%0 Journal Article %A Thierry Wurch %A Junko Okuda %A Petrus J. Pauwels %T Reciprocal Modulation of α2A-Adrenoceptor and Gαο Protein States as Determined by Carboxy-Terminal Mutagenesis of a Gαο Protein %D 2001 %J Molecular Pharmacology %P 666-673 %V 60 %N 4 %X The C-terminal portion of Gα proteins plays a key role in their selective activation by cognate receptors. α2A-Adrenoceptors (α2A-ARs) can differentially inhibit or stimulate adenylyl cyclases by the activation of distinct Gi/o and Gs protein families. The implication of the C-terminal portion of Gαo and Gαs proteins in their activation by α2A-ARs was analyzed by constructing mutant Gαo proteins in which each of the last five amino acid positions were exchanged for those corresponding to a Gαs protein. Agonist-dependent, pertussis toxin-resistant binding of guanosine 5′-O-(3-[35S]thio)triphosphate ([35S]GTPγS) revealed that the degree of positive efficacy of clonidine was highly dependent on the presence of a Gαo protein-derived Gly amino acid as the −3 residue at the C-terminal portion of the protein. In contrast, antagonist properties for clonidine were observed for those mutants carrying a Gαs protein-derived Glu residue at this position. (−)-Epinephrine yielded almost similar maximal [35S]GTPγS binding responses, but its potency was decreased 22- to 150-fold at the −3 Glu containing mutant Gαo proteins compared with those mutants containing a Gly. A 9- to 39-fold increase in the α2A-AR agonist equilibrium dissociation constants further reflected changes in the Gα protein-induced α2A-AR state mediated by the specific Gly to Glu mutation in the C-terminal portion of the Gαo protein. The present data emphasize the unique role of the −3 position at the Gα protein C-terminal portion, independent of its surrounding peptidic environment, in constraining a structure favorable for activated receptor interaction and transmission of the mutation-induced conformational change from the Gαo protein to the α2A-AR. The American Society for Pharmacology and Experimental Therapeutics %U https://molpharm.aspetjournals.org/content/molpharm/60/4/666.full.pdf