Potassium channel openers require ATP to bind to and act through sulfonylurea receptors.
KATP channels are composed of a small inwardly rectifying K+ channel subunit, either KIR6.1 or KIR6.2, plus a sulfonylurea receptor, SUR1 or SUR2 (A or B), which belong to the ATP-binding cassette superfamily. SUR1/KIR6.2 reconstitute the neuronal/pancreatic beta-cell channel, whereas SUR2A/KIR6.2 and SUR2B/KIR6.1 (or KIR6.2) are proposed to reconstitute the cardiac and the vascular-smooth-muscle-type KATP channels, respectively. We report that potassium channel openers (KCOs) bind to and act through SURs and that binding to SUR1, SUR2A and SUR2B requires ATP. Non-hydrolysable ATP-analogues do not support binding, and Mg2+ or Mn2+ are required. Point mutations in the Walker A motifs or linker regions of both nucleotide-binding folds (NBFs) abolish or weaken [3H]P1075 binding to SUR2B, rendering reconstituted SUR2B/KIR6.2 channels insensitive towards KCOs. The C-terminus of SUR affects KCO affinity with SUR2B approximately SUR1 > SUR2A. KCOs belonging to different structural classes inhibited specific [3H]P1075 binding to SUR2B in a monophasic manner, with the exception of minoxidil sulfate, which induced a biphasic displacement. The affinities of KCO binding to SUR2B were 3.5-8-fold higher than their potencies for activation of SUR2B/KIR6.2 channels. The results establish that SURs are the KCO receptors of KATP channels and suggest that KCO binding requires a conformational change induced by ATP hydrolysis in both NBFs.
Institut für Pharmakologie und Toxikologie, Universität Braunschweig, Mendelssohnstrasse 1, 38106 Braunschweig, Germany. M.Schwanstecher@tu-bs.de
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Schwanstecher
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Sieverding
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Dörschner
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Gross
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Aguilar-Bryan
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Bryan
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D006224:Cricetinae; D003981:Diazoxide / Q000378:metabolism; D005905:Glyburide / Q000378:metabolism; D006146:Guanidines / Q000378:metabolism; D006801:Humans; D009154:Mutation; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D020110:Pinacidil / Q000378:metabolism; D015221:Potassium Channels / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000378:metabolism; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; C577510:ABCC9 protein, human; D018528:ATP-Binding Cassette Transporters; D006146:Guanidines; D010446:Peptide Fragments; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D011725:Pyridines; D011955:Receptors, Drug; D011994:Recombinant Proteins; D064233:Sulfonylurea Receptors; C073896:N-cyano-N'-(1,1-dimethylpropyl)-N''-(3-pyridinyl)guanidine; D020110:Pinacidil; D000255:Adenosine Triphosphate; D003981:Diazoxide; D005905:Glyburide