1
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Patton BL, Zhu P, ElSheikh A, Driggers CM, Shyng SL. Dynamic duo: Kir6 and SUR in K ATP channel structure and function. Channels (Austin) 2024; 18:2327708. [PMID: 38489043 PMCID: PMC10950283 DOI: 10.1080/19336950.2024.2327708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 01/14/2024] [Indexed: 03/17/2024] Open
Abstract
KATP channels are ligand-gated potassium channels that couple cellular energetics with membrane potential to regulate cell activity. Each channel is an eight subunit complex comprising four central pore-forming Kir6 inward rectifier potassium channel subunits surrounded by four regulatory subunits known as the sulfonylurea receptor, SUR, which confer homeostatic metabolic control of KATP gating. SUR is an ATP binding cassette (ABC) protein family homolog that lacks membrane transport activity but is essential for KATP expression and function. For more than four decades, understanding the structure-function relationship of Kir6 and SUR has remained a central objective of clinical significance. Here, we review progress in correlating the wealth of functional data in the literature with recent KATP cryoEM structures.
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Affiliation(s)
- Bruce L. Patton
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Phillip Zhu
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Assmaa ElSheikh
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
- Department of Medical Biochemistry, Tanta University, Tanta, Egypt
| | - Camden M. Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
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2
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Ding D, Hou T, Wei M, Wu JX, Chen L. The inhibition mechanism of the SUR2A-containing K ATP channel by a regulatory helix. Nat Commun 2023; 14:3608. [PMID: 37330603 PMCID: PMC10276813 DOI: 10.1038/s41467-023-39379-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 06/10/2023] [Indexed: 06/19/2023] Open
Abstract
KATP channels are metabolic sensors for intracellular ATP/ADP ratios, play essential roles in many physiological processes, and are implicated in a spectrum of pathological conditions. SUR2A-containing KATP channels differ from other subtypes in their sensitivity to Mg-ADP activation. However, the underlying structural mechanism remains poorly understood. Here we present a series of cryo-EM structures of SUR2A in the presence of different combinations of Mg-nucleotides and the allosteric inhibitor repaglinide. These structures uncover regulatory helix (R helix) on the NBD1-TMD2 linker, which wedges between NBD1 and NBD2. R helix stabilizes SUR2A in the NBD-separated conformation to inhibit channel activation. The competitive binding of Mg-ADP with Mg-ATP to NBD2 mobilizes the R helix to relieve such inhibition, allowing channel activation. The structures of SUR2B in similar conditions suggest that the C-terminal 42 residues of SUR2B enhance the structural dynamics of NBD2 and facilitate the dissociation of the R helix and the binding of Mg-ADP to NBD2, promoting NBD dimerization and subsequent channel activation.
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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
| | - Tianyi Hou
- 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
| | - Miao Wei
- 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
| | - 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
| | - 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.
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China.
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3
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Luppi P, Drain P. Uncoupling a unique couple by chopping off one of its tails: insights into the K ATP channels of the heart and pancreas. J Physiol 2018; 596:6135-6136. [PMID: 30387493 DOI: 10.1113/jp277099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Patrizia Luppi
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Peter Drain
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
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4
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Vedovato N, Rorsman O, Hennis K, Ashcroft FM, Proks P. Role of the C-terminus of SUR in the differential regulation of β-cell and cardiac K ATP channels by MgADP and metabolism. J Physiol 2018; 596:6205-6217. [PMID: 30179258 PMCID: PMC6292810 DOI: 10.1113/jp276708] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Accepted: 08/29/2018] [Indexed: 12/14/2022] Open
Abstract
Key points β‐Cell KATP channels are partially open in the absence of metabolic substrates, whereas cardiac KATP channels are closed. Using cloned channels heterologously expressed in Xenopus oocytes we measured the effect of MgADP on the MgATP concentration–inhibition curve immediately after patch excision. MgADP caused a far more striking reduction in ATP inhibition of Kir6.2/SUR1 channels than Kir6.2/SUR2A channels; this effect declined rapidly after patch excision. Exchanging the final 42 amino acids of SUR was sufficient to switch the Mg‐nucleotide regulation of Kir6.2/SUR1 and Kir6.2/SUR2A channels, and partially switch their sensitivity to metabolic inhibition. Deletion of the C‐terminal 42 residues of SUR abolished MgADP activation of both Kir6.2/SUR1 and Kir6.2/SUR2A channels. We conclude that the different metabolic sensitivity of Kir6.2/SUR1 and Kir6.2/SUR2A channels is at least partially due to their different regulation by Mg‐nucleotides, which is determined by the final 42 amino acids.
Abstract ATP‐sensitive potassium (KATP) channels couple the metabolic state of a cell to its electrical activity and play important physiological roles in many tissues. In contrast to β‐cell (Kir6.2/SUR1) channels, which open when extracellular glucose levels fall, cardiac (Kir6.2/SUR2A) channels remain closed. This is due to differences in the SUR subunit rather than cell metabolism. As ATP inhibition and MgADP activation are similar for both types of channels, we investigated channel inhibition by MgATP in the presence of 100 μm MgADP immediately after patch excision [when the channel open probability (PO) is near maximal]. The results were strikingly different: 100 μm MgADP substantially reduced MgATP inhibition of Kir6.2/SUR1, but had no effect on MgATP inhibition of Kir6.2/SUR2A. Exchanging the final 42 residues of SUR2A with that of SUR1 switched the channel phenotype (and vice versa), and deleting this region abolished Mg‐nucleotide activation. This suggests the C‐terminal 42 residues are important for the ability of MgADP to influence ATP inhibition at Kir6.2. This region was also necessary, but not sufficient, for activation of the KATP channel in intact cells by metabolic inhibition (azide). We conclude that the ability of MgADP to impair ATP inhibition at Kir6.2 accounts, in part, for the differential metabolic sensitivities of β‐cell and cardiac KATP channels. β‐Cell KATP channels are partially open in the absence of metabolic substrates, whereas cardiac KATP channels are closed. Using cloned channels heterologously expressed in Xenopus oocytes we measured the effect of MgADP on the MgATP concentration–inhibition curve immediately after patch excision. MgADP caused a far more striking reduction in ATP inhibition of Kir6.2/SUR1 channels than Kir6.2/SUR2A channels; this effect declined rapidly after patch excision. Exchanging the final 42 amino acids of SUR was sufficient to switch the Mg‐nucleotide regulation of Kir6.2/SUR1 and Kir6.2/SUR2A channels, and partially switch their sensitivity to metabolic inhibition. Deletion of the C‐terminal 42 residues of SUR abolished MgADP activation of both Kir6.2/SUR1 and Kir6.2/SUR2A channels. We conclude that the different metabolic sensitivity of Kir6.2/SUR1 and Kir6.2/SUR2A channels is at least partially due to their different regulation by Mg‐nucleotides, which is determined by the final 42 amino acids.
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Affiliation(s)
- Natascia Vedovato
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Olof Rorsman
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Konstantin Hennis
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Peter Proks
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
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5
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López-Alonso JP, de Araujo ED, Kanelis V. NMR and fluorescence studies of drug binding to the first nucleotide binding domain of SUR2A. Biochemistry 2012; 51:9211-22. [PMID: 23078514 DOI: 10.1021/bi301019e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
ATP sensitive potassium (K(ATP)) channels are composed of four copies of a pore-forming inward rectifying potassium channel (Kir6.1 or Kir6.2) and four copies of a sulfonylurea receptor (SUR1, SUR2A, or SUR2B) that surround the pore. SUR proteins are members of the ATP-binding cassette (ABC) superfamily of proteins. Binding of MgATP at the SUR nucleotide binding domains (NBDs) results in NBD dimerization, and hydrolysis of MgATP at the NBDs leads to channel opening. The SUR proteins also mediate interactions with K(ATP) channel openers (KCOs) that activate the channel, with KCO binding and/or activation involving residues in the transmembrane helices and cytoplasmic loops of the SUR proteins. Because the cytoplasmic loops make extensive interactions with the NBDs, we hypothesized that the NBDs may also be involved in KCO binding. Here, we report nuclear magnetic resonance (NMR) spectroscopy studies that demonstrate a specific interaction of the KCO pinacidil with the first nucleotide binding domain (NBD1) from SUR2A, the regulatory SUR protein in cardiac K(ATP) channels. Intrinsic tryptophan fluorescence titrations also demonstrate binding of pinacidil to SUR2A NBD1, and fluorescent nucleotide binding studies show that pinacidil binding increases the affinity of SUR2A NBD1 for ATP. In contrast, the KCO diazoxide does not interact with SUR2A NBD1 under the same conditions. NMR relaxation experiments and size exclusion chromatography indicate that SUR2A NBD1 is monomeric under the conditions used in drug binding studies. These studies identify additional binding sites for commonly used KCOs and provide a foundation for testing binding of drugs to the SUR NBDs.
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Affiliation(s)
- Jorge P López-Alonso
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6
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6
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Tang L, Bergevoet SM, Gilissen C, de Witte T, Jansen JH, van der Reijden BA, Raymakers RAP. Hematopoietic stem cells exhibit a specific ABC transporter gene expression profile clearly distinct from other stem cells. BMC Pharmacol 2010; 10:12. [PMID: 20836839 PMCID: PMC2945345 DOI: 10.1186/1471-2210-10-12] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Accepted: 09/13/2010] [Indexed: 12/16/2022] Open
Abstract
Background ATP-binding cassette (ABC) transporters protect cells against unrelated (toxic) substances by pumping them across cell membranes. Earlier we showed that many ABC transporters are highly expressed in hematopoietic stem cells (HSCs) compared to more committed progenitor cells. The ABC transporter expression signature may guarantee lifelong protection of HSCs but may also preserve stem cell integrity by extrusion of agents that trigger their differentiation. Here we have studied whether non-hematopoietic stem cells (non-HSCs) exhibit a similar ABC transporter expression signature as HSCs. Results ABC transporter expression profiles were determined in non-hematopoietic stem cells (non-HSCs) from embryonic, neonatal and adult origin as well as in various mature blood cell types. Over 11,000 individual ABC transporter expression values were generated by Taqman Low Density Arrays (TLDA) to obtain a sensitivity comparable with quantitative real-time polymerase chain reactions. We found that the vast majority of transporters are significantly higher expressed in HSCs compared to non-HSCs. Furthermore, regardless their origin, non-HSCs exhibited strikingly similar ABC transporter expression profiles that were distinct from those in HSCs. Yet, sets of transporters characteristic for different stem cell types could be identified, suggesting restricted functions in stem cell physiology. Remarkably, in HSCs we could not pinpoint any single transporter expressed at an evidently elevated level when compared to all the mature blood cell types studied. Conclusions These findings challenge the concept that individual ABC transporters are implicated in maintaining stem cell integrity. Instead, a distinct ABC transporter expression signature may be essential for stem cell function. The high expression of specific transporters in non-HSCs and mature blood cells suggests a specialized, cell type dependent function and warrants further functional experiments to determine their exact roles in cellular (patho)physiology.
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Affiliation(s)
- Leilei Tang
- Department of Laboratory Medicine, Laboratory of Hematology, Radboud University Nijmegen Medical Centre/Nijmegen Centre for Molecular Life Sciences, Geert Grooteplein 8, 6525GA Nijmegen, The Netherlands
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7
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Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y. Inwardly rectifying potassium channels: their structure, function, and physiological roles. Physiol Rev 2010; 90:291-366. [PMID: 20086079 DOI: 10.1152/physrev.00021.2009] [Citation(s) in RCA: 1074] [Impact Index Per Article: 76.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.
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Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Graduate School of Medicine and The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka 565-0871, Japan
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8
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Jilkina O, Kuzio B, Kupriyanov VV. Potassium fluxes, energy metabolism, and oxygenation in intact diabetic rat hearts under normal and stress conditions. Can J Physiol Pharmacol 2008; 86:710-25. [DOI: 10.1139/y08-076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We evaluated the function of Na+/K+ATPase and sarcolemmal KATPchannels in diabetic rat hearts. Six weeks after streptozotocin (STZ) injection, unidirectional K+fluxes were assayed by using87rubidium (87Rb+) MRS. The hearts were loaded with Rb+by perfusion with Krebs–Henseleit buffer, in which 50% of K+was substituted with Rb+. The rate constant of Rb+uptake via Na+/K+ATPase was reduced. KATP-mediated Rb+efflux was activated metabolically with 2,4-dinitrophenol (DNP, 50 µmol·L–1) or pharmacologically with a KATPchannel opener, P-1075 (5 µmol·L–1). Cardiac energetics were monitored by using31P MRS and optical spectroscopy. DNP produced a smaller ATP decrease, yet similar Rb+efflux activation in STZ hearts. In K+-arrested hearts, P-1075 had no effect on high-energy phosphates and stimulated Rb+efflux by interaction with SUR2A subunit of KATPchannel; this stimulation was greater in STZ hearts. In normokalemic hearts, P-1075 caused cardiac arrest and ATP decline, and the stimulation of Rb+efflux was lower in normokalemic STZ hearts arrested by P-1075. Thus, the Rb+efflux stimulation in STZ hearts was altered depending on the mode of KATPchannel activation: pharmacologic stimulation (P-1075) was enhanced, whereas metabolic stimulation (DNP) was reduced. Both the basal concentration of phosphocreatine ([PCr]) and [PCr]/[ATP] were reduced; nevertheless, the STZ hearts were more or equally resistant to metabolic stress.
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Affiliation(s)
- Olga Jilkina
- Institute for Biodiagnostics, National Research Council of Canada, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada
- Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Manitoba, Canada
- Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Bozena Kuzio
- Institute for Biodiagnostics, National Research Council of Canada, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada
- Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Manitoba, Canada
- Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Valery V. Kupriyanov
- Institute for Biodiagnostics, National Research Council of Canada, 435 Ellice Avenue, Winnipeg, MB R3B 1Y6, Canada
- Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Manitoba, Canada
- Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Manitoba, Canada
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9
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Park S, Lim BBC, Perez-Terzic C, Mer G, Terzic A. Interaction of asymmetric ABCC9-encoded nucleotide binding domains determines KATP channel SUR2A catalytic activity. J Proteome Res 2008; 7:1721-8. [PMID: 18311911 DOI: 10.1021/pr7007847] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nucleotide binding domains (NBDs) secure ATP-binding cassette (ABC) transporter function. Distinct from traditional ABC transporters, ABCC9-encoded sulfonylurea receptors (SUR2A) form, with Kir6.2 potassium channels, ATP-sensitive K+ (K ATP) channel complexes. SUR2A contains ATPase activity harbored within NBD2 and, to a lesser degree, NBD1, with catalytically driven conformations exerting determinate linkage on the Kir6.2 channel pore. While homodomain interactions typify NBDs of conventional ABC transporters, heterodomain NBD interactions and their functional consequence have not been resolved for the atypical SUR2A protein. Here, nanoscale protein topography mapped assembly of monodisperse purified recombinant SUR2A NBD1/NBD2 domains, precharacterized by dynamic light scattering. Heterodomain interaction produced conformational rearrangements inferred by secondary structural change in circular dichroism, and validated by atomic force and transmission electron microscopy. Physical engagement of NBD1 with NBD2 translated into enhanced intrinsic ATPase activity. Molecular modeling delineated a complemental asymmetry of NBD1/NBD2 ATP-binding sites. Mutation in the predicted catalytic base residue, D834E of NBD1, altered NBD1 ATPase activity disrupting potentiation of catalytic behavior in the NBD1/NBD2 interactome. Thus, NBD1/NBD2 assembly, resolved by a panel of proteomic approaches, provides a molecular substrate that determines the optimal catalytic activity in SUR2A, establishing a paradigm for the structure-function relationship within the K ATP channel complex.
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Affiliation(s)
- Sungjo Park
- Marriott Heart Disease Research Program, Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA
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10
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Burke MA, Mutharasan RK, Ardehali H. The Sulfonylurea Receptor, an Atypical ATP-Binding Cassette Protein, and Its Regulation of the KATPChannel. Circ Res 2008; 102:164-76. [DOI: 10.1161/circresaha.107.165324] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Michael A. Burke
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
| | - R. Kannan Mutharasan
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
| | - Hossein Ardehali
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
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11
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de Wet H, Rees MG, Shimomura K, Aittoniemi J, Patch AM, Flanagan SE, Ellard S, Hattersley AT, Sansom MSP, Ashcroft FM. Increased ATPase activity produced by mutations at arginine-1380 in nucleotide-binding domain 2 of ABCC8 causes neonatal diabetes. Proc Natl Acad Sci U S A 2007; 104:18988-92. [PMID: 18025464 PMCID: PMC2141895 DOI: 10.1073/pnas.0707428104] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Indexed: 12/16/2022] Open
Abstract
Gain-of-function mutations in the genes encoding the ATP-sensitive potassium (K(ATP)) channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) are a common cause of neonatal diabetes mellitus. Here we investigate the molecular mechanism by which two heterozygous mutations in the second nucleotide-binding domain (NBD2) of SUR1 (R1380L and R1380C) separately cause neonatal diabetes. SUR1 is a channel regulator that modulates the gating of the pore formed by Kir6.2. K(ATP) channel activity is inhibited by ATP binding to Kir6.2 but is stimulated by MgADP binding, or by MgATP binding and hydrolysis, at the NBDs of SUR1. Functional analysis of purified NBD2 showed that each mutation enhances MgATP hydrolysis by purified isolated fusion proteins of maltose-binding protein and NBD2. Inhibition of ATP hydrolysis by MgADP was unaffected by mutation of R1380, but inhibition by beryllium fluoride (which traps the ATPase cycle in the prehydrolytic state) was reduced. MgADP-dependent activation of K(ATP) channel activity was unaffected. These data suggest that the R1380L and R1380C mutations enhance the off-rate of P(i), thereby enhancing the hydrolytic rate. Molecular modeling studies supported this idea. Because mutant channels were inhibited less strongly by MgATP, this would increase K(ATP) currents in pancreatic beta cells, thus reducing insulin secretion and producing diabetes.
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MESH Headings
- ATP-Binding Cassette Transporters/antagonists & inhibitors
- ATP-Binding Cassette Transporters/chemistry
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Adenosine Diphosphate/pharmacology
- Adenosine Triphosphate/metabolism
- Adenosine Triphosphate/pharmacology
- Amino Acid Substitution
- Arginine/chemistry
- Beryllium/pharmacology
- Binding Sites
- Diabetes Mellitus, Type 1/congenital
- Diabetes Mellitus, Type 1/genetics
- Fluorides/pharmacology
- Humans
- Hydrolysis
- Infant, Newborn
- Insulin/metabolism
- Insulin Secretion
- Ion Channel Gating/drug effects
- Kinetics
- Models, Molecular
- Mutation, Missense
- Point Mutation
- Potassium/metabolism
- Potassium Channels/chemistry
- Potassium Channels/genetics
- Potassium Channels/metabolism
- Potassium Channels, Inwardly Rectifying/antagonists & inhibitors
- Potassium Channels, Inwardly Rectifying/chemistry
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- Protein Structure, Tertiary/genetics
- Receptors, Drug/antagonists & inhibitors
- Receptors, Drug/chemistry
- Receptors, Drug/genetics
- Receptors, Drug/metabolism
- Structure-Activity Relationship
- Sulfonylurea Receptors
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Affiliation(s)
- Heidi de Wet
- *Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, United Kingdom
| | - Mathew G. Rees
- *Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, United Kingdom
| | - Kenju Shimomura
- *Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, United Kingdom
| | - Jussi Aittoniemi
- *Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, United Kingdom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom; and
| | - Ann-Marie Patch
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, United Kingdom
| | - Sarah E. Flanagan
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, United Kingdom
| | - Sian Ellard
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, United Kingdom
| | - Andrew T. Hattersley
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter EX2 5DW, United Kingdom
| | - Mark S. P. Sansom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom; and
| | - Frances M. Ashcroft
- *Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, United Kingdom
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12
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Zingman LV, Alekseev AE, Hodgson-Zingman DM, Terzic A. ATP-sensitive potassium channels: metabolic sensing and cardioprotection. J Appl Physiol (1985) 2007; 103:1888-93. [PMID: 17641217 DOI: 10.1152/japplphysiol.00747.2007] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The cardiovascular system operates under a wide scale of demands, ranging from conditions of rest to extreme stress. How the heart muscle matches rates of ATP production with utilization is an area of active investigation. ATP-sensitive potassium (K(ATP)) channels serve a critical role in the orchestration of myocardial energetic well-being. K(ATP) channel heteromultimers consist of inwardly-rectifying K(+) channel 6.2 and ATP-binding cassette sulfonylurea receptor 2A that translates local ATP/ADP levels, set by ATPases and phosphotransfer reactions, to the channel pore function. In cells in which the mobility of metabolites between intracellular microdomains is limited, coupling of phosphotransfer pathways with K(ATP) channels permits a high-fidelity transduction of nucleotide fluxes into changes in membrane excitability, matching energy demands with metabolic resources. This K(ATP) channel-dependent optimization of cardiac action potential duration preserves cellular energy balance at varying workloads. Mutations of K(ATP) channels result in disruption of the nucleotide signaling network and generate a stress-vulnerable phenotype with excessive susceptibility to injury, development of cardiomyopathy, and arrhythmia. Solving the mechanisms underlying the integration of K(ATP) channels into the cellular energy network will advance the understanding of endogenous cardioprotection and the development of strategies for the management of cardiovascular injury and disease progression.
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Affiliation(s)
- L V Zingman
- Univ. of Iowa, Carver College of Medicine, 285 Newton Rd., CBRB2296, Iowa City, IA 52242, USA.
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Olson TM, Alekseev AE, Moreau C, Liu XK, Zingman LV, Miki T, Seino S, Asirvatham SJ, Jahangir A, Terzic A. KATP channel mutation confers risk for vein of Marshall adrenergic atrial fibrillation. ACTA ACUST UNITED AC 2007; 4:110-6. [PMID: 17245405 PMCID: PMC2013306 DOI: 10.1038/ncpcardio0792] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2006] [Accepted: 10/12/2006] [Indexed: 01/23/2023]
Abstract
BACKGROUND A 53-year-old female presented with a 10-year history of paroxysmal atrial fibrillation (AF), precipitated by activity and refractory to medical therapy. In the absence of traditional risk factors for disease, a genetic defect in electrical homeostasis underlying stress-induced AF was explored. INVESTIGATIONS Echocardiography, cardiac perfusion stress imaging, invasive electrophysiology with isoproterenol provocation, genomic DNA sequencing of K(ATP) channel genes, exclusion of mutation in 2,000 individuals free of AF, reconstitution of channel defect with molecular phenotyping, and verification of pathogenic link in targeted knockout. DIAGNOSIS K(ATP) channelopathy caused by missense mutation (Thr1547Ile) of the ABCC9 gene conferring predisposition to adrenergic AF originating from the vein of Marshall. MANAGEMENT Disruption of arrhythmogenic gene-environment substrate at the vein of Marshall by radiofrequency ablation.
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Affiliation(s)
- Timothy M Olson
- Marriott Heart Disease Research Program, Division of Cardiovascular Diseases, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
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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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15
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Klein A, Lichtenberg J, Stephan D, Quast U. Lipids modulate ligand binding to sulphonylurea receptors. Br J Pharmacol 2006; 145:907-15. [PMID: 15895108 PMCID: PMC1576209 DOI: 10.1038/sj.bjp.0706252] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
ATP-sensitive K(+) channels (K(ATP) channels) are complexes of inwardly rectifying K(+) channels (Kir6.x) and sulphonylurea receptors (SURs). Kir6.2-containing channels are closed by ATP binding to Kir6.2, and opened by MgADP binding to SUR. Channel activity is modulated by synthetic compounds such as the channel-blocking sulphonylureas and the K(ATP) channel openers, which both act by binding to SUR. By interacting with Kir6.2, phosphatidylinositol-4,5-bisphosphate (PIP(2)) and oleoyl-coenzyme A (OCoA) decrease the ATP-sensitivity of the channel and abolish the effect of the synthetic channel modulators. Here, we have investigated whether lipids and related compounds interfered with the binding of the sulphonylurea, glibenclamide (GBC) and of the opener, N-cyano-N'-(1,1-dimethylpropyl)-N''-3-pyridylguanidine (P1075), to the SUR subtypes. Lipids (100-300 microM) inhibited binding of [(3)H]GBC and [(3)H]P1075 to SUR subtypes in the rank order OCoA>dioleylglycerol-succinyl-nitriloacetic acid (DOGS-NTA)>oleate>malonyl-CoA>PIP(2.)OCoA inhibited radioligand binding to SUR completely, with IC(50) values ranging from 6 to 44 microM. Inhibition was reversed by increasing the concentration of the radioligands in agreement with an essentially competitive mechanism. MgATP and coexpression with Kir6.2 decreased the potency of OCoA. DOGS-NTA inhibited radioligand binding to SUR by 40-88%, with IC(50) values ranging from 38 to 120 microM. Poly-lysine increased radioligand binding to SUR by up to 30% but did not affect much the inhibition of ligand binding by OCoA and DOGS-NTA. Radioligand binding to SUR2A but not to the other SUR subtypes was slightly (10-20%) stimulated by lipids at concentrations approximately 10 x lower than required for inhibition. The data show that certain lipids, at high concentrations, interact with SUR and inhibit the binding of GBC and P1075; with SUR2A, a modest stimulation of ligand binding precedes inhibition. Regarding K(ATP) channel activity, these effects will be overruled by the interaction of the lipids with Kir6.2 at lower (physiological) concentrations. They are, however, of pharmacological importance and must be taken into account if high concentrations of these compounds (e.g. OCoA>10 microM) are used to interfere with the action of sulphonylureas and openers on K(ATP) channel activity.
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Affiliation(s)
- Alexander Klein
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Jochen Lichtenberg
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Damian Stephan
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Ulrich Quast
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
- Author for correspondence:
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Stephan D, Stauß E, Lange U, Felsch H, Löffler-Walz C, Hambrock A, Russ U, Quast U. The mutation Y1206S increases the affinity of the sulphonylurea receptor SUR2A for glibenclamide and enhances the effects of coexpression with Kir6.2. Br J Pharmacol 2005; 144:1078-88. [PMID: 15711591 PMCID: PMC1576091 DOI: 10.1038/sj.bjp.0706142] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
1. ATP-sensitive K(+) channels (K(ATP) channels) are tetradimeric complexes of inwardly rectifying K(+) channels (Kir6.x) and sulphonylurea receptors (SURs). The SURs SUR2A (cardiac) and SUR2B (smooth muscle) differ only in the last 42 amino acids. In SUR2B, the mutation Y1206S, located at intracellular loop 8, increases the affinity for glibenclamide (GBC) about 10-fold. Here, we examined whether the mutation Y1206S in SUR2A had effects similar to those in SUR2B.2. GBC bound to SUR2A with K(D)=20 nM; the mutation increased affinity approximately 5 x. 3. In cells, coexpression of SUR2A with Kir6.2 increased the affinity for GBC approximately 3 x; with the mutant, the increase was 9 x. 4. The mutation did not affect the affinity of SUR2A for openers; coexpression with Kir6.2 reduced opener affinity of wild-type and mutant SUR2A by about 2 x. 5. The negative allosteric interaction between the opener, P1075, and GBC at wild-type and mutant SUR2A was markedly affected by the presence of MgATP and by coexpression with Kir6.2. 6. In inside-out patches, GBC inhibited the wild-type Kir6.2/SUR2A and 2B channels with IC(50) values of 27 nM; the mutation shifted the IC(50) values to approximately 1 nM. 7. The data show that the mutation Y1206S increased the affinity of SUR2A for GBC and modulated the effects of coexpression. Overall, the changes were similar to those observed with SUR2B(Y1206S), suggesting that the differences in the last 42 carboxy-terminal amino acids of SUR2A and 2B are of limited influence on the binding of GBC and P1075 to the SUR2 isoforms.
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Affiliation(s)
- Damian Stephan
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Eva Stauß
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulf Lange
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Holger Felsch
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Cornelia Löffler-Walz
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulrich Russ
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulrich Quast
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
- Author for correspondence:
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17
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Alekseev AE, Hodgson DM, Karger AB, Park S, Zingman LV, Terzic A. ATP-sensitive K+ channel channel/enzyme multimer: metabolic gating in the heart. J Mol Cell Cardiol 2005; 38:895-905. [PMID: 15910874 PMCID: PMC2736952 DOI: 10.1016/j.yjmcc.2005.02.022] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Accepted: 02/16/2005] [Indexed: 10/25/2022]
Abstract
Cardiac ATP-sensitive K(+) (K(ATP)) channels, gated by cellular metabolism, are formed by association of the inwardly rectifying potassium channel Kir6.2, the potassium conducting subunit, and SUR2A, the ATP-binding cassette protein that serves as the regulatory subunit. Kir6.2 is the principal site of ATP-induced channel inhibition, while SUR2A regulates K(+) flux through adenine nucleotide binding and catalysis. The ATPase-driven conformations within the regulatory SUR2A subunit of the K(ATP) channel complex have determinate linkage with the states of the channel's pore. The probability and life-time of ATPase-induced SUR2A intermediates, rather than competitive nucleotide binding alone, defines nucleotide-dependent K(ATP) channel gating. Cooperative interaction, instead of independent contribution of individual nucleotide binding domains within the SUR2A subunit, serves a decisive role in defining K(ATP) channel behavior. Integration of K(ATP) channels with the cellular energetic network renders these channel/enzyme heteromultimers high-fidelity metabolic sensors. This vital function is facilitated through phosphotransfer enzyme-mediated transmission of controllable energetic signals. By virtue of coupling with cellular energetic networks and the ability to decode metabolic signals, K(ATP) channels set membrane excitability to match demand for homeostatic maintenance. This new paradigm in the operation of an ion channel multimer is essential in providing the basis for K(ATP) channel function in the cardiac cell, and for understanding genetic defects associated with life-threatening diseases that result from the inability of the channel complex to optimally fulfill its physiological role.
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Affiliation(s)
- Alexey E Alekseev
- Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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18
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Yamada M, Kurachi Y. A functional role of the C-terminal 42 amino acids of SUR2A and SUR2B in the physiology and pharmacology of cardiovascular ATP-sensitive K(+) channels. J Mol Cell Cardiol 2005; 39:1-6. [PMID: 15978900 DOI: 10.1016/j.yjmcc.2004.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2004] [Revised: 07/19/2004] [Accepted: 11/12/2004] [Indexed: 11/16/2022]
Abstract
The ATP-sensitive K(+) (K(ATP)) channel is composed of four pore-forming Kir6.2 subunits and four sulfonylurea receptors (SUR). Intracellular ATP inhibits K(ATP) channels through Kir6.2. SUR is an ABC protein bearing transmembrane domains and two nucleotide-binding domains (NBD1 and NBD2). SUR increases the open probability of K(ATP) channels by interacting with ATP and ADP through NBDs and with K(+) channel openers such as nicorandil through its transmembrane domain. Because NBDs and the drug receptor allosterically interact with each other, nucleotides and drugs probably activate K(ATP) channels by causing the same conformational change of SUR. SUR2A and SUR2B have the identical drug receptor and NBDs and differ only in the C-terminal 42 amino acids (C42). Nonetheless, nicorandil ~100 times more potently activates SUR2B/Kir6.2 than SUR2A/Kir6.2 channels. Based on our allosteric model, we have analyzed the interaction between NBDs and the drug receptor in SUR2A and SUR2B and found that both nucleotide-bound NBD1 and NBD2 more strongly induce the conformational change in SUR2B than SUR2A. Therefore, C42 modulates the function of not only NBD2 which is close to C42 in a primary structure but NBD1 which is more than 630 amino acid N-terminal to C42. This raises the possibility that in the presence of nucleotides, NBD1 and NBD2 dimerize to induce the conformational change and that the dimerization enables C42 to gain access to both NBDs. Modulation of the nucleotide-NBD1 and -NBD2 interactions by C42 would determine the stability of the nucleotide-dependent dimer and thus, the physiological and pharmacological properties of K(ATP) channels.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine, Faculty of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
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19
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Ehses S, Leonhardt RM, Hansen G, Knittler MR. Functional Role of C-Terminal Sequence Elements in the Transporter Associated with Antigen Processing. THE JOURNAL OF IMMUNOLOGY 2004; 174:328-39. [PMID: 15611256 DOI: 10.4049/jimmunol.174.1.328] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
TAP delivers antigenic peptides into the endoplasmic reticulum (ER) that are subsequently bound by MHC class I molecules. TAP consists of two subunits (TAP1 and TAP2), each with a transmembrane (TMD) and a nucleotide-binding (NBD) domain. The two TAP-NBDs have distinct biochemical properties and control different steps during the peptide translocation process. We noted previously that the nonhomologous C-terminal tails of rat TAP1 and TAP2 determine the distinct functions of TAP-NBD1 and -NBD2. To identify the sequence elements responsible for the asymmetrical NBD function, we constructed chimeric rat TAP variants in which we systematically exchanged sequence regions of different length between the two TAP-NBDs. Our fine-mapping studies demonstrate that a nonhomologous region containing the alpha6/beta10-loop in conjunction with the downstream switch region is directly responsible for the functional separation of the TAP-NBDs. The alpha6/beta10-loop determines the nonsynonymous nucleotide binding of NBD1 and NBD2, whereas the switch region seems to play a critical role in regulating the functional cross-talk between the structural domains of TAP. Based on our findings, we postulate that these two sequence elements build a minimal functional unit that controls the asymmetry of the two TAP-NBDs.
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Affiliation(s)
- Sarah Ehses
- Institute for Genetics, University of Cologne, Zülpicher Strasse 47, 50674 Cologne, Germany
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20
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Campbell JD, Proks P, Lippiat JD, Sansom MSP, Ashcroft FM. Identification of a functionally important negatively charged residue within the second catalytic site of the SUR1 nucleotide-binding domains. Diabetes 2004; 53 Suppl 3:S123-7. [PMID: 15561899 DOI: 10.2337/diabetes.53.suppl_3.s123] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The ATP-sensitive K+ channel (KATP channel) couples glucose metabolism to insulin secretion in pancreatic beta-cells. It is comprised of sulfonylurea receptor (SUR)-1 and Kir6.2 proteins. Binding of Mg nucleotides to the nucleotide-binding domains (NBDs) of SUR1 stimulates channel opening and leads to membrane hyperpolarization and inhibition of insulin secretion. To elucidate the structural basis of this regulation, we constructed a molecular model of the NBDs of SUR1, based on the crystal structures of mammalian proteins that belong to the same family of ATP-binding cassette transporter proteins. This model is a dimer in which there are two nucleotide-binding sites, each of which contains residues from NBD1 as well as from NBD2. It makes the novel prediction that residue D860 in NBD1 helps coordinate Mg nucleotides at site 2. We tested this prediction experimentally and found that, unlike wild-type channels, channels containing the SUR1-D860A mutation were not activated by MgADP in either the presence or absence of MgATP. Our model should be useful for designing experiments aimed at elucidating the relationship between the structure and function of the KATP channel.
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Affiliation(s)
- Jeff D Campbell
- University Laboratory of Physiology, University of Oxford, Parks Rd., Oxford, OX1 3PT, UK
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21
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Westlake CJ, Payen L, Gao M, Cole SPC, Deeley RG. Identification and characterization of functionally important elements in the multidrug resistance protein 1 COOH-terminal region. J Biol Chem 2004; 279:53571-83. [PMID: 15459206 DOI: 10.1074/jbc.m402528200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ATP binding cassette (ABC) transporter, multidrug resistance protein 1 (MRP1/ABCC1), transports a broad spectrum of conjugated and unconjugated compounds, including natural product chemotherapeutic agents. In this study, we have investigated the importance of the COOH-terminal region of MRP1 for transport activity and basolateral plasma membrane trafficking. The COOH-terminal regions of some ABCC proteins have been implicated in protein trafficking, but the function of this region of MRP1 has not been defined. In contrast to results obtained with other ABCC proteins, we found that the COOH-proximal 30 amino acids of MRP1 can be removed without affecting trafficking to basolateral membranes. However, the truncated protein is inactive. Furthermore, removal of as few as 4 COOH-terminal amino acids profoundly decreases transport activity. Although amino acid sequence conservation of the COOH-terminal regions of ABC proteins is low, secondary structure predictions indicate that they consist of a broadly conserved helix-sheet-sheet-helix-helix structure. Consistent with a conservation of secondary and tertiary structure, MRP1 hybrids containing the COOH-terminal regions of either the homologous MRP2 or the distantly related P-glycoprotein were fully active and trafficked normally. Using mutated proteins, we have identified structural elements containing five conserved hydrophobic amino acids that are required for activity. We show that these are important for binding and hydrolysis of ATP by nucleotide binding domain 2. Based on crystal structures of several ABC proteins, we suggest that the conserved amino acids may stabilize a helical bundle formed by the COOH-terminal three helices and may contribute to interactions between the COOH-terminal region and the protein's two nucleotide binding domains.
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Yamada M, Ishii M, Hibino H, Kurachi Y. 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. Mol Pharmacol 2004; 66:807-16. [PMID: 15258252 DOI: 10.1124/mol.104.002717] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine Osaka University, 2-2 Yamada-oka, Suita, 565-0871, Japan
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Rainbow RD, James M, Hudman D, Al Johi M, Singh H, Watson PJ, Ashmole I, Davies NW, Lodwick D, Norman RI. Proximal C-terminal domain of sulphonylurea receptor 2A interacts with pore-forming Kir6 subunits in KATP channels. Biochem J 2004; 379:173-81. [PMID: 14672537 PMCID: PMC1224041 DOI: 10.1042/bj20031087] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2003] [Revised: 12/11/2003] [Accepted: 12/12/2003] [Indexed: 11/17/2022]
Abstract
Functional KATP (ATP-sensitive potassium) channels are hetero-octamers of four Kir6 (inwardly rectifying potassium) channel subunits and four SUR (sulphonylurea receptor) subunits. Possible interactions between the C-terminal domain of SUR2A and Kir6.2 were investigated by co-immunoprecipitation of rat SUR2A C-terminal fragments with full-length Kir6.2 and by analysis of cloned KATP channel function and distribution in HEK-293 cells (human embryonic kidney 293 cells) in the presence of competing rSUR2A fragments. Three maltose-binding protein-SUR2A fusions, rSUR2A-CTA (rSUR2A residues 1254-1545), rSUR2A-CTB (residues 1254-1403) and rSUR2A-CTC (residues 1294-1403), were co-immunoprecipitated with full-length Kir6.2 using a polyclonal anti-Kir6.2 antiserum. A fourth C-terminal domain fragment, rSUR2A-CTD (residues 1358-1545) did not co-immunoprecipitate with Kir6.2 under the same conditions, indicating a direct interaction between Kir6.2 and a 65-amino-acid section of the cytoplasmic C-terminal region of rSUR2A between residues 1294 and 1358. ATP- and glibenclamide-sensitive K+ currents were decreased in HEK-293 cells expressing full-length Kir6 and SUR2 subunits that were transiently transfected with fragments rSUR2A-CTA, rSUR2A-CTC and rSUR2A-CTE (residues 1294-1359) compared with fragment rSUR2A-CTD or mock-transfected cells, suggesting either channel inhibition or a reduction in the number of functional KATP channels at the cell surface. Anti-KATP channel subunit-associated fluorescence in the cell membrane was substantially lower and intracellular fluorescence increased in rSUR2A-CTE expressing cells; thus, SUR2A fragments containing residues 1294-1358 reduce current by decreasing the number of channel subunits in the cell membrane. These results identify a site in the C-terminal domain of rSUR2A, between residues 1294 and 1358, whose direct interaction with full-length Kir6.2 is crucial for the assembly of functional KATP channels.
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Affiliation(s)
- Richard D Rainbow
- Department of Cell Physiology and Pharmacology, University of Leicester, University Road, Leicester LE1 9HN, UK
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Yamada M, Kurachi Y. The nucleotide-binding domains of sulfonylurea receptor 2A and 2B play different functional roles in nicorandil-induced activation of ATP-sensitive K+ channels. Mol Pharmacol 2004; 65:1198-207. [PMID: 15102948 DOI: 10.1124/mol.65.5.1198] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nicorandil activates ATP-sensitive K(+) channels composed of Kir6.2 and either sulfonylurea receptor (SUR) 2A or 2B. Although SUR2A and SUR2B differ only in their C-terminal 42 amino acids (C42) and possess identical drug receptors and nucleotide-binding domains (NBDs), nicorandil more potently activates SUR2B/Kir6.2 than SUR2A/Kir6.2 channels. Here, we analyzed the roles of NBDs in these channels' response to nicorandil with the inside-out configuration of the patch-clamp method. Binding and hydrolysis of nucleotides by NBDs were impaired by mutations in the Walker A motif of NBD1 (K708A) and NBD2 (K1349A) and in the Walker B motif of NBD2 (D1470N). Experiments were done with internal ATP (1 mM). In SUR2A/Kir6.2 channels, the K708A mutation abolished, and the K1349A but not D1470N mutation reduced the sensitivity to nicorandil. ADP (100 microM) significantly increased the wild-type channels' sensitivity to nicorandil, which was abolished by the K1349A or D1470N mutation. Thus, the SUR2A/Kir6.2 channels' response to nicorandil critically depends on ATP-NBD1 interaction and is facilitated by interactions of ATP or ADP with NBD2. In SUR2B/Kir6.2 channels, either the K708A or K1349A mutation partially suppressed the response to nicorandil, and double mutations abolished it. The D1470N mutation also significantly impaired the response. ADP did not sensitize the channels. Thus, NBD2 hydrolyzes ATP, and NBD1 and NBD2 equally contribute to the response by interacting with ATP and ADP, accounting for the higher nicorandil sensitivity of SUR2B/Kir6.2 than SUR2A/Kir6.2 channels in the presence of ATP alone. Thus, C42 modulates the interaction of both NBDs with intracellular nucleotides.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine, Osaka University, Suita, Japan
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Bienengraeber M, Olson TM, Selivanov VA, Kathmann EC, O'Cochlain F, Gao F, Karger AB, Ballew JD, Hodgson DM, Zingman LV, Pang YP, Alekseev AE, Terzic A. ABCC9 mutations identified in human dilated cardiomyopathy disrupt catalytic KATP channel gating. Nat Genet 2004; 36:382-7. [PMID: 15034580 PMCID: PMC1995438 DOI: 10.1038/ng1329] [Citation(s) in RCA: 265] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2003] [Accepted: 02/13/2004] [Indexed: 11/09/2022]
Abstract
Stress tolerance of the heart requires high-fidelity metabolic sensing by ATP-sensitive potassium (K(ATP)) channels that adjust membrane potential-dependent functions to match cellular energetic demand. Scanning of genomic DNA from individuals with heart failure and rhythm disturbances due to idiopathic dilated cardiomyopathy identified two mutations in ABCC9, which encodes the regulatory SUR2A subunit of the cardiac K(ATP) channel. These missense and frameshift mutations mapped to evolutionarily conserved domains adjacent to the catalytic ATPase pocket within SUR2A. Mutant SUR2A proteins showed aberrant redistribution of conformations in the intrinsic ATP hydrolytic cycle, translating into abnormal K(ATP) channel phenotypes with compromised metabolic signal decoding. Defective catalysis-mediated pore regulation is thus a mechanism for channel dysfunction and susceptibility to dilated cardiomyopathy.
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Affiliation(s)
- Martin Bienengraeber
- Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine, Mayo Foundation, Rochester, Minnesota 55905, USA
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Bouabe H, Knittler MR. The distinct nucleotide binding states of the transporter associated with antigen processing (TAP) are regulated by the nonhomologous C-terminal tails of TAP1 and TAP2. ACTA ACUST UNITED AC 2004; 270:4531-46. [PMID: 14622282 DOI: 10.1046/j.1432-1033.2003.03848.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The transporter associated with antigen processing (TAP) delivers peptides into the lumen of the endoplasmic reticulum for binding onto major histocompatibility complex class I molecules. TAP comprises two polypeptides, TAP1 and TAP2, each with an N-terminal transmembrane domain and a C-terminal cytosolic nucleotide binding domain (NBD). The two NBDs have distinct intrinsic nucleotide binding properties. In the resting state of TAP, the NBD1 has a much higher binding activity for ATP than the NBD2, while the binding of ADP to the two NBDs is equivalent. To attribute the different nucleotide binding behaviour of NBD1 and NBD2 to specific sequences, we generated chimeric TAP1 and TAP2 polypeptides in which either the nonhomologous C-terminal tails downstream of the Walker B motif, or the core NBDs which are enclosed by the conserved Walker A and B motifs, were reciprocally exchanged. Our biochemical and functional studies on the different TAP chimeras show that the distinct nucleotide binding behaviour of TAP1 and TAP2 is controlled by the nonhomologous C-terminal tails of the two TAP chains. In addition, our data suggest that the C-terminal tail of TAP2 is required for a functional transporter by regulating ATP binding. Further experiments indicate that ATP binding to NBD2 is important because it prevents simultaneous uptake of ATP by TAP1. We propose that the C-terminal tails of TAP1 and TAP2 play a crucial regulatory role in the coordination of nucleotide binding and ATP hydrolysis by TAP.
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Affiliation(s)
- Hicham Bouabe
- Institute for Genetics, University of Cologne, Germany
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Hodgson DM, Zingman LV, Kane GC, Perez-Terzic C, Bienengraeber M, Ozcan C, Gumina RJ, Pucar D, O'Coclain F, Mann DL, Alekseev AE, Terzic A. Cellular remodeling in heart failure disrupts K(ATP) channel-dependent stress tolerance. EMBO J 2003; 22:1732-42. [PMID: 12682006 PMCID: PMC154482 DOI: 10.1093/emboj/cdg192] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are required for maintenance of homeostasis during the metabolically demanding adaptive response to stress. However, in disease, the effect of cellular remodeling on K(ATP) channel behavior and associated tolerance to metabolic insult is unknown. Here, transgenic expression of tumor necrosis factor alpha induced heart failure with typical cardiac structural and energetic alterations. In this paradigm of disease remodeling, K(ATP) channels responded aberrantly to metabolic signals despite intact intrinsic channel properties, implicating defects proximal to the channel. Indeed, cardiomyocytes from failing hearts exhibited mitochondrial and creatine kinase deficits, and thus a reduced potential for metabolic signal generation and transmission. Consequently, K(ATP) channels failed to properly translate cellular distress under metabolic challenge into a protective membrane response. Failing hearts were excessively vulnerable to metabolic insult, demonstrating cardiomyocyte calcium loading and myofibrillar contraction banding, with tolerance improved by K(ATP) channel openers. Thus, disease-induced K(ATP) channel metabolic dysregulation is a contributor to the pathobiology of heart failure, illustrating a mechanism for acquired channelopathy.
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Affiliation(s)
- Denice M Hodgson
- Department of Medicine, Mayo Clinic, Mayo Foundation, Rochester, MN 55905, USA
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Abstract
ATP-sensitive potassium channels (K(ATP)) of vascular smooth muscle cells represent potential therapeutic targets for control of abnormal vascular contractility. The biophysical properties, regulation and pharmacology of these channels have received intense scrutiny during the past twenty years, however, the molecular basis of vascular K(ATP) channels remains ill-defined. This review summarizes the recent advancements made in our understanding of the molecular composition of vascular K(ATP) channels with a focus on the evidence that hetero-octameric complexes of Kir6.1 and SUR2B subunits constitute the vascular K(ATP) subtype responsible for control of arterial diameter by vasoactive agonists.
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Affiliation(s)
- William C Cole
- The Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
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Zingman LV, Hodgson DM, Bast PH, Kane GC, Perez-Terzic C, Gumina RJ, Pucar D, Bienengraeber M, Dzeja PP, Miki T, Seino S, Alekseev AE, Terzic A. Kir6.2 is required for adaptation to stress. Proc Natl Acad Sci U S A 2002; 99:13278-83. [PMID: 12271142 PMCID: PMC130624 DOI: 10.1073/pnas.212315199] [Citation(s) in RCA: 247] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Reaction to stress requires feedback adaptation of cellular functions to secure a response without distress, but the molecular order of this process is only partially understood. Here, we report a previously unrecognized regulatory element in the general adaptation syndrome. Kir6.2, the ion-conducting subunit of the metabolically responsive ATP-sensitive potassium (K(ATP)) channel, was mandatory for optimal adaptation capacity under stress. Genetic deletion of Kir6.2 disrupted K(ATP) channel-dependent adjustment of membrane excitability and calcium handling, compromising the enhancement of cardiac performance driven by sympathetic stimulation, a key mediator of the adaptation response. In the absence of Kir6.2, vigorous sympathetic challenge caused arrhythmia and sudden death, preventable by calcium-channel blockade. Thus, this vital function identifies a physiological role for K(ATP) channels in the heart.
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Affiliation(s)
- Leonid V Zingman
- Division of Cardiovascular Diseases, Departments of Medicine and Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN 55905, USA
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