Closely related G-protein-coupled receptors use multiple and distinct domains on G-protein alpha-subunits for selective coupling.

Slessareva JE, Ma H, Depree KM, Flood LA, Bae H, Cabrera-Vera TM, Hamm HE, Graber SG
J Biol Chem. 2003 278 (50): 50530-6

PMID: 14525988 · DOI:10.1074/jbc.M304417200

The molecular basis of selectivity in G-protein receptor coupling has been explored by comparing the abilities of G-protein heterotrimers containing chimeric Galpha subunits, comprised of various regions of Gi1alpha, Gtalpha, and Gqalpha, to stabilize the high affinity agonist binding state of serotonin, adenosine, and muscarinic receptors. The data indicate that multiple and distinct determinants of selectivity exist for individual receptors. While the A1 adenosine receptor does not distinguish between Gi1alpha and Gtalpha sequences, the 5-HT1A and 5-HT1B serotonin and M2 muscarinic receptors can couple with Gi1 but not Gt. It is possible to distinguish domains that eliminate coupling and are defined as "critical," from those that impair coupling and are defined as "important." Domains within the N terminus, alpha4-helix, and alpha4-helix-alpha4/beta6-loop of Gi1alpha are involved in 5-HT and M2 receptor interactions. Chimeric Gi1alpha/Gqalpha subunits verify the critical role of the Galpha C terminus in receptor coupling, however, the individual receptors differ in the C-terminal amino acids required for coupling. Furthermore, the EC50 for interactions with Gi1 differ among the individual receptors. These results suggest that coupling selectivity ultimately involves subtle and cooperative interactions among various domains on both the G-protein and the associated receptor as well as the G-protein concentration.

MeSH Terms (19)

Amino Acid Sequence Animals Cell Line Cell Membrane Dimerization Dose-Response Relationship, Drug GTP-Binding Protein alpha Subunits, Gi-Go GTP-Binding Protein alpha Subunits, Gq-G11 Insecta Models, Molecular Molecular Sequence Data Mutation Point Mutation Protein Binding Protein Structure, Secondary Protein Structure, Tertiary Radioligand Assay Sequence Homology, Amino Acid Transducin

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