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 IKACh, an inward rectifier K+ channel (IRK). Activation of the GIRK subunit of IKACh 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.
Department of Molecular and Cellular Biology Harvard University Cambridge, Massachusetts 02138, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D011485:Protein Binding / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014982:Xenopus laevis
D015221:Potassium Channels; D011993:Recombinant Fusion Proteins; D019204:GTP-Binding Proteins