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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: 98] [Impact Index Per Article: 24.5] [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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2
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Eftekhari M, Hoseinsalari A, Mansourian M, Farjadmand F, Shams Ardekani MR, Sharifzadeh M, Hassanzadeh G, Khanavi M, Gholami M. Trachyspermum ammi (L.) Sprague, superb essential oil and its major components on peptic ulcers: in vivo combined in silico studies. ACTA ACUST UNITED AC 2019; 27:317-327. [PMID: 31218527 DOI: 10.1007/s40199-019-00279-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 06/05/2019] [Indexed: 11/30/2022]
Abstract
BACKGROUND Trachyspermum ammi (L.) Sprague is used for treating gastrointestinal disorders. Several studies indicated gastric antiulcer activity of T. ammi extract, yet the effect of its essential oil has not been studied on. OBJECTIVES The present study evaluates chemical composition of T. ammi essential oil and anti-peptic ulcer effect of the essential oil as well as its three major components in ethanol induced-gastric ulcers in rats. METHODS Primarily chemical composition of the essential oil was analyzed by gas chromatography-mass spectrometry (GC/MS). Rats received the essential oil (500, 250, 125, 62.5, 31.25 mg/kg), thymol (30, 100 mg/kg), para-cymene (100, 150 mg/kg) and gamma-terpinene (100, 150 mg/kg) using gavage tube along with ethanol 80%. Finally, dissected stomachs were assessed both macroscopically and microscopically to evaluate anti-ulcerative effect of the essential oil and the pure compounds. Moreover, molecular docking was utilized to explore the interactive behavior of the main components with active site residues of H+/K+ ATPase. RESULTS Analysis of the essential oil indicated that para-cymene (37.18%), gamma-terpinene (35.36%) and thymol (20.51%) are the main components. Administration of different doses of the essential oil noticeably diminished the number of peptic ulcers in a dose-dependent manner. Among the main components, thymol was more potent than para-cymene and gamma-terpinene. Administration of the essential oil (500 mg/kg) and thymol (100 mg/kg) observed maximum inhibition percentage (98.58% and 79.37%, respectively). Molecular docking study provides the evidence of thymol ability to inhibit H+/K+ ATPase. CONCLUSIONS The findings revealed that T. ammi essential oil can be applied to treat gastric ulcer as a natural agent. Graphical abstract.
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Affiliation(s)
- Mahdieh Eftekhari
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Afsaneh Hoseinsalari
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Mahboubeh Mansourian
- Medicinal Plants Research Center, Yasuj University of Medical Sciences, Yasuj, Iran.,Department of Pharmacology, Faculty of Medicine, Yasuj University of Medical Sciences, Yasuj, Iran
| | - Fatemeh Farjadmand
- Food and Drug Organization, Ministry of Health and Medical Education of Iran, Tehran, Iran
| | | | - Mohammad Sharifzadeh
- Department of Toxicology and Pharmacology, Tehran University of Medical Sciences, Tehran, Iran.,The institute of Pharmaceutical Sciences, Tehran University of Medical Sciences, Tehran, Iran
| | - Gholamreza Hassanzadeh
- Department of Anatomy, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Mahnaz Khanavi
- Department of Pharmacognosy, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. .,Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada.
| | - Mahdi Gholami
- Department of Toxicology and Pharmacology, Tehran University of Medical Sciences, Tehran, Iran
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3
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Dubey V, Han M, Kopec W, Solov'yov IA, Abe K, Khandelia H. K + binding and proton redistribution in the E 2P state of the H +, K +-ATPase. Sci Rep 2018; 8:12732. [PMID: 30143663 PMCID: PMC6109069 DOI: 10.1038/s41598-018-30885-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 08/07/2018] [Indexed: 12/13/2022] Open
Abstract
The H+, K+-ATPase (HKA) uses ATP to pump protons into the gastric lumen against a million-fold proton concentration gradient while counter-transporting K+ from the lumen. The mechanism of release of a proton into a highly acidic stomach environment, and the subsequent binding of a K+ ion necessitates a network of protonable residues and dynamically changing protonation states in the cation binding pocket dominated by five acidic amino acid residues E343, E795, E820, D824, and D942. We perform molecular dynamics simulations of spontaneous K+ binding to all possible protonation combinations of the acidic amino acids and carry out free energy calculations to determine the optimal protonation state of the luminal-open E2P state of the pump which is ready to bind luminal K+. A dynamic pKa correlation analysis reveals the likelihood of proton transfer events within the cation binding pocket. In agreement with in-vitro measurements, we find that E795 is likely to be protonated, and that E820 is at the center of the proton transfer network in the luminal-open E2P state. The acidic residues D942 and D824 are likely to remain protonated, and the proton redistribution occurs predominantly amongst the glutamate residues exposed to the lumen. The analysis also shows that a lower number of K+ ions bind at lower pH, modeled by a higher number of protons in the cation binding pocket, in agreement with the 'transport stoichiometry variation' hypothesis.
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Affiliation(s)
- Vikas Dubey
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark
| | - Minwoo Han
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark
| | - Wojciech Kopec
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Ilia A Solov'yov
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark
| | - Kazuhiro Abe
- Cellular and Structural Physiology Institute and Department of Medicinal Science, Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan
| | - Himanshu Khandelia
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, 5230 M, Denmark.
- MEMPHYS-Center for Biomembrane Physics, Odense, Denmark.
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4
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Molecular docking, binding free energy analysis, and biological evaluation of bisabolonalone hydrazone carboxamides as H+,K+-ATPase reversible inhibitors. Med Chem Res 2018. [DOI: 10.1007/s00044-017-2048-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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5
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Abe K, Shimokawa J, Naito M, Munson K, Vagin O, Sachs G, Suzuki H, Tani K, Fujiyoshi Y. The cryo-EM structure of gastric H +,K +-ATPase with bound BYK99, a high-affinity member of K +-competitive, imidazo[1,2-a]pyridine inhibitors. Sci Rep 2017; 7:6632. [PMID: 28747707 PMCID: PMC5529566 DOI: 10.1038/s41598-017-06698-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 06/21/2017] [Indexed: 12/13/2022] Open
Abstract
The gastric proton pump H+,K+-ATPase acidifies the gastric lumen, and thus its inhibitors, including the imidazo[1,2-a]pyridine class of K+-competitive acid blockers (P-CABs), have potential application as acid-suppressing drugs. We determined the electron crystallographic structure of H+,K+-ATPase at 6.5 Å resolution in the E2P state with bound BYK99, a potent P-CAB with a restricted ring structure. The BYK99 bound structure has an almost identical profile to that of a previously determined structure with bound SCH28080, the original P-CAB prototype, but is significantly different from the previously reported P-CAB-free form, illustrating a common conformational change is required for P-CAB binding. The shared conformational changes include a distinct movement of transmembrane helix 2 (M2), from its position in the previously reported P-CAB-free form, to a location proximal to the P-CAB binding site in the present BYK99-bound structure. Site-specific mutagenesis within M2 revealed that D137 and N138, which face the P-CAB binding site in our model, significantly affect the inhibition constant (Ki) of P-CABs. We also found that A335 is likely to be near the bridging nitrogen at the restricted ring structure of the BYK99 inhibitor. These provide clues to elucidate the binding site parameters and mechanism of P-CAB inhibition of gastric acid secretion.
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Affiliation(s)
- Kazuhiro Abe
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan. .,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan. .,Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Chiyoda, Tokyo, 100-0004, Japan.
| | - Jun Shimokawa
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan
| | - Mao Naito
- Graduate School of Pharmaceutical Sciences, Nagoya University, Nagoya, 464-8601, Japan.,Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
| | | | | | | | - Hiroshi Suzuki
- Laboratory of Molecular Electron Microscopy, Rockefeller University, New York, 10065, USA
| | - Kazutoshi Tani
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan
| | - Yoshinori Fujiyoshi
- Cellular and Structural Physiology Institute, Nagoya University, Nagoya, 464-8601, Japan.,Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Chiyoda, Tokyo, 100-0004, Japan.,CeSPIA Inc., 2-1-1, Otemachi, Chiyoda, Tokyo, 100-0004, Japan
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6
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Huang NY, Wang WB, Chen L, Luo HJ, Wang JZ, Deng WQ, Zou K. Design, synthesis and biological evaluation of bisabolangelone oxime derivatives as potassium-competitive acid blockers (P-CABs). Bioorg Med Chem Lett 2016; 26:2268-72. [DOI: 10.1016/j.bmcl.2016.03.051] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2015] [Revised: 02/29/2016] [Accepted: 03/14/2016] [Indexed: 10/22/2022]
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7
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Sakai H, Fujii T, Takeguchi N. Proton-Potassium (H+/K+) ATPases: Properties and Roles in Health and Diseases. Met Ions Life Sci 2016; 16:459-83. [DOI: 10.1007/978-3-319-21756-7_13] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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8
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Luo HJ, Wang JZ, Huang NY, Deng WQ, Zou K. Computational insights into the interaction mechanism of triazolyl substituted tetrahydrobenzofuran derivatives with H(+),K(+)-ATPase at different pH. J Comput Aided Mol Des 2015; 30:27-37. [PMID: 26667240 DOI: 10.1007/s10822-015-9886-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 12/07/2015] [Indexed: 11/29/2022]
Abstract
The interaction mechanism of triazolyl substituted tetrahydrobenzofuran derivatives (compound 1 (N, N-Dipropyl-1-(2-phenyl-4,5,6,7-tetrahydrobenzofuran-4-yl)-1H-1,2,3-triazole-4-methanamine) and 2 (1-(2-Phenyl-4,5,6,7-tetrahydrobenzofuran-4-yl)-4-(morpholin-4-ylmethyl)-1H-1,2,3-triazole)) with H(+),K(+)-ATPase at different pH were studied by induced-fit docking, QM/MM optimization and MM/GBSA binding free energy calculations of two forms (neutral and protonated form) of compounds. The inhibition activity of compound 1 is measured and almost unchanged at different pH, while the activity of compound 2 increases significantly with pH value decreased. This phenomenon could be explained by their protonated form percentages and the calculated binding free energies of protonated and neutral mixture of compounds at different pH. The binding free energy of protonated form is higher than that of neutral form of compound, and the protonated form could be a powerful inhibitor of H(+),K(+)-ATPase. By the decomposed energy comparisons of residues in binding sites, Asp137 should be the key binding site to protonated form of compound because of the hydrogen bond and electrostatic interactions. These calculation results could help for further rational design of novel H(+),K(+)-ATPase inhibitors.
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Affiliation(s)
- Hua-Jun Luo
- Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical Science, China Three Gorges University, Yichang, China.
| | - Jun-Zhi Wang
- Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical Science, China Three Gorges University, Yichang, China
| | - Nian-Yu Huang
- Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical Science, China Three Gorges University, Yichang, China
| | - Wei-Qiao Deng
- Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical Science, China Three Gorges University, Yichang, China.,State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China
| | - Kun Zou
- Hubei Key Laboratory of Natural Products Research and Development, College of Biological and Pharmaceutical Science, China Three Gorges University, Yichang, China
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9
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Luo HJ, Deng WQ, Zou K. Protonated form: the potent form of potassium-competitive acid blockers. PLoS One 2014; 9:e97688. [PMID: 24845980 PMCID: PMC4028304 DOI: 10.1371/journal.pone.0097688] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Accepted: 04/23/2014] [Indexed: 11/18/2022] Open
Abstract
Potassium-competitive acid blockers (P-CABs) are highly safe and active drugs targeting H+,K+-ATPase to cure acid-related gastric diseases. In this study, we for the first time investigate the interaction mechanism between the protonated form of P-CABs and human H+,K+-ATPase using homology modeling, molecular docking, molecular dynamics and binding free energy calculation methods. The results explain why P-CABs have higher activities with higher pKa values or at lower pH. With positive charge, the protonated forms of P-CABs have more competitive advantage to block potassium ion into luminal channel and to bind with H+,K+-ATPase via electrostatic interactions. The binding affinity of the protonated form is more favorable than that of the neutral P-CABs. In particular, Asp139 should be a very important binding site for the protonated form of P-CABs through hydrogen bonds and electrostatic interactions. These findings could promote the rational design of novel P-CABs.
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Affiliation(s)
- Hua-Jun Luo
- Hubei Key Laboratory of Natural Products Research and Development, College of Chemistry & Life Science, China Three Gorges University, Yichang, Hubei, China
| | - Wei-Qiao Deng
- Hubei Key Laboratory of Natural Products Research and Development, College of Chemistry & Life Science, China Three Gorges University, Yichang, Hubei, China
- Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, China
| | - Kun Zou
- Hubei Key Laboratory of Natural Products Research and Development, College of Chemistry & Life Science, China Three Gorges University, Yichang, Hubei, China
- * E-mail:
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10
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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11
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ATP4A gene regulatory network for fine-tuning of proton pump and ion channels. SYSTEMS AND SYNTHETIC BIOLOGY 2013; 7:23-32. [PMID: 24432139 DOI: 10.1007/s11693-012-9103-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 12/31/2012] [Accepted: 12/31/2012] [Indexed: 12/11/2022]
Abstract
The ATP4A encodes α subunit of H(+), K(+)-ATPase that contains catalytic sites of the enzyme forming pores through cell membrane which allows the ion transport. H(+), K(+)-ATPase is a membrane bound P-type ATPase enzyme which is found on the surface of parietal cells and uses the energy derived from each cycle of ATP hydrolysis that can help in exchanging ions (H(+), K(+) and Cl(-)) across the cell membrane secreting acid into the gastric lumen. The 3-D model of α-subunit of H(+), K(+)-ATPase was generated by homology modeling. It was evaluated and validated on the basis of free energies and amino acid residues. The inhibitor binding amino acid active pockets were identified in the 3-D model by molecular docking. The two drugs Omeprazole and Rabeprazole were found more potent interactions with generated model of α-subunit of H(+), K(+)-ATPase on the basis of their affinity between drug-protein interactions. We have generated ATP4A gene regulatory networks for interactions with other proteins which involved in regulation that can help in fine-tuning of proton pump and ion channels. These findings provide a new dimension for discovery and development of proton pump inhibitors and gene regulation of the ATPase. It can be helpful in better understanding of human physiology and also using synthetic biology strategy for reprogramming of parietal cells for control of gastric ulcers.
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12
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Abe K, Tani K, Fujiyoshi Y. Conformational rearrangement of gastric H(+),K(+)-ATPase induced by an acid suppressant. Nat Commun 2011; 2:155. [PMID: 21224846 PMCID: PMC3105306 DOI: 10.1038/ncomms1154] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Accepted: 12/01/2010] [Indexed: 12/12/2022] Open
Abstract
Acid-related gastric diseases are associated with disorder of digestive tract acidification. The gastric proton pump, H(+),K(+)-ATPase, exports H(+) in exchange for luminal K(+) to generate a highly acidic environment in the stomach, and is a main target for acid suppressants. Here, we report the three-dimensional structure of gastric H(+),K(+)-ATPase with bound SCH28080, a representative K(+)-competitive acid blocker, at 7 Å resolution based on electron crystallography of two-dimensional crystals. The density of the bound SCH28080 is found near transmembrane (TM) helices 4, 5 and 6, in the luminal cavity. The SCH28080-binding site is formed by the rearrangement of TM helices, which is in turn transmitted to the cytoplasmic domains, resulting in a luminal-open conformation. These results represent the first structural evidence for a binding site of an acid suppressant on H(+),K(+)-ATPase, and the conformational change induced by this class of drugs.
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Affiliation(s)
- Kazuhiro Abe
- Department of Biophysics, Faculty of Science, Kyoto University, Oiwake, Kitashirakawa, Sakyo-ku, Kyoto 606-0852, Japan
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13
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Dürr KL, Seuffert I, Friedrich T. Deceleration of the E1P-E2P transition and ion transport by mutation of potentially salt bridge-forming residues Lys-791 and Glu-820 in gastric H+/K+-ATPase. J Biol Chem 2010; 285:39366-79. [PMID: 20921224 DOI: 10.1074/jbc.m110.133470] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A lysine residue within the highly conserved center of the fifth transmembrane segment in P(IIC)-type ATPase α-subunits is uniquely found in H,K-ATPases instead of a serine in all Na,K-ATPase isoforms. Because previous studies suggested a prominent role of this residue in determining the electrogenicity of non-gastric H,K-ATPase and in pK(a) modulation of the proton-translocating residues in the gastric H,K-ATPases as well, we investigated its functional significance for ion transport by expressing several Lys-791 variants of the gastric H,K-ATPase in Xenopus oocytes. Although the mutant proteins were all detected at the cell surface, none of the investigated mutants displayed any measurable K(+)-induced stationary currents. In Rb(+) uptake measurements, replacement of Lys-791 by Arg, Ala, Ser, and Glu substantially impaired transport activity and reduced the sensitivity toward the E(2)-specific inhibitor SCH28080. Furthermore, voltage clamp fluorometry using a reporter site in the TM5/TM6 loop for labeling with tetra-methylrhodamine-6-maleimide revealed markedly changed fluorescence signals. All four investigated mutants exhibited a strong shift toward the E(1)P state, in agreement with their reduced SCH28080 sensitivity, and an about 5-10-fold decreased forward rate constant of the E(1)P ↔ E(2)P conformational transition, thus explaining the E(1)P shift and the reduced Rb(+) transport activity. When Glu-820 in TM6 adjacent to Lys-791 was replaced by non-charged or positively charged amino acids, severe effects on fluorescence signals and Rb(+) transport were also observed, whereas substitution by aspartate was less disturbing. These results suggest that formation of an E(2)P-stabilizing interhelical salt bridge is essential to prevent futile proton exchange cycles of H(+) pumping P-type ATPases.
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Affiliation(s)
- Katharina L Dürr
- Technical University of Berlin, Institute of Chemistry, Secr. PC 14, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
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14
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Bamford M. 3 H+/K+ ATPase Inhibitors in the Treatment of Acid-Related Disorders. PROGRESS IN MEDICINAL CHEMISTRY 2009; 47:75-162. [DOI: 10.1016/s0079-6468(08)00203-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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15
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Shin JM, Munson K, Vagin O, Sachs G. The gastric HK-ATPase: structure, function, and inhibition. Pflugers Arch 2008; 457:609-22. [PMID: 18536934 DOI: 10.1007/s00424-008-0495-4] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Revised: 03/07/2008] [Accepted: 03/11/2008] [Indexed: 02/06/2023]
Abstract
The gastric H,K-ATPase, a member of the P(2)-type ATPase family, is the integral membrane protein responsible for gastric acid secretion. It is an alpha,beta-heterodimeric enzyme that exchanges cytoplasmic hydronium with extracellular potassium. The catalytic alpha subunit has ten transmembrane segments with a cluster of intramembranal carboxylic amino acids located in the middle of the transmembrane segments TM4, TM5,TM6, and TM8. Comparison to the known structure of the SERCA pump, mutagenesis, and molecular modeling has identified these as constituents of the ion binding domain. The beta subunit has one transmembrane segment with N terminus in cytoplasmic region. The extracellular domain of the beta subunit contains six or seven N-linked glycosylation sites. N-glycosylation is important for the enzyme assembly, maturation, and sorting. The enzyme pumps acid by a series of conformational changes from an E(1) (ion site in) to an E(2) (ion site out) configuration following binding of MgATP and phosphorylation. Several experimental observations support the hypothesis that expulsion of the proton at 160 mM (pH 0.8) results from movement of lysine 791 into the ion binding site in the E(2)P configuration. Potassium access from the lumen depends on activation of a K and Cl conductance via a KCNQ1/KCNE2 complex and Clic6. K movement through the luminal channel in E(2)P is proposed to displace the lysine along with dephosphorylation to return the enzyme to the E(1) configuration. This enzyme is inhibited by the unique proton pump inhibitor class of drug, allowing therapy of acid-related diseases.
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Affiliation(s)
- Jai Moo Shin
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles and VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA
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16
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Herrmann M, Selige J, Raffael S, Sachs G, Brambilla A, Klein T. Systematic expression profiling of the gastric H+/K+ ATPase in human tissue. Scand J Gastroenterol 2007; 42:1275-88. [PMID: 17852870 DOI: 10.1080/00365520701405579] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
OBJECTIVE The potassium-competitive acid blockers (P-CABs), comprise a new, innovative group of competitive and reversible inhibitors of the gastric H+/K+ ATPase. Our aim was to identify sites of expression of the H+/K+ ATPase that are potential targets of these compounds by examining the expression profile of the gastric H+/K+ ATPase in the human body from a broad range of tissues. MATERIAL AND METHODS Expression profiling was done by quantitative mRNA analysis (TaqMan PCR). Tissues that were mRNA-positive for the alpha subunit were investigated further by Western blot and immunohistochemistry (IHC) for the presence of gastric H+/K+ ATPase protein. RESULTS In addition to the very high expression levels in the stomach, the adrenal gland, cerebellum and pancreas gave unexpectedly positive mRNA signals for the alpha subunit of gastric H +/K+ ATPase. However, they were negative for mRNA of the beta subunit, and Western blot and IHC were negative for alpha and beta subunit protein. Another group of tissues with low alpha subunit mRNA expression including the frontal cortex, cortex grey matter, testis, thymus and larynx submucosa were also found negative for both alpha and beta subunit protein. In contrast to mouse kidney, no gastric H+/K+ ATPase could be detected in human kidney. CONCLUSIONS We therefore conclude that the only organ in humans expressing significant levels of the P-CAB target gastric H+/K+ ATPase is the stomach.
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Affiliation(s)
- Michael Herrmann
- Department of Biochemistry Gastroenterology, ALTANA Pharma AG, Konstanz, Germany
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17
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Munson K, Law RJ, Sachs G. Analysis of the gastric H,K ATPase for ion pathways and inhibitor binding sites. Biochemistry 2007; 46:5398-417. [PMID: 17425287 PMCID: PMC2837483 DOI: 10.1021/bi062305h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
New models of the gastric H,K ATPase in the E1K and E2P states are presented as the first structures of a K+ counter-transport P2-type ATPase exhibiting ion entry and exit paths. Homology modeling was first used to generate a starting conformation from the srCa ATPase E2P form (PDB code 1wpg) that contains bound MgADP. Energy minimization of the model showed a conserved adenosine site but nonconserved polyphosphate contacts compared to the srCa ATPase. Molecular dynamics was then employed to expand the luminal entry sufficiently to allow access of the rigid K+ competitive naphthyridine inhibitor, Byk99, to its binding site within the membrane domain. The new E2P model had increased separation between transmembrane segments M3 through M8, and addition of water in this space showed not only an inhibitor entry path to the luminal vestibule but also a channel leading to the ion binding site. Addition of K+ to the hydrated channel with molecular dynamics modeling of ion movement identified a pathway for K+ from the lumen to the ion binding site to give E2K. A K+ exit path to the cytoplasm operating during the normal catalytic cycle is also proposed on the basis of an E1K homology model derived from the E12Ca2+ form of the srCa ATPase (PDB code 1su4). Autodock analyses of the new E2P model now correctly discriminate between high- and low-affinity K+ competitive inhibitors. Finally, the expanded luminal vestibule of the E2P model explains high-affinity ouabain binding in a mutant of the H,K ATPase [Qiu et al. (2005) J. Biol. Chem. 280, 32349-32355].
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Affiliation(s)
- Keith Munson
- Laboratory of Membrane Biology, David Geffen School of Medicine at UCLA, and VA GLAHS, Los Angeles, California 90073, USA.
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18
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Gedda K, Briving C, Svensson K, Maxvall I, Andersson K. Mechanism of action of AZD0865, a K+-competitive inhibitor of gastric H+,K+-ATPase. Biochem Pharmacol 2007; 73:198-205. [PMID: 17081503 DOI: 10.1016/j.bcp.2006.09.020] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2006] [Revised: 09/20/2006] [Accepted: 09/20/2006] [Indexed: 01/28/2023]
Abstract
AZD0865 is a member of a drug class that inhibits gastric H(+),K(+)-ATPase by K(+)-competitive binding. The objective of these experiments was to characterize the mechanism of action, selectivity and inhibitory potency of AZD0865 in vitro. In porcine ion-leaky vesicles at pH 7.4, AZD0865 concentration-dependently inhibited K(+)-stimulated H(+),K(+)-ATPase activity (IC(50) 1.0+/-0.2 microM) but was more potent at pH 6.4 (IC(50) 0.13+/-0.01 microM). The IC(50) values for a permanent cation analogue, AR-H070091, were 11+/-1.2 microM at pH 7.4 and 16+/-1.8 microM at pH 6.4. These results suggest that the protonated form of AZD0865 inhibits H(+),K(+)-ATPase. In ion-tight vesicles, AZD0865 inhibited H(+),K(+)-ATPase more potently (IC(50) 6.9+/-0.4 nM) than in ion-leaky vesicles, suggesting a luminal site of action. AZD0865 inhibited acid formation in histamine- or dibutyryl-cAMP-stimulated rabbit gastric glands (IC(50) 0.28+/-0.01 and 0.26+/-0.003 microM, respectively). In ion-leaky vesicles at pH 7.4, AZD0865 (3 microM) immediately inhibited H(+),K(+)-ATPase activity by 88+/-1%. Immediately after a 10-fold dilution H(+),K(+)-ATPase inhibition was 41%, indicating reversible binding of AZD0865 to gastric H(+),K(+)-ATPase. In contrast to omeprazole, AZD0865 inhibited H(+),K(+)-ATPase activity in a K(+)-competitive manner (K(i) 46+/-3 nM). AZD0865 inhibited the process of cation occlusion concentration-dependently (IC(50) 1.7+/-0.06 microM). At 100 microM, AZD0865 reduced porcine renal Na(+),K(+)-ATPase activity by 9+/-2%, demonstrating a high selectivity for H(+),K(+)-ATPase. Thus, AZD0865 potently, K(+)-competitively, and selectively inhibits gastric H(+),K(+)-ATPase activity and acid formation in vitro, with a fast onset of effect.
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19
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Parsons ME, Keeling DJ. Novel approaches to the pharmacological blockade of gastric acid secretion. Expert Opin Investig Drugs 2006; 14:411-21. [PMID: 15882117 DOI: 10.1517/13543784.14.4.411] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Research into new methods of controlling acid secretion is driven by existing medical needs in gastro-oesophageal reflux disease treatment. Histamine receptor subtype 3 agonists offer one approach for acid inhibition but no agent is yet undergoing clinical testing. Other, as yet unrealized strategies include preventing the fusion of the tubulovesicular elements that contain H+/K+-ATPase with the parietal cell membrane, or blocking channels that recycle K+ in the parietal cell. Of more promise are gastrin (cholecystokinin) receptor antagonists and potassium-competitive acid blockers; examples of both are in clinical development. It is probable that gastrin receptor antagonists would be used adjunctively with proton pump inhibitors, possibly for meal-induced reflux. The potassium-competitive acid blockers have attributes that may facilitate use as monotherapy for the treatment of gastro-oesophageal reflux disease. The early promise of gastrin receptor antagonists and potassium-competitive acid blockers remains to be defined in large-scale trials.
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Affiliation(s)
- Michael E Parsons
- Department of Biosciences, University of Hertfordshire, Hatfield, Hertfordshire AL10 9AB, UK.
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20
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Swarts HGP, Koenderink JB, Willems PHGM, De Pont JJHHM. The human non-gastric H,K-ATPase has a different cation specificity than the rat enzyme. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1768:580-9. [PMID: 17137554 DOI: 10.1016/j.bbamem.2006.10.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 10/02/2006] [Accepted: 10/19/2006] [Indexed: 11/24/2022]
Abstract
The primary sequence of non-gastric H,K-ATPase differs much more between species than that of Na,K-ATPase or gastric H,K-ATPase. To investigate whether this causes species-dependent differences in enzymatic properties, we co-expressed the catalytic subunit of human non-gastric H,K-ATPase in Sf9 cells with the beta(1) subunit of rat Na,K-ATPase and compared its properties with those of the rat enzyme (Swarts et al., J. Biol. Chem. 280, 33115-33122, 2005). Maximal ATPase activity was obtained with NH(4)(+) as activating cation. The enzyme was also stimulated by Na(+), but in contrast to the rat enzyme, hardly by K(+). SCH 28080 inhibited the NH(4)(+)-stimulated activity of the human enzyme much more potently than that of the rat enzyme. The steady-state phosphorylation level of the human enzyme decreased with increasing pH, [K(+)], and [Na(+)] and nearly doubled in the presence of oligomycin. Oligomycin increased the sensitivity of the phosphorylated intermediate to ADP, demonstrating that it inhibited the conversion of E(1)P to E(2)P. All three cations stimulated the dephosphorylation rate dose-dependently. Our studies support a role of the human enzyme in H(+)/Na(+) and/or H(+)/NH(4)(+) transport but not in Na(+)/K(+) transport.
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Affiliation(s)
- Herman G P Swarts
- Department of Biochemistry, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
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21
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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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22
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Abstract
Gastric acid secretion is a complex process that requires hormonal, neuronal, or calcium-sensing receptor activation for insertion of pumps into the apical surface of the parietal cell. Activation of any or all these pathways causes the parietal cell to secrete concentrated acid with a pH at or close to 1. This acidic fluid combines with enzymes that are secreted from neighbouring chief cells and passes out of the gland up through a mucous gel layer covering the surface of the stomach producing a final intragastric pH of less than 4 during the active phase of acid secretion. Defects in either the mucosal barrier or in the regulatory mechanisms that modulate the secretory pathways will result in erosion of the barrier and ulcerations of the stomach or esophagus. The entire process of acid secretion relies on activation of the catalytic cycle of the gastric H+,K+-ATPase, resulting in the secretion of acid into the parietal cell canaliculus, with K+ being the important and rate-limiting ion in this activation process. In addition to K+ as a rate limiter for acid production, Cl- secretion via an apical channel must also occur. In this review we present a discussion of the mechanics of acid secretion and a discussion of recently identified transporter proteins and receptors. Included is a discussion of some of the recent candidates for the apical K' recycling channel, as well as two recently identified apical proteins (NHE-3, PAT-1), and the newly characterized calcium-sensing receptor (CaSR). We hope that this review will give additional insight into the complex process of acid secretion.
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Affiliation(s)
- J P Geibel
- Yale University School of Medicine, Department of Surgery, BML 265, New Haven, 06520 CT, USA.
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23
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Kim CG, Watts JA, Watts A. Ligand Docking in the Gastric H+/K+-ATPase: Homology Modeling of Reversible Inhibitor Binding Sites. J Med Chem 2005; 48:7145-52. [PMID: 16279772 DOI: 10.1021/jm050326o] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Using the recent high-resolution X-ray structures determined for the Ca2+-ATPase, we have generated two homology models of the gastric H+/K+-ATPase reflecting the E1 and E2 conformations adopted by P-type ATPases in their catalytic cycle. In regimes where the in situ solid-state NMR-determined structure for 1,2,3-trimethyl-8-(pentafluorophenylmethoxy)imidazo[1,2-a]pyridinium iodide (TMPFPIP), a reversible inhibitor of the gastric H+/K+-ATPase, was retained in its predefined conformation and was allowed full torsional flexibility in docking, the ligands localized to discrete binding volumes in the E1 model and to a single central binding space, together with secondary peripheral locations, in the E2 conformation. The results of these binding studies are in good agreement with current site-directed mutagenesis data and support the suggestion that the binding site is proximal to the loop between TM5 and TM6 and TM8, the transmembrane (TM) region considered important for cation translocation. Furthermore, the results of the simulation with the flexible ligand complement the solid-state NMR structural constraints of this inhibitor when bound in situ to the protein.
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Affiliation(s)
- Chang G Kim
- Biomembrane Structure Unit, Department of Biochemistry, Oxford University, South Parks Road, Oxford OX1 3QU, UK
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24
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Abstract
Potassium (K+) ions are critical for the activation and catalytic cycle of the gastric H+,K+-ATPase, resulting in the secretion of hydrochloric acid into the parietal cell canaliculus. As both symptom, severity and esophageal mucosal damage in gastro-esophageal reflux disease (GERD) are related to the degree of acid exposure, K+ is a logical target for approaches to inhibit acid production. The probable K+ binding site on the gastric H+,K+-ATPase has recently been described and studies are elucidating how K+ activates the enzyme. K+ channels in the apical membrane of the parietal cell are implicated in the recycling of K+ and, to date, three potential K+ channels (KCNQ1, Kir2.1 and Kir4.1) have been identified. The channels represent theoretical sites for agents to control acid secretion but it will be difficult to develop selective blockers. An alternative strategy is to prevent K+ from activating gastric H+,K+-ATPase; the potassium-competitive acid blocker (P-CAB) class inhibits acid secretion by binding at or near the K+ binding site. Ongoing research is further defining the role of K+ in the functioning of the gastric H+,K+-ATPase, as well as determining the clinical utility of agents directed toward this important cation.
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Affiliation(s)
- John-P Geibel
- Department of Surgery, Yale University School of Medicine, BML 265, New Haven, CT 06520, USA.
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25
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Andersson K, Carlsson E. Potassium-competitive acid blockade: a new therapeutic strategy in acid-related diseases. Pharmacol Ther 2005; 108:294-307. [PMID: 16000224 DOI: 10.1016/j.pharmthera.2005.05.005] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Accepted: 05/04/2005] [Indexed: 02/06/2023]
Abstract
Current therapies to treat gastroesophageal reflux disease (GERD), peptic ulcer disease (PUD), and other acid-related diseases either prevent stimulation of the parietal cell (H2 receptor antagonists, H2RAs) or inhibit gastric H+,K+-ATPase (e.g., proton pump inhibitors, PPIs). Of the 2 approaches, the inhibition of the final step in acid production by PPIs provides more effective relief of symptoms and healing. Despite the documented efficacy of the PPIs, therapeutic doses have a gradual onset of effect and do not provide complete symptom relief in all patients. There is scope for further improvements in acid suppressive therapy to maximize healing and offer more complete symptom relief. It is unlikely that cholecystokinin2 (CCK2, gastrin) receptor antagonists, a class in clinical trials, will be superior to H2RAs or PPIs. However, a new class of acid suppressant, the potassium-competitive acid blockers (P-CABs), is undergoing clinical trials in GERD and other acid-related diseases. These drugs block gastric H+,K+-ATPase by reversible and K+-competitive ionic binding. After oral doses, P-CABs rapidly achieve high plasma concentrations and have linear, dose-dependent pharmacokinetics. The pharmacodynamic properties reflect the pharmacokinetics of this group (i.e., the effect on acid secretion is correlated with plasma concentrations). These agents dose dependently inhibit gastric acid secretion with a fast onset of action and have similar effects after single and repeated doses (i.e., full effect from the first dose). Animal studies comparing P-CABs with PPIs suggest some important pharmacodynamic differences (e.g., faster and better control of 24-hr intragastric acidity). Studies in humans comparing PPIs with P-CABs will help to define the place of this new class in the management of acid-related diseases.
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26
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Abstract
The fluorescent styryl dye RH421 was used to identify and investigate electrogenic reaction steps of the H,K-ATPase pump cycle. Equilibrium titration experiments were performed with membrane vesicles isolated from hog gastric mucosa, and cytoplasmic and luminal binding of K(+) and H(+) ions was studied. It was found that the binding and release steps of both ion species in both principal conformations of the ion pump, E(1) and P-E(2), are electrogenic, whereas the conformation transitions do not contribute significantly to a charge movement within the membrane dielectric. This behavior is in agreement with the transport mechanism found for the Na,K-ATPase and the sarcoplasmic reticulum Ca-ATPase. The data were analyzed on the basis of the Post-Albers reaction cycle. For proton binding, two pK values were found in both conformations: 6.7 and </=4.5 in the E(1) conformation; 6.7 and </=2 in the P-E(2) conformation. The equilibrium dissociation constants for K(+) binding on the cytoplasmic side were 11 and 16 mM. The respective equilibrium dissociation constants on the luminal side were obtained via K(+) concentration dependence of the enzyme activity and determined to be 0.11 mM for both luminal binding sites.
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Affiliation(s)
- Anna Diller
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
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27
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Koenderink JB, Swarts HGP, Willems PHGM, Krieger E, De Pont JJHHM. A conformation-specific interhelical salt bridge in the K+ binding site of gastric H,K-ATPase. J Biol Chem 2004; 279:16417-24. [PMID: 14761952 DOI: 10.1074/jbc.m400020200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Homology modeling of gastric H,K-ATPase based on the E2 model of sarcoplasmic reticulum Ca2+-ATPase (Toyoshima, C., and Nomura, H. (2002) Nature 392, 835-839) revealed the presence of a single high-affinity binding site for K+ and an E2 form-specific salt bridge between Glu820 (M6) and Lys791 (M5). In the E820Q mutant this salt bridge is no longer possible, and the head group of Lys791, together with a water molecule, fills the position of the K+ ion and apparently mimics the K+-filled cation binding pocket. This gives an explanation for the K+-independent ATPase activity and dephosphorylation step of the E820Q mutant (Swarts, H. G. P., Hermsen, H. P. H., Koenderink, J. B., Schuurmans Stekhoven, F. M. A. H., and De Pont, J. J. H. H. M. (1998) EMBO J. 17, 3029-3035) and, indirectly, for its E1 preference. The model is strongly supported by a series of reported mutagenesis studies on charged and polar amino acid residues in the membrane domain. To further test this model, Lys791 was mutated alone and in combination with other crucial residues. In the K791A mutant, the K+ affinity was markedly reduced without altering the E2 preference of the enzyme. The K791A mutation prevented, in contrast to the K791R mutation, the spontaneous dephosphorylation of the E820Q mutant as well as its conformational equilibrium change toward E1. This indicates that the salt bridge is essential for high-affinity K+ binding and the E2 preference of H,K-ATPase. Moreover, its breakage (E820Q) can generate a K+-insensitive activity and an E1 preference. In addition, the study gives a molecular explanation for the electroneutrality of H,K-ATPases.
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Affiliation(s)
- Jan B Koenderink
- Department of Biochemistry, Nijmegen Center for Molecular Life Sciences, University of Nijmegen, Nijmegen, The Netherlands
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28
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Asano S, Morii M, Takeguchi N. Molecular and Cellular Regulation of the Gastric Proton Pump. Biol Pharm Bull 2004; 27:1-12. [PMID: 14743830 DOI: 10.1248/bpb.27.1] [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: 11/22/2022]
Abstract
The gastric H+, K+-ATPase is a proton pump that is responsible for gastric acid secretion and that actively transports protons and K+ ions in opposite directions to generate in excess of a million-fold gradient across the membrane under physiological conditions. This pump is also a target molecule of proton pump inhibitors which are used for the clinical treatment of hyperacidity. In this review, we wish to summarize the molecular regulation of this pump based on mutational studies, particularly those used for the identification of binding sites for cations and specific inhibitors. Recent reports by Toyoshima et al (2000, 2002) presented precise three-dimensional (3-D) structures of the sarcoplasmic reticulum (SR) Ca2+-ATPase, which belongs to the same family as the gastric H+, K+-ATPase. We have studied the structure-function relationships for the gastric H+, K+-ATPase using 3-D structures constructed by homology modeling of the related SR Ca2+-ATPase, which was used as a template molecule. We also discuss in this review, the regulation of cell surface expression and synthesis control of the gastric proton pump.
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Affiliation(s)
- Shinji Asano
- Life Scientific Research Center, Toyama Medican and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
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29
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Asano S, Yoshida A, Yashiro H, Kobayashi Y, Morisato A, Ogawa H, Takeguchi N, Morii M. The cavity structure for docking the K(+)-competitive inhibitors in the gastric proton pump. J Biol Chem 2003; 279:13968-75. [PMID: 14699149 DOI: 10.1074/jbc.m308934200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
2-Methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine-3-acetonitrile (SCH 28080) is a reversible inhibitor specific for the gastric proton pump. The inhibition pattern is competitive with K(+). Here we studied the binding sites of this inhibitor on the putative three-dimensional structure of the gastric proton pump alpha-subunit that was constructed by homology modeling based on the structure of sarcoplasmic reticulum Ca(2+) pump. Alanine and serine mutants of Tyr(801) located in the fifth transmembrane segment of the gastric proton pump alpha-subunit retained the (86)Rb transport and K(+)-dependent ATPase (K(+)-ATPase) activities. These mutants showed 60-80-times lower sensitivity to SCH 28080 than the wild type in the (86)Rb transport activity. The K(+)-ATPase activities of these mutants were not completely inhibited by SCH 28080. The sensitivity to SCH 28080 was dependent on the bulkiness of the side chain at this position. Therefore, the side chain of Tyr(801) is important for the interaction with this inhibitor. In the three-dimensional structure of the E(2) form (conformation with high affinity for K(+)) of the gastric proton pump, Tyr(801) faces a cavity surrounded by the first, fourth, fifth, sixth, and eighth transmembrane segments and fifth/sixth, seventh/eighth, and ninth/tenth loops. SCH 28080 can dock in this cavity. However, SCH 28080 cannot dock in the same location in the E(1) form (conformation with high affinity for proton) of the gastric proton pump due to the drastic rearrangement of the transmembrane helices between the E(1) and E(2) forms. These results support the idea that this cavity is the binding pocket of SCH 28080.
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Affiliation(s)
- Shinji Asano
- Life Scientific Research Center, Faculty of Pharmaceutical Sciences, Toyama Medical & Pharmaceutical University, Toyama, Japan.
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30
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Burnay M, Crambert G, Kharoubi-Hess S, Geering K, Horisberger JD. Electrogenicity of Na,K- and H,K-ATPase activity and presence of a positively charged amino acid in the fifth transmembrane segment. J Biol Chem 2003; 278:19237-44. [PMID: 12637496 DOI: 10.1074/jbc.m300946200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transport activity of the Na,K-ATPase (a 3 Na+ for 2 K+ ion exchange) is electrogenic, whereas the closely related gastric and non-gastric H,K-ATPases perform electroneutral cation exchange. We have studied the role of a highly conserved serine residue in the fifth transmembrane segment of the Na,K-ATPase, which is replaced with a lysine in all known H,K-ATPases. Ouabain-sensitive 86Rb uptake and K+-activated currents were measured in Xenopus oocytes expressing the Bufo bladder H,K-ATPase or the Bufo Na,K-ATPase in which these residues, Lys800 and Ser782, respectively, were mutated. Mutants K800A and K800E of the H,K-ATPase showed K+-stimulated and ouabain-sensitive electrogenic transport. In contrast, when the positive charge was conserved (K800R), no K+-induced outward current could be measured, even though rubidium transport activity was present. Conversely, the S782R mutant of the Na,K-ATPase had non-electrogenic transport activity, whereas the S782A mutant was electrogenic. The K800S mutant of the H,K-ATPase had a more complex behavior, with electrogenic transport only in the absence of extracellular Na+. Thus, a single positively charged residue in the fifth transmembrane segment of the alpha-subunit can determine the electrogenicity and therefore the stoichiometry of cation transport by these ATPases.
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Affiliation(s)
- Muriel Burnay
- Institute of Pharmacology and Toxicology, University of Lausanne, CH-1005 Lausanne, Switzerland
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31
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De Pont JJHHM, Swarts HGP, Willems PHGM, Koenderink JB. The E1/E2-preference of gastric H,K-ATPase mutants. Ann N Y Acad Sci 2003; 986:175-82. [PMID: 12763793 DOI: 10.1111/j.1749-6632.2003.tb07157.x] [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: 01/13/2023]
Abstract
Gastric H,K-ATPase has, in the absence of ATP and added ions, a preference for the E(2) conformation. Mutations in the cation-binding pocket often result in a preference for the E(1)-conformation. This can be paralleled by the occurrence of K(+)-independent ATPase activity. These two phenomena could be separated by combined mutagenesis of several residues in and around the cation-binding pocket. Models of the three-dimensional structure of H,K-ATPase visualize the relationship between the E(1)/E(2) preference and the structure.
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Affiliation(s)
- Jan Joep H H M De Pont
- Department of Biochemistry, Nijmegen Center for Molecular Life Sciences, University of Nijmegen, the Netherlands.
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32
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Munson K, Vagin O, Sachs G, Karlish S. Molecular modeling of SCH28080 binding to the gastric H,K-ATPase and MgATP interactions with SERCA- and Na,K-ATPases. Ann N Y Acad Sci 2003; 986:106-10. [PMID: 12763782 DOI: 10.1111/j.1749-6632.2003.tb07146.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have used homology molecular modeling based on the srCaATPase E(2) conformation, pdb1kju, to predict side chains involved in docking the K(+) competitive inhibitor, SCH28080, to the H,K-ATPase. A model for SCH28080 binding between residues L809 and A335 in the same space utilized by omeprazole is proposed. We also describe modeling MgATP binding to the E(1) structure of the srATPase, pdb1eul, as a paradigm for the Na,K- and H,K-ATPases. The resulting model, E(1).MgATP, visualizes a conformation not yet available by crystallization and successfully predicts a range of published results, including backbone cleavages near V440 (N domain) and V712 (P domain) mediated by FeATP in the Na,K-ATPase. A separate model for MgATP docked to E(2) (pdb1kju) shows that access of the gamma phosphate to D351 is blocked by the A domain. The E(2). MgATP model explains FeATP-mediated cleavages of the Na,K-ATPase near V440 and E214 (A domain) and homologous results in the H,K-ATPase.
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33
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Sachs G, Shin JM, Vagin O, Munson K, Weeks D, Scott DR, Voland P. Current trends in the treatment of upper gastrointestinal disease. Best Pract Res Clin Gastroenterol 2002; 16:835-49. [PMID: 12473294 DOI: 10.1053/bega.2002.0338] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The past 25 years have seen an amazing improvement in the treatment and understanding of acid-related disorders. In particular, the introduction of selective histamine receptor antagonists and proton pump inhibitors has made the medical control of acid secretion an effective means of therapy. The demonstration that infection with Helicobacter pylori is responsible for most cases of peptic ulcer disease resulted in another major improvement in therapy in these areas as a result of the eradication of the organism. Research continues in an attempt to find improved means of acid control and better methods for the eradication of H. pylori based on unique proteins expressed by the organism to resist gastric acidity.
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Affiliation(s)
- George Sachs
- Geffen School of Medicine at UCLA and GWLA Health Center, Los Angeles, USA
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34
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Abstract
BACKGROUND & AIMS Proton pump inhibitors (PPIs) are covalent inhibitors of the gastric H+,K+-adenosine triphosphatase (ATPase) forming disulfide bonds. Recovery of acid secretion after PPI inhibition may be due to de novo synthesis of pump protein and/or disulfide reduction and reactivation of inhibited pump. The half-time of recovery of acid secretion in rats following omeprazole treatment is approximately 15 hours, whereas pump protein half-life is 54 hours. In humans, the half-life of the inhibitory effect on acid secretion is approximately 28 hours for omeprazole and approximately 46 hours for pantoprazole. Whereas all PPIs bind to cysteine 813, pantoprazole additionally binds to cysteine 822, deeper in the membrane domain of TM6. Their different durations of action may reflect different rates of pump reactivation due to differing accessibility of the disulfides to glutathione. METHODS Rats were stimulated and treated with 30 mg/kg of each PPI. Gastric ATPase was prepared and reversal of inhibition of the H+,K+-ATPase was measured as the time-dependent restoration of activity by incubation with dithiothreitol or glutathione. RESULTS One hundred percent reactivation of ATPase following inhibition in vivo by omeprazole or its enantiomers was seen with dithiothreitol and 89% with glutathione. Similar data were found for lansoprazole or rabeprazole. No reactivation by either reducing agent was seen following inhibition by pantoprazole. CONCLUSIONS Recovery of acid secretion following inhibition by all PPIs, other than pantoprazole, may depend on both protein turnover and reversal of the inhibitory disulfide bond. In contrast, recovery of acid secretion after pantoprazole may depend entirely on new protein synthesis.
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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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