title: Localization of PIP2 activation gate in inward rectifier K+ channels.
abstract: Ion channels respond to changes in transmembrane voltage or ligand concentration by opening or closing an activation gate. In voltage-gated K+ channels, this gate has been localized to an intracellular bundle crossing. Here we examined whether this bundle crossing, or the more internal cytoplasmic pore, acts as a gate for PIP2 activation of inward rectifier K+ (Kir) channels expressed in Xenopus laevis oocytes. We studied the open/closed state-dependence of the accessibility of intracellular cationic modifiers to a position (residue Ile176 in the TM2 helix of Kir2.1) more external to the bundle crossing. Cd2+ blocked I176C mutant channels much more weakly in the closed state than in the open state, but Ag+ and sulfhydryl-specific methanethiosulfonate reagents modified the channels with similar rates in both states. These results suggest that the TM2 helices undergo conformation changes upon PIP2 binding/unbinding, but neither they nor the cytoplasmic pore close fully to form a physical gate for K+ conduction.
authors.affiliation: Department of Biological Sciences, Columbia University, 915 Fairchild Center, MC2462, New York, New York 10027, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiao
authors.forename: Xiao-guang
authors.initials: XG
authors.lastname: Zhen
authors.forename: Jian
authors.initials: J
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D003545:Cysteine; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives* / Q000378:metabolism; D015640:Ion Channel Gating / Q000235:genetics*; D008698:Mesylates / Q000378:metabolism; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012834:Silver / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D008698:Mesylates; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; C093171:methanethiosulfonate ethylammonium; D002104:Cadmium; C109154:(2-(trimethylammonium)ethyl)methanethiosulfonate; D012834:Silver; D005020:Ethyl Methanesulfonate; D003545:Cysteine