Role of βγ Subunits of G Proteins in Targeting the β-Adrenergic Receptor Kinase to Membrane-Bound Receptors

The rate and extent of the agonist-dependent phosphorylation of beta 2-adrenergic receptors and rhodopsin by beta-adrenergic receptor kinase (beta ARK) are markedly enhanced on addition of G protein beta gamma subunits. With a model peptide substrate it was demonstrated that direct activation of the kinase could not account for this effect. G protein beta gamma subunits were shown to interact directly with the COOH-terminal region of beta ARK, and formation of this beta ARK-beta gamma complex resulted in receptor-facilitated membrane localization of the enzyme. The beta gamma subunits of transducin were less effective at both enhancing the rate of receptor phosphorylation and binding to the COOH-terminus of beta ARK, suggesting that the enzyme preferentially binds specific beta gamma complexes. The beta gamma-mediated membrane localization of beta ARK serves to intimately link receptor activation to beta ARK-mediated desensitization.