G‐protein‐coupled receptors (GPCRs) transmit downstream signals predominantly via G‐protein pathways. However, the conformational basis of selective coupling of primary G‐protein remains elusive. Histamine receptors H2R and H3R couple with Gs‐ or Gi‐proteins respectively. Here, three cryo‐EM structures of H2R‐Gs and H3R‐Gi complexes are presented at a global resolution of 2.6‐2.7 Å. These structures reveal the unique binding pose for endogenous histamine in H3R, wherein the amino group interacts with E2065.46 of H3R instead of the conserved D1143.32 of other aminergic receptors. Furthermore, comparative analysis of the H2R‐Gs and H3R‐Gi complexes reveals that the structural geometry of TM5/TM6 determines the primary G‐protein selectivity in histamine receptors. Machine learning (ML)‐based structuromic profiling and functional analysis of class A GPCR–G‐protein complexes illustrate that TM5 length, TM5 tilt, and TM6 outward movement are key determinants of the Gs and Gi/o selectivity among the whole Class A family. Collectively, the findings uncover the common structural geometry within class A GPCRs that determines the primary Gs‐ and Gi/o‐coupling selectivity.

中文翻译：

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A 类 GPCR 选择性偶联初级 G 蛋白的分子决定因素

G 蛋白偶联受体 (GPCR) 主要通过 G 蛋白途径传递下游信号。然而，初级 G 蛋白选择性偶联的构象基础仍然难以捉摸。组胺受体 H2R和H3R 与 G 配对s- 或 G我分别为-蛋白质。这里，H的三个冷冻电镜结构2R-Gs和H3R-G我复合物的整体分辨率为 2.6-2.7 Å。这些结构揭示了 H 中内源性组胺的独特结合姿势3R，其中氨基与E206相互作用5.46的 H3R代替保守的D1143.32其他胺能受体。此外，H的比较分析2R-Gs和H3R-G我复合物揭示TM5/TM6的结构几何形状决定组胺受体中的主要G蛋白选择性。基于机器学习 (ML) 的 A 类 GPCR-G 蛋白复合物的结构组学分析和功能分析表明，TM5 长度、TM5 倾斜和 TM6 向外运动是 G 的关键决定因素。s和G输入/输出整个A类家族之间的选择性。总的来说，这些发现揭示了 A 类 GPCR 中决定主要 G 的常见结构几何形状。s‐ 和 G输入/输出‐耦合选择性。