title: Kir6.2 channel gating by intracellular protons: subunit stoichiometry for ligand binding and channel gating.
abstract: The adenosine triphosphate-sensitive K(+) (K(ATP)) channels are gated by several metabolites, whereas the gating mechanism remains unclear. Kir6.2, a pore-forming subunit of the K(ATP) channels, has all machineries for ligand binding and channel gating. In Kir6.2, His175 is the protonation site and Thr71 and Cys166 are involved in channel gating. Here, we show how individual subunits act in proton binding and channel gating by selectively disrupting functional subunits using these residues. All homomeric dimers and tetramers showed pH sensitivity similar to the monomeric channels. Concatenated construction of wild type with disrupted subunits revealed that none of these residues had a dominant-negative effect on the proton-dependent channel gating. Subunit action in proton binding was almost identical to that for channel gating involving Cys166, suggesting a one-to-one coupling from the C terminus to the M2 helix. This was significantly different from the effect of T71Y heteromultimers, suggesting distinct contributions of M1 and M2 helices to channel gating. Subunits underwent concerted rather than independent action. Two wild-type subunits appeared to act as a functional dimer in both cis and trans configurations. The understanding of K(ATP) channel gating by intracellular pH has a profound impact on cellular responses to metabolic stress as a significant drop in intracellular pH is more frequently seen under a number of physiological and pathophysiological conditions than a sole decrease in intracellular ATP levels.
authors.affiliation: Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, Georgia, 30303-4010, USA.
authors.forename: Runping
authors.initials: R
authors.lastname: Wang
authors.forename: Junda
authors.initials: J
authors.lastname: Su
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhang
authors.forename: Yun
authors.initials: Y
authors.lastname: Shi
authors.forename: Ningren
authors.initials: N
authors.lastname: Cui
authors.forename: Vivian A
authors.initials: VA
authors.lastname: Onyebuchi
authors.forename: Chun
authors.initials: C
authors.lastname: Jiang
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D015640:Ion Channel Gating; D008024:Ligands; D051379:Mice; D009154:Mutation; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D011522:Protons; D014982:Xenopus laevis; D000099161:Kcnj11 Channel
chemical_list: D008024:Ligands; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011522:Protons; D000099161:Kcnj11 Channel