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Ding D, Wu JX, Duan X, Ma S, Lai L, Chen L. Structural identification of vasodilator binding sites on the SUR2 subunit. Nat Commun 2022; 13:2675. [PMID: 35562524 PMCID: PMC9106677 DOI: 10.1038/s41467-022-30428-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 04/28/2022] [Indexed: 11/09/2022] Open
Abstract
ATP-sensitive potassium channels (KATP), composed of Kir6 and SUR subunits, convert the metabolic status of the cell into electrical signals. Pharmacological activation of SUR2- containing KATP channels by class of small molecule drugs known as KATP openers leads to hyperpolarization of excitable cells and to vasodilation. Thus, KATP openers could be used to treat cardiovascular diseases. However, where these vasodilators bind to KATP and how they activate the channel remains elusive. Here, we present cryo-EM structures of SUR2A and SUR2B subunits in complex with Mg-nucleotides and P1075 or levcromakalim, two chemically distinct KATP openers that are specific to SUR2. Both P1075 and levcromakalim bind to a common site in the transmembrane domain (TMD) of the SUR2 subunit, which is between TMD1 and TMD2 and is embraced by TM10, TM11, TM12, TM14, and TM17. These KATP openers synergize with Mg-nucleotides to stabilize SUR2 in the NBD-dimerized occluded state to activate the channel.
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Affiliation(s)
- Dian Ding
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, 100871, Beijing, China.,Academy for Advanced Interdisciplinary Studies, Peking University, 100871, Beijing, China.,National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Jing-Xiang Wu
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China.,National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Xinli Duan
- Beijing Jingtai Technology Co., Ltd., Beijing, China
| | - Songling Ma
- Beijing Jingtai Technology Co., Ltd., Beijing, China
| | - Lipeng Lai
- Beijing Jingtai Technology Co., Ltd., Beijing, China
| | - Lei Chen
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China. .,Peking-Tsinghua Center for Life Sciences, Peking University, 100871, Beijing, China. .,Academy for Advanced Interdisciplinary Studies, Peking University, 100871, Beijing, China. .,National Biomedical Imaging Center, Peking University, 100871, Beijing, China.
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2
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Puljung MC. Cryo-electron microscopy structures and progress toward a dynamic understanding of K ATP channels. J Gen Physiol 2018; 150:653-669. [PMID: 29685928 PMCID: PMC5940251 DOI: 10.1085/jgp.201711978] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/26/2018] [Indexed: 12/11/2022] Open
Abstract
Puljung reviews recent cryo-EM KATP channel structures and proposes a mechanism by which ligand binding results in channel opening. Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.
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Affiliation(s)
- Michael C Puljung
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, England, UK
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3
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Pashynska V, Stepanian S, Gömöry Á, Vékey K, Adamowicz L. New cardioprotective agent flokalin and its supramolecular complexes with target amino acids: An integrated mass-spectrometry and quantum-chemical study. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.06.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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4
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Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
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Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
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5
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Ortiz D, Voyvodic P, Gossack L, Quast U, Bryan J. Two neonatal diabetes mutations on transmembrane helix 15 of SUR1 increase affinity for ATP and ADP at nucleotide binding domain 2. J Biol Chem 2012; 287:17985-95. [PMID: 22451668 DOI: 10.1074/jbc.m112.349019] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
K(ATP) channels, (SUR1/Kir6.2)(4) (sulfonylurea receptor type 1/potassium inward rectifier type 6.2) respond to the metabolic state of pancreatic β-cells, modulating membrane potential and insulin exocytosis. Mutations in both subunits cause neonatal diabetes by overactivating the pore. Hyperactive channels fail to close appropriately with increased glucose metabolism; thus, β-cell hyperpolarization limits insulin release. K(ATP) channels are inhibited by ATP binding to the Kir6.2 pore and stimulated, via an uncertain mechanism, by magnesium nucleotides at SUR1. Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. GBC binds with high affinity to aporeceptors, presumably in the inward facing ATP-binding cassette configuration; MgATP reduces binding affinity via a shift to the outward facing conformation. To determine nucleotide affinities under equilibrium, non-hydrolytic conditions, Mg(2+) was eliminated. A four-state equilibrium model describes the allosteric linkage. The K(D) for ATP(4-) is ~1 versus 12 mM, Q1178R versus wild type, respectively. The linkage constant is ~10, implying that outward facing conformations bind GBC with a lower affinity, 9-10 nM for Q1178R. Thus, nucleotides cannot completely inhibit GBC binding. Binding of channel openers is reported to require ATP hydrolysis, but diazoxide, a SUR1-selective agonist, concentration-dependently augments ATP(4-) action. An eight-state model describes linkage between diazoxide and ATP(4-) binding; diazoxide markedly increases the affinity of Q1178R for ATP(4-) and ATP(4-) augments diazoxide binding. NBD2, but not NBD1, has a higher affinity for ATP (and ADP) in mutant versus wild type (with or without Mg(2+)). Thus, the mutants spend more time in nucleotide-bound conformations, with reduced affinity for GBC, that activate the pore.
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Affiliation(s)
- David Ortiz
- Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
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6
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Flagg TP, Enkvetchakul D, Koster JC, Nichols CG. Muscle KATP channels: recent insights to energy sensing and myoprotection. Physiol Rev 2010; 90:799-829. [PMID: 20664073 DOI: 10.1152/physrev.00027.2009] [Citation(s) in RCA: 202] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of K(ATP) channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle K(ATP) channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle K(ATP) activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.
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Affiliation(s)
- Thomas P Flagg
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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Ackermann S, Hiller S, Osswald H, Lösle M, Grenz A, Hambrock A. 17beta-Estradiol modulates apoptosis in pancreatic beta-cells by specific involvement of the sulfonylurea receptor (SUR) isoform SUR1. J Biol Chem 2008; 284:4905-13. [PMID: 19095654 DOI: 10.1074/jbc.m807638200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Apoptosis of pancreatic beta-cells is an important factor in the pathophysiology of diabetes. Previously, we have shown that the "phytoestrogen" resveratrol can induce beta-cell apoptosis dependent on the expression of sulfonylurea receptor (SUR) 1, the regulatory subunit of pancreatic ATP-sensitive K(+) channels. Here, we investigate whether 17beta-estradiol also influences beta-cell apoptosis in a SUR1-dependent manner. Therefore, islets from wild type or SUR1 knock-out mice, clonal beta-cells, or HEK293 cells expressing different SUR forms were treated with 17beta-estradiol or estrone. Different apoptotic parameters were determined and estrogen binding to SUR was analyzed. In murine islets, 17beta-estradiol treatment resulted in significant apoptotic changes, which in their nature (either apoptotic or anti-apoptotic) were dependent on the age of the animal. These effects were not observed in SUR1 knock-out mice. Furthermore, 17beta-estradiol, which specifically binds to SUR, induced enhanced apoptosis in SUR1-expressing HEK293 cells and clonal beta-cells, whereas apoptosis in recombinant cells expressing SUR2A or SUR2B (cardiac or vascular SUR-isoforms) or sham-transfected control cells was significantly lower. The apoptotic potency of 17beta-estradiol was much higher than that of resveratrol or estrone. SUR1-specific 17beta-estradiol-induced apoptosis was either abolished by the mutation M1289T in transmembrane helix 17 of SUR1 or clearly enhanced by two mutations in nucleotide binding fold 2 (R1379C, R1379L). In conclusion, 17beta-estradiol treatment modulates beta-cell apoptosis under specific involvement of SUR1 in an age-dependent manner. 17beta-Estradiol-induced apoptosis can be influenced by certain SUR1 mutations. These findings may contribute to the understanding of pathophysiological changes in beta-cell mass and could, for instance, provide interesting aspects concerning the etiology of gestational diabetes.
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Affiliation(s)
- Stefanie Ackermann
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany
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8
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Hambrock A, de Oliveira Franz CB, Hiller S, Grenz A, Ackermann S, Schulze DU, Drews G, Osswald H. Resveratrol binds to the sulfonylurea receptor (SUR) and induces apoptosis in a SUR subtype-specific manner. J Biol Chem 2006; 282:3347-56. [PMID: 17138562 DOI: 10.1074/jbc.m608216200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptors (SURs) constitute the regulatory subunits of ATP-sensitive K+ channels (K(ATP) channels). SUR binds nucleotides and synthetic K(ATP) channel modulators, e.g. the antidiabetic sulfonylurea glibenclamide, which acts as a channel blocker. However, knowledge about naturally occurring ligands of SUR is very limited. In this study, we show that the plant phenolic compound trans-resveratrol can bind to SUR and displace binding of glibenclamide. Electrophysiological measurements revealed that resveratrol is a blocker of pancreatic SUR1/K(IR)6.2 K(ATP) channels. We further demonstrate that, like glibenclamide, resveratrol induces enhanced apoptosis. This was shown by analyzing different apoptotic parameters (cell detachment, nuclear condensation and fragmentation, and activities of different caspase enzymes). The observed apoptotic effect was specific to cells expressing the SUR1 isoform and was not mediated by the electrical activity of K(ATP) channels, as it was observed in human embryonic kidney 293 cells expressing SUR1 alone. Enhanced susceptibility to resveratrol was not observed in pancreatic beta-cells from SUR1 knock-out mice or in cells expressing the isoform SUR2A or SUR2B or the mutant SUR1(M1289T). Resveratrol was much more potent than glibenclamide in inducing SUR1-specific apoptosis. Treatment with etoposide, a classical inducer of apoptosis, did not result in SUR isoform-specific apoptosis. In conclusion, resveratrol is a natural SUR ligand that can induce apoptosis in a SUR isoform-specific manner. Considering the tissue-specific expression patterns of SUR isoforms and the possible effects of SUR mutations on susceptibility to apoptosis, these observations could be important for diabetes and/or cancer research.
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MESH Headings
- ATP-Binding Cassette Transporters/drug effects
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/physiology
- Animals
- Apoptosis/drug effects
- Apoptosis/physiology
- Caspases/drug effects
- Caspases/metabolism
- Cell Adhesion/drug effects
- Cell Line
- Etoposide/pharmacology
- Female
- Humans
- Hypoglycemic Agents/pharmacology
- Islets of Langerhans/cytology
- Islets of Langerhans/drug effects
- Islets of Langerhans/metabolism
- Islets of Langerhans/physiology
- Kidney
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Potassium Channels/deficiency
- Potassium Channels/drug effects
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/deficiency
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Receptors, Drug/deficiency
- Receptors, Drug/drug effects
- Receptors, Drug/genetics
- Receptors, Drug/physiology
- Recombinant Proteins/drug effects
- Recombinant Proteins/metabolism
- Resveratrol
- Stilbenes/pharmacokinetics
- Stilbenes/pharmacology
- Sulfonylurea Receptors
- Transfection
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany.
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Stene LC, Thorsby PM, Berg JP, Rønningen KS, Undlien DE, Joner G. The relation between size at birth and risk of type 1 diabetes is not influenced by adjustment for the insulin gene (-23HphI) polymorphism or HLA-DQ genotype. Diabetologia 2006; 49:2068-73. [PMID: 16691379 DOI: 10.1007/s00125-006-0292-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2006] [Accepted: 03/31/2006] [Indexed: 10/24/2022]
Abstract
AIMS/HYPOTHESIS Associations have been described between higher birthweight and increased risk of type 1 diabetes, and of insulin (INS) and human leucocyte antigen (HLA) genotypes that protect against diabetes with larger size at birth. We studied simultaneously the effects of size at birth, INS and HLA genotypes on the risk of type 1 diabetes to test whether the relation between size at birth and risk of type 1 diabetes would be strengthened after adjustment for INS and HLA genotypes. SUBJECTS AND METHODS We designed a population-based case-control study in Norway with 471 cases of childhood-onset type 1 diabetes and 1,369 control subjects who were genotyped for the INS -23HphI polymorphism (surrogate for INS variable number of tandem repeats) and HLA-DQ alleles associated with type 1 diabetes. Data on birthweight and other perinatal factors were obtained from the Medical Birth Registry of Norway by record linkage. RESULTS The data fitted a multiplicative model for the protective INS class III allele both within the INS locus and for the model with INS- and HLA-DQ-conferred risk of type 1 diabetes. We found no overall significant association between weight or head circumference at birth and the risk of type 1 diabetes, and adjustment for INS and HLA genotype did not influence this result. There was also no evidence for association of INS or HLA with size at birth among control subjects. CONCLUSIONS/INTERPRETATION In contrast to suggestions from previous indirect studies, direct adjustment for INS and HLA genotypes did not lead to a stronger relation between birthweight and the risk of type 1 diabetes.
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Affiliation(s)
- L C Stene
- Division of Epidemiology, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway.
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Stephan D, Salamon E, Weber H, Russ U, Lemoine H, Quast U. KATP channel openers of the benzopyran type reach their binding site via the cytosol. Br J Pharmacol 2006; 149:199-205. [PMID: 16921394 PMCID: PMC2013803 DOI: 10.1038/sj.bjp.0706858] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE ATP-sensitive K+ (KATP) channels are composed of pore-forming subunits (Kir6.x) and of sulphonylurea receptors (SUR). Both sulphonylureas and K(ATP) channel openers act by binding to SUR. Sulphonylureas reach their binding site from the cytosol but it remains unknown whether this holds for openers too. EXPERIMENTAL APPROACH A poorly membrane-permeant sulphonic acid derivative of the benzopyran-type opener, bimakalim, was synthesized, descyano-bimakalim-6-sulphonic acid (BMSA). Binding of BMSA and bimakalim was compared in membranes and intact cells expressing the Kir6.2/SUR2B channel and channel opening was compared in inside-out patches and whole cells. KEY RESULTS In membranes, bimakalim and BMSA bound to Kir6.2/SUR2B with Ki values of 61 nM and 4.3 microM, showing that the negative charge decreased affinity 69-fold. In intact cells, however, binding of BMSA was much weaker than in membranes (75-fold) whereas that of bimakalim was unchanged. The Ki value of BMSA decreased with increasing incubation time. In inside-out patches, bimakalim (1 microM) and BMSA (100 microM) opened the Kir6.2/SUR2B channel closed by MgATP to a similar degree whereas in whole-cell experiments, only bimakalim was effective. CONCLUSIONS AND IMPLICATIONS Despite its negative charge, BMSA is an effective channel opener. The fact that BMSA binds and acts more effectively when applied to the inner side of the cell membrane shows that benzopyran openers reach their binding site at SUR from the cytosol. This suggests that the binding pocket of SUR is only open on the cytoplasmic side.
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Affiliation(s)
- D Stephan
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany
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11
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Frelet A, Klein M. Insight in eukaryotic ABC transporter function by mutation analysis. FEBS Lett 2006; 580:1064-84. [PMID: 16442101 DOI: 10.1016/j.febslet.2006.01.024] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 01/10/2006] [Accepted: 01/10/2006] [Indexed: 11/21/2022]
Abstract
With regard to structure-function relations of ATP-binding cassette (ABC) transporters several intriguing questions are in the spotlight of active research: Why do functional ABC transporters possess two ATP binding and hydrolysis domains together with two ABC signatures and to what extent are the individual nucleotide-binding domains independent or interacting? Where is the substrate-binding site and how is ATP hydrolysis functionally coupled to the transport process itself? Although much progress has been made in the elucidation of the three-dimensional structures of ABC transporters in the last years by several crystallographic studies including novel models for the nucleotide hydrolysis and translocation catalysis, site-directed mutagenesis as well as the identification of natural mutations is still a major tool to evaluate effects of individual amino acids on the overall function of ABC transporters. Apart from alterations in characteristic sequence such as Walker A, Walker B and the ABC signature other parts of ABC proteins were subject to detailed mutagenesis studies including the substrate-binding site or the regulatory domain of CFTR. In this review, we will give a detailed overview of the mutation analysis reported for selected ABC transporters of the ABCB and ABCC subfamilies, namely HsCFTR/ABCC7, HsSUR/ABCC8,9, HsMRP1/ABCC1, HsMRP2/ABCC2, ScYCF1 and P-glycoprotein (Pgp)/MDR1/ABCB1 and their effects on the function of each protein.
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Affiliation(s)
- Annie Frelet
- Zurich Basel Plant Science Center, University of Zurich, Plant Biology, Zollikerstrasse 107, CH-8008 Zurich, Switzerland
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12
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Hambrock A, de Oliveira Franz CB, Hiller S, Osswald H. Glibenclamide-induced apoptosis is specifically enhanced by expression of the sulfonylurea receptor isoform SUR1 but not by expression of SUR2B or the mutant SUR1(M1289T). J Pharmacol Exp Ther 2005; 316:1031-7. [PMID: 16306272 DOI: 10.1124/jpet.105.097501] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptor 1 (SUR1) is the regulatory subunit of the pancreatic ATP-sensitive K+ channel (K(ATP) channel), which is essential for triggering insulin secretion via membrane depolarization. Sulfonylureas, such as glibenclamide and tolbutamide, act as K(ATP) channel blockers and are widely used in diabetes treatment. These antidiabetic substances are known to induce apoptosis in pancreatic beta-cells or beta-cell lines under certain conditions. However, the precise molecular mechanisms of this sulfonylurea-induced apoptosis are still unidentified. To investigate the role of SUR in apoptosis induction, we tested the effect of glibenclamide on recombinant human embryonic kidney 293 cells expressing either SUR1, the smooth muscular isoform SUR2B, or the mutant SUR1(M1289T) at which a single amino acid in transmembrane helix 17 (TM17) was exchanged by the corresponding amino acid of SUR2. By analyzing cell detachment, nuclear condensation, DNA fragmentation, and caspase-3-like activity, we observed a SUR1-specific enhancement of glibenclamide-induced apoptosis that was not seen in SUR2B, SUR1(M1289T), or control cells. Coexpression with the pore-forming Kir6.2 subunit did not significantly alter the apoptotic effect of glibenclamide on SUR1 cells. In conclusion, expression of SUR1, but not of SUR2B or SUR1(M1289T), renders cells more susceptible to glibenclamide-induced apoptosis. Therefore, SUR1 as a pancreatic protein could be involved in specific variation of beta-cell mass and might also contribute to the regulation of insulin secretion at this level. According to our results, TM17 is essentially involved in SUR1-mediated apoptosis. This effect does not require the presence of functional Kir6.2-containing K(ATP) channels, which points to additional, so far unknown functions of SUR.
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany.
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