School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, 16419, Republic of Korea.
Beijing Advanced Innovation Center for Structural Biology, School of Medicine, Tsinghua University, Beijing, 100084, China.
Nat Commun. 2020 Jun 22;11(1):3160. doi: 10.1038/s41467-020-16975-2.
Heterotrimeric G proteins are categorized into four main families based on their function and sequence, Gs, Gi/o, Gq/11, and G12/13. One receptor can couple to more than one G protein subtype, and the coupling efficiency varies depending on the GPCR-G protein pair. However, the precise mechanism underlying different coupling efficiencies is unknown. Here, we study the structural mechanism underlying primary and secondary Gi/o coupling, using the muscarinic acetylcholine receptor type 2 (M2R) as the primary Gi/o-coupling receptor and the β-adrenergic receptor (βAR, which primarily couples to Gs) as the secondary Gi/o-coupling receptor. Hydrogen/deuterium exchange mass spectrometry and mutagenesis studies reveal that the engagement of the distal C-terminus of Gαi/o with the receptor differentiates primary and secondary Gi/o couplings. This study suggests that the conserved hydrophobic residue within the intracellular loop 2 of the receptor (residue 34.51) is not critical for primary Gi/o-coupling; however, it might be important for secondary Gi/o-coupling.
异三聚体 G 蛋白根据其功能和序列分为四大类，分别为 Gs、Gi/o、Gq/11 和 G12/13。一种受体可以与多种 G 蛋白亚型偶联，而偶联效率取决于 GPCR-G 蛋白对。然而，不同偶联效率的精确机制尚不清楚。在这里，我们使用毒蕈碱型乙酰胆碱受体 2（M2R）作为主要 Gi/o 偶联受体，β-肾上腺素能受体（βAR，主要与 Gs 偶联）作为次要 Gi/o 偶联受体，研究了初级和次级 Gi/o 偶联的结构机制。氢氘交换质谱和突变研究表明，Gαi/o 的远端 C 末端与受体的结合区分了初级和次级 Gi/o 偶联。本研究表明，受体细胞内环 2 内的保守疏水性残基（残基 34.51）对于初级 Gi/o 偶联并非关键；然而，它可能对次级 Gi/o 偶联很重要。
