G(BETA-GAMMA) DIRECTLY BINDS TO THE CARBOXYL-TERMINUS OF THE G-PROTEIN-GATED MUSCARINIC K+ CHANNEL, GIRK1

beta gamma Subunits of heterotrimeric GTP-binding proteins (G(beta gamma)) activate the inwardly rectifying muscarinic K+ channel, GIRK1. The significant role for the carboxyl (C) terminus of GIRK1 in this interaction has been suggested. However, it is still unknown whether G(beta gamma) directly interacts with GIRK1. To elucidate the molecular basis of G(beta gamma)-activation of GIRK1, we examined the binding properties of G(beta gamma) to the C terminus of GIRK1 cloned from mouse brain cDNA library (MB-GTPK1). The C terminus of MB-GIRK1 fused with glutathione S-transferase directly bound to purified G(beta gamma). Incubation of the C terminus with G(i) pretreated with GTP gamma S, but not with GDP, resulted in the binding of G(i beta gamma) to the protein. Purified G(alpha)-GDP, but not G(alpha)-GTP gamma S, inhibited the binding of G(beta gamma) to the fusion protein. These results indicate that G(beta gamma) dissociated from G(alpha) may directly bind to the C terminus of GIRK1. (C) 1995 Academic Press, Inc.