The technique of cryogenic-electron microscopy (cryo-EM) has revolutionized the field of membrane protein structure and function with a focus on the dominantly observed molecular species. This report describes the structural characterization of a fully active human apelin receptor (APJR) complexed with heterotrimeric G protein observed in both 2:1 and 1:1 stoichiometric ratios. We use cryo-EM single-particle analysis to determine the structural details of both species from the same sample preparation. Protein preparations, in the presence of the endogenous peptide ligand ELA or a synthetic small molecule, both demonstrate these mixed stoichiometric states. Structural differences in G protein engagement between dimeric and monomeric APJR suggest a role for the stoichiometry of G protein-coupled receptor- (GPCR-)G protein coupling on downstream signaling and receptor pharmacology. Furthermore, a small, hydrophobic dimer interface provides a starting framework for additional class A GPCR dimerization studies. Together, these findings uncover a mechanism of versatile regulation through oligomerization by which GPCRs can modulate their signaling.

低温电子显微镜 (cryo-EM) 技术彻底改变了膜蛋白结构和功能领域，重点关注主要观察到的分子种类。本报告描述了以 2:1 和 1:1 化学计量比观察到的与异源三聚体 G 蛋白复合的完全活性人爱帕林受体 (APJR) 的结构特征。我们使用冷冻电镜单粒子分析来确定同一样品制备中两种物种的结构细节。在存在内源性肽配体 ELA 或合成小分子的情况下，蛋白质制剂都表现出这些混合的化学计量状态。二聚体和单体 APJR 之间 G 蛋白结合的结构差异表明 G 蛋白偶联受体 - (GPCR-)G 蛋白偶联的化学计量对下游信号和受体药理学的作用。此外，一个小的疏水二聚体界面为其他 A 类 GPCR 二聚化研究提供了一个起始框架。总之，这些发现揭示了一种通过寡聚化进行多功能调节的机制，GPCR 可以通过这种机制调节其信号传导。