Activation of inwardly rectifying K+ channels by distinct PtdIns(4,5)P2 interactions.
Direct interactions of phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) with inwardly rectifying potassium channels are stronger with channels rendered constitutively active by binding to PtdIns(4,5)P2, such as IRK1, than with G-protein-gated channels (GIRKs). As a result, PtdIns(4,5)P2 alone can activate IRK1 but not GIRKs, which require extra gating molecules such as the beta gamma subunits of G proteins or sodium ions. Here we identify two conserved residues near the inner-membrane interface of these channels that are critical in interactions with PtdIns(4,5)P2. Between these two arginines, a conservative change of isoleucine residue 229 in GIRK4 to the corresponding leucine found in IRK1 strengthens GIRK4-PtdIns(4,5)P2 interactions, eliminating the need for extra gating molecules. A negatively charged GIRK4 residue, two positions away from the most strongly interacting arginine, mediates stimulation of channel activity by sodium by strengthening channel-PtdIns(4,5)P2 interactions. Our results provide a mechanistic framework for understanding how distinct gating mechanisms of inwardly rectifying potassium channels allow these channels to subserve their physiological roles.
Zhang
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Howard Hughes Medical Institute, Department of Physiology and Biophysics, Mount Sinai School of Medicine, CUNY, New York 10029, USA.
He
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Yan
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Mirshahi
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Logothetis
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D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D017124:Conserved Sequence; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000494:pharmacology*; D017354:Point Mutation; D015221:Potassium Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014981:Xenopus
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins