核苷酸快照的有限观点，包括负责信号传导和 G 蛋白偶联特异性的其他状态和结构特征。