The G Protein β Subunit is a Determinant in the Coupling of G s to the β1-Adrenergic and A2a Adenosine Receptors

Abstract

The signaling specificity of five purified G protein βγ dimers, β1γ2, β2γ2, β3γ2, β4γ2, and β5γ2, was explored by reconstituting them with Gs α and receptors or effectors in the adenylyl cyclase cascade. The ability of the five βγ dimers to support receptor-α-βγ interactions was examined using membranes expressing the β1-adrenergic or A2a adenosine receptors. These receptors discriminated among the defined heterotrimers based solely on the β isoform. The β4γ2 dimer demonstrated the highest coupling efficiency to either receptor. The β 5γ2 dimer coupled poorly to each receptor, with EC50 values 40-200-fold higher than those observed with β 4γ2. Strikingly, whereas the EC50 of the β1γ2 dimer at the β 1-adrenergic receptor was similar to β4γ 2, its EC50 was 20-fold higher at the A2a adenosine receptor. Inhibition of adenylyl cyclase type I (AC1) and stimulation of type II (AC2) by the βγ dimers were measured. βγ dimers containing Gβ1-4 were able to stimulate AC2 similarly, and β5γ2 was much less potent. β 3γ2, β2γ2, and β4γ2 inhibited AC1 equally; β 3γ2 was 10-fold less effective, and β 5γ2 had no effect. These data argue that the β isoform in the βγ dimer can determine the specificity of signaling at both receptors and effectors.