Molecular Analysis of β2-Adrenoceptor Coupling to Gs-, Gi-, and Gq-Proteins

By K. Wenzel‐Seifert, Roland Seifert. Molecular Pharmacology, 2000

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The β 2 -adrenoceptor (β 2 AR) couples to the G-protein G s to activate adenylyl cyclase. Intriguingly, several studies have demonstrated that the β 2 AR can also interact with G-proteins of the G i - and G q -family. To assess the efficiency of β 2 AR interaction with various G-protein α-subunits (G xα ), we expressed fusion proteins of the β 2 AR with the long (G sα L ) and short (G sα S ) splice variants of G sα , the G i -proteins G iα 2 and G iα 3 , and the G q -proteins G qα and G 16α in Sf9 cells. Fusion proteins provide a rigorous approach for comparing the coupling of a given receptor to G xα because of the defined 1:1 stoichiometry of receptor and G-protein and the efficient coupling. Here, we show that the β 2 AR couples to G s -, G i -, and G q -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 β 2 AR with the various classes of G-proteins. Comparison of the coupling of the β 2 AR and formyl peptide receptor to G iα 2 revealed receptor-specific differences in the kinetics of GTPγS binding. We also detected highly efficient stimulation of GTPγS dissociation from G sα L , but not from G qα and G 16α , by a β 2 AR 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 β 2 AR couples differentially to G s -, G i -, and G q -proteins, 2) that there is ligand-specific coupling of the β 2 AR 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.

Subfields: Cellular and Molecular Neuroscience, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/4e4d6bec034fa8501c3d021c52f81aa85469a75f

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