Identification of a potassium channel site that interacts with G protein betagamma subunits to mediate agonist-induced signaling.
Activation of heterotrimeric GTP-binding (G) proteins by their coupled receptors, causes dissociation of the G protein alpha and betagamma subunits. Gbetagamma subunits interact directly with G protein-gated inwardly rectifying K+ (GIRK) channels to stimulate their activity. In addition, free Gbetagamma subunits, resulting from agonist-independent dissociation of G protein subunits, can account for a major component of the basal channel activity. Using a series of chimeric constructs between GIRK4 and a Gbetagamma-insensitive K+ channel, IRK1, we have identified a critical site of interaction of GIRK with Gbetagamma. Mutation of Leu339 to Glu within this site impaired agonist-induced sensitivity and decreased binding to Gbetagamma, without removing the Gbetagamma contribution to basal currents. Mutation of the corresponding residue in GIRK1 (Leu333) resulted in a similar phenotype. Both the GIRK1 and GIRK4 subunits contributed equally to the agonist-induced sensitivity of the heteromultimeric channel. Thus, we have identified a channel site that interacts specifically with Gbetagamma subunits released through receptor stimulation.
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Department of Physiology and Biophysics, Mount Sinai School of Medicine, City University of New York, New York, New York 10029, USA.
Zhang
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Mirshahi
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Logothetis
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D001665:Binding Sites; D001704:Biopolymers; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D006801:Humans; D007930:Leucine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D001704:Biopolymers; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins; D007930:Leucine