AbstractG protein-coupled receptors (GPCRs) induce signal transduction pathways through coupling to four main subtypes of G proteins (Gs, Gi, Gq, G12/13), selectively. However, G protein selective activation mechanisms and residual determinants in GPCRs have remained obscure. Here, we identified conserved G protein selective activation mechanisms determining receptors’ ability to couple to a type of G protein. Herein, we performed an extensive phylogenetic analysis and identified specifically conserved residues for the receptors having similar coupling profiles in each aminergic receptor. By integrating our methodology of differential evolutionary conservation of G protein-specific amino acids with structural analyses, we identified selective activation networks for Gs, Gi1, Go, and Gq. We found that G protein selectivity is determined by not only the G protein interaction site but also other parts of the receptor including the ligand binding pocket. To validate our findings, we further studied an amino acid residue that we revealed as a selectivity-determining in Gs coupling and performed molecular dynamics (MD) simulations. We showed that previously uncharacterized Glycine at position 7×41 plays an important role in both receptor activation and Gs coupling. Finally, we gathered our results into a comprehensive model of G protein selectivity called “sequential switches of activation” describing three main molecular switches controlling GPCR activation: ligand binding, G protein selective activation mechanisms and G protein contact. We believe that our work provides a broader view on receptor-level determinants of G protein coupling selectivity.
Ligand recognition, unconventional activation, and G protein coupling of the prostaglandin E2 receptor EP2 subtype
