title: The ATP-sensitive K(+) channel ABCC8 S1369A type 2 diabetes risk variant increases MgATPase activity.
abstract: Pancreatic β-cell ATP-sensitive K(+) (K(ATP)) channels are composed of Kir6.2 and SUR1 subunits encoded by the KCNJ11 and ABCC8 genes, respectively. Although rare monogenic activating mutations in these genes cause overt neonatal diabetes, the common variants E23K (KCNJ11) and S1369A (ABCC8) form a tightly heritable haplotype that is associated with an increased susceptibility to type 2 diabetes (T2D) risk. However, the molecular mechanism(s) underlying this risk remain to be elucidated. A homology model of the SUR1 nucleotide-binding domains (NBDs) indicates that residue 1369 is in close proximity to the major MgATPase site. Therefore, we investigated the intrinsic MgATPase activity of K(ATP) channels containing these variants. Electrophysiological and biochemical techniques were used to study the MgATPase activity of recombinant human K(ATP) channels or glutathione S-transferase and NBD2 fusion proteins containing the E23/S1369 (nonrisk) or K23/A1369 (risk) variant haplotypes. K(ATP) channels containing the K23/A1369 haplotype displayed a significantly increased stimulation by guanosine triphosphate compared with the E23/S1369 haplotype (3.2- vs. 1.8-fold). This effect was dependent on the presence of the A1369 variant and was lost in the absence of Mg(2+) ions or in the presence of the MgATPase inhibitor beryllium fluoride. Direct biochemical assays also confirmed an increase in MgATPase activity in NBD2 fusion proteins containing the A1369 variant. Our findings demonstrate that the A1369 variant increases K(ATP) channel MgATPase activity, providing a plausible molecular mechanism by which the K23/A1369 haplotype increases susceptibility to T2D in humans homozygous for these variants.
authors.affiliation: Alberta Diabetes Institute, Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Fatehi
authors.forename: Mobeen
authors.initials: M
authors.lastname: Raja
authors.forename: Christian
authors.initials: C
authors.lastname: Carter
authors.forename: Daniel
authors.initials: D
authors.lastname: Soliman
authors.forename: Andrew
authors.initials: A
authors.lastname: Holt
authors.forename: Peter E
authors.initials: PE
authors.lastname: Light
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution / Q000502:physiology; D002478:Cells, Cultured; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D004789:Enzyme Activation; D020022:Genetic Predisposition to Disease; D006801:Humans; D054086:KATP Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D008958:Models, Molecular; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics; D011955:Receptors, Drug / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D012307:Risk Factors; D012694:Serine / Q000235:genetics; D064233:Sulfonylurea Receptors; D014162:Transfection
chemical_list: C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D012694:Serine; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000409:Alanine