TY - JOUR T1 - Molecular Analysis of β<sub>2</sub>-Adrenoceptor Coupling to G<sub>s</sub>-, G<sub>i</sub>-, and G<sub>q</sub>-Proteins JF - Molecular Pharmacology JO - Mol Pharmacol SP - 954 LP - 966 DO - 10.1124/mol.58.5.954 VL - 58 IS - 5 AU - Katharina Wenzel-Seifert AU - Roland Seifert Y1 - 2000/11/01 UR - http://molpharm.aspetjournals.org/content/58/5/954.abstract N2 - The β2-adrenoceptor (β2AR) couples to the G-protein Gs to activate adenylyl cyclase. Intriguingly, several studies have demonstrated that the β2AR can also interact with G-proteins of the Gi- and Gq-family. To assess the efficiency of β2AR interaction with various G-protein α-subunits (Gxα), we expressed fusion proteins of the β2AR with the long (Gsα L) and short (Gsα S) splice variants of Gsα, the Gi-proteins Giα 2 and Giα 3, and the Gq-proteins Gqα and G16α in Sf9 cells. Fusion proteins provide a rigorous approach for comparing the coupling of a given receptor to Gxα because of the defined 1:1 stoichiometry of receptor and G-protein and the efficient coupling. Here, we show that the β2AR couples to Gs-, Gi-, and Gq-proteins as assessed by ternary complex formation and ligand-regulated guanosine 5′-O-(3-thiotriphosphate) (GTPγS) binding. The combined analysis of ternary complex formation, GTPγS binding, agonist efficacies, and agonist potencies revealed substantial differences in the interaction of the β2AR with the various classes of G-proteins. Comparison of the coupling of the β2AR and formyl peptide receptor to Giα 2 revealed receptor-specific differences in the kinetics of GTPγS binding. We also detected highly efficient stimulation of GTPγS dissociation from Gsα L, but not from Gqα and G16α, by a β2AR agonist. Moreover, we show that the 1:1 stoichiometry of receptor to G-protein in fusion proteins reflects the in vivo stoichiometry of receptor/G-protein coupling more closely than was previously assumed. Collectively, our data show 1) that the β2AR couples differentially to Gs-, Gi-, and Gq-proteins, 2) that there is ligand-specific coupling of the β2AR to G-proteins, 3) that receptor-specific G-protein conformational states may exist, and 4) that nucleotide dissociation is an important mechanism for G-protein deactivation. ER -