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Padhi Y, Chatterjee S. XdfA, a novel membrane-associated DedA family protein of Xanthomonas campestris, is required for optimum virulence, maintenance of magnesium, and membrane homeostasis. mBio 2023; 14:e0136123. [PMID: 37498088 PMCID: PMC10470534 DOI: 10.1128/mbio.01361-23] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 06/15/2023] [Indexed: 07/28/2023] Open
Abstract
Xanthomonas campestris is an important member of the Xanthomonas group of phytopathogens that causes diseases in crucifers. In X. campestris, several virulence-associated functions, including some belonging to unknown predicted functions, have been implicated in the colonization and disease processes. However, the role of many of these unknown predicted proteins in Xanthomonas-host interaction and their exact physiological function is not clearly known. In this study, we identified a novel membrane-associated protein belonging to the DedA super family, XdfA, which is required for virulence in X. campestris. The DedA family of proteins are generally ubiquitous in bacteria; however, their function and actual physiological role are largely elusive. Characterization of ∆xdfA by homology modeling, membrane localization, and physiological studies indicated that XdfA is a membrane-associated protein that plays a role in the maintenance of membrane integrity. Furthermore, functional homology modeling analysis revealed that the XdfA exhibits structural similarity to a CorA-like magnesium transporter and is required for optimum growth under low magnesium ion concentration. We report for the first time that a putative DedA family of protein in Xanthomonas is required for optimum virulence and plays a role in the maintenance of membrane-associated functions and magnesium homeostasis. IMPORTANCE Bacterial DedA family proteins are involved in a range of cellular processes such as ion transport, signal transduction, and cell division. Here, we have discussed about a novel DedA family protein XdfA in Xanthomonas campestris pv. campestris that has a role in membrane homeostasis, magnesium transport, and virulence. Understanding membrane and magnesium homeostasis will aid in our comprehension of bacterial physiology and eventually will help us devise effective antimicrobial strategies to safeguard horticulturally and agriculturally important crop plants.
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Affiliation(s)
- Yasobanta Padhi
- Laboratory of Plant-Microbe Interactions, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, Telangana, India
- Graduate Studies, Manipal Academy of Higher Education, Udupi, Karnataka, India
| | - Subhadeep Chatterjee
- Laboratory of Plant-Microbe Interactions, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, Telangana, India
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2
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Rombolá-Caldentey B, Mendoza I, Quintero FJ, Pardo JM. Structure-Guided Identification of Critical Residues in the Vacuolar Cation/Proton Antiporter NHX1 from Arabidopsis thaliana. PLANTS (BASEL, SWITZERLAND) 2023; 12:2778. [PMID: 37570932 PMCID: PMC10421325 DOI: 10.3390/plants12152778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 07/24/2023] [Accepted: 07/24/2023] [Indexed: 08/13/2023]
Abstract
Cation/Proton Antiporters (CPA) acting in all biological membranes regulate the volume and pH of cells and of intracellular organelles. A key issue with these proteins is their structure-function relationships since they present intrinsic regulatory features that rely on structural determinants, including pH sensitivity and the stoichiometry of ion exchange. Crystal structures are only available for prokaryotic CPA, whereas the eukaryotic ones have been modeled using the former as templates. Here, we present an updated and improved structural model of the tonoplast-localized K+, Na+/H+ antiporter NHX1 of Arabidopsis as a representative of the vacuolar NHX family that is essential for the accumulation of K+ into plant vacuoles. Conserved residues that were judged as functionally important were mutated, and the resulting protein variants were tested for activity in the yeast Saccharomyces cerevisiae. The results indicate that residue N184 in the ND-motif characteristic of CPA1 could be replaced by the DD-motif of CPA2 family members with minimal consequences for their activity. Attempts to alter the electroneutrality of AtNHX1 by different combinations of amino acid replacements at N184, R353 and R390 residues resulted in inactive or partly active proteins with a differential ability to control the vacuolar pH of the yeast.
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Affiliation(s)
| | | | | | - José M. Pardo
- Instituto de Bioquimica Vegetal y Fotosintesis, cicCartuja, Consejo Superior de Investigaciones Cientificas, Universidad de Sevilla, 41092 Sevilla, Spain; (B.R.-C.); (I.M.); (F.J.Q.)
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3
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Prokaryotic Na+/H+ Exchangers—Transport Mechanism and Essential Residues. Int J Mol Sci 2022; 23:ijms23169156. [PMID: 36012428 PMCID: PMC9408914 DOI: 10.3390/ijms23169156] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 08/09/2022] [Accepted: 08/13/2022] [Indexed: 11/16/2022] Open
Abstract
Na+/H+ exchangers are essential for Na+ and pH homeostasis in all organisms. Human Na+/H+ exchangers are of high medical interest, and insights into their structure and function are aided by the investigation of prokaryotic homologues. Most prokaryotic Na+/H+ exchangers belong to either the Cation/Proton Antiporter (CPA) superfamily, the Ion Transport (IT) superfamily, or the Na+-translocating Mrp transporter superfamily. Several structures have been solved so far for CPA and Mrp members, but none for the IT members. NhaA from E. coli has served as the prototype of Na+/H+ exchangers due to the high amount of structural and functional data available. Recent structures from other CPA exchangers, together with diverse functional information, have allowed elucidation of some common working principles shared by Na+/H+ exchangers from different families, such as the type of residues involved in the substrate binding and even a simple mechanism sufficient to explain the pH regulation in the CPA and IT superfamilies. Here, we review several aspects of prokaryotic Na+/H+ exchanger structure and function, discussing the similarities and differences between different transporters, with a focus on the CPA and IT exchangers. We also discuss the proposed transport mechanisms for Na+/H+ exchangers that explain their highly pH-regulated activity profile.
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4
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Tiwari V, Panta PR, Billiot CE, Douglass MV, Herrera CM, Trent MS, Doerrler WT. A Klebsiella pneumoniae DedA family membrane protein is required for colistin resistance and for virulence in wax moth larvae. Sci Rep 2021; 11:24365. [PMID: 34934166 PMCID: PMC8692421 DOI: 10.1038/s41598-021-03834-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Accepted: 12/10/2021] [Indexed: 12/15/2022] Open
Abstract
Ineffectiveness of carbapenems against multidrug resistant pathogens led to the increased use of colistin (polymyxin E) as a last resort antibiotic. A gene belonging to the DedA family encoding conserved membrane proteins was previously identified by screening a transposon library of K. pneumoniae ST258 for sensitivity to colistin. We have renamed this gene dkcA (dedA of Klebsiella required for colistin resistance). DedA family proteins are likely membrane transporters required for viability of Escherichia coli and Burkholderia spp. at alkaline pH and for resistance to colistin in a number of bacterial species. Colistin resistance is often conferred via modification of the lipid A component of bacterial lipopolysaccharide with aminoarabinose (Ara4N) and/or phosphoethanolamine. Mass spectrometry analysis of lipid A of the ∆dkcA mutant shows a near absence of Ara4N in the lipid A, suggesting a requirement for DkcA for lipid A modification with Ara4N. Mutation of K. pneumoniae dkcA resulted in a reduction of the colistin minimal inhibitory concentration to approximately what is found with a ΔarnT strain. We also identify a requirement of DkcA for colistin resistance that is independent of lipid A modification, instead requiring maintenance of optimal membrane potential. K. pneumoniae ΔdkcA displays reduced virulence in Galleria mellonella suggesting colistin sensitivity can cause loss of virulence.
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Affiliation(s)
- Vijay Tiwari
- grid.64337.350000 0001 0662 7451Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA
| | - Pradip R. Panta
- grid.64337.350000 0001 0662 7451Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA
| | - Caitlin E. Billiot
- grid.64337.350000 0001 0662 7451Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA
| | - Martin V. Douglass
- grid.213876.90000 0004 1936 738XDepartment of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA USA
| | - Carmen M. Herrera
- grid.213876.90000 0004 1936 738XDepartment of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA USA
| | - M. Stephen Trent
- grid.213876.90000 0004 1936 738XDepartment of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA USA
| | - William T. Doerrler
- grid.64337.350000 0001 0662 7451Department of Biological Sciences, Louisiana State University, Baton Rouge, LA USA
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5
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Characterization of modeled inhibitory binding sites on isoform one of the Na +/H + exchanger. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183648. [PMID: 33992631 DOI: 10.1016/j.bbamem.2021.183648] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 05/07/2021] [Accepted: 05/10/2021] [Indexed: 12/31/2022]
Abstract
Mammalian Na+/H+ exchanger isoform one (NHE1) is a plasma membrane protein responsible for pH regulation in mammalian cells. Excess activity of the protein promotes heart disease and is a trigger of metastasis in cancer. Inhibitors of the protein exist but problems in specificity have delayed their clinical application. Here we examined amino acids involved in two modeled inhibitor binding sites (A, B) in human NHE1. Twelve mutations (Asp159, Phe348, Ser351, Tyr381, Phe413, Leu465, Gly466, Tyr467, Leu468, His473, Met476, Leu481) were made and characterized. Mutants S351A, F413A, Y467A, L468A, M476A and L481A had 40-70% of wild type expression levels, while G466A and H473A expressed 22% ~ 30% of the wild type levels. Most mutants, were targeted to the cell surface at levels similar to wild type NHE1, approximately 50-70%, except for F413A and G466A, which had very low surface targeting. Most of the mutants had measurable activity except for D159A, F413A and G466A. Resistance to inhibition by EMD87580 was elevated in mutants F438A, L465A and L468A and reduced in mutants S351A, Y381A, H473A, M476A and L481A. All mutants with large alterations in inhibitory properties showed reduced Na+ affinity. The greatest changes in activity and inhibitor sensitivity were in mutants present in binding site B which is more closely associated with TM4 and C terminal of extracellular loop 5, and is situated between the putative scaffolding domain and transport domain. The results help define the inhibitor binding domain of the NHE1 protein and identify new amino acids involved in inhibitor binding.
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6
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Panta PR, Kumar S, Stafford CF, Billiot CE, Douglass MV, Herrera CM, Trent MS, Doerrler WT. A DedA Family Membrane Protein Is Required for Burkholderia thailandensis Colistin Resistance. Front Microbiol 2019; 10:2532. [PMID: 31827463 PMCID: PMC6849406 DOI: 10.3389/fmicb.2019.02532] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Accepted: 10/21/2019] [Indexed: 12/15/2022] Open
Abstract
Colistin is a “last resort” antibiotic for treatment of infections caused by some multidrug resistant Gram-negative bacterial pathogens. Resistance to colistin varies between bacterial species. Some Gram-negative bacteria such as Burkholderia spp. are intrinsically resistant to very high levels of colistin with minimal inhibitory concentrations (MIC) often above 0.5 mg/ml. We have previously shown DedA family proteins YqjA and YghB are conserved membrane transporters required for alkaline tolerance and resistance to several classes of dyes and antibiotics in Escherichia coli. Here, we show that a DedA family protein in Burkholderia thailandensis (DbcA; DedA of Burkholderia required for colistin resistance) is a membrane transporter required for resistance to colistin. Mutation of dbcA results in >100-fold greater sensitivity to colistin. Colistin resistance is often conferred via covalent modification of lipopolysaccharide (LPS) lipid A. Mass spectrometry of lipid A of ΔdbcA showed a sharp reduction of aminoarabinose in lipid A compared to wild type. Complementation of colistin sensitivity of B. thailandensis ΔdbcA was observed by expression of dbcA, E. coli yghB or E. coli yqjA. Many proton-dependent transporters possess charged amino acids in transmembrane domains that take part in the transport mechanism and are essential for function. Site directed mutagenesis of conserved and predicted membrane embedded charged amino acids suggest that DbcA functions as a proton-dependent transporter. Direct measurement of membrane potential shows that B. thailandensis ΔdbcA is partially depolarized suggesting that loss of protonmotive force can lead to alterations in LPS structure and severe colistin sensitivity in this species.
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Affiliation(s)
- Pradip R Panta
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States
| | - Sujeet Kumar
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States
| | - Caroline F Stafford
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States
| | - Caitlin E Billiot
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States
| | - Martin V Douglass
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA, United States.,Center for Vaccines and Immunology, University of Georgia College of Veterinary Medicine, Athens, GA, United States
| | - Carmen M Herrera
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA, United States.,Center for Vaccines and Immunology, University of Georgia College of Veterinary Medicine, Athens, GA, United States
| | - M Stephen Trent
- Department of Infectious Diseases, University of Georgia College of Veterinary Medicine, Athens, GA, United States.,Center for Vaccines and Immunology, University of Georgia College of Veterinary Medicine, Athens, GA, United States
| | - William T Doerrler
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, United States
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7
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Windler F, Bönigk W, Körschen HG, Grahn E, Strünker T, Seifert R, Kaupp UB. The solute carrier SLC9C1 is a Na +/H +-exchanger gated by an S4-type voltage-sensor and cyclic-nucleotide binding. Nat Commun 2018; 9:2809. [PMID: 30022052 PMCID: PMC6052114 DOI: 10.1038/s41467-018-05253-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 06/15/2018] [Indexed: 11/30/2022] Open
Abstract
Voltage-sensing (VSD) and cyclic nucleotide-binding domains (CNBD) gate ion channels for rapid electrical signaling. By contrast, solute carriers (SLCs) that passively redistribute substrates are gated by their substrates themselves. Here, we study the orphan sperm-specific solute carriers SLC9C1 that feature a unique tripartite structure: an exchanger domain, a VSD, and a CNBD. Voltage-clamp fluorimetry shows that SLC9C1 is a genuine Na+/H+ exchanger gated by voltage. The cellular messenger cAMP shifts the voltage range of activation. Mutations in the transport domain, the VSD, or the CNBD strongly affect Na+/H+ exchange, voltage gating, or cAMP sensitivity, respectively. Our results establish SLC9C1 as a phylogenetic chimaera that combines the ion-exchange mechanism of solute carriers with the gating mechanism of ion channels. Classic SLCs slowly readjust changes in the intra- and extracellular milieu, whereas voltage gating endows the Na+/H+ exchanger with the ability to produce a rapid pH response that enables downstream signaling events. The sperm-specific solute carrier SLC9C1 is a phylogenetic chimaera that carries a voltage-sensing (VSD) and a cyclic nucleotide-binding domain (CNBD). Here authors show by electrophysiology and fluorimetry that SLC9C1 is a genuine Na+/H+ exchanger gated by voltage and cAMP.
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Affiliation(s)
- F Windler
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany.,Marine Biological Laboratory, 7 MBL Street, Woods Hole, 02543, MA, USA
| | - W Bönigk
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany
| | - H G Körschen
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany
| | - E Grahn
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany
| | - T Strünker
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany.,Marine Biological Laboratory, 7 MBL Street, Woods Hole, 02543, MA, USA.,University Hospital Münster, Center of Reproductive Medicine and Andrology, Albert-Schweitzer-Campus 1, Geb. D11, 48149, Münster, Germany
| | - R Seifert
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany. .,Marine Biological Laboratory, 7 MBL Street, Woods Hole, 02543, MA, USA.
| | - U B Kaupp
- Center of Advanced European Studies and Research (caesar), Department Molecular Sensory Systems, Ludwig-Erhard-Allee 2, 53175, Bonn, Germany. .,Marine Biological Laboratory, 7 MBL Street, Woods Hole, 02543, MA, USA. .,University of Bonn, Life & Medical Sciences Institute (LIMES), Carl-Troll-Str. 31, 53115, Bonn, Germany.
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Shao L, Abdel-Motaal H, Chen J, Chen H, Xu T, Meng L, Zhang Z, Meng F, Jiang J. Characterization of a Functionally Unknown Arginine-Aspartate-Aspartate Family Protein From Halobacillus andaensis and Functional Analysis of Its Conserved Arginine/Aspartate Residues. Front Microbiol 2018; 9:807. [PMID: 29922240 PMCID: PMC5996927 DOI: 10.3389/fmicb.2018.00807] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 04/10/2018] [Indexed: 01/15/2023] Open
Abstract
Arginine–aspartate–aspartate (RDD) family, representing a category of transmembrane proteins containing one highly conserved arginine and two highly conserved aspartates, has been functionally uncharacterized as yet. Here we present the characterization of a member of this family designated RDD from the moderate halophile Halobacillus andaensis NEAU-ST10-40T and report for the first time that RDD should function as a novel Na+(Li+, K+)/H+ antiporter. It’s more interesting whether the highly conserved arginine/aspartate residues among the whole family or between RDD and its selected homologs are related to the protein function. Therefore, we analyzed their roles in the cation-transporting activity through site-directed mutagenesis and found that D154, R124, R129, and D158 are indispensable for Na+(Li+, K+)/H+ antiport activity whereas neither R35 nor D42 is involved in Na+(Li+, K+)/H+ antiport activity. As a dual representative of Na+(Li+, K+)/H+ antiporters and RDD family proteins, the characterization of RDD and the analysis of its important residues will positively contribute to the knowledge of the cation-transporting mechanisms of this novel antiporter and the roles of highly conserved arginine/aspartate residues in the functions of RDD family proteins.
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Affiliation(s)
- Li Shao
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Heba Abdel-Motaal
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Jin Chen
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Huiwen Chen
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Tong Xu
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Lin Meng
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Zhenglai Zhang
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Fankui Meng
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
| | - Juquan Jiang
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China
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9
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Dutta D, Fliegel L. Structure and function of yeast and fungal Na + /H + antiporters. IUBMB Life 2017; 70:23-31. [PMID: 29219228 DOI: 10.1002/iub.1701] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Accepted: 11/21/2017] [Indexed: 12/22/2022]
Abstract
Sodium proton antiporters (or sodium proton exchangers [NHEs]) are a critical family of membrane proteins that exchange sodium for protons across cell membranes. In yeast and plants, their primary function is to keep the sodium concentration low inside the cytoplasm. One class of NHE constitutively expressed in yeast is the plasma membrane Na+ /H+ antiporter, and another class is expressed on the endosomal/vacuolar membrane. At present, four bacterial plasma membrane antiporter structures are known and nuclear magnetic resonance structures are available for the membrane spanning transmembrane helices of mammalian and yeast NHEs. Additionally, a vast amount of mutational data are available on the role of individual amino acids and critical motifs involved in transport. We combine this information to obtain a more detailed picture of the yeast NHE plasma membrane protein and review mechanisms of transport, conserved motifs, unique residues important in function, and regulation of these proteins. The Na+ /H+ antiporter of Schizosaccharomyces pombe, SpNHE1, is an interesting model protein in an easy to study system and is representative of fungal Na+ /H+ antiporters. © IUBMB Life, 70(1):23-31, 2018.
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Affiliation(s)
- Debajyoti Dutta
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
| | - Larry Fliegel
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
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10
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Harding T, Roger AJ, Simpson AGB. Adaptations to High Salt in a Halophilic Protist: Differential Expression and Gene Acquisitions through Duplications and Gene Transfers. Front Microbiol 2017; 8:944. [PMID: 28611746 PMCID: PMC5447177 DOI: 10.3389/fmicb.2017.00944] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 05/11/2017] [Indexed: 11/13/2022] Open
Abstract
The capacity of halophiles to thrive in extreme hypersaline habitats derives partly from the tight regulation of ion homeostasis, the salt-dependent adjustment of plasma membrane fluidity, and the increased capability to manage oxidative stress. Halophilic bacteria, and archaea have been intensively studied, and substantial research has been conducted on halophilic fungi, and the green alga Dunaliella. By contrast, there have been very few investigations of halophiles that are phagotrophic protists, i.e., protozoa. To gather fundamental knowledge about salt adaptation in these organisms, we studied the transcriptome-level response of Halocafeteria seosinensis (Stramenopiles) grown under contrasting salinities. We provided further evolutionary context to our analysis by identifying genes that underwent recent duplications. Genes that were highly responsive to salinity variations were involved in stress response (e.g., chaperones), ion homeostasis (e.g., Na+/H+ transporter), metabolism and transport of lipids (e.g., sterol biosynthetic genes), carbohydrate metabolism (e.g., glycosidases), and signal transduction pathways (e.g., transcription factors). A significantly high proportion (43%) of duplicated genes were also differentially expressed, accentuating the importance of gene expansion in adaptation by H. seosinensis to high salt environments. Furthermore, we found two genes that were lateral acquisitions from bacteria, and were also highly up-regulated and highly expressed at high salt, suggesting that this evolutionary mechanism could also have facilitated adaptation to high salt. We propose that a transition toward high-salt adaptation in the ancestors of H. seosinensis required the acquisition of new genes via duplication, and some lateral gene transfers (LGTs), as well as the alteration of transcriptional programs, leading to increased stress resistance, proper establishment of ion gradients, and modification of cell structure properties like membrane fluidity.
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Affiliation(s)
- Tommy Harding
- Department of Biochemistry and Molecular Biology, Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie UniversityHalifax, NS, Canada
| | - Andrew J. Roger
- Department of Biochemistry and Molecular Biology, Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie UniversityHalifax, NS, Canada
| | - Alastair G. B. Simpson
- Department of Biology and Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie UniversityHalifax, NS, Canada
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11
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Abstract
The structures of transport proteins have been steadily revealed in the last few decades, and yet the conversion of this information into molecular-level understanding of their function is still lagging behind. In this study, we try to elucidate how the action of the archaeal sodium/proton antiporter MjNhaP1 depends on its structure-energy relationship. To this end, we calculate the binding energies of its substrates and evaluate the conformational change barrier, focusing on the rotation of the catalytic residue D161. We find that sodium ions and protons compete against a common binding site and that the accessibility of this binding site is restricted to either the inside or outside of the cell. We suggest that the rotation of D161 χ1 angle correlates with the conformational change and is energetically unfavorable when D161 does not bind any substrate. This restriction ensures coupling between the sodium ions and the protons, allowing MjNhaP1 and probably other similar transporters to exchange substrates with minimal leak. Using Monte Carlo simulations we demonstrate the feasibility of our model. Overall we present a complete picture that reproduces the electroneutral (at 1:1 substrate ratio) and coupled transport activity of MjNhaP1 including the energetic basis for the criteria provided by Jardetzky half a century ago.
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Affiliation(s)
- Raphael Alhadeff
- Department of Chemistry, University of Southern California , SGM 418, 3620 McClintock Avenue, Los Angeles, California 90089, United States
| | - Arieh Warshel
- Department of Chemistry, University of Southern California , SGM 418, 3620 McClintock Avenue, Los Angeles, California 90089, United States
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12
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Kumar S, Bradley CL, Mukashyaka P, Doerrler WT. Identification of essential arginine residues ofEscherichia coliDedA/Tvp38 family membrane proteins YqjA and YghB. FEMS Microbiol Lett 2016; 363:fnw133. [DOI: 10.1093/femsle/fnw133] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/14/2016] [Indexed: 12/15/2022] Open
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13
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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: 2.1] [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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14
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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: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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15
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Castro PJ, Silva AF, Marreiros BC, Batista AP, Pereira MM. Respiratory complex I: A dual relation with H(+) and Na(+)? BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:928-37. [PMID: 26711319 DOI: 10.1016/j.bbabio.2015.12.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 12/10/2015] [Accepted: 12/17/2015] [Indexed: 10/22/2022]
Abstract
Respiratory complex I couples NADH:quinone oxidoreduction to ion translocation across the membrane, contributing to the buildup of the transmembrane difference of electrochemical potential. H(+) is well recognized to be the coupling ion of this system but some studies suggested that this role could be also performed by Na(+). We have previously observed NADH-driven Na(+) transport opposite to H(+) translocation by menaquinone-reducing complexes I, which indicated a Na(+)/H(+) antiporter activity in these systems. Such activity was also observed for the ubiquinone-reducing mitochondrial complex I in its deactive form. The relation of Na(+) with complex I may not be surprising since the enzyme has three subunits structurally homologous to bona fide Na(+)/H(+) antiporters and translocation of H(+) and Na(+) ions has been described for members of most types of ion pumps and transporters. Moreover, no clearly distinguishable motifs for the binding of H(+) or Na(+) have been recognized yet. We noticed that in menaquinone-reducing complexes I, less energy is available for ion translocation, compared to ubiquinone-reducing complexes I. Therefore, we hypothesized that menaquinone-reducing complexes I perform Na(+)/H(+) antiporter activity in order to achieve the stoichiometry of 4H(+)/2e(-). In agreement, the organisms that use ubiquinone, a high potential quinone, would have kept such Na(+)/H(+) antiporter activity, only operative under determined conditions. This would imply a physiological role(s) of complex I besides a simple "coupling" of a redox reaction and ion transport, which could account for the sophistication of this enzyme. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.
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Affiliation(s)
- Paulo J Castro
- Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal
| | - Andreia F Silva
- Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal
| | - Bruno C Marreiros
- Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal
| | - Ana P Batista
- Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal
| | - Manuela M Pereira
- Instituto de Tecnologia Química e Biológica, António Xavier, Universidade Nova de Lisboa, Av. da Republica EAN, 2780-157 Oeiras, Portugal.
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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: 6.7] [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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17
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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: 82] [Impact Index Per Article: 8.2] [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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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: 3.3] [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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19
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Abstract
We examined substrate-induced conformational changes in MjNhaP1, an archaeal electroneutral Na(+)/H(+)-antiporter resembling the human antiporter NHE1, by electron crystallography of 2D crystals in a range of physiological pH and Na(+) conditions. In the absence of sodium, changes in pH had no major effect. By contrast, changes in Na(+) concentration caused a marked conformational change that was largely pH-independent. Crystallographically determined, apparent dissociation constants indicated ∼10-fold stronger Na(+) binding at pH 8 than at pH 4, consistent with substrate competition for a common ion-binding site. Projection difference maps indicated helix movements by about 2 Å in the 6-helix bundle region of MjNhaP1 that is thought to contain the ion translocation site. We propose that these movements convert the antiporter from the proton-bound, outward-open state to the Na(+)-bound, inward-open state. Oscillation between the two states would result in rapid Na(+)/H(+) antiport. DOI: http://dx.doi.org/10.7554/eLife.01412.001.
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Affiliation(s)
- Cristina Paulino
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
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20
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Hendus-Altenburger R, Kragelund BB, Pedersen SF. Structural dynamics and regulation of the mammalian SLC9A family of Na⁺/H⁺ exchangers. CURRENT TOPICS IN MEMBRANES 2014; 73:69-148. [PMID: 24745981 DOI: 10.1016/b978-0-12-800223-0.00002-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mammalian Na⁺/H⁺ exchangers of the SLC9A family are widely expressed and involved in numerous essential physiological processes. Their primary function is to mediate the 1:1 exchange of Na⁺ for H⁺ across the membrane in which they reside, and they play central roles in regulation of body, cellular, and organellar pH. Their function is tightly regulated through mechanisms involving interactions with multiple protein and lipid-binding partners, phosphorylations, and other posttranslational modifications. Biochemical and mutational analyses indicate that the SLC9As have a short intracellular N-terminus, 12 transmembrane (TM) helices necessary and sufficient for ion transport, and a C-terminal cytoplasmic tail region with essential regulatory roles. No high-resolution structures of the SLC9As exist; however, models based on crystal structures of the bacterial NhaAs support the 12 TM organization and suggest that TMIV and XI may form a central part of the ion-translocation pathway, whereas pH sensing may involve TMII, TMIX, and several intracellular loops. Similar to most ion transporters studied, SLC9As likely exist as coupled dimers in the membrane, and this appears to be important for the well-studied cooperativity of H⁺ binding. The aim of this work is to summarize and critically discuss the currently available evidence on the structural dynamics, regulation, and binding partner interactions of SLC9As, focusing in particular on the most widely studied isoform, SLC9A1/NHE1. Further, novel bioinformatic and structural analyses are provided that to some extent challenge the existing paradigm on how ions are transported by mammalian SLC9As.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark; Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Birthe B Kragelund
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Stine Falsig Pedersen
- Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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21
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Identification of important charged residues for alkali cation exchange or pH regulation of NhaH, a Na+/H+ antiporter of Halobacillus dabanensis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013. [DOI: 10.1016/j.bbamem.2012.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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22
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Resch CT, Winogrodzki JL, Häse CC, Dibrov P. Insights into the biochemistry of the ubiquitous NhaP family of cation/H+ antiportersThis paper is one of a selection of papers published in a Special Issue entitled CSBMCB 53rd Annual Meeting — Membrane Proteins in Health and Disease, and has undergone the Journal’s usual peer review process. Biochem Cell Biol 2011; 89:130-7. [DOI: 10.1139/o10-149] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Na+/H+ antiporters are integral membrane proteins that exchange Na+ for H+ across the cytoplasmic or organellar membranes of virtually all living cells. They are essential for control of cellular pH, volume homeostasis, and regulation of Na+ levels. Na+/H+ antiporters have become increasingly characterized and are now becoming important drug targets. The recently identified NhaP family of Na+/H+ antiporters, from the CPA1 superfamily, contains proteins with a surprisingly broad collective range of transported cations, exchanging protons for alkali cations such as Na+, Li+, K+, or Rb+ as well as for Ca2+ and, possibly, NH4+. Questions about ion selectivity and the physiological impact of each particular NhaP antiporter are far from trivial. For example, Vc-NhaP2 from Vibrio cholerae has recently been shown to function in vivo as a specific K+/H+ antiporter while retaining the ability to exchange H+ for Na+ and bind (but not exchange with H+) Li+ in a competitive manner. These and other findings reviewed in this communication make antiporters of the NhaP type attractive systems to study intimate molecular mechanisms of cation exchange. In an evolutionary perspective, the NhaP family seems to be a phylogenetic entity undergoing active divergent evolution. In this minireview, to rationalize peculiarities of the cation specificity in the NhaP family, the “size-exclusion principle” and the idea of “ligand shading” are discussed.
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Affiliation(s)
- Craig T. Resch
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
- Department of Biomedical Sciences, College of Veterinary Sciences, Oregon State University, Corvallis, OR 97331, USA
| | - Judith L. Winogrodzki
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
- Department of Biomedical Sciences, College of Veterinary Sciences, Oregon State University, Corvallis, OR 97331, USA
| | - Claudia C. Häse
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
- Department of Biomedical Sciences, College of Veterinary Sciences, Oregon State University, Corvallis, OR 97331, USA
| | - Pavel Dibrov
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
- Department of Biomedical Sciences, College of Veterinary Sciences, Oregon State University, Corvallis, OR 97331, USA
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Goswami P, Paulino C, Hizlan D, Vonck J, Yildiz O, Kühlbrandt W. Structure of the archaeal Na+/H+ antiporter NhaP1 and functional role of transmembrane helix 1. EMBO J 2010; 30:439-49. [PMID: 21151096 DOI: 10.1038/emboj.2010.321] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 11/10/2010] [Indexed: 11/09/2022] Open
Abstract
We have determined the structure of the archaeal sodium/proton antiporter NhaP1 at 7 Å resolution by electron crystallography of 2D crystals. NhaP1 is a dimer in the membrane, with 13 membrane-spanning α-helices per protomer, whereas the distantly related bacterial NhaA has 12. Dimer contacts in the two antiporters are very different, but the structure of a six-helix bundle at the tip of the protomer is conserved. The six-helix bundle of NhaA contains two partially unwound α-helices thought to harbour the ion-translocation site, which is thus similar in NhaP1. A model of NhaP1 based on detailed sequence comparison and the NhaA structure was fitted to the 7 Å map. The additional N-terminal helix 1 of NhaP1, which appears to be an uncleaved signal sequence, is located near the dimer interface. Similar sequences are present in many eukaryotic homologues of NhaP1, including NHE1. Although fully folded and able to dimerize, NhaP1 constructs without helix 1 are inactive. Possible reasons are investigated and discussed.
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Affiliation(s)
- Panchali Goswami
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
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24
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Infrared spectroscopic study of the structural and functional properties of the Na+/H+ antiporter MjNhaP1 from Methanococcus jannaschii. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:730-7. [DOI: 10.1016/j.bbabio.2009.04.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2009] [Revised: 04/02/2009] [Accepted: 04/02/2009] [Indexed: 11/23/2022]
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25
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Conformations of NhaA, the Na+/H+ exchanger from Escherichia coli, in the pH-activated and ion-translocating states. J Mol Biol 2009; 388:659-72. [PMID: 19396973 DOI: 10.1016/j.jmb.2009.03.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
NhaA, the main sodium-proton exchanger in the inner membrane of Escherichia coli, regulates the cytosolic concentrations of H+ and Na+. It is inactive at acidic pH, becomes active between pH 6 and pH 7, and reaches maximum activity at pH 8. By cryo-electron microscopy of two-dimensional crystals grown at pH 4 and incubated at higher pH, we identified two sequential conformational changes in the protein in response to pH or substrate ions. The first change is induced by a rise in pH from 6 to 7 and marks the transition from the inactive state to the pH-activated state. pH activation, which precedes the ion-induced conformational change, is accompanied by an overall expansion of the NhaA monomer and a local ordering of the N-terminus. The second conformational change is induced by the substrate ions Na+ and Li+ at pH above 7 and involves a 7-A displacement of helix IVp. This movement would cause a charge imbalance at the ion-binding site that may trigger the release of the substrate ion and open a periplasmic exit channel.
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26
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Conformations of NhaA, the Na/H Exchanger from Escherichia coli, in the pH-Activated and Ion-Translocating States. J Mol Biol 2009; 386:351-65. [DOI: 10.1016/j.jmb.2008.12.042] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 12/11/2008] [Accepted: 12/15/2008] [Indexed: 12/25/2022]
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27
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Furrer EM, Ronchetti MF, Verrey F, Pos KM. Functional characterization of a NapA Na+/H+antiporter fromThermus thermophilus. FEBS Lett 2007; 581:572-8. [PMID: 17254570 DOI: 10.1016/j.febslet.2006.12.059] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Accepted: 12/29/2006] [Indexed: 10/23/2022]
Abstract
Na(+)/H(+) antiporters are ubiquitous membrane proteins and play an important role in cell homeostasis. We amplified a gene encoding a member of the monovalent cation:proton antiporter-2 (CPA2) family (TC 2.A.37) from the Thermus thermophilus genome and expressed it in Escherichia coli. The gene product was identified as a member of the NapA subfamily and was found to be an active Na(+)(Li(+))/H(+) antiporter as it conferred resistance to the Na(+) and Li(+) sensitive strain E. coli EP432 (DeltanhaA, DeltanhaB) upon exposure to high concentration of these salts in the growth medium. Fluorescence measurements using the pH sensitive dye 9-amino-6-chloro-2-methoxyacridine in everted membrane vesicles of complemented E. coli EP432 showed high Li(+)/H(+) exchange activity at pH 6, but marginal Na(+)/H(+) antiport activity. Towards more alkaline conditions, Na(+)/H(+) exchange activity increased to a relative maximum at pH 8, where by contrast the Li(+)/H(+) exchange activity reached its relative minimum. Substitution of conserved residues D156 and D157 (located in the putative transmembrane helix 6) with Ala resulted in the complete loss of Na(+)/H(+) activity. Mutation of K305 (putative transmembrane helix 10) to Ala resulted in a compromised phenotype characterized by an increase in apparent K(m) for Na(+) (36 vs. 7.6 mM for the wildtype) and Li(+) (17 vs. 0.22 mM), In summary, the Na(+)/H(+) antiport activity profile of the NapA type transporter of T. thermophilus resembles that of NhaA from E. coli, whereas in contrast to NhaA the T. thermophilus NapA antiporter is characterized by high Li(+)/H(+) antiport activity at acidic pH.
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Affiliation(s)
- Esther M Furrer
- Institute of Physiology and Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Winterthurerstrasse 190, Zürich, Switzerland
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Zeilinger C, Steffens M, Kolb HA. Length of C-terminus of rCx46 influences oligomerization and hemichannel properties. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1720:35-43. [PMID: 16388779 DOI: 10.1016/j.bbamem.2005.10.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Revised: 10/05/2005] [Accepted: 10/07/2005] [Indexed: 11/20/2022]
Abstract
Wild type connexin 46 of rat (wtrCx46), and human connexin 26 (wthCx26) and derivates from rCx46 elongated at the C-terminus by 25 amino acids (rCx46Ct) as well as C-terminal truncated constructs (rCx28.1, rCx45.3) were expressed in frog oocytes of Xenopus laevis. Single oocyte voltage-clamp analysis revealed that connexons or hemichannels of rCx46Ct exhibit similar conducting properties as those of wtrCx46. Insertion of a stop codon at C-terminal domains at position 243 and 409 resulted in a significant reduction in the corresponding hemichannel conductance. This result was also found for wthCx26, the shortest human connexin. Tagged connexin constructs rCx46Ct and hCx26Ct could be expressed in E. coli as monomers. The monomers of rCx46Ct and hCx26Ct were purified and electro-eluted from corresponding SDS gels. Studies of in vitro oligomerization showed that hexamers of these connexins were formed in presence of kinase and specific lipids. Purified rCx46Ct formed some oligomers in vitro if a lipid mixture of POPE/POPG and casein kinase I (CKI) was added, but in the presence of POPC, phosphorylated rCx46Ct monomers preferentially formed hexamers. Purified hCx26Ct formed hexamers in the presence of POPE/POPG. In addition, N-terminal truncated rCx46 (Cx35) oligomerized after phosphorylation. Reconstitution of purified recombinant connexin rCx46Ct in planar lipid bilayers mediated Ca(2+)-sensitive single channel activity. It is discussed whether the specific C-terminal end of the expressed connexins are responsible for hexamer formation as well as channel opening.
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Affiliation(s)
- Carsten Zeilinger
- Universität Hannover, Institut für Biophysik, Herrenhäuserstr. 2, D-30419 Hannover, Germany.
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29
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Padan E, Bibi E, Ito M, Krulwich TA. Alkaline pH homeostasis in bacteria: new insights. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1717:67-88. [PMID: 16277975 PMCID: PMC3072713 DOI: 10.1016/j.bbamem.2005.09.010] [Citation(s) in RCA: 475] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2005] [Revised: 08/19/2005] [Accepted: 09/07/2005] [Indexed: 10/25/2022]
Abstract
The capacity of bacteria to survive and grow at alkaline pH values is of widespread importance in the epidemiology of pathogenic bacteria, in remediation and industrial settings, as well as in marine, plant-associated and extremely alkaline ecological niches. Alkali-tolerance and alkaliphily, in turn, strongly depend upon mechanisms for alkaline pH homeostasis, as shown in pH shift experiments and growth experiments in chemostats at different external pH values. Transcriptome and proteome analyses have recently complemented physiological and genetic studies, revealing numerous adaptations that contribute to alkaline pH homeostasis. These include elevated levels of transporters and enzymes that promote proton capture and retention (e.g., the ATP synthase and monovalent cation/proton antiporters), metabolic changes that lead to increased acid production, and changes in the cell surface layers that contribute to cytoplasmic proton retention. Targeted studies over the past decade have followed up the long-recognized importance of monovalent cations in active pH homeostasis. These studies show the centrality of monovalent cation/proton antiporters in this process while microbial genomics provides information about the constellation of such antiporters in individual strains. A comprehensive phylogenetic analysis of both eukaryotic and prokaryotic genome databases has identified orthologs from bacteria to humans that allow better understanding of the specific functions and physiological roles of the antiporters. Detailed information about the properties of multiple antiporters in individual strains is starting to explain how specific monovalent cation/proton antiporters play dominant roles in alkaline pH homeostasis in cells that have several additional antiporters catalyzing ostensibly similar reactions. New insights into the pH-dependent Na(+)/H(+) antiporter NhaA that plays an important role in Escherichia coli have recently emerged from the determination of the structure of NhaA. This review highlights the approaches, major findings and unresolved problems in alkaline pH homeostasis, focusing on the small number of well-characterized alkali-tolerant and extremely alkaliphilic bacteria.
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Affiliation(s)
- Etana Padan
- Alexander Silberman Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel.
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Vinothkumar KR, Smits SHJ, Kühlbrandt W. pH-induced structural change in a sodium/proton antiporter from Methanococcus jannaschii. EMBO J 2005; 24:2720-9. [PMID: 16015376 PMCID: PMC1182236 DOI: 10.1038/sj.emboj.7600727] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Accepted: 06/02/2005] [Indexed: 11/08/2022] Open
Abstract
Na+/H+ antiporters are pH-dependent membrane transport proteins that maintain the homeostasis of H+ and Na+ in living cells. MjNhaP1 from Methanococcus jannaschii, a hyperthermophilic archaeon that grows optimally at 85 degrees C, was cloned and expressed in Escherichia coli. Two-dimensional crystals were obtained from purified protein at pH 4. Electron cryomicroscopy yielded an 8 A projection map. Like the related E. coli antiporter NhaA, MjNhaP1 is a dimer, but otherwise the structures of the two antiporters differ significantly. The map of MjNhaP1 shows elongated densities in the centre of the dimer and a cluster of density peaks on either side of the dimer core, indicative of a bundle of 4-6 membrane-spanning helices. The effect of pH on the structure of MjNhaP1 was studied in situ. A major change in density distribution within the helix bundle, and an approximately 2 A shift in the position of the helix bundle relative to the dimer core occurred at pH 6 and above. The two conformations at low and high pH most likely represent the closed and open states of the antiporter.
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Affiliation(s)
- Kutti R Vinothkumar
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Sander H J Smits
- 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
- Department of Structural Biology, Max Planck Institute of Biophysics, Max-von-Laue Str. 3, 60438 Frankfurt am Main, Germany. Tel.: +49 69 63033001; Fax: +49 69 63033002; E-mail:
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Padan E, Tzubery T, Herz K, Kozachkov L, Rimon A, Galili L. NhaA of Escherichia coli, as a model of a pH-regulated Na+/H+antiporter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2004; 1658:2-13. [PMID: 15282168 DOI: 10.1016/j.bbabio.2004.04.018] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2004] [Revised: 03/17/2004] [Accepted: 04/20/2004] [Indexed: 11/18/2022]
Abstract
Na(+)/H(+) antiporters are ubiquitous membrane proteins that are involved in homeostasis of H(+) and Na(+) throughout the biological kingdom. Corroborating their role in pH homeostasis, many of the Na(+)/H(+) antiporter proteins are regulated directly by pH. The pH regulation of NhaA, the Escherichia coli Na(+)/H(+) antiporter (EcNhaA), as of other, both eukaryotic and prokaryotic Na(+)/H(+) antiporters, involves a pH sensor and conformational changes in different parts of the protein that transduce the pH signal into a change in activity. Thus, residues that affect the pH response, the translocation or both activities cluster in separate domains along the antiporter molecules. Importantly, in the NhaA family, these domains are conserved. Helix-packing model of EcNhaA based on cross-linking data suggests, that in the three dimensional structure of NhaA, residues that affect the pH response may be in close proximity, forming a single pH sensitive domain. Therefore, it is suggested that, despite considerable differences in the primary structure of the antiporters from the bacterial NhaA to the mammalian NHEs, their three-dimensional architectures are conserved. Test of this possibility awaits the atomic resolution of the 3D structure of the antiporters.
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Affiliation(s)
- E Padan
- Division of Microbial and Molecular Ecology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
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Hellmer J, Zeilinger C. MjK1, a K+ channel from M. jannaschii, mediates K+ uptake and K+ sensitivity in E. coli. FEBS Lett 2003; 547:165-9. [PMID: 12860407 DOI: 10.1016/s0014-5793(03)00706-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The methanogenic and hyperthermophilic deep-sea archaeon Methanococcus jannaschii has three putative K+ channels, MVP (Mj0139), MjK1 (Mj0138.1) and MjK2 (Mj1357). The physiological function of these K+ channels was examined in a viability assay, using the Escherichia coli mutant LB2003 (kup1, DeltakdpABC5, DeltatrkA). While MjK2 expression had no effects on the potassium-dependent phenotype of LB2003, MVP and MjK1 complemented the deficiency at a concentration of 1 mM KCl. In contrast to KcsA, MthK and MVP, MjK1 strongly affected host cell viability at 10 and 100 mM KCl. The toxic effects were less pronounced when growth media were supplemented with the K+ channel blocker BaCl2.
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Affiliation(s)
- Jens Hellmer
- Universität Hannover, Institut für Biophysik, Herrenhäuserstr. 2, D-30419, Hannover, Germany
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