The adenosine A_2A receptor (A_2AR) engages several G proteins, notably G_o and its cognate G_s protein. This coupling promiscuity is facilitated by a dynamic ensemble, revealed by ¹⁹F nuclear magnetic resonance imaging of A_2AR and G protein. Two transmembrane helix 6 (TM6) activation states, formerly associated with partial and full agonism, accommodate the differing volumes of G_s and G_o. While nucleotide depletion biases TM7 toward a fully active state in A_2AR–G_s, A_2AR–G_o is characterized by a dynamic inactive/intermediate fraction. Molecular dynamics simulations reveal that the NPxxY motif, a highly conserved switch, establishes a unique configuration in the A_2AR–G_o complex, failing to stabilize the helix-8 interface with G_s, and adoption of the active state. The resulting TM7 dynamics hamper G protein coupling, suggesting kinetic gating may be responsible for reduced efficacy in the noncognate G protein complex. Thus, dual TM6 activation states enable greater diversity of coupling partners while TM7 dynamics dictate coupling efficacy.

腺苷 A_2A 受体 （A_2AR） 与多种 G 蛋白结合，特别是 G_o 及其同源 G_s 蛋白。这种耦合混杂由动态集成促进，由 A_2AR 和 G 蛋白的 ¹⁹F 核磁共振成像揭示。两种跨膜螺旋 6 （TM6） 激活状态，以前与部分和完全激动相关，可容纳不同体积的 G_{s 和 GO。}虽然核苷酸耗竭使 TM7 在_{A 2A}R-G_s 中偏向于完全活性状态，但_{A 2A}R-G_o 的特征是动态无活性/中间级分。分子动力学模拟表明，NPxxY 基序（一种高度保守的开关）在 A_2AR-G_o 复合物中建立了独特的构型，无法稳定 G_s 的螺旋-8 界面，并采用活性状态。由此产生的 TM7 动力学阻碍了 G 蛋白偶联，表明动力学门控可能是导致非同源 G 蛋白复合物疗效降低的原因。因此，双 TM6 激活状态可实现更多样化的偶联伴侣，而 TM7 动力学决定了偶联功效。