G-protein βγ-subunits contribute to the coupling specificity of the β2-adrenergic receptor to Gs

Receptors and heterotrimeric G-proteins interact with a high degree of specificity, the molecular basis of which is only partially understood. In the present study, we analyzed the influence of different G-protein βγ-subunits on the coupling of the β2-adrenergic receptor to Gs. Sf9-cells were infected with baculoviruses coding for the β2-adrenergic receptor, αs,Short or αs,Long, and various β- and γ-subunits. The ability of different β- and γ-subunits to correctly dimerize was assessed by limited proteolysis of proteins expressed in Sf9-cells and additionally by analysis of β/γ-interaction in the yeast two-hybrid system. Agonist-induced GTPγS-binding to αs,Shortβ1γ-trimers was significantly higher than to αs,Shortβ2γ-combinations, when γ4, γ5, or γ7 were co-expressed. Because β5 did not support coupling of the β2-adrenergic receptor to Gs, the 87 C-terminal amino acids of Gβ5 assumed to encompass the β-subunit interface with the receptor were substituted by the corresponding sequence of β1. Whereas this β5/β1-chimera did not promote GTPγS-binding to αs, histamine H1-receptor-dependent GTPγS-binding to αq was supported by this chimeric β-subunit and by wild-type β5. Our findings argue that the βγ-subunit composition contributes directly to the specificity of β2-adrenergic receptor-mediated Gs-activation.