151
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Czerny DD, Padmanaban S, Anishkin A, Venema K, Riaz Z, Sze H. Protein architecture and core residues in unwound α-helices provide insights to the transport function of plant AtCHX17. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1983-1998. [PMID: 27179641 DOI: 10.1016/j.bbamem.2016.05.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/13/2016] [Accepted: 05/08/2016] [Indexed: 01/27/2023]
Abstract
Using Arabidopsis thaliana AtCHX17 as an example, we combine structural modeling and mutagenesis to provide insights on its protein architecture and transport function which is poorly characterized. This approach is based on the observation that protein structures are significantly more conserved in evolution than linear sequences, and mechanistic similarities among diverse transporters are emerging. Two homology models of AtCHX17 were obtained that show a protein fold similar to known structures of bacterial Na(+)/H(+) antiporters, EcNhaA and TtNapA. The distinct secondary and tertiary structure models highlighted residues at positions potentially important for CHX17 activity. Mutagenesis showed that asparagine-N200 and aspartate-D201 inside transmembrane5 (TM5), and lysine-K355 inside TM10 are critical for AtCHX17 activity. We reveal previously unrecognized threonine-T170 and lysine-K383 as key residues at unwound regions in the middle of TM4 and TM11 α-helices, respectively. Mutation of glutamate-E111 located near the membrane surface inhibited AtCHX17 activity, suggesting a role in pH sensing. The long carboxylic tail of unknown purpose has an alternating β-sheet and α-helix secondary structure that is conserved in prokaryote universal stress proteins. These results support the overall architecture of AtCHX17 and identify D201, N200 and novel residues T170 and K383 at the functional core which likely participates in ion recognition, coordination and/or translocation, similar to characterized cation/H(+) exchangers. The core of AtCHX17 models according to EcNhaA and TtNapA templates faces inward and outward, respectively, which may reflect two conformational states of the alternating access transport mode for proteins belonging to the plant CHX family.
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Affiliation(s)
- Daniel D Czerny
- Department of Cell Biology and Molecular Genetics (DC, SP, ZR, HS), University of Maryland, College Park, MD 20742, USA
| | - Senthilkumar Padmanaban
- Department of Cell Biology and Molecular Genetics (DC, SP, ZR, HS), University of Maryland, College Park, MD 20742, USA
| | - Andriy Anishkin
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | - Kees Venema
- Dpto de Bioquímica, Biología Celular y Molecular de Plantas, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, c/. Profesor Albareda 1, 18008Granada, Spain
| | - Zoya Riaz
- Department of Cell Biology and Molecular Genetics (DC, SP, ZR, HS), University of Maryland, College Park, MD 20742, USA
| | - Heven Sze
- Department of Cell Biology and Molecular Genetics (DC, SP, ZR, HS), University of Maryland, College Park, MD 20742, USA; Maryland Agricultural Experiment Station, Department of Plant Science and Landscape Architecture (HS), University of Maryland, College Park, MD 20742, USA.
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152
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Boudour-Boucheker N, Boulo V, Charmantier-Daures M, Anger K, Charmantier G, Lorin-Nebel C. Osmoregulation in larvae and juveniles of two recently separated Macrobrachium species: Expression patterns of ion transporter genes. Comp Biochem Physiol A Mol Integr Physiol 2016; 195:39-45. [DOI: 10.1016/j.cbpa.2016.02.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 02/02/2016] [Accepted: 02/07/2016] [Indexed: 11/27/2022]
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153
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Belda E, van Heck RGA, José Lopez-Sanchez M, Cruveiller S, Barbe V, Fraser C, Klenk HP, Petersen J, Morgat A, Nikel PI, Vallenet D, Rouy Z, Sekowska A, Martins dos Santos VAP, de Lorenzo V, Danchin A, Médigue C. The revisited genome ofPseudomonas putidaKT2440 enlightens its value as a robust metabolicchassis. Environ Microbiol 2016; 18:3403-3424. [DOI: 10.1111/1462-2920.13230] [Citation(s) in RCA: 217] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 01/16/2016] [Indexed: 01/08/2023]
Affiliation(s)
- Eugeni Belda
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
- Institut Pasteur, Unit of Insect Vector Genetics and Genomics, Department of Parasitology and Mycology; 28, rue du Dr. Roux, Paris, Cedex 15 75724 France
| | - Ruben G. A. van Heck
- Laboratory of Systems and Synthetic Biology, Wageningen University; Dreijenplein 10, Building number 316 6703 HB Wageningen The Netherlands
| | - Maria José Lopez-Sanchez
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
- AMAbiotics SAS, Institut du Cerveau et de la Moëlle Épinière, Hôpital de la Pitié-Salpêtrière; Paris France
| | - Stéphane Cruveiller
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
| | - Valérie Barbe
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute, National Sequencing Center; 2 rue Gaston Crémieux 91057 Evry France
| | - Claire Fraser
- Institute for Genome Sciences, Department of Microbiology and Immunology, University of Maryland School of Medicine; Baltimore MD USA
| | - Hans-Peter Klenk
- Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures; Braunschweig Germany
- School of Biology, Newcastle University; Newcastle upon Tyne NE1 7RU UK
| | - Jörn Petersen
- Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures; Braunschweig Germany
| | - Anne Morgat
- Swiss-Prot Group, SIB Swiss Institute of Bioinformatics; Geneva CH-1206 Switzerland
| | - Pablo I. Nikel
- Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC); C/Darwin 3 28049 Madrid Spain
| | - David Vallenet
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
| | - Zoé Rouy
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
| | - Agnieszka Sekowska
- AMAbiotics SAS, Institut du Cerveau et de la Moëlle Épinière, Hôpital de la Pitié-Salpêtrière; Paris France
| | - Vitor A. P. Martins dos Santos
- Laboratory of Systems and Synthetic Biology, Wageningen University; Dreijenplein 10, Building number 316 6703 HB Wageningen The Netherlands
| | - Víctor de Lorenzo
- Systems and Synthetic Biology Program, Centro Nacional de Biotecnología (CNB-CSIC); C/Darwin 3 28049 Madrid Spain
| | - Antoine Danchin
- AMAbiotics SAS, Institut du Cerveau et de la Moëlle Épinière, Hôpital de la Pitié-Salpêtrière; Paris France
| | - Claudine Médigue
- Alternative Energies and Atomic Energy Commission (CEA), Genomic Institute & CNRS-UMR8030 & Evry University, Laboratory of Bioinformatics Analysis in Genomics and Metabolism; 2 rue Gaston Crémieux 91057 Evry France
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154
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The Ec-NhaA antiporter switches from antagonistic to synergistic antiport upon a single point mutation. Sci Rep 2016; 6:23339. [PMID: 27021484 PMCID: PMC4810432 DOI: 10.1038/srep23339] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 03/04/2016] [Indexed: 12/14/2022] Open
Abstract
The Na+, Li+/H+ antiporter of Escherichia coli (Ec-NhaA) maintains pH, Na+ homeostasis in enterobacteria. We used isothermal titration calorimetry to perform a detailed thermodynamic analysis of Li+ binding to Ec-NhaA and several of its mutants. We found that, in line with the canonical alternative access mechanistic model of secondary transporters, Li+/H+ binding to the antiporter is antagonistically coupled. Binding of Li+ displaces 2 H+ from the binding site. The process is enthalpically driven, the enthalpic gain just compensating for an entropic loss and the buffer-associated enthalpic changes dominate the overall free-energy change. Li+ binding, H+ release and antiporter activity were all affected to the same extent by mutations in the Li+ binding site (D163E, D163N, D164N, D164E), while D133C changed the H+/Li+ stoichiometry to 4. Most striking, however, was the mutation, A167P, which converted the Ec-NhaA antagonistic binding into synergistic binding which is only known to occur in Cl−/H+ antiporter.
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155
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Expression and characterization of the SOS1 Arabidopsis salt tolerance protein. Mol Cell Biochem 2016; 415:133-43. [DOI: 10.1007/s11010-016-2685-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 03/12/2016] [Indexed: 10/22/2022]
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156
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Wu X, Kim H, Seravalli J, Barycki JJ, Hart PJ, Gohara DW, Di Cera E, Jung WH, Kosman DJ, Lee J. Potassium and the K+/H+ Exchanger Kha1p Promote Binding of Copper to ApoFet3p Multi-copper Ferroxidase. J Biol Chem 2016; 291:9796-806. [PMID: 26966178 DOI: 10.1074/jbc.m115.700500] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Indexed: 01/24/2023] Open
Abstract
Acquisition and distribution of metal ions support a number of biological processes. Here we show that respiratory growth of and iron acquisition by the yeast Saccharomyces cerevisiae relies on potassium (K(+)) compartmentalization to the trans-Golgi network via Kha1p, a K(+)/H(+) exchanger. K(+) in the trans-Golgi network facilitates binding of copper to the Fet3p multi-copper ferroxidase. The effect of K(+) is not dependent on stable binding with Fet3p or alteration of the characteristics of the secretory pathway. The data suggest that K(+) acts as a chemical factor in Fet3p maturation, a role similar to that of cations in folding of nucleic acids. Up-regulation of KHA1 gene in response to iron limitation via iron-specific transcription factors indicates that K(+) compartmentalization is linked to cellular iron homeostasis. Our study reveals a novel functional role of K(+) in the binding of copper to apoFet3p and identifies a K(+)/H(+) exchanger at the secretory pathway as a new molecular factor associated with iron uptake in yeast.
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Affiliation(s)
- Xiaobin Wu
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0664, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, China 200234
| | - Heejeong Kim
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0664
| | - Javier Seravalli
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0664
| | - Joseph J Barycki
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0664
| | - P John Hart
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900
| | - David W Gohara
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104
| | - Enrico Di Cera
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104
| | - Won Hee Jung
- Department of Systems Biotechnology, Chung-Ang University, Anseong, Korea 456-756, and
| | - Daniel J Kosman
- Department of Biochemistry, University at Buffalo, Buffalo, New York 14214-3000
| | - Jaekwon Lee
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0664,
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157
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Zhao H, Carney KE, Falgoust L, Pan JW, Sun D, Zhang Z. Emerging roles of Na⁺/H⁺ exchangers in epilepsy and developmental brain disorders. Prog Neurobiol 2016; 138-140:19-35. [PMID: 26965387 DOI: 10.1016/j.pneurobio.2016.02.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/03/2016] [Accepted: 02/27/2016] [Indexed: 12/15/2022]
Abstract
Epilepsy is a common central nervous system (CNS) disease characterized by recurrent transient neurological events occurring due to abnormally excessive or synchronous neuronal activity in the brain. The CNS is affected by systemic acid-base disorders, and epileptic seizures are sensitive indicators of underlying imbalances in cellular pH regulation. Na(+)/H(+) exchangers (NHEs) are a family of membrane transporter proteins actively involved in regulating intracellular and organellar pH by extruding H(+) in exchange for Na(+) influx. Altering NHE function significantly influences neuronal excitability and plays a role in epilepsy. This review gives an overview of pH regulatory mechanisms in the brain with a special focus on the NHE family and the relationship between epilepsy and dysfunction of NHE isoforms. We first discuss how cells translocate acids and bases across the membrane and establish pH homeostasis as a result of the concerted effort of enzymes and ion transporters. We focus on the specific roles of the NHE family by detailing how the loss of NHE1 in two NHE mutant mice results in enhanced neuronal excitability in these animals. Furthermore, we highlight new findings on the link between mutations of NHE6 and NHE9 and developmental brain disorders including epilepsy, autism, and attention deficit hyperactivity disorder (ADHD). These studies demonstrate the importance of NHE proteins in maintaining H(+) homeostasis and their intricate roles in the regulation of neuronal function. A better understanding of the mechanisms underlying NHE1, 6, and 9 dysfunctions in epilepsy formation may advance the development of new epilepsy treatment strategies.
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Affiliation(s)
- Hanshu Zhao
- Department of Neurology, The First Affiliated Hospital of the Harbin Medical University, Harbin, China.,Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Karen E Carney
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Lindsay Falgoust
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Jullie W Pan
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Dandan Sun
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA.,Veterans Affairs Pittsburgh Health Care System, Geriatric Research, Educational and Clinical Center, Pittsburgh, PA 15213, USA
| | - Zhongling Zhang
- Department of Neurology, The First Affiliated Hospital of the Harbin Medical University, Harbin, China
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158
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Kleist TJ, Luan S. Constant change: dynamic regulation of membrane transport by calcium signalling networks keeps plants in tune with their environment. PLANT, CELL & ENVIRONMENT 2016; 39:467-481. [PMID: 26139029 DOI: 10.1111/pce.12599] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 05/20/2015] [Accepted: 05/21/2015] [Indexed: 06/04/2023]
Abstract
Despite substantial variation and irregularities in their environment, plants must conform to spatiotemporal demands on the molecular composition of their cytosol. Cell membranes are the major interface between organisms and their environment and the basis for controlling the contents and intracellular organization of the cell. Membrane transport proteins (MTPs) govern the flow of molecules across membranes, and their activities are closely monitored and regulated by cell signalling networks. By continuously adjusting MTP activities, plants can mitigate the effects of environmental perturbations, but effective implementation of this strategy is reliant on precise coordination among transport systems that reside in distinct cell types and membranes. Here, we examine the role of calcium signalling in the coordination of membrane transport, with an emphasis on potassium transport. Potassium is an exceptionally abundant and mobile ion in plants, and plant potassium transport has been intensively studied for decades. Classic and recent studies have underscored the importance of calcium in plant environmental responses and membrane transport regulation. In reviewing recent advances in our understanding of the coding and decoding of calcium signals, we highlight established and emerging roles of calcium signalling in coordinating membrane transport among multiple subcellular locations and distinct transport systems in plants, drawing examples from the CBL-CIPK signalling network. By synthesizing classical studies and recent findings, we aim to provide timely insights on the role of calcium signalling networks in the modulation of membrane transport and its importance in plant environmental responses.
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Affiliation(s)
- Thomas J Kleist
- University of California, Berkeley, Department of Plant & Microbial Biology, Berkeley, CA, 94720, USA
| | - Sheng Luan
- University of California, Berkeley, Department of Plant & Microbial Biology, Berkeley, CA, 94720, USA
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159
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Fehsenfeld S, Weihrauch D. Mechanisms of acid–base regulation in seawater-acclimated green crabs (Carcinus maenas). CAN J ZOOL 2016. [DOI: 10.1139/cjz-2015-0132] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study investigated acid–base regulatory mechanisms in seawater-acclimated green crabs (Carcinus maenas (L., 1758)). In full-strength seawater, green crabs are osmoconformers so that the majority of the observed responses were attributed to ion fluxes based on acid–base compensatory responses alone. Similar to observations in brackish-water-acclimated C. maenas, seawater-acclimated green crabs exposed to hypercapnia rapidly accumulated HCO3− in their hemolymph, compensating for the respiratory acidosis caused by excess hemolymph pCO2. A full recovery from the decreased hemolymph pH after 48 h, however, was not observed. Gill perfusion experiments on anterior gill No. 5 indicated the involvement of all investigated genes (i.e., bicarbonate transporters, V-(H+)-ATPase, Na+/K+-ATPase, K+-channels, Na+/H+-exchanger, and carbonic anhydrase) in the excretion of acid–base equivalents. The most significant effects were observed when targeting a potentially cytoplasmic and (or) basolaterally localized V-(H+)-ATPase, as well as potentially basolaterally localized bicarbonate transporter (likely a Na+/HCO3−-cotransporter). In both cases, H+ accumulated in the hemolymph and CO2 excretion across the gill epithelium was significantly reduced or even reversed when blocking bicarbonate transporters. Based on the findings in this study, a working model for acid–base regulatory mechanisms and their link to ammonia excretion in the gill epithelium of C. maenas has been developed.
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Affiliation(s)
- S. Fehsenfeld
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB R3T 2N2, Canada
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB R3T 2N2, Canada
| | - D. Weihrauch
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB R3T 2N2, Canada
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB R3T 2N2, Canada
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160
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Crystal structures reveal the molecular basis of ion translocation in sodium/proton antiporters. Nat Struct Mol Biol 2016; 23:248-55. [PMID: 26828964 DOI: 10.1038/nsmb.3164] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Accepted: 12/30/2015] [Indexed: 11/09/2022]
Abstract
To fully understand the transport mechanism of Na(+)/H(+) exchangers, it is necessary to clearly establish the global rearrangements required to facilitate ion translocation. Currently, two different transport models have been proposed. Some reports have suggested that structural isomerization is achieved through large elevator-like rearrangements similar to those seen in the structurally unrelated sodium-coupled glutamate-transporter homolog GltPh. Others have proposed that only small domain movements are required for ion exchange, and a conventional rocking-bundle model has been proposed instead. Here, to resolve these differences, we report atomic-resolution structures of the same Na(+)/H(+) antiporter (NapA from Thermus thermophilus) in both outward- and inward-facing conformations. These data combined with cross-linking, molecular dynamics simulations and isothermal calorimetry suggest that Na(+)/H(+) antiporters provide alternating access to the ion-binding site by using elevator-like structural transitions.
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161
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Cao B, Long D, Zhang M, Liu C, Xiang Z, Zhao A. Molecular characterization and expression analysis of the mulberry Na(+)/H(+) exchanger gene family. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2016; 99:49-58. [PMID: 26730882 DOI: 10.1016/j.plaphy.2015.12.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 12/16/2015] [Accepted: 12/16/2015] [Indexed: 06/05/2023]
Abstract
Na(+)/H(+) exchangers (NHXs) have important roles in cellular pH, and Na(+) and K(+) homeostasis in plants. Mulberry is not only an important traditional economic woody plant known for its leaves, which are the exclusive food source of the silkworm Bombyx mori, but it can also adapt to many different adverse conditions, including saline environments. However, little is known about the NHXs in this important perennial tree. In this study, we identified and cloned seven putative NHX gene family members from Morus atropurpurea based on a genome-wide analysis of the Morus genome database. A phylogenetic analysis and genomic organization of mulberry NHXs suggested that the mulberry NHX family forms three distinct subgroups. Transcriptome data and real-time PCR of different mulberry varieties under normal culture conditions revealed that the mulberry NHX family has a different tissue-specific pattern in the two mulberry species. The MaNHX genes' expression analyses under different stresses (salt and drought) and signal molecules (abscisic acid, salicylic acid, hydrogen peroxide and methyl jasmonate) revealed that MaNHXs not only could be induced by salt, drought and abscisic acid as describe in the literature, but were also induced by other signal molecules, which indicated that MaNHX members exhibited diverse and complicated expression patterns in different mulberry tissues under various abiotic stresses, phytohormones and plant signaling molecules. Our results provide some insights into new and emerging cellular and physiological functions of this group of H(+)-coupled cation exchangers, beyond their function in salt tolerance, and also provide the basis for further characterizations of MaNHXs' physiological functions.
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Affiliation(s)
- Boning Cao
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China
| | - Dingpei Long
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China
| | - Meng Zhang
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China
| | - Changying Liu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China
| | - Zhonghuai Xiang
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China
| | - Aichun Zhao
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing 400716, China.
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162
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Sodium-Proton (Na+/H+) Antiporters: Properties and Roles in Health and Disease. Met Ions Life Sci 2016; 16:391-458. [DOI: 10.1007/978-3-319-21756-7_12] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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163
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Abstract
Despite diverse and changing extracellular environments, fungi maintain a relatively constant cytosolic pH and numerous organelles of distinct lumenal pH. Key players in fungal pH control are V-ATPases and the P-type proton pump Pma1. These two proton pumps act in concert with a large array of other transporters and are highly regulated. The activities of Pma1 and the V-ATPase are coordinated under some conditions, suggesting that pH in the cytosol and organelles is not controlled independently. Genomic studies, particularly in the highly tractable S. cerevisiae, are beginning to provide a systems-level view of pH control, including transcriptional responses to acid or alkaline ambient pH and definition of the full set of regulators required to maintain pH homeostasis. Genetically encoded pH sensors have provided new insights into localized mechanisms of pH control, as well as highlighting the dynamic nature of pH responses to the extracellular environment. Recent studies indicate that cellular pH plays a genuine signaling role that connects nutrient availability and growth rate through a number of mechanisms. Many of the pH control mechanisms found in S. cerevisiae are shared with other fungi, with adaptations for their individual physiological contexts. Fungi deploy certain proton transport and pH control mechanisms not shared with other eukaryotes; these regulators of cellular pH are potential antifungal targets. This review describes current and emerging knowledge proton transport and pH control mechanisms in S. cerevisiae and briefly discusses how these mechanisms vary among fungi.
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164
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Fan SHY, Numata Y, Numata M. Endosomal Na+/H+ exchanger NHE5 influences MET recycling and cell migration. Mol Biol Cell 2015; 27:702-15. [PMID: 26700318 PMCID: PMC4750928 DOI: 10.1091/mbc.e15-04-0257] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Accepted: 12/18/2015] [Indexed: 12/17/2022] Open
Abstract
The neuron-enriched Na+/H+ exchanger NHE5 is expressed in C6 glioma cells, acidifies recycling endosomes, and modulates cell surface abundance of receptor tyrosine kinases MET and EGFR. NHE5 depletion impairs MET recycling and facilitates degradation, thereby impairing cell migration and polarity. Increased recycling and elevated cell surface expression of receptors serve as a mechanism for persistent receptor-mediated signaling. We show that the neuron-enriched Na+/H+ exchanger NHE5 is abundantly expressed in C6 glioma cells and plays an important part in regulating cell surface expression of the receptor tyrosine kinases MET and EGF receptor. NHE5 is associated with transferrin receptor (TfR)- and Rab11-positive recycling endosomal membranes, and NHE5 knockdown by short hairpin RNA significantly elevates pH of TfR-positive recycling endosomes. We present evidence that NHE5 facilitates MET recycling to the plasma membrane, protects MET from degradation, and modulates HGF-induced phosphatidylinositol-3-kinase and mitogen-activated protein kinase signaling. Moreover, NHE5 depletion abrogates Rac1 and Cdc42 signaling and actin cytoskeletal remodeling. We further show that NHE5 knockdown impairs directed cell migration and causes loss of cell polarity. Our study highlights a possible role of recycling endosomal pH in regulating receptor-mediated signaling through vesicular trafficking.
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Affiliation(s)
- Steven Hung-Yi Fan
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Yuka Numata
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Masayuki Numata
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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165
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166
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Nusrat S, Miner PB. New pharmacological treatment options for irritable bowel syndrome with constipation. Expert Opin Emerg Drugs 2015; 20:625-36. [PMID: 26548544 DOI: 10.1517/14728214.2015.1105215] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
INTRODUCTION Constipation predominant irritable bowel syndrome (IBS-C) is a common disorder and accounts for a large number of ambulatory visits. Sensory abnormalities, that is, presence of abdominal pain and discomfort, distinguish IBS-C from chronic idiopathic constipation. AREA COVERED This review focuses on the pharmacology, efficacy, safety, and future of prucalopride, YKP-10811, DSP-6952, dexloxiglumide, linaclotide, plecanatide, tenapanor, and elobixibat. EXPERT OPINION It is now well established that treatment focusing only on bowel transit provides incomplete relief to patients with IBS-C. Improved understanding of pathophysiology of IBS-C has led to use of sensory end points like complete spontaneous bowel movements and the FDA combined end point (abdominal pain and complete spontaneous bowel movements) in clinical trials. A number of drugs are in development and provide hope for this challenging group of patients. However, because of recent failures secondary to ineffectiveness and/or adverse events, we cautiously await how clinical data play out in larger studies and in clinical practice.
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Affiliation(s)
- Salman Nusrat
- a Section of Digestive Diseases and Nutrition, Department of Medicine , Oklahoma University School of Medicine , 920 Stanton L. Young Blvd. WP 1345, Oklahoma City , OK 73104 , USA
| | - Philip B Miner
- a Section of Digestive Diseases and Nutrition, Department of Medicine , Oklahoma University School of Medicine , 920 Stanton L. Young Blvd. WP 1345, Oklahoma City , OK 73104 , USA
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167
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Ashnest JR, Huynh DL, Dragwidge JM, Ford BA, Gendall AR. Arabidopsis Intracellular NHX-Type Sodium-Proton Antiporters are Required for Seed Storage Protein Processing. PLANT & CELL PHYSIOLOGY 2015; 56:2220-33. [PMID: 26416852 DOI: 10.1093/pcp/pcv138] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 09/18/2015] [Indexed: 05/26/2023]
Abstract
The Arabidopsis intracellular sodium-proton exchanger (NHX) proteins AtNHX5 and AtNHX6 have a well-documented role in plant development, and have been used to improve salt tolerance in a variety of species. Despite evidence that intracellular NHX proteins are important in vacuolar trafficking, the mechanism of this role is poorly understood. Here we show that NHX5 and NHX6 are necessary for processing of the predominant seed storage proteins, and also influence the processing and activity of a vacuolar processing enzyme. Furthermore, we show by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) technology that the C-terminal tail of NHX6 interacts with a component of Retromer, another component of the cell sorting machinery, and that this tail is critical for NHX6 activity. These findings demonstrate that NHX5 and NHX6 are important in processing and activity of vacuolar cargo, and suggest a mechanism by which NHX intracellular (IC)-II antiporters may be involved in subcellular trafficking.
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Affiliation(s)
- Joanne R Ashnest
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, 5 Ring Road, La Trobe University, Bundoora, VIC 3086, Australia
| | - Dung L Huynh
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, 5 Ring Road, La Trobe University, Bundoora, VIC 3086, Australia
| | - Jonathan M Dragwidge
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, 5 Ring Road, La Trobe University, Bundoora, VIC 3086, Australia
| | - Brett A Ford
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, 5 Ring Road, La Trobe University, Bundoora, VIC 3086, Australia Present address: Commonwealth Scientific and Industrial Research Organization Agriculture Flagship, Clunies Ross Street, Acton, ACT 2601, Australia
| | - Anthony R Gendall
- Department of Animal, Plant and Soil Sciences, AgriBio, Centre for AgriBiosciences, 5 Ring Road, La Trobe University, Bundoora, VIC 3086, Australia
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168
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Transport proteins NHA1 and NHA2 are essential for survival, but have distinct transport modalities. Proc Natl Acad Sci U S A 2015; 112:11720-5. [PMID: 26324901 DOI: 10.1073/pnas.1508031112] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The cation/proton antiporter (CPA) family includes the well-known sodium/proton exchanger (NHE; SLC9A) family of Na(+)/H(+) exchangers, and the more recently discovered and less well understood CPA2s (SLC9B), found widely in living organisms. In Drosophila, as in humans, they are represented by two genes, Nha1 (Slc9b1) and Nha2 (Slc9b2), which are enriched and functionally significant in renal tubules. The importance of their role in organismal survival has not been investigated in animals, however. Here we show that single RNAi knockdowns of either Nha1 or Nha2 reduce survival and in combination are lethal. Knockdown of either gene alone results in up-regulation of the other, suggesting functional complementation of the two genes. Under salt stress, knockdown of either gene decreases survival, demonstrating a key role for the CPA2 family in ion homeostasis. This is specific to Na(+) stress; survival on K(+) intoxication is not affected by sodium/hydrogen antiporter (NHA) knockdown. A direct functional assay in Xenopus oocytes shows that Nha2 acts as a Na(+)/H(+) exchanger. In contrast, Nha1 expressed in Xenopus oocytes shows strong Cl(-) conductance and acts as a H(+)-Cl(-) cotransporter. The activity of Nha1 is inhibited by chloride-binding competitors 4,4'-diiso-thiocyano-2,2'-disulfonic acid stilbene and 4,4'-dibenzamido-2,2'-stilbenedisulphonate. Salt stress induces a massive up-regulation of NHA gene expression not in the major osmoregulatory tissues of the alimentary canal, but in the crop, cuticle, and associated tissues. Thus, it is necessary to revise the classical view of the coordination of different tissues in the coordination of the response to osmoregulatory stress.
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169
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Takemoto H, Miyata K, Nishiyama N, Kataoka K. Bioresponsive polymer-based nucleic acid carriers. ADVANCES IN GENETICS 2015; 88:289-323. [PMID: 25409610 DOI: 10.1016/b978-0-12-800148-6.00010-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Nucleic acid carriers need to possess multifunctionality for overcoming biological barriers, such as the stable encapsulation of nucleic acids in extracellular milieu, internalization by target cells, controlled intracellular distribution, and release of nucleic acids at the target site of action. To fulfill these stepwise functionalities, "bioresponsive" polymers that can alter their structure responding to site-specific biological signals are highly useful. Notably, pH, redox potential, and enzymatic activities vary along with microenvironments in the body, and thus, the responsiveness to these signals enables to construct nucleic acid carriers with programmed functionalities. This chapter describes the design of bioresponsive polymers that respond to various biological microenvironments for smart nucleic acids delivery.
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Affiliation(s)
- Hiroyasu Takemoto
- Polymer Chemistry Division, Chemical Resources Laboratory, Tokyo Institute of Technology, Japan
| | - Kanjiro Miyata
- Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Japan
| | - Nobuhiro Nishiyama
- Polymer Chemistry Division, Chemical Resources Laboratory, Tokyo Institute of Technology, Japan
| | - Kazunori Kataoka
- Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Japan; Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, Japan
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170
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Ma Y, Wang J, Zhong Y, Geng F, Cramer GR, Cheng ZM(M. Subfunctionalization of cation/proton antiporter 1 genes in grapevine in response to salt stress in different organs. HORTICULTURE RESEARCH 2015; 2:15031. [PMID: 26504576 PMCID: PMC4591679 DOI: 10.1038/hortres.2015.31] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Revised: 06/04/2015] [Accepted: 06/04/2015] [Indexed: 05/20/2023]
Abstract
Cation/proton antiporter 1 (CPA1) proteins function as regulators of monovalent ions, pH homeostasis, and other developmental processes in plants. Better understanding of the expression and regulation of CPA1 in plant responses to salinity would help the development of scientific practices in crops worldwide. In this report, we characterized all seven CPA1 family genes in grapevine (Vitis vinifera) in response to short-term osmotic and NaCl stresses. We found that two of the seven genes have subfunctionalized to be differentially expressed in response to NaCl stress in the early stage in different organs, whereas the other five members seem to play little or no role in this response. Specifically, VIT_19s0090g01480 may control Na(+) compartmentalization in grapevine roots; and VIT_05s0020g01960 may influence Na(+) transfer in stems. Based on the dynamics of ion concentrations, electrolyte leakage rates, and CPA1 gene expression in root, stem, and leaf tissues under osmotic and NaCl stresses, we suggest how grapevine responds physiologically and molecularly to the osmotic and ion toxicity of NaCl stress in the short term. This work lays a foundation for future research on the CPA1 gene family regarding its evolutionary history and biological functions for modulating salt responses in grapevine.
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Affiliation(s)
- Yuanchun Ma
- The Laboratory of Fruit Crop Systems Biology, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu Province 210095, The People’s Republic of China
| | - Jiaoyang Wang
- The Laboratory of Fruit Crop Systems Biology, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu Province 210095, The People’s Republic of China
| | - Yan Zhong
- The Laboratory of Fruit Crop Systems Biology, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu Province 210095, The People’s Republic of China
| | - Fang Geng
- The Laboratory of Fruit Crop Systems Biology, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu Province 210095, The People’s Republic of China
| | - Grant R Cramer
- Department of Biochemistry and Molecular Biology, University of Nevada, Reno, NV 89557, USA
| | - Zong-Ming (Max) Cheng
- The Laboratory of Fruit Crop Systems Biology, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu Province 210095, The People’s Republic of China
- Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996, USA
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171
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Guffey SC, Fliegel L, Goss GG. Cloning and characterization of Na(+)/H(+) Exchanger isoforms NHE2 and NHE3 from the gill of Pacific dogfish Squalus suckleyi. Comp Biochem Physiol B Biochem Mol Biol 2015; 188:46-53. [PMID: 26112825 DOI: 10.1016/j.cbpb.2015.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 06/16/2015] [Accepted: 06/17/2015] [Indexed: 01/26/2023]
Abstract
Na(+)/H(+) Exchanger (NHE) proteins mediate cellular and systemic homeostasis of sodium and acid and may be the major sodium uptake method for fishes. We cloned and sequenced NHE2 and NHE3 from the gill of the North Pacific Spiny Dogfish shark Squalus suckleyi and expressed them in functional form in NHE-deficient (AP-1) cell lines. Estimated IC50 for inhibition of NHE activity by amiloride and EIPA were 55 μmol l(-1) and 4.8 μmol l(-1), respectively, for NHE2 and 9 μmol l(-1) and 24 μmol l(-1), respectively, for NHE3. Phenamil at 100 μmol l(-1) caused less than 16% inhibition of activity for each isoform. Although the IC50 are similar for the two isoforms, dfNHE2 is less sensitive than human NHE2 to inhibition by amiloride and EIPA, while dfNHE3 is more sensitive than human NHE3. These IC50 estimates should be considered when selecting inhibitor doses for fishes and for reinterpretation of previous studies that use these pharmacological agents.
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Affiliation(s)
- Samuel C Guffey
- Department of Biological Sciences, Z512 Biological Sciences Bldg, University of Alberta, Edmonton, AB T6G 2E9, Canada; Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC V0R 1B0, Canada.
| | - Larry Fliegel
- Department of Biochemistry, 347 Medical Sciences Bldg, University of Alberta, Edmonton, AB T6G 2H7, Canada.
| | - Greg G Goss
- Department of Biological Sciences, Z512 Biological Sciences Bldg, University of Alberta, Edmonton, AB T6G 2E9, Canada; Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC V0R 1B0, Canada.
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172
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Jinadasa T, Josephson CB, Boucher A, Orlowski J. Determinants of Cation Permeation and Drug Sensitivity in Predicted Transmembrane Helix 9 and Adjoining Exofacial Re-entrant Loop 5 of Na+/H+ Exchanger NHE1. J Biol Chem 2015; 290:18173-18186. [PMID: 26063808 DOI: 10.1074/jbc.m115.642199] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Indexed: 12/25/2022] Open
Abstract
Mammalian Na(+)/H(+) exchangers (NHEs) regulate numerous physiological processes and are involved in the pathogenesis of several diseases, including tissue ischemia and reperfusion injuries, cardiac hypertrophy and failure, and cancer progression. Hence, NHEs are being targeted for pharmaceutical-based clinical therapies, but pertinent information regarding the structural elements involved in cation translocation and drug binding remains incomplete. Molecular manipulations of the prototypical NHE1 isoform have implicated several predicted membrane-spanning (M) helices, most notably M4, M9, and M11, as important determinants of cation permeation and drug sensitivity. Here, we have used substituted-cysteine accessibility mutagenesis and thiol-modifying methanethiosulfonate (MTS) reagents to further probe the involvement of evolutionarily conserved sites within M9 (residues 342-363) and the adjacent exofacial re-entrant loop 5 between M9 and M10 (EL5; residues 364-415) of a cysteine-less variant of rat NHE1 on its kinetic and pharmacological properties. MTS treatment significantly reduced the activity of mutants containing substitutions within M9 (H353C, S355C, and G356C) and EL5 (G403C and S405C). In the absence of MTS, mutants S355C, G403C, and S405C showed modest to significant decreases in their apparent affinities for Na(+) o and/or H(+) i. In addition, mutations Y370C and E395C within EL5, whereas failing to confer sensitivity to MTS, nevertheless, reduced the affinity for Na(+) o, but not for H(+) i. The Y370C mutant also exhibited higher affinity for ethylisopropylamiloride, a competitive antagonist of Na(+) o transport. Collectively, these results further implicate helix M9 and EL5 of NHE1 as important elements involved in cation transport and inhibitor sensitivity, which may inform rational drug design.
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Affiliation(s)
- Tushare Jinadasa
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6
| | - Colin B Josephson
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6; Division of Clinical Neurosciences, University of Calgary Foothills Medical Centre, Calgary, Alberta T2N 2T9, Canada
| | - Annie Boucher
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6
| | - John Orlowski
- Department of Physiology, McGill University, Montréal, Québec H3G 1Y6.
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173
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Kinclova-Zimmermannova O, Falson P, Cmunt D, Sychrova H. A Hydrophobic Filter Confers the Cation Selectivity of Zygosaccharomyces rouxii Plasma-Membrane Na+/H+ Antiporter. J Mol Biol 2015; 427:1681-94. [DOI: 10.1016/j.jmb.2015.02.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 02/10/2015] [Accepted: 02/11/2015] [Indexed: 10/24/2022]
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174
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Lee JC, Cho JH, Kim IH, Ahn JH, Park JH, Cho GS, Chen BH, Shin BN, Tae HJ, Park SM, Ahn JY, Kim DW, Cho JH, Bae EJ, Yong JH, Kim YM, Won MH, Lee YL. Ischemic preconditioning inhibits expression of Na + /H + exchanger 1 (NHE1) in the gerbil hippocampal CA1 region after transient forebrain ischemia. J Neurol Sci 2015; 351:146-153. [DOI: 10.1016/j.jns.2015.03.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 02/09/2015] [Accepted: 03/03/2015] [Indexed: 12/26/2022]
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175
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Xia CH, Liu H, Cheung D, Tang F, Chang B, Li M, Gong X. NHE8 is essential for RPE cell polarity and photoreceptor survival. Sci Rep 2015; 5:9358. [PMID: 25791178 PMCID: PMC4366848 DOI: 10.1038/srep09358] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 03/02/2015] [Indexed: 11/09/2022] Open
Abstract
A new N-ethyl-N-nitrosourea (ENU)-induced mouse recessive mutation, identified by fundus examination of the eye, develops depigmented patches, indicating retinal disorder. Histology data show aberrant retinal pigment epithelium (RPE) and late-onset photoreceptor cell loss in the mutant retina. Chromosomal mapping and DNA sequencing reveal a point mutation (T to A) of the Slc9a8 gene, resulting in mutant sodium/proton exchanger 8 (NHE8)-M120K protein. The lysine substitution decreases the probability of forming the 3(rd) transmembrane helix, which impairs the pore structure of the Na(+)/H(+) exchanger. Various RPE defects, including mislocalization of the apical marker ezrin, and disrupted apical microvilli and basal infoldings are observed in mutant mice. We have further generated NHE8 knockout mice and confirmed similar phenotypes, including abnormal RPE cells and late-onset photoreceptor cell loss. Both in vivo and in vitro data indicate that NHE8 co-localizes with ER, Golgi and intracellular vesicles in RPE cells. Thus, NHE8 function is necessary for the survival of photoreceptor cells and NHE8 is important for RPE cell polarity and function. Dysfunctional RPE may ultimately lead to photoreceptor cell death in the NHE8 mutants. Further studies will be needed to elucidate whether or not NHE8 regulates pH homeostasis in the protein secretory pathways of RPE.
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Affiliation(s)
- Chun-hong Xia
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Haiquan Liu
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Debra Cheung
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Felicia Tang
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Bo Chang
- The Jackson Laboratory, Bar Harbor, ME 04609, USA
| | - Mei Li
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Xiaohua Gong
- School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, CA 94720, USA
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176
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Verkhratsky A, Parpura V. Physiology of Astroglia: Channels, Receptors, Transporters, Ion Signaling and Gliotransmission. ACTA ACUST UNITED AC 2015. [DOI: 10.4199/c00123ed1v01y201501ngl004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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177
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Kumar PL, James PF. Identification and characterization of methylation-dependent/independent DNA regulatory elements in the human SLC9B1 gene. Gene 2015; 561:235-48. [PMID: 25701605 DOI: 10.1016/j.gene.2015.02.050] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 02/09/2015] [Accepted: 02/13/2015] [Indexed: 12/15/2022]
Abstract
The human NHEDC1 (hNHEDC1) protein is thought to be essential for sperm motility and fertility however the mechanisms regulating its gene expression are largely unknown. In this study we have identified multiple DNA regulatory elements in the 5' end of the gene encoding hNHEDC1 (SLC9B1) and have explored the role that DNA methylation at these elements plays in the regulation of its expression. We first show that the full-length hNHEDC1 protein is testis-specific for the tissues that we tested and that it localizes to the cells of the seminiferous tubules. In silico analysis of the SLC9B1 gene locus identified two putative promoters (P1 and P2) and two CpG islands - CpGI (overlapping with P1) and CpGII (intragenic) - at the 5' end of the gene. By deletion analysis of P1, we show that the region from -23 bp to +200 bp relative to the transcription start site (TSS) is sufficient for optimal promoter activity in a germ cell line. Additionally, in vitro methylation of the P1 (the -500 bp to +200 bp region relative to the TSS) abolishes its activity in germ cells and somatic cells strongly suggesting that DNA methylation at this promoter could regulate SLC9B1 expression. Furthermore, bisulfite-sequencing analysis of the P1/CpGI uncovered reduced methylation in the testis vs. lung whereas CpGII displayed no differences in methylation between these two tissues. Additionally, treatment of HEK 293 cells with 5-aza-2-Deoxycytidine led to upregulation of NHEDC1 transcript and reduced methylation in the promoter CpGI. Finally, we have uncovered both enhancer and silencer functions of the intragenic SLC9B1 CpGII. In all, our data suggests that SLC9B1 gene expression could be regulated via a concerted action of DNA methylation-dependent and independent mechanisms mediated by these multiple DNA regulatory elements.
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Affiliation(s)
- Priya L Kumar
- Department of Biology, Miami University, Oxford, OH, United States
| | - Paul F James
- Department of Biology, Miami University, Oxford, OH, United States.
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178
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Na+-H+ exchanger-1 (NHE1) regulation in kidney proximal tubule. Cell Mol Life Sci 2015; 72:2061-74. [PMID: 25680790 DOI: 10.1007/s00018-015-1848-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 01/28/2015] [Accepted: 01/29/2015] [Indexed: 01/17/2023]
Abstract
The ubiquitously expressed plasma membrane Na(+)-H(+) exchanger NHE1 is a 12 transmembrane-spanning protein that directs important cell functions such as homeostatic intracellular volume and pH control. The 315 amino acid cytosolic tail of NHE1 binds plasma membrane phospholipids and multiple proteins that regulate additional, ion-translocation independent functions. This review focuses on NHE1 structure/function relationships, as well as the role of NHE1 in kidney proximal tubule functions, including pH regulation, vectorial Na(+) transport, cell volume control and cell survival. The implications of these functions are particularly critical in the setting of progressive, albuminuric kidney diseases, where the accumulation of reabsorbed fatty acids leads to disruption of NHE1-membrane phospholipid interactions and tubular atrophy, which is a poor prognostic factor for progression to end stage renal disease. This review amplifies the vital role of the proximal tubule NHE1 Na(+)-H(+) exchanger as a kidney cell survival factor.
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179
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Jinadasa T, Szabó EZ, Numat M, Orlowski J. Activation of AMP-activated protein kinase regulates hippocampal neuronal pH by recruiting Na(+)/H(+) exchanger NHE5 to the cell surface. J Biol Chem 2015; 289:20879-97. [PMID: 24936055 DOI: 10.1074/jbc.m114.555284] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Strict regulation of intra- and extracellular pH is an important determinant of nervous system function as many voltage-, ligand-, and H(+)-gated cationic channels are exquisitely sensitive to transient fluctuations in pH elicited by neural activity and pathophysiologic events such as hypoxia-ischemia and seizures. Multiple Na(+)/H(+) exchangers (NHEs) are implicated in maintenance of neural pH homeostasis. However, aside from the ubiquitous NHE1 isoform, their relative contributions are poorly understood. NHE5 is of particular interest as it is preferentially expressed in brain relative to other tissues. In hippocampal neurons, NHE5 regulates steady-state cytoplasmic pH, but intriguingly the bulk of the transporter is stored in intracellular vesicles. Here, we show that NHE5 is a direct target for phosphorylation by the AMP-activated protein kinase (AMPK), a key sensor and regulator of cellular energy homeostasis in response to metabolic stresses. In NHE5-transfected non-neuronal cells, activation of AMPK by the AMP mimetic AICAR or by antimycin A, which blocks aerobic respiration and causes acidification, increased cell surface accumulation and activity of NHE5, and elevated intracellular pH. These effects were effectively blocked by the AMPK antagonist compound C, the NHE inhibitor HOE694, and mutation of a predicted AMPK recognition motif in the NHE5 C terminus. This regulatory pathway was also functional in primary hippocampal neurons, where AMPK activation of NHE5 protected the cells from sustained antimycin A-induced acidification. These data reveal a unique role for AMPK and NHE5 in regulating the pH homeostasis of hippocampal neurons during metabolic stress.
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180
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Kondapalli KC, Llongueras JP, Capilla-González V, Prasad H, Hack A, Smith C, Guerrero-Cázares H, Quiñones-Hinojosa A, Rao R. A leak pathway for luminal protons in endosomes drives oncogenic signalling in glioblastoma. Nat Commun 2015; 6:6289. [PMID: 25662504 PMCID: PMC4354686 DOI: 10.1038/ncomms7289] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 01/12/2015] [Indexed: 12/15/2022] Open
Abstract
Epidermal growth factor receptor (EGFR) signalling is a potent driver of glioblastoma, a malignant and lethal form of brain cancer. Disappointingly, inhibitors targeting receptor tyrosine kinase activity are not clinically effective and EGFR persists on the plasma membrane to maintain tumour growth and invasiveness. Here we show that endolysosomal pH is critical for receptor sorting and turnover. By functioning as a leak pathway for protons, the Na(+)/H(+) exchanger NHE9 limits luminal acidification to circumvent EGFR turnover and prolong downstream signalling pathways that drive tumour growth and migration. In glioblastoma, NHE9 expression is associated with stem/progenitor characteristics, radiochemoresistance, poor prognosis and invasive growth in vitro and in vivo. Silencing or inhibition of NHE9 in brain tumour-initiating cells attenuates tumoursphere formation and improves efficacy of EGFR inhibitor. Thus, NHE9 mediates inside-out control of oncogenic signalling and is a highly druggable target for pan-specific receptor clearance in cancer therapy.
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Affiliation(s)
- Kalyan C. Kondapalli
- Department of Physiology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Jose P. Llongueras
- Department of Physiology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Vivian Capilla-González
- Department of Neurosurgery, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Hari Prasad
- Department of Physiology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Anniesha Hack
- Department of Physiology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Christopher Smith
- Department of Neurosurgery, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Hugo Guerrero-Cázares
- Department of Neurosurgery, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Alfredo Quiñones-Hinojosa
- Department of Neurosurgery, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Rajini Rao
- Department of Physiology, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
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2-DE Mapping of the Blue Mussel Gill Proteome: The Usual Suspects Revisited. Proteomes 2015; 3:3-41. [PMID: 28248261 PMCID: PMC5302490 DOI: 10.3390/proteomes3010003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Accepted: 12/04/2014] [Indexed: 11/17/2022] Open
Abstract
The Blue Mussel (Mytilus edulis, L. 1758) is an ecologically important and commercially relevant bivalve. Because of its ability to bioconcentrate xenobiotics, it is also a widespread sentinel species for environmental pollution, which has been used in ecotoxicological studies for biomarker assessment. Consequently, numerous proteomics studies have been carried out in various research contexts using mussels of the genus Mytilus, which intended to improve our understanding of complex physiological processes related to reproduction, adaptation to physical stressors or shell formation and for biomarker discovery. Differential-display 2-DE proteomics relies on an extensive knowledge of the proteome with as many proteoforms identified as possible. To this end, extensive characterization of proteins was performed in order to increase our knowledge of the Mytilus gill proteome. On average, 700 spots were detected on 2-DE gels by colloidal blue staining, of which 122 different, non-redundant proteins comprising 203 proteoforms could be identified by tandem mass spectrometry. These proteins could be attributed to four major categories: (i) “metabolism”, including antioxidant defence and degradation of xenobiotics; (ii) “genetic information processing”, comprising transcription and translation as well as folding, sorting, repair and degradation; (iii) “cellular processes”, such as cell motility, transport and catabolism; (iv) “environmental information processing”, including signal transduction and signalling molecules and interaction. The role of cytoskeleton proteins, energetic metabolism, chaperones/stress proteins, protein trafficking and the proteasome are discussed in the light of the exigencies of the intertidal environment, leading to an enhanced stress response, as well as the structural and physiological particularities of the bivalve gill tissue.
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182
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Prasad H, Rao R. The Na+/H+ exchanger NHE6 modulates endosomal pH to control processing of amyloid precursor protein in a cell culture model of Alzheimer disease. J Biol Chem 2015; 290:5311-27. [PMID: 25561733 DOI: 10.1074/jbc.m114.602219] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Early intervention may be key to safe and effective therapies in patients with Alzheimer disease. Endosomal dysfunction is an early step in neurodegeneration. Endosomes are a major site of production of Aβ peptide from the processing of amyloid precursor protein (APP) by clipping enzymes (β- and γ-secretases). The β-secretase enzyme BACE1 requires acidic lumen pH for optimum function, and acid pH promotes Aβ aggregation. The Na(+)/H(+) exchanger NHE6 provides a leak pathway for protons, limiting luminal acidification by proton pumps. Like APP, NHE6 expression was induced upon differentiation of SH-SY5Y neuroblastoma cells and localized to an endosomal compartment. Therefore, we investigated whether NHE6 expression altered APP localization and processing in a stably transfected cell culture model of human APP expression. We show that co-expression with NHE6 or treatment with the Na(+)/H(+) ionophore monensin shifted APP away from the trans-Golgi network into early and recycling endosomes in HEK293 cells. NHE6 alkalinized the endosomal lumen, similar to monensin, and significantly attenuated APP processing and Aβ secretion. In contrast, Aβ production was elevated upon NHE6 knockdown. We show that NHE6 transcript and protein levels are lowered in Alzheimer brains relative to control. These findings, taken together with emerging genetic evidence linking endosomal Na(+)/H(+) exchangers with Alzheimer disease, suggest that proton leak pathways may regulate Aβ generation and contribute to disease etiology.
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Affiliation(s)
- Hari Prasad
- From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Rajini Rao
- From the Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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183
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184
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Bassil E, Blumwald E. The ins and outs of intracellular ion homeostasis: NHX-type cation/H(+) transporters. CURRENT OPINION IN PLANT BIOLOGY 2014; 22:1-6. [PMID: 25173972 DOI: 10.1016/j.pbi.2014.08.002] [Citation(s) in RCA: 128] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Revised: 08/14/2014] [Accepted: 08/14/2014] [Indexed: 05/18/2023]
Abstract
The biochemical characterization of cation/H(+) exchange has been known since 1985 [1], yet only recently have we begun to understand the contribution of individual exchangers to ion homeostasis in plants. One particularly important class of exchangers is the NHX-type that is associated with Na(+) transport and therefore salinity tolerance. New evidence suggests that under normal growth conditions NHXs are critical regulators of K(+) and pH homeostasis and have important roles, depending on their cellular localization, in the generation of turgor as well as in vesicular trafficking. Recent advances highlight novel and exciting functions of intracellular NHXs in growth and development, stress adaptation and osmotic adjustment. Here, we elaborate on new and emerging cellular and physiological functions of this group of H(+)-coupled cation exchangers.
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Affiliation(s)
- Elias Bassil
- Department of Plant Sciences, University of California, Davis, CA 95616, United States
| | - Eduardo Blumwald
- Department of Plant Sciences, University of California, Davis, CA 95616, United States.
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185
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Paulino C, Wöhlert D, Kapotova E, Yildiz Ö, Kühlbrandt W. Structure and transport mechanism of the sodium/proton antiporter MjNhaP1. eLife 2014; 3:e03583. [PMID: 25426803 PMCID: PMC4381896 DOI: 10.7554/elife.03583] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 11/14/2014] [Indexed: 11/13/2022] Open
Abstract
Sodium/proton antiporters are essential for sodium and pH homeostasis and play a major role in human health and disease. We determined the structures of the archaeal sodium/proton antiporter MjNhaP1 in two complementary states. The inward-open state was obtained by x-ray crystallography in the presence of sodium at pH 8, where the transporter is highly active. The outward-open state was obtained by electron crystallography without sodium at pH 4, where MjNhaP1 is inactive. Comparison of both structures reveals a 7° tilt of the 6 helix bundle. (22)Na(+) uptake measurements indicate non-cooperative transport with an activity maximum at pH 7.5. We conclude that binding of a Na(+) ion from the outside induces helix movements that close the extracellular cavity, open the cytoplasmic funnel, and result in a ∼5 Å vertical relocation of the ion binding site to release the substrate ion into the cytoplasm.
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Affiliation(s)
- Cristina Paulino
- Department of Structural
Biology, Max Planck Institute of
Biophysics, Frankfurt
am Main, Germany
| | - David Wöhlert
- Department of Structural
Biology, Max Planck Institute of
Biophysics, Frankfurt
am Main, Germany
| | - Ekaterina Kapotova
- Department of Structural
Biology, Max Planck Institute of
Biophysics, Frankfurt
am Main, Germany
| | - Özkan Yildiz
- Department of Structural
Biology, Max Planck Institute of
Biophysics, Frankfurt
am Main, Germany
| | - Werner Kühlbrandt
- Department of Structural
Biology, Max Planck Institute of
Biophysics, Frankfurt
am Main, Germany
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186
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Wöhlert D, Kühlbrandt W, Yildiz O. Structure and substrate ion binding in the sodium/proton antiporter PaNhaP. eLife 2014; 3:e03579. [PMID: 25426802 PMCID: PMC4381880 DOI: 10.7554/elife.03579] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 11/25/2014] [Indexed: 11/29/2022] Open
Abstract
Sodium/proton antiporters maintain intracellular pH and sodium levels. Detailed
structures of antiporters with bound substrate ions are essential for understanding
how they work. We have resolved the substrate ion in the dimeric, electroneutral
sodium/proton antiporter PaNhaP from Pyrococcus abyssi at 3.2
Å, and have determined its structure in two different conformations at pH 8 and
pH 4. The ion is coordinated by three acidic sidechains, a water molecule, a serine
and a main-chain carbonyl in the unwound stretch of trans-membrane helix 5 at the
deepest point of a negatively charged cytoplasmic funnel. A second narrow polar
channel may facilitate proton uptake from the cytoplasm. Transport activity of PaNhaP
is cooperative at pH 6 but not at pH 5. Cooperativity is due to pH-dependent
allosteric coupling of protomers through two histidines at the dimer interface.
Combined with comprehensive transport studies, the structures of PaNhaP offer unique
new insights into the transport mechanism of sodium/proton antiporters. DOI:http://dx.doi.org/10.7554/eLife.03579.001 Although the membrane that surrounds a cell is effective at separating the inside of
a cell from the outside environment, certain molecules must enter or leave the cell
for it to work correctly. One way this transport can occur is via proteins embedded
in the cell membrane, called transporters. Transporters that are found in all organisms include the sodium/proton antiporters,
which exchange protons from inside the cell with sodium ions from outside. However,
exactly how the antiporter works was unknown. Previous work suggested that the structure and activity of the sodium/proton
antiporter changes as the acidity of its environment changes, but the precise details
of how this occurs were unclear. Wöhlert et al. have now crystallised a
sodium/proton antiporter from a single-celled organism called Pyrococcus
abyssi, a species of archaea that has been found living in hydrothermal
vents deep in the Pacific Ocean. The structures the protein takes on in different
functional states were then deduced from these crystals using a technique called
X-ray crystallography. Using heavy thallium ions instead of sodium ions, which are
less visible to X-rays, Wöhlert et al. found the site in the antiporter where
the transported ion binds as it moves through the membrane. The antiporter has a funnel-shaped cavity that faces inwards (into the cell) in both
acidic and alkaline conditions, although a second narrow channel that is open in
alkaline conditions is blocked in acidic conditions by small protein rearrangements.
Wöhlert et al. suggest that the differences between both structures explain how
the antiporter tunes its ability to bind to the ions it transports. Wöhlert et al. further measured the activity of the antiporter and observed that
the transport of ions was most rapid under slightly acidic conditions. In more acidic
conditions, the sodium ion cannot bind to the antiporter, and in an alkaline
environment, the sodium ions bind too strongly to the antiporter; in both cases, the
ions cannot be transported. Comparing the findings presented here with separate work that uncovers the structure
of the sodium/proton antiporter in a different species of archaea revealed very
similar structures. Related transporters are also found in mammals, and defects in
these transporters can lead to problems with the heart and kidneys. A better
understanding of the sodium/proton antiporter structure could therefore help to
develop new treatments for these conditions. DOI:http://dx.doi.org/10.7554/eLife.03579.002
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Affiliation(s)
- David Wöhlert
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Werner Kühlbrandt
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Ozkan Yildiz
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
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187
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Xu W, Hong SJ, Zeitchek M, Cooper G, Jia S, Xie P, Qureshi HA, Zhong A, Porterfield MD, Galiano RD, Surmeier DJ, Mustoe TA. Hydration status regulates sodium flux and inflammatory pathways through epithelial sodium channel (ENaC) in the skin. J Invest Dermatol 2014; 135:796-806. [PMID: 25371970 DOI: 10.1038/jid.2014.477] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 09/22/2014] [Accepted: 10/05/2014] [Indexed: 02/03/2023]
Abstract
Although it is known that the inflammatory response that results from disruption of epithelial barrier function after injury results in excessive scarring, the upstream signals remain unknown. It has also been observed that epithelial disruption results in reduced hydration status and that the use of occlusive dressings that prevent water loss from wounds decreases scar formation. We hypothesized that hydration status changes sodium homeostasis and induces sodium flux in keratinocytes, which result in activation of pathways responsible for keratinocyte-fibroblast signaling and ultimately lead to activation of fibroblasts. Here, we demonstrate that perturbations in epithelial barrier function lead to increased sodium flux in keratinocytes. We identified that sodium flux in keratinocytes is mediated by epithelial sodium channels (ENaCs) and causes increased secretion of proinflammatory cytokines, which activate fibroblast via the cyclooxygenase 2 (COX-2)/prostaglandin E2 (PGE2) pathway. Similar changes in signal transduction and sodium flux occur by increased sodium concentration, which simulates reduced hydration, in the media in epithelial cultures or human ex vivo skin cultures. Blockade of ENaC, prostaglandin synthesis, or PGE2 receptors all reduce markers of fibroblast activation and collagen synthesis. In addition, employing a validated in vivo excessive scar model in the rabbit ear, we demonstrate that utilization of either an ENaC blocker or a COX-2 inhibitor results in a marked reduction in scarring. Other experiments demonstrate that the activation of COX-2 in response to increased sodium flux is mediated through the PIK3/Akt pathway. Our results indicate that ENaC responds to small changes in sodium concentration with inflammatory mediators and suggest that the ENaC pathway is a potential target for a strategy to prevent fibrosis.
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Affiliation(s)
- Wei Xu
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Seok Jong Hong
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Michael Zeitchek
- Department of Agricultural and Biological Engineering, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA
| | - Garry Cooper
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Shengxian Jia
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Ping Xie
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Hannan A Qureshi
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Aimei Zhong
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Plastic Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Marshall D Porterfield
- Department of Agricultural and Biological Engineering, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA
| | - Robert D Galiano
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - D James Surmeier
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Thomas A Mustoe
- Laboratory for Wound Repair and Regenerative Medicine, Department of Surgery/Plastic Surgery Division, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
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188
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Sultan A, Luo M, Yu Q, Riederer B, Xia W, Chen M, Lissner S, Gessner JE, Donowitz M, Yun CC, deJonge H, Lamprecht G, Seidler U. Differential association of the Na+/H+ Exchanger Regulatory Factor (NHERF) family of adaptor proteins with the raft- and the non-raft brush border membrane fractions of NHE3. Cell Physiol Biochem 2014; 32:1386-402. [PMID: 24297041 DOI: 10.1159/000356577] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/24/2013] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND/AIMS Trafficking, brush border membrane (BBM) retention, and signal-specific regulation of the Na+/H+ exchanger NHE3 is regulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adaptor proteins, which enable the formation of multiprotein complexes. It is unclear, however, what determines signal specificity of these NHERFs. Thus, we studied the association of NHE3, NHERF1 (EBP50), NHERF2 (E3KARP), and NHERF3 (PDZK1) with lipid rafts in murine small intestinal BBM. METHODS Detergent resistant membranes ("lipid rafts") were isolated by floatation of Triton X-incubated small intestinal BBM from a variety of knockout mouse strains in an Optiprep step gradient. Acid-activated NHE3 activity was measured fluorometrically in BCECF-loaded microdissected villi, or by assessment of CO2/HCO3(-) mediated increase in fluid absorption in perfused jejunal loops of anethetized mice. RESULTS NHE3 was found to partially associate with lipid rafts in the native BBM, and NHE3 raft association had an impact on NHE3 transport activity and regulation in vivo. NHERF1, 2 and 3 were differentially distributed to rafts and non-rafts, with NHERF2 being most raft-associated and NHERF3 entirely non-raft associated. NHERF2 expression enhanced the localization of NHE3 to membrane rafts. The use of acid sphingomyelinase-deficient mice, which have altered membrane lipid as well as lipid raft composition, allowed us to test the validity of the lipid raft concept in vivo. CONCLUSIONS The differential association of the NHERFs with the raft-associated and the non-raft fraction of NHE3 in the brush border membrane is one component of the differential and signal-specific NHE3 regulation by the different NHERFs.
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189
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Wang L, Feng X, Zhao H, Wang L, An L, Qiu QS. Functional analysis of the Na+,K+/H+ antiporter PeNHX3 from the tree halophyte Populus euphratica in yeast by model-guided mutagenesis. PLoS One 2014; 9:e104147. [PMID: 25093858 PMCID: PMC4122410 DOI: 10.1371/journal.pone.0104147] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 07/08/2014] [Indexed: 01/08/2023] Open
Abstract
Na+,K+/H+ antiporters are H+-coupled cotransporters that are crucial for cellular homeostasis. Populus euphratica, a well-known tree halophyte, contains six Na+/H+ antiporter genes (PeNHX1-6) that have been shown to function in salt tolerance. However, the catalytic mechanisms governing their ion transport remain largely unknown. Using the crystal structure of the Na+/H+ antiporter from the Escherichia coli (EcNhaA) as a template, we built the three-dimensional structure of PeNHX3 from P. euphratica. The PeNHX3 model displays the typical TM4-TM11 assembly that is critical for ion binding and translocation. The PeNHX3 structure follows the 'positive-inside' rule and exhibits a typical physicochemical property of the transporter proteins. Four conserved residues, including Tyr149, Asn187, Asp188, and Arg356, are indentified in the TM4-TM11 assembly region of PeNHX3. Mutagenesis analysis showed that these reserved residues were essential for the function of PeNHX3: Asn187 and Asp188 (forming a ND motif) controlled ion binding and translocation, and Tyr149 and Arg356 compensated helix dipoles in the TM4-TM11 assembly. PeNHX3 mediated Na+, K+ and Li+ transport in a yeast growth assay. Domain-switch analysis shows that TM11 is crucial to Li+ transport. The novel features of PeNHX3 in ion binding and translocation are discussed.
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Affiliation(s)
- Liguang Wang
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
| | - Xueying Feng
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
| | - Hong Zhao
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
| | - Lidong Wang
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
| | - Lizhe An
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
| | - Quan-Sheng Qiu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China
- * E-mail:
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190
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Sorting Nexin 27 regulates basal and activity-dependent trafficking of AMPARs. Proc Natl Acad Sci U S A 2014; 111:11840-5. [PMID: 25071192 DOI: 10.1073/pnas.1412415111] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Activity-dependent changes in synaptic strength have long been postulated as cellular correlates of learning and memory. Long-term potentiation (LTP), a well characterized form of synaptic plasticity, is often expressed as an increase in the number of postsynaptic AMPA-type glutamate receptors (AMPARs). Although the precise molecular mechanisms governing LTP remain elusive, this study identifies one member of the sorting nexin family, Sorting Nexin 27 (SNX27), as a critical component in this process. The ability of sorting nexins to bind specific phospholipids as well as their propensity to form protein-protein complexes, points to a role for these proteins in membrane trafficking and protein sorting. Here, we demonstrate that SNX27 binds to AMPARs, and that this interaction is regulated in an activity-dependent manner. Furthermore, we provide evidence that SNX27 is synaptically enriched and its level of expression regulates targeting of AMPARs to the neuronal surface. Loss of SNX27 abolishes recruitment of surface AMPARs during chemical LTP. Collectively, our data suggest a role for SNX27 in modulating synaptic plasticity through regulated interaction with AMPARs.
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191
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Hine RM, Rouhier MF, Park ST, Qi Z, Piermarini PM, Beyenbach KW. The excretion of NaCl and KCl loads in mosquitoes. 1. Control data. Am J Physiol Regul Integr Comp Physiol 2014; 307:R837-49. [PMID: 25056103 DOI: 10.1152/ajpregu.00105.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The handling of Na(+) and K(+) loads was investigated in isolated Malpighian tubules and in whole mosquitoes of Aedes aegypti. Isolated Malpighian tubules bathed in Na(+)-rich Ringer solution secreted Na(+)-rich fluid, and tubules bathed in K(+)-rich Ringer solution secreted K(+)-rich fluid. Upon Na(+) loading the hemolymph, the mosquito removed 77% the injected Na(+) within the next 30 min. The rapid onset and magnitude of this diuresis and the excretion of more Na(+) than can be accounted for by tubular secretion in vitro is consistent with the release of the calcitonin-like diuretic hormone in the mosquito to remove the Na(+) load from the hemolymph. Downstream, K(+) was reabsorbed with water in the hindgut, which concentrated Na(+) in excreted urine hyperosmotic to the hemolymph. Upon K(+) loading the hemolymph, the mosquito took 2 h to remove 100% of the injected K(+) from the hemolymph. The excretion of K(+)-rich isosmotic urine was limited to clearing the injected K(+) from the hemolymph with a minimum of Cl(-) and water. As a result, 43.3% of the injected Cl(-) and 48.1% of the injected water were conserved. The cation retained in the hemolymph with Cl(-) was probably N-methyl-d-glucamine, which replaced Na(+) in the hemolymph injection of the K(+) load. Since the tubular secretion of K(+) accounts for the removal of the K(+) load from the hemolymph, the reabsorption of K(+), Na(+), Cl(-), and water must be inhibited in the hindgut. The agents mediating this inhibition are unknown.
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Affiliation(s)
- Rebecca M Hine
- Department of Biomedical Sciences, Cornell University, Ithaca, New York
| | - Matthew F Rouhier
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio; and
| | | | - Zhijun Qi
- Institute of Pesticide Science, Northwestern Agricultural and Forestry University, Yangling, Shaanxi, China
| | - Peter M Piermarini
- Department of Entomology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio; and
| | - Klaus W Beyenbach
- Department of Biomedical Sciences, Cornell University, Ithaca, New York;
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192
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Balanced versus unbalanced salt solutions: what difference does it make? Best Pract Res Clin Anaesthesiol 2014; 28:235-47. [PMID: 25208959 DOI: 10.1016/j.bpa.2014.07.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Revised: 06/30/2014] [Accepted: 07/02/2014] [Indexed: 12/24/2022]
Abstract
BACKGROUND The infusion of crystalloid solutions is a fundamental part of the management of critically ill patients. These solutions are used to maintain the balance of water and essential electrolytes and replace losses when patients have limited gastrointestinal intake. They also act as carriers for intravenous infusion of medication and red cells. The most commonly used solution, 0.9% saline, has equal concentrations of Na(+) and Cl(-) even though the plasma concentration of Na(+) normally is 40 meq/L higher than that of Cl(-). The use of this fluid thus can produce a hyperchloremic acidosis in a dose-dependent manner, but it is not known whether this has clinical significance. APPROACH The first part of this article deals with the significance of Na(+) and Cl(-) in normal physiology. This begins with examination of their roles in the regulation of osmolality, acid-base balance, and generation of electrochemical gradients and why the concentration of Cl(-) normally is considerably lower than that of Na(+). The next part deals with how their concentrations are regulated by the gastrointestinal tract and kidney. Based on the physiology, it would seem that solutions in which the concentration of Na(+) is "balanced" by a substance other than Cl(-) would be advantageous. The final part examines the evidence to support that point. CONCLUSIONS There are strong observational data that support the notion that avoiding an elevated Cl(-) concentration or using fluids that reduce the rise in Cl(-) reduces renal dysfunction, infections, and possibly even mortality. However, observational studies only can indicate an association and cannot indicate causality. Unfortunately, randomized trials to date are far too limited to address this crucial issue. What is clear is that appropriate randomized trials will require very large populations. It also is not known whether the important variable is the concentration of Cl(-), the difference in concentrations of Na(+) and Cl(-), or the total body mass of Cl(-).
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193
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Lentes CJ, Mir SH, Boehm M, Ganea C, Fendler K, Hunte C. Molecular characterization of the Na+/H+-antiporter NhaA from Salmonella Typhimurium. PLoS One 2014; 9:e101575. [PMID: 25010413 PMCID: PMC4092016 DOI: 10.1371/journal.pone.0101575] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 06/06/2014] [Indexed: 11/29/2022] Open
Abstract
Na+/H+ antiporters are integral membrane proteins that are present in almost every cell and in every kingdom of life. They are essential for the regulation of intracellular pH-value, Na+-concentration and cell volume. These secondary active transporters exchange sodium ions against protons via an alternating access mechanism, which is not understood in full detail. Na+/H+ antiporters show distinct species-specific transport characteristics and regulatory properties that correlate with respective physiological functions. Here we present the characterization of the Na+/H+ antiporter NhaA from Salmonella enterica serovar Thyphimurium LT2, the causing agent of food-born human gastroenteritis and typhoid like infections. The recombinant antiporter was functional in vivo and in vitro. Expression of its gene complemented the Na+-sensitive phenotype of an E. coli strain that lacks the main Na+/H+ antiporters. Purified to homogeneity, the antiporter was a dimer in solution as accurately determined by size-exclusion chromatography combined with multi-angle laser-light scattering and refractive index monitoring. The purified antiporter was fully capable of electrogenic Na+(Li+)/H+-antiport when reconstituted in proteoliposomes and assayed by solid-supported membrane-based electrophysiological measurements. Transport activity was inhibited by 2-aminoperimidine. The recorded negative currents were in agreement with a 1Na+(Li+)/2H+ stoichiometry. Transport activity was low at pH 7 and up-regulation above this pH value was accompanied by a nearly 10-fold decrease of KmNa (16 mM at pH 8.5) supporting a competitive substrate binding mechanism. K+ does not affect Na+ affinity or transport of substrate cations, indicating that selectivity of the antiport arises from the substrate binding step. In contrast to homologous E. coli NhaA, transport activity remains high at pH values above 8.5. The antiporter from S. Typhimurium is a promising candidate for combined structural and functional studies to contribute to the elucidation of the mechanism of pH-dependent Na+/H+ antiporters and to provide insights in the molecular basis of species-specific growth and survival strategies.
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Affiliation(s)
- Christopher J. Lentes
- Institute for Biochemistry and Molecular Biology, ZBMZ, BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Syed H. Mir
- Institute for Biochemistry and Molecular Biology, ZBMZ, BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
- Department of Clinical Biochemistry, University of Kashmir, Srinagar, India
| | - Marc Boehm
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Constanta Ganea
- Biophysical Department, Faculty of Medicine, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Carola Hunte
- Institute for Biochemistry and Molecular Biology, ZBMZ, BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
- * E-mail:
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194
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Species differences in bacterial NhaA Na+/H+ exchangers. FEBS Lett 2014; 588:3111-6. [PMID: 25017436 DOI: 10.1016/j.febslet.2014.05.066] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 04/30/2014] [Accepted: 05/02/2014] [Indexed: 11/20/2022]
Abstract
Bacteria have adapted their NhaA Na(+)/H(+) exchangers responsible for salt homeostasis to their different habitats. We present an electrophysiological and kinetic analysis of NhaA from Helicobacter pylori and compare it to the previously investigated exchangers from Escherichia coli and Salmonella typhimurium. Properties of all three transporters are described by a simple model using a single binding site for H(+) and Na(+). We show that H.pylori NhaA only has a small acidic shift of its pH-dependent activity profile compared to the other transporters and discuss why a more drastic change in its pH activity profile is not physiologically required.
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195
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196
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Kondapalli KC, Prasad H, Rao R. An inside job: how endosomal Na(+)/H(+) exchangers link to autism and neurological disease. Front Cell Neurosci 2014; 8:172. [PMID: 25002837 PMCID: PMC4066934 DOI: 10.3389/fncel.2014.00172] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Accepted: 06/04/2014] [Indexed: 12/02/2022] Open
Abstract
Autism imposes a major impediment to childhood development and a huge emotional and financial burden on society. In recent years, there has been rapidly accumulating genetic evidence that links the eNHE, a subset of Na(+)/H(+) exchangers that localize to intracellular vesicles, to a variety of neurological conditions including autism, attention deficit hyperactivity disorder (ADHD), intellectual disability, and epilepsy. By providing a leak pathway for protons pumped by the V-ATPase, eNHE determine luminal pH and regulate cation (Na(+), K(+)) content in early and recycling endosomal compartments. Loss-of-function mutations in eNHE cause hyperacidification of endosomal lumen, as a result of imbalance in pump and leak pathways. Two isoforms, NHE6 and NHE9 are highly expressed in brain, including hippocampus and cortex. Here, we summarize evidence for the importance of luminal cation content and pH on processing, delivery and fate of cargo. Drawing upon insights from model organisms and mammalian cells we show how eNHE affect surface expression and function of membrane receptors and neurotransmitter transporters. These studies lead to cellular models of eNHE activity in pre- and post-synaptic neurons and astrocytes, where they could impact synapse development and plasticity. The study of eNHE has provided new insight on the mechanism of autism and other debilitating neurological disorders and opened up new possibilities for therapeutic intervention.
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Affiliation(s)
| | | | - Rajini Rao
- Department of Physiology, The Johns Hopkins University School of MedicineBaltimore, MD, USA
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197
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Jarvis DE, Ryu CH, Beilstein MA, Schumaker KS. Distinct Roles for SOS1 in the Convergent Evolution of Salt Tolerance in Eutrema salsugineum and Schrenkiella parvula. Mol Biol Evol 2014; 31:2094-107. [DOI: 10.1093/molbev/msu152] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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198
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Müller M, Kunz HH, Schroeder JI, Kemp G, Young HS, Neuhaus HE. Decreased capacity for sodium export out of Arabidopsis chloroplasts impairs salt tolerance, photosynthesis and plant performance. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2014; 78:646-58. [PMID: 24617758 DOI: 10.1111/tpj.12501] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 02/05/2014] [Accepted: 02/26/2014] [Indexed: 05/06/2023]
Abstract
Salt stress is a widespread phenomenon, limiting plant performance in large areas around the world. Although various types of plant sodium/proton antiporters have been characterized, the physiological function of NHD1 from Arabidopsis thaliana has not been elucidated in detail so far. Here we report that the NHD1-GFP fusion protein localizes to the chloroplast envelope. Heterologous expression of AtNHD1 was sufficient to complement a salt-sensitive Escherichia coli mutant lacking its endogenous sodium/proton exchangers. Transport competence of NHD1 was confirmed using recombinant, highly purified carrier protein reconstituted into proteoliposomes, proving Na(+) /H(+) antiport. In planta NHD1 expression was found to be highest in mature and senescent leaves but was not induced by sodium chloride application. When compared to wild-type controls, nhd1 T-DNA insertion mutants showed decreased biomasses and lower chlorophyll levels after sodium feeding. Interestingly, if grown on sand and supplemented with high sodium chloride, nhd1 mutants exhibited leaf tissue Na(+) levels similar to those of wild-type plants, but the Na(+) content of chloroplasts increased significantly. These high sodium levels in mutant chloroplasts resulted in markedly impaired photosynthetic performance as revealed by a lower quantum yield of photosystem II and increased non-photochemical quenching. Moreover, high Na(+) levels might hamper activity of the plastidic bile acid/sodium symporter family protein 2 (BASS2). The resulting pyruvate deficiency might cause the observed decreased phenylalanine levels in the nhd1 mutants due to lack of precursors.
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Affiliation(s)
- Maria Müller
- Plant Physiology, University of Kaiserslautern, Erwin Schrödinger Straße, Kaiserslautern, D-67653, Germany
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199
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Alkoby D, Rimon A, Burdak M, Patino-Ruiz M, Călinescu O, Fendler K, Padan E. NhaA Na+/H+ antiporter mutants that hardly react to the membrane potential. PLoS One 2014; 9:e93200. [PMID: 24699187 PMCID: PMC3974702 DOI: 10.1371/journal.pone.0093200] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2014] [Accepted: 02/28/2014] [Indexed: 12/23/2022] Open
Abstract
pH and Na+ homeostasis in all cells requires Na+/H+ antiporters. The crystal structure, obtained at pH 4, of NhaA, the main antiporter of Escherichia coli, has provided general insights into an antiporter mechanism and its unique pH regulation. Here, we describe a general method to select various NhaA mutants from a library of randomly mutagenized NhaA. The selected mutants, A167P and F267C are described in detail. Both mutants are expressed in Escherichia coli EP432 cells at 70–95% of the wild type but grow on selective medium only at neutral pH, A167P on Li+ (0.1 M) and F267C on Na+ (0.6 M). Surprising for an electrogenic secondary transporter, and opposed to wild type NhaA, the rates of A167P and F267C are almost indifferent to membrane potential. Detailed kinetic analysis reveals that in both mutants the rate limiting step of the cation exchange cycle is changed from an electrogenic to an electroneutral reaction.
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Affiliation(s)
- Dudu Alkoby
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem, Israel
| | - Abraham Rimon
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem, Israel
| | - Maral Burdak
- Department of Biophysical Chemistry, Max-Planck Institute for Biophysics, Frankfurt/Main, Germany
| | - Miyer Patino-Ruiz
- Department of Biophysical Chemistry, Max-Planck Institute for Biophysics, Frankfurt/Main, Germany
| | - Octavian Călinescu
- Department of Biophysical Chemistry, Max-Planck Institute for Biophysics, Frankfurt/Main, Germany
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max-Planck Institute for Biophysics, Frankfurt/Main, Germany
| | - Etana Padan
- Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem, Israel
- * E-mail:
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200
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Călinescu O, Paulino C, Kühlbrandt W, Fendler K. Keeping it simple, transport mechanism and pH regulation in Na+/H+ exchangers. J Biol Chem 2014; 289:13168-76. [PMID: 24644283 PMCID: PMC4036328 DOI: 10.1074/jbc.m113.542993] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Na+/H+ exchangers are essential for regulation of intracellular proton and sodium concentrations in all living organisms. We examined and experimentally verified a kinetic model for Na+/H+ exchangers, where a single binding site is alternatively occupied by Na+ or one or two H+ ions. The proposed transport mechanism inherently down-regulates Na+/H+ exchangers at extreme pH, preventing excessive cytoplasmic acidification or alkalinization. As an experimental test system we present the first electrophysiological investigation of an electroneutral Na+/H+ exchanger, NhaP1 from Methanocaldococcus jannaschii (MjNhaP1), a close homologue of the medically important eukaryotic NHE Na+/H+ exchangers. The kinetic model describes the experimentally observed substrate dependences of MjNhaP1, and the transport mechanism explains alkaline down-regulation of MjNhaP1. Because this model also accounts for acidic down-regulation of the electrogenic NhaA Na+/H+ exchanger from Escherichia coli (EcNhaA, shown in a previous publication) we conclude that it applies generally to all Na+/H+ exchangers, electrogenic as well as electroneutral, and elegantly explains their pH regulation. Furthermore, the electrophysiological analysis allows insight into the electrostatic structure of the translocation complex in electroneutral and electrogenic Na+/H+ exchangers.
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