title: Mutation in nucleotide-binding domains of sulfonylurea receptor 2 evokes Na-ATP-dependent activation of ATP-sensitive K+ channels: implication for dimerization of nucleotide-binding domains to induce channel opening.
abstract: The ATP-sensitive K+ (KATP) channel is composed of a sulfonylurea receptor (SUR) and a pore-forming subunit, Kir6.2. SUR is an ATP-binding cassette (ABC) protein with two nucleotide-binding domains (NBD1 and NBD2). Intracellular ATP inhibits KATP channels through Kir6.2 and activates them through NBDs. However, it is still unknown how ATP-bound NBDs activate KATP channels. A prokaryotic ABC protein, MJ0796, which is entirely NBD, forms a dimer in the presence of Na-ATP when its glutamate at position 171 is substituted with glutamine. Mg2+ or K+ destabilizes the dimer. We made the corresponding mutation in the NBD1 (D834N) and/or NBD2 (E1471Q) of SUR2A and SUR2B. As measured in the inside-out configuration of the patch-clamp method, SUR2x(D834N, E1471)/Kir6.2 channels mediated significantly larger currents in the presence of internal 1 mM Na-ATP than K-ATP alone or Mg-ATP. The response to Na-ATP resulted from an increase in the open probability but not single-channel amplitude of the channels and was abolished by glibenclamide (10(-5) M). In the presence of 1 mM Mg2+ -free ATP, Na+ increased the activity of the channels in a concentration-dependent manner. The Na-ATP-dependent activation was never observed with KATP channels including either the wild-type SUR2x, SUR2x(D834N), or SUR2x(E1471). Nicorandil activated SUR2x(D834N, E1471Q)/Kir6.2 channels more strongly in the presence of Na-ATP than K-ATP alone, whereas the reverse was true for wild-type SUR2x/Kir6.2 channels. Therefore, it is likely that NBDs of SUR2x dimerize in response to ATP and nicorandil. The dimerization induces the opening of the KATP channel, probably by causing a conformational change of SUR2x.
authors.affiliation: Department of Pharmacology II, Graduate School of Medicine Osaka University, 2-2 Yamada-oka, Suita, 565-0871, Japan.
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Yamada
authors.forename: Masaru
authors.initials: M
authors.lastname: Ishii
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hibino
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kurachi
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D019943:Amino Acid Substitution; D000818:Animals; D001216:Asparagine / Q000235:genetics; D001224:Aspartic Acid / Q000235:genetics; D001665:Binding Sites; D019281:Dimerization; D018698:Glutamic Acid / Q000235:genetics; D005973:Glutamine / Q000235:genetics; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D020108:Nicorandil / Q000494:pharmacology; D009711:Nucleotides / Q000378:metabolism; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D017434:Protein Structure, Tertiary; D011955:Receptors, Drug; D012964:Sodium / Q000378:metabolism*; D064233:Sulfonylurea Receptors
chemical_list: C577510:ABCC9 protein, human; D018528:ATP-Binding Cassette Transporters; C577511:Abcc9 protein, mouse; D008565:Membrane Proteins; D009711:Nucleotides; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; C117780:mitochondrial K(ATP) channel; D005973:Glutamine; D020108:Nicorandil; D001224:Aspartic Acid; D018698:Glutamic Acid; D001216:Asparagine; D000255:Adenosine Triphosphate; D012964:Sodium