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Dimerization of SERCA2a Enhances Transport Rate and Improves Energetic Efficiency in Living Cells. Biophys J 2020; 119:1456-1465. [PMID: 32946770 DOI: 10.1016/j.bpj.2020.08.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 08/07/2020] [Accepted: 08/25/2020] [Indexed: 11/21/2022] Open
Abstract
The type 2a sarco/endoplasmic reticulum (ER) Ca2+-ATPase (SERCA2a) plays a key role in intracellular Ca2+ regulation in the heart. We have previously shown evidence of stable homodimers of SERCA2a in heterologous cells and cardiomyocytes. However, the functional significance of the pump dimerization remains unclear. Here, we analyzed how SERCA2a dimerization affects ER Ca2+ transport. Fluorescence resonance energy transfer experiments in HEK293 cells transfected with fluorescently labeled SERCA2a revealed increasing dimerization of Ca2+ pumps with increasing expression level. This concentration-dependent dimerization provided means of comparison of the functional characteristics of monomeric and dimeric pumps. SERCA-mediated Ca2+ uptake was measured with the ER-targeted Ca2+ sensor R-CEPIA1er in cells cotransfected with SERCA2a and ryanodine receptor. For each individual cell, the maximal ER Ca2+ uptake rate and the maximal Ca2+ load, together with the pump expression level, were analyzed. This analysis revealed that the ER Ca2+ uptake rate increased as a function of SERCA2a expression, with a particularly steep, nonlinear increase at high expression levels. Interestingly, the maximal ER Ca2+ load also increased with an increase in the pump expression level, suggesting improved catalytic efficiency of the dimeric species. Reciprocally, thapsigargin inhibition of a fraction of the population of SERCA2a reduced not only the maximal ER Ca2+ uptake rate but also the maximal Ca2+ load. These data suggest that SERCA2a dimerization regulates Ca2+ transport by improving both the SERCA2a turnover rate and catalytic efficacy. Analysis of ER Ca2+ uptake in cells cotransfected with human wild-type SERCA2a (SERCA2aWT) and SERCA2a mutants with different catalytic activity revealed that an intact catalytic cycle in both protomers is required for enhancing the efficacy of Ca2+ transport by a dimer. The data are consistent with the hypothesis of functional coupling of two SERCA2a protomers in a dimer that reduces the energy barrier of rate-limiting steps of the catalytic cycle of Ca2+ transport.
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Engevik AC, Kaji I, Goldenring JR. The Physiology of the Gastric Parietal Cell. Physiol Rev 2020; 100:573-602. [PMID: 31670611 PMCID: PMC7327232 DOI: 10.1152/physrev.00016.2019] [Citation(s) in RCA: 91] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 10/10/2019] [Accepted: 10/13/2019] [Indexed: 12/11/2022] Open
Abstract
Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.
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Affiliation(s)
- Amy C Engevik
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - Izumi Kaji
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - James R Goldenring
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
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3
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Paresi CJ, Liu Q, Li YM. Benzimidazole covalent probes and the gastric H(+)/K(+)-ATPase as a model system for protein labeling in a copper-free setting. MOLECULAR BIOSYSTEMS 2017; 12:1772-80. [PMID: 26952080 DOI: 10.1039/c6mb00024j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Affinity probes are useful tools for determining molecular targets and elucidating mechanism of action for novel, bioactive compounds. In the case of covalent inhibitors, activity based probes are particularly valuable for ensuring acceptable selectivity margins. However, there is a variety of bioorthogonal chemistry reactions available for modifying compounds of interest with clickable tags. Here, we describe a direct comparison of tetrazine ligation and strain promoted azide-alkyne cycloaddition using benzimidazole based probes to bind their known target, the gastric proton pump, ATP4A. This study validates the use of chemical probes for target identification and illustrates the superior efficiency of tetrazine ligation for copper-free click systems. In addition, we have identified several novel binding partners of benzimidazole probes: Isoform 2 of deleted in malignant brain tumors 1 protein (DMBT1) and three uncharacterized proteins.
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Affiliation(s)
- Chelsea J Paresi
- Chemical Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA. and Program of Pharmacology, Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA
| | - Qi Liu
- Chemical Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
| | - Yue-Ming Li
- Chemical Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA. and Program of Pharmacology, Weill Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA
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4
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Walentek P, Beyer T, Hagenlocher C, Müller C, Feistel K, Schweickert A, Harland RM, Blum M. ATP4a is required for development and function of the Xenopus mucociliary epidermis - a potential model to study proton pump inhibitor-associated pneumonia. Dev Biol 2015; 408:292-304. [PMID: 25848696 DOI: 10.1016/j.ydbio.2015.03.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2014] [Revised: 03/23/2015] [Accepted: 03/24/2015] [Indexed: 12/12/2022]
Abstract
Proton pump inhibitors (PPIs), which target gastric H(+)/K(+)ATPase (ATP4), are among the most commonly prescribed drugs. PPIs are used to treat ulcers and as a preventative measure against gastroesophageal reflux disease in hospitalized patients. PPI treatment correlates with an increased risk for airway infections, i.e. community- and hospital-acquired pneumonia. The cause for this correlation, however, remains elusive. The Xenopus embryonic epidermis is increasingly being used as a model to study airway-like mucociliary epithelia. Here we use this model to address how ATP4 inhibition may affect epithelial function in human airways. We demonstrate that atp4a knockdown interfered with the generation of cilia-driven extracellular fluid flow. ATP4a and canonical Wnt signaling were required in the epidermis for expression of foxj1, a transcriptional regulator of motile ciliogenesis. The ATP4/Wnt module activated foxj1 downstream of ciliated cell fate specification. In multiciliated cells (MCCs) of the epidermis, ATP4a was also necessary for normal myb expression, apical actin formation, basal body docking and alignment of basal bodies. Furthermore, ATP4-dependent Wnt/β-catenin signaling in the epidermis was a prerequisite for foxa1-mediated specification of small secretory cells (SSCs). SSCs release serotonin and other substances into the medium, and thereby regulate ciliary beating in MCCs and protect the epithelium against infection. Pharmacological inhibition of ATP4 in the mature mucociliary epithelium also caused a loss of MCCs and led to impaired mucociliary clearance. These data strongly suggest that PPI-associated pneumonia in human patients might, at least in part, be linked to dysfunction of mucociliary epithelia of the airways.
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Affiliation(s)
- Peter Walentek
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany; Department of Molecular and Cell Biology, Center for Integrative Genomics, University of California at Berkeley, Berkeley, CA 94720, USA.
| | - Tina Beyer
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Cathrin Hagenlocher
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Christina Müller
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Kerstin Feistel
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Axel Schweickert
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
| | - Richard M Harland
- Department of Molecular and Cell Biology, Center for Integrative Genomics, University of California at Berkeley, Berkeley, CA 94720, USA
| | - Martin Blum
- Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
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5
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Sachs G, Shin JM, Munson K, Scott DR. Gastric acid-dependent diseases: a twentieth-century revolution. Dig Dis Sci 2014; 59:1358-69. [PMID: 24852882 DOI: 10.1007/s10620-014-3104-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- George Sachs
- Department of Medicine, David Geffen School of Medicine, The Veterans Administration Greater Los Angeles Healthcare System, University of California at Los Angeles, Bldg 113, Rm 324 11301 Wilshire Blvd., Los Angeles, CA, 90073, USA,
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6
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Abstract
The gastric H(+),K(+)-ATPase is responsible for gastric acid secretion. This ATPase is composed of two subunits, the catalytic α subunit and the structural β subunit. The α subunit with molecular mass of about 100 kDa has 10 transmembrane domains and is strongly associated with the β subunit with a single transmembrane segment and a peptide mass of 35 kDa. Its three-dimensional structure is based on homology modeling and site-directed mutagenesis resulting in a proton extrusion and K(+) reabsorption model. There are three conserved H3O(+)-binding sites in the middle of the membrane domain and H3O(+) secretion depends on a conformational change involving Lys(791) insertion into the second H3O(+) site enclosed by E795, E820, and D824 that allows export of protons at a concentration of 160 mM. K(+) countertransport involves binding to this site after the release of protons with retrograde displacement of Lys(791) and then K(+) transfer to E343 and exit to the cytoplasm. This ATPase is the major therapeutic target in treatment of acid-related diseases and there are several known luminal inhibitors allowing analysis of the luminal vestibule. One class contains the acid-activated covalent, thiophilic proton pump inhibitors, the most effective of current acid-suppressive drugs. Their binding sites and trypsinolysis allowed identification of all ten transmembrane segments of the ATPase. In addition, various K(+)-competitive inhibitors of the ATPase are being developed, with the advantage of complete and rapid inhibition of acid secretion independent of pump activity and allowing further refinement of the structure of the luminal vestibule of the E2 form of this ATPase.
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Affiliation(s)
- Jai Moo Shin
- Department of Physiology and Medicine, University of California at Los Angeles, and VA Greater Los Angeles Healthcare System, Los Angeles, California, USA.
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7
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Dach I, Olesen C, Signor L, Nissen P, le Maire M, Møller JV, Ebel C. Active detergent-solubilized H+,K+-ATPase is a monomer. J Biol Chem 2012; 287:41963-78. [PMID: 23055529 DOI: 10.1074/jbc.m112.398768] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The H(+),K(+)-ATPase pumps protons or hydronium ions and is responsible for the acidification of the gastric fluid. It is made up of an α-catalytic and a β-glycosylated subunit. The relation between cation translocation and the organization of the protein in the membrane are not well understood. We describe here how pure and functionally active pig gastric H(+),K(+)-ATPase with an apparent Stokes radius of 6.3 nm can be obtained after solubilization with the non-ionic detergent C(12)E(8), followed by exchange of C(12)E(8) with Tween 20 on a Superose 6 column. Mass spectroscopy indicates that the β-subunit bears an excess mass of 9 kDa attributable to glycosylation. From chemical analysis, there are 0.25 g of phospholipids and around 0.024 g of cholesterol bound per g of protein. Analytical ultracentrifugation shows one main complex, sedimenting at s(20,)(w) = 7.2 ± 0.1 S, together with minor amounts of irreversibly aggregated material. From these data, a buoyant molecular mass is calculated, corresponding to an H(+),K(+)-ATPase α,β-protomer of 147.3 kDa. Complementary sedimentation velocity with deuterated water gives a picture of an α,β-protomer with 0.9-1.4 g/g of bound detergent and lipids and a reasonable frictional ratio of 1.5, corresponding to a Stokes radius of 7.1 nm. An α(2),β(2) dimer is rejected by the data. Light scattering coupled to gel filtration confirms the monomeric state of solubilized H(+),K(+)-ATPase. Thus, α,β H(+),K(+)-ATPase is active at least in detergent and may plausibly function as a monomer, as has been established for other P-type ATPases, Ca(2+)-ATPase and Na(+),K(+)-ATPase.
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Affiliation(s)
- Ingrid Dach
- Center for Membrane Pumps in Cells and Diseases, Danish Research Foundation, DK-8000 Aarhus, Denmark
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8
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Seo KA, Lee SJ, Kim KB, Bae SK, Liu KH, Kim DH, Shin JG. Ilaprazole, a new proton pump inhibitor, is primarily metabolized to ilaprazole sulfone by CYP3A4 and 3A5. Expert Opin Ther Pat 2011. [PMID: 22022918 DOI: 10.1517/13543776.2013.741121] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Ilaprazole is a new proton pump inhibitor, designed for treatment of gastric ulcers, and developed by Il-Yang Pharmaceutical Co (Seoul, Korea). It is extensively metabolised to the major metabolite ilaprazole sulfone. In the present study, several in vitro approaches were used to identify the cytochrome P450 (CYP) enzymes responsible for ilaprazole sulfone formation. Concentrations of ilaprazole sulfone were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Incubation of ilaprazole with cDNA-expressed recombinant CYPs indicated that CYP3A was the major enzyme that catalyses ilaprozole to ilaprazole sulfone. This reaction was inhibited significantly by ketoconazole, a CYP3A inhibitor, and azamulin, a mechanism-based inhibitor of CYP3A, while no substantial effect was observed using selective inhibitors for eight other P450s (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP2E1). In addition, the formation of ilaprazole sulfone correlated well with CYP3A-catalysed testosterone 6β-hydroxylation and midazolam 1'-hydroxylation in 20 different human liver microsome panels. The intrinsic clearance of the formation of ilaprazole sulfone by CYP3A4 was 16-fold higher than that by CYP3A5. Collectively, these results indicate that the formation of the major metabolite of ilaprazole, ilaprazole sulfone, is predominantly catalysed by CYP3A4/5.
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Affiliation(s)
- Kyung-Ah Seo
- Department of Pharmacology and PharmacoGenomics Research Center, Inje University College of Medicine, Busan, Korea
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10
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Abstract
The parietal cell is responsible for secreting concentrated hydrochloric acid into the gastric lumen. To fulfill this task, it is equipped with a broad variety of functionally coupled apical and basolateral ion transport proteins. The concerted scientific effort over the last years by a variety of researchers has provided us with the molecular identity of many of these transport mechanisms, thereby contributing to the clarification of persistent controversies in the field. This article will briefly review the current model of parietal cell physiology and ion transport in particular and will update the existing models of apical and basolateral transport in the parietal cell.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
| | - Michael Murek
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
| | - John P. Geibel
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
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11
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Heitkamp T, Kalinowski R, Böttcher B, Börsch M, Altendorf K, Greie JC. K+-Translocating KdpFABC P-Type ATPase from Escherichia coli Acts as a Functional and Structural Dimer. Biochemistry 2008; 47:3564-75. [DOI: 10.1021/bi702038e] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Thomas Heitkamp
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - René Kalinowski
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Bettina Böttcher
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Michael Börsch
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Karlheinz Altendorf
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Jörg-Christian Greie
- Universität Osnabrück, Fachbereich Biologie/Chemie, Arbeitsgruppe Mikrobiologie, 49069 Osnabrück, Germany, Scriptor Dokumentations Service GmbH, Krackser Strasse 12C, 33659 Bielefeld, Germany, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany, and Physikalisches Institut, Pfaffenwaldring 57, 70550 Stuttgart, Germany
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12
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Sachs G, Shin JM, Vagin O, Lambrecht N, Yakubov I, Munson K. The gastric H,K ATPase as a drug target: past, present, and future. J Clin Gastroenterol 2007; 41 Suppl 2:S226-42. [PMID: 17575528 PMCID: PMC2860960 DOI: 10.1097/mcg.0b013e31803233b7] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The recent progress in therapy if acid disease has relied heavily on the performance of drugs targeted against the H,K ATPase of the stomach and the H2 receptor antagonists. It has become apparent in the last decade that the proton pump is the target that has the likelihood of being the most sustainable area of therapeutic application in the regulation of acid suppression. The process of activation of acid secretion requires a change in location of the ATPase from cytoplasmic tubules into the microvilli of the secretory canaliculus of the parietal cell. Stimulation of the resting parietal cell, with involvement of F-actin and ezrin does not use significant numbers of SNARE proteins, because their message is depleted in the pure parietal cell transcriptome. The cell morphology and gene expression suggest a tubule fusion-eversion event. As the active H,K ATPase requires efflux of KCl for activity we have, using the transcriptome derived from 99% pure parietal cells and immunocytochemistry, provided evidence that the KCl pathway is mediated by a KCQ1/KCNE2 complex for supplying K and CLIC6 for supplying the accompanying Cl. The pump has been modeled on the basis of the structures of different conformations of the sr Ca ATPase related to the catalytic cycle. These models use the effects of site directed mutations and identification of the binding domain of the K competitive acid pump antagonists or the defined site of binding for the covalent class of proton pump inhibitors. The pump undergoes conformational changes associated with phosphorylation to allow the ion binding site to change exposure from cytoplasmic to luminal exposure. We have been able to postulate that the very low gastric pH is achieved by lysine 791 motion extruding the hydronium ion bound to carboxylates in the middle of the membrane domain. These models also allow description of the K entry to form the K liganded form of the enzyme and the reformation of the ion site inward conformation thus relating the catalytic cycle of the pump to conformational models. The mechanism of action of the proton pump inhibitor class of drug is discussed along with the cysteines covalently bound with these inhibitors. The review concludes with a discussion of the mechanism of action and binding regions of a possible new class of drug for acid control, the K competitive acid pump antagonists.
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Affiliation(s)
- George Sachs
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, CA, USA.
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13
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Affiliation(s)
- Jai Moo Shin
- Department of Physiology and Medicine, University of California at Los Angeles, and VA Greater Los Angeles Healthcare System, Los Angeles, California 90073, USA
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14
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Abe K, Kaya S, Imagawa T, Taniguchi K. K+ induced simultaneous liberation of two moles of Pi, one from one mole of EP and the other from EATP, of oligomeric H/K-ATPase from pig stomach. Ann N Y Acad Sci 2003; 986:281-2. [PMID: 12763822 DOI: 10.1111/j.1749-6632.2003.tb07186.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kazuhiro Abe
- Department of Biological Chemistry, Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
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15
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Costa CJ, Gatto C, Kaplan JH. Interactions between Na,K-ATPase alpha-subunit ATP-binding domains. J Biol Chem 2003; 278:9176-84. [PMID: 12511576 DOI: 10.1074/jbc.m212351200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The reaction mechanism of the Na,K-ATPase is thought to involve a number of ligand-induced conformational changes. The specific amino acid residues responsible for binding many of the important ligands have been identified; however, details of the specific conformational changes produced by ligand binding are largely undescribed. The experiments described in this paper begin to identify interactions between domains of the Na,K-ATPase alpha-subunit that depend on the presence of particular ligands. The major cytoplasmic loop (between TM4 and TM5), which we have previously shown contains the ATP-binding domain, was overexpressed in bacteria either with a His(6) tag or as a fusion protein with glutathione S-transferase. We have observed that these polypeptides associate in the presence of MgATP. Incubation with [gamma-(32)P]ATP under conditions that result in phosphorylation of the full-length Na,K-ATPase did not result in (32)P incorporation into either the His(6) tag or glutathione S-transferase fusion proteins. The MgATP-induced association was strongly inhibited by prior modification of the fusion proteins with fluorescein isothiocyanate or by simultaneous incubation with 10 microm eosin, indicating that the effect of MgATP is due to interactions within the nucleotide-binding domain. These data are consistent with Na,K-ATPase associating within cells via interactions in the nucleotide-binding domains. Although any functional significance of these associations for ion transport remains unresolved, they may play a role in cell function and in modulating interactions between the Na,K-ATPase and other proteins.
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Affiliation(s)
- Charles J Costa
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97201, USA
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16
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Ivanov AV, Modyanov NN, Askari A. Role of the self-association of beta subunits in the oligomeric structure of Na+/K+-ATPase. Biochem J 2002; 364:293-9. [PMID: 11988103 PMCID: PMC1222572 DOI: 10.1042/bj3640293] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The two subunits of Na(+)/K(+)-ATPase that are essential for function are alpha and beta. Previous cross-linking studies on the oligomeric structure of the membrane-bound enzyme identified alpha,beta and alpha,alpha associations, but only the former and not the latter could be detected after solubilization. To study the possibility of direct beta,beta association, the purified membrane enzyme and a trypsin-digested enzyme that occludes cations and contains an essentially intact beta and fragments of alpha were subjected to oxidative cross-linking in the presence of Cu(2+)-phenanthroline. Resolution of products on polyacrylamide gels, N-terminal analysis and reactivity with anti-beta antibody showed that, in addition to previously identified products (e.g. alpha,alpha and alpha,beta dimers), a beta,beta dimer, most likely linked through intramembrane Cys(44) residues of two chains, is also formed. This dimer was also noted when digitonin-solubilized intact enzyme, and the trypsin-digested enzyme solubilized with digitonin or polyoxyethylene 10-laurylether were subjected to cross-linking, indicating that the detected beta,beta association was not due to random collisions. In the digested enzyme, K(+) but not Na(+) enhanced beta,beta dimer formation. The alternative cross-linking of beta-Cys(44) to a Cys residue of a transmembrane alpha-helix was antagonized specifically by K(+) or Na(+). The findings (i) indicate the role of beta,beta association in maintaining the minimum oligomeric structure of (alpha,beta)(2), (ii) provide further support for conformation-dependent flexibilities of the spatial relations of the transmembrane helices of alpha and beta and (iii) suggest the possibility of significant differences between the quaternary structures of the P-type ATPases that do and do not contain a beta subunit.
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Affiliation(s)
- Alexander V Ivanov
- Department of Pharmacology, Medical College of Ohio, 3035 Arlington Avenue, Toledo, OH 43614-5804, U.S.A.
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17
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Jaisser F, Beggah AT. The nongastric H+-K+-ATPases: molecular and functional properties. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:F812-24. [PMID: 10362770 DOI: 10.1152/ajprenal.1999.276.6.f812] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na-K/H-K-ATPase gene family is divided in three subgroups including the Na-K-ATPases, mainly involved in whole body and cellular ion homeostasis, the gastric H-K-ATPase involved in gastric fluid acidification, and the newly described nongastric H-K-ATPases for which the identification of physiological roles is still in its infancy. The first member of this last subfamily was first identified in 1992, rapidly followed by the molecular cloning of several other members. The relationship between each member remains unclear. The functional properties of these H-K-ATPases have been studied after their ex vivo expression in various functional expression systems, including the Xenopus laevis oocyte, the insect Sf9 cell line, and the human HEK 293 cells. All these H-K-ATPase alpha-subunits appear to encode H-K-ATPases when exogenously expressed in such expression systems. Recent data suggest that these H-K-ATPases could also transport Na+ in exchange for K+, revealing a complex cation transport selectivity. Moreover, they display a unique pharmacological profile compared with the canonical Na-K-ATPases or the gastric H-K-ATPase. In addition to their molecular and functional characterizations, a major goal is to correlate the molecular expression of these cloned H-K-ATPases with the native K-ATPases activities described in vivo. This appears to be more complex than anticipated. The discrepancies between the functional data obtained by exogenous expression of the nongastric H-K-ATPases and the physiological data obtained in native organs could have several explanations as discussed in the present review. Extensive studies will be required in the future to better understand the physiological role of these H-K-ATPases, especially in disease processes including ionic or acid-base disorders.
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Affiliation(s)
- F Jaisser
- Institut National de la Santé et de la Recherche Médicale, Unité 478, Institut Fédératif de Recherche Cellules Epithéliales, Faculté de Médecine Xavier Bichat, Université Paris VII, F-75870 Paris Cedex 18, France.
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Suzuki H, Kamakura M, Morii M, Takeguchi N. The phospholipid flippase activity of gastric vesicles. J Biol Chem 1997; 272:10429-34. [PMID: 9099684 DOI: 10.1074/jbc.272.16.10429] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We found that isolated gastric vesicles contain a novel Mg2+-ATP-dependent phospholipid translocation (flippase) activity. Fluorescence analogue of phosphatidylcholine, 2-(12-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)dodecanoyl-1-hexadecanoyl-sn-glycero-3- phosphocholine, was ATP-dependently translocated from the outer (cytosolic) to inner (luminal) leaflet of the lipid membrane bilayer of hog gastric vesicles. The translocation was saturable and depended on time and the ATP concentration (Km = 3.1 microM). The basal Mg2+-ATPase activity of gastric vesicles in the absence of K+ showed high (Km = 1.6 microM) and low (Km = 80 microM) affinities for ATP, indicating that the present flippase activity is driven mostly by the high affinity Mg2+-ATPase activity. It required Mg2+ but not K+. Verapamil, which is an inhibitor of mouse mdr2 phosphatidylcholine flippase, did not inhibit the present flippase activity. Isolated sarcoplasmic reticulum vesicles that contain Ca2+-ATPase did not show any flippase activity. Fluorescence analogues of phosphatidylserine and phosphatidylethanolamine were similarly translocated by the gastric flippase. These phospholipid flippase activities were inhibited by 2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine-3-acetonitrile (SCH 28080) (IC50 = 0.14-0.25 microM), a specific K+-ATPase inhibitor of gastric H+,K+-ATPase rich in gastric vesicles. IC50 value for the SCH 28080-inhibitable Mg2+-ATPase activity was about 0.13 microM, indicating that the phospholipid translocation was driven mostly by the SCH 28080-sensitive Mg2+-ATPase activity. Possible physiological roles of flippases were discussed in relation with the gastric acid secretory and cytoprotective mechanisms.
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Affiliation(s)
- H Suzuki
- Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-01, Japan
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