IDENTIFICATION OF DOMAINS CONFERRING G-PROTEIN REGULATION ON INWARD RECTIFIER POTASSIUM CHANNELS

Cardiac m2 muscarinic acetylcholine receptors reduce heart rate by coupling to heterotrimeric (alpha beta gamma) guanine nucleotide-binding (G) proteins that activate I-KaCh, an inward rectifier K+ channel (IRK), Activation of the GIRK subunit of I-KaCh requires G(beta gamma) subunits; however, the structural basis of channel regulation is unknown. To determine which sequences confer G(beta gamma) regulation upon IRKs, we generated chimeric proteins composed of GIRK and RB-IRK2, a related, G protein-insensitive channel, Importantly, a chimeric channel containing the hydrophobic pore region of RB-IRK2 joined to the amino and carboxyl termini of GIRK exhibited voltage- and receptor-dependent activation in Xenopus oocytes, Furthermore, carboxy-terminal sequences specific to this chimera and GIRK bound G(beta gamma) subunits in vitro. Thus, G(beta gamma), may regulate IRKs by interacting with sequences adjacent to the putative channel pore.