Identification of a potassium channel site that interacts with G protein beta gamma subunits to mediate agonist-induced signaling

Activation of heterotrimeric GTP-binding (G) proteins by their coupled rece ptors, causes dissociation of the G protein alpha and beta gamma subunits, G(beta gamma) Subunits interact directly with G protein-gated inwardly rect ifying K+ (GIRK) channels to stimulate their activity. In addition, free G( beta gamma) subunits, resulting from agonist-independent dissociation of G protein subunits, can account for a major component of the basal channel ac tivity. Using a series of chimeric constructs between GIRK4 and a G(beta gamma)-ins ensitive K+ channel, IRK1, we have identified a critical site of interactio n of GIRK with G(beta gamma). Mutation of Leu(339) to Glu within this site impaired agonist-induced sensitivity and decreased binding to G(beta gamma) , without removing the G(beta gamma) contribution to basal currents. Mutati on of the corresponding residue in GIRK1 (Leu(333)) resulted in a similar p henotype, Both the GIRK1 and GIRK4 subunits contributed equally to the agon ist-induced sensitivity of the heteromultimeric channel. Thus, we have iden tified a channel site that interacts specifically with G(beta gamma) subuni ts released through receptor stimulation.