1
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Partial proteolysis improves the identification of the extracellular segments of transmembrane proteins by surface biotinylation. Sci Rep 2020; 10:8880. [PMID: 32483232 PMCID: PMC7264363 DOI: 10.1038/s41598-020-65831-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 05/08/2020] [Indexed: 01/11/2023] Open
Abstract
Transmembrane proteins (TMP) play a crucial role in several physiological processes. Despite their importance and diversity, only a few TMP structures have been determined by high-resolution protein structure characterization methods so far. Due to the low number of determined TMP structures, the parallel development of various bioinformatics and experimental methods was necessary for their topological characterization. The combination of these methods is a powerful approach in the determination of TMP topology as in the Constrained Consensus TOPology prediction. To support the prediction, we previously developed a high-throughput topology characterization method based on primary amino group-labelling that is still limited in identifying all TMPs and their extracellular segments on the surface of a particular cell type. In order to generate more topology information, a new step, a partial proteolysis of the cell surface has been introduced to our method. This step results in new primary amino groups in the proteins that can be biotinylated with a membrane-impermeable agent while the cells still remain intact. Pre-digestion also promotes the emergence of modified peptides that are more suitable for MS/MS analysis. The modified sites can be utilized as extracellular constraints in topology predictions and may contribute to the refined topology of these proteins.
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2
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Maynard A, Butler NL, Ito T, da Silva AJ, Murai M, Chen T, Koffas MAG, Miyoshi H, Barquera B. Antibiotic Korormicin A Kills Bacteria by Producing Reactive Oxygen Species. J Bacteriol 2019; 201:e00718-18. [PMID: 30858300 PMCID: PMC6509656 DOI: 10.1128/jb.00718-18] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 03/07/2019] [Indexed: 11/20/2022] Open
Abstract
Korormicin is an antibiotic produced by some pseudoalteromonads which selectively kills Gram-negative bacteria that express the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR.) We show that although korormicin is an inhibitor of Na+-NQR, the antibiotic action is not a direct result of inhibiting enzyme activity. Instead, perturbation of electron transfer inside the enzyme promotes a reaction between O2 and one or more redox cofactors in the enzyme (likely the flavin adenine dinucleotide [FAD] and 2Fe-2S center), leading to the production of reactive oxygen species (ROS). All Pseudoalteromonas contain the nqr operon in their genomes, including Pseudoalteromonas strain J010, which produces korormicin. We present activity data indicating that this strain expresses an active Na+-NQR and that this enzyme is not susceptible to korormicin inhibition. On the basis of our DNA sequence data, we show that the Na+-NQR of Pseudoalteromonas J010 carries an amino acid substitution (NqrB-G141A; Vibrio cholerae numbering) that in other Na+-NQRs confers resistance against korormicin. This is likely the reason that a functional Na+-NQR is able to exist in a bacterium that produces a compound that typically inhibits this enzyme and causes cell death. Korormicin is an effective antibiotic against such pathogens as Vibrio cholerae, Aliivibrio fischeri, and Pseudomonas aeruginosa but has no effect on Bacteroides fragilis and Bacteroides thetaiotaomicron, microorganisms that are important members of the human intestinal microflora.IMPORTANCE As multidrug antibiotic resistance in pathogenic bacteria continues to rise, there is a critical need for novel antimicrobial agents. An essential requirement for a useful antibiotic is that it selectively targets bacteria without significant effects on the eukaryotic hosts. Korormicin is an excellent candidate in this respect because it targets a unique respiratory enzyme found only in prokaryotes, the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR). Korormicin is synthesized by some species of the marine bacterium Pseudoalteromonas and is a potent and specific inhibitor of Na+-NQR, an enzyme that is essential for the survival and proliferation of many Gram-negative human pathogens, including Vibrio cholerae and Pseudomonas aeruginosa, among others. Here, we identified how korormicin selectively kills these bacteria. The binding of korormicin to Na+-NQR promotes the formation of reactive oxygen species generated by the reaction of the FAD and the 2Fe-2S center cofactors with O2.
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Affiliation(s)
- Adam Maynard
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York, USA
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Nicole L Butler
- Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, New York, USA
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Takeshi Ito
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Adilson José da Silva
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA
- Chemical Engineering Department, Federal University of Sao Carlos, Sao Paulo, Brazil
| | - Masatoshi Murai
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Tsute Chen
- The Forsyth Institute, Cambridge, Massachusetts, USA
- School of Dental Medicine, Harvard University, Boston, Massachusetts, USA
| | - Mattheos A G Koffas
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York, USA
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
- Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Hideto Miyoshi
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Blanca Barquera
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York, USA
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
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3
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Dibrov P, Dibrov E, Pierce GN. Na+-NQR (Na+-translocating NADH:ubiquinone oxidoreductase) as a novel target for antibiotics. FEMS Microbiol Rev 2017; 41:653-671. [PMID: 28961953 DOI: 10.1093/femsre/fux032] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 05/17/2017] [Indexed: 01/08/2023] Open
Abstract
The recent breakthrough in structural studies on Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae creates a perspective for the systematic design of inhibitors for this unique enzyme, which is the major Na+ pump in aerobic pathogens. Widespread distribution of Na+-NQR among pathogenic species, its key role in energy metabolism, its relation to virulence in different species as well as its absence in eukaryotic cells makes this enzyme especially attractive as a target for prospective antibiotics. In this review, the major biochemical, physiological and, especially, the pharmacological aspects of Na+-NQR are discussed to assess its 'target potential' for drug development. A comparison to other primary bacterial Na+ pumps supports the contention that NQR is a first rate prospective target for a new generation of antimicrobials. A new, narrowly targeted furanone inhibitor of NQR designed in our group is presented as a molecular platform for the development of anti-NQR remedies.
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Affiliation(s)
- Pavel Dibrov
- Department of Microbiology, University of Manitoba, Winnipeg, Canada
| | - Elena Dibrov
- Institute of Cardiovascular Sciences, Albrechtsen Research Centre, St. Boniface Hospital, Winnipeg, Canada.,Department of Physiology and Pathophysiology, Colleges of Medicine and Pharmacy, Faculty of Health Sciences, Winnipeg, Canada
| | - Grant N Pierce
- Institute of Cardiovascular Sciences, Albrechtsen Research Centre, St. Boniface Hospital, Winnipeg, Canada.,Department of Physiology and Pathophysiology, Colleges of Medicine and Pharmacy, Faculty of Health Sciences, Winnipeg, Canada
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4
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Cytoplasmic Localization of Sulfide:Quinone Oxidoreductase and Persulfide Dioxygenase of Cupriavidus pinatubonensis JMP134. Appl Environ Microbiol 2017; 83:AEM.01820-17. [PMID: 28939597 DOI: 10.1128/aem.01820-17] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 09/13/2017] [Indexed: 12/11/2022] Open
Abstract
Heterotrophic bacteria have recently been reported to oxidize sulfide to sulfite and thiosulfate by using sulfide:quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO). In chemolithotrophic bacteria, both SQR and PDO have been reported to function in the periplasmic space, with SQR as a peripheral membrane protein whose C terminus inserts into the cytoplasmic membrane and PDO as a soluble protein. Cupriavidus pinatubonensis JMP134, best known for its ability to degrade 2,4-dichlorophenoxyacetic acid and other aromatic pollutants, has a gene cluster of sqr and pdo encoding C. pinatubonensis SQR (CpSQR) and CpPDO2. When cloned in Escherichia coli, the enzymes are functional. Here we investigated whether they function in the periplasmic space or in the cytoplasm in heterotrophic bacteria. By using sequence analysis, biochemical detection, and green fluorescent protein (GFP)/PhoA fusion proteins, we found that CpSQR was located on the cytoplasmic side of the membrane and CpPDO2 was a soluble protein in the cytoplasm with a tendency to be peripherally located near the membrane. The location proximity of these proteins near the membrane in the cytoplasm may facilitate sulfide oxidation in heterotrophic bacteria. The information may guide the use of heterotrophic bacteria in bioremediation of organic pollutants as well as H2S.IMPORTANCE Sulfide (H2S, HS-, and S2-), which is common in natural gas and wastewater, causes a serious malodor at low levels and is deadly at high levels. Microbial oxidation of sulfide is a valid bioremediation method, in which chemolithotrophic bacteria that use sulfide as the energy source are often used to remove sulfide. Heterotrophic bacteria with SQR and PDO have recently been reported to oxidize sulfide to sulfite and thiosulfate. Cupriavidus pinatubonensis JMP134 has been extensively characterized for its ability to degrade organic pollutants, and it also contains SQR and PDO. This paper shows the localization of SQR and PDO inside the cytoplasm in the vicinity of the membrane. The information may provide guidance for using heterotrophic bacteria in sulfide bioremediation.
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5
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Langó T, Róna G, Hunyadi-Gulyás É, Turiák L, Varga J, Dobson L, Várady G, Drahos L, Vértessy BG, Medzihradszky KF, Szakács G, Tusnády GE. Identification of Extracellular Segments by Mass Spectrometry Improves Topology Prediction of Transmembrane Proteins. Sci Rep 2017; 7:42610. [PMID: 28211907 PMCID: PMC5304180 DOI: 10.1038/srep42610] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 01/11/2017] [Indexed: 01/17/2023] Open
Abstract
Transmembrane proteins play crucial role in signaling, ion transport, nutrient uptake, as well as in maintaining the dynamic equilibrium between the internal and external environment of cells. Despite their important biological functions and abundance, less than 2% of all determined structures are transmembrane proteins. Given the persisting technical difficulties associated with high resolution structure determination of transmembrane proteins, additional methods, including computational and experimental techniques remain vital in promoting our understanding of their topologies, 3D structures, functions and interactions. Here we report a method for the high-throughput determination of extracellular segments of transmembrane proteins based on the identification of surface labeled and biotin captured peptide fragments by LC/MS/MS. We show that reliable identification of extracellular protein segments increases the accuracy and reliability of existing topology prediction algorithms. Using the experimental topology data as constraints, our improved prediction tool provides accurate and reliable topology models for hundreds of human transmembrane proteins.
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Affiliation(s)
- Tamás Langó
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - Gergely Róna
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary.,Department of Applied Biotechnology and Food Sciences, Budapest University of Technology and Economics, Szent Gellért tér 4, Budapest, H-1111, Hungary.,Department of Biochemistry and Molecular Pharmacology, Perlmutter NYU Cancer Center, New York University School of Medicine, 522 First Avenue, SRB 1107, New York, NY 10016, USA
| | - Éva Hunyadi-Gulyás
- Laboratory of Proteomics Research, Biological Research Center of the Hungarian Academy of Sciences, Temesvari krt. 62, Szeged, H-6726, Hungary
| | - Lilla Turiák
- Institute of Organic Chemistry, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - Julia Varga
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - László Dobson
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - György Várady
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - László Drahos
- Institute of Organic Chemistry, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - Beáta G Vértessy
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary.,Department of Applied Biotechnology and Food Sciences, Budapest University of Technology and Economics, Szent Gellért tér 4, Budapest, H-1111, Hungary
| | - Katalin F Medzihradszky
- Laboratory of Proteomics Research, Biological Research Center of the Hungarian Academy of Sciences, Temesvari krt. 62, Szeged, H-6726, Hungary
| | - Gergely Szakács
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
| | - Gábor E Tusnády
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, Magyar Tudósok krt 2, Budapest, H-1117 Hungary
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6
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Tuz K, Li C, Fang X, Raba DA, Liang P, Minh DDL, Juárez O. Identification of the Catalytic Ubiquinone-binding Site of Vibrio cholerae Sodium-dependent NADH Dehydrogenase: A NOVEL UBIQUINONE-BINDING MOTIF. J Biol Chem 2017; 292:3039-3048. [PMID: 28053088 DOI: 10.1074/jbc.m116.770982] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 12/29/2016] [Indexed: 11/06/2022] Open
Abstract
The sodium-dependent NADH dehydrogenase (Na+-NQR) is a key component of the respiratory chain of diverse prokaryotic species, including pathogenic bacteria. Na+-NQR uses the energy released by electron transfer between NADH and ubiquinone (UQ) to pump sodium, producing a gradient that sustains many essential homeostatic processes as well as virulence factor secretion and the elimination of drugs. The location of the UQ binding site has been controversial, with two main hypotheses that suggest that this site could be located in the cytosolic subunit A or in the membrane-bound subunit B. In this work, we performed alanine scanning mutagenesis of aromatic residues located in transmembrane helices II, IV, and V of subunit B, near glycine residues 140 and 141. These two critical glycine residues form part of the structures that regulate the site's accessibility. Our results indicate that the elimination of phenylalanine residue 211 or 213 abolishes the UQ-dependent activity, produces a leak of electrons to oxygen, and completely blocks the binding of UQ and the inhibitor HQNO. Molecular docking calculations predict that UQ interacts with phenylalanine 211 and pinpoints the location of the binding site in the interface of subunits B and D. The mutagenesis and structural analysis allow us to propose a novel UQ-binding motif, which is completely different compared with the sites of other respiratory photosynthetic complexes. These results are essential to understanding the electron transfer pathways and mechanism of Na+-NQR catalysis.
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Affiliation(s)
- Karina Tuz
- From the Departments of Biological Sciences and
| | - Chen Li
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
| | - Xuan Fang
- From the Departments of Biological Sciences and
| | | | | | - David D L Minh
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
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7
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Belevich NP, Bertsova YV, Verkhovskaya ML, Baykov AA, Bogachev AV. Identification of the coupling step in Na(+)-translocating NADH:quinone oxidoreductase from real-time kinetics of electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:141-149. [PMID: 26655930 DOI: 10.1016/j.bbabio.2015.12.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Revised: 11/02/2015] [Accepted: 12/03/2015] [Indexed: 10/22/2022]
Abstract
Bacterial Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) uses a unique set of prosthetic redox groups-two covalently bound FMN residues, a [2Fe-2S] cluster, FAD, riboflavin and a Cys4[Fe] center-to catalyze electron transfer from NADH to ubiquinone in a reaction coupled with Na(+) translocation across the membrane. Here we used an ultra-fast microfluidic stopped-flow instrument to determine rate constants and the difference spectra for the six consecutive reaction steps of Vibrio harveyi Na(+)-NQR reduction by NADH. The instrument, with a dead time of 0.25 ms and optical path length of 1 cm allowed collection of visible spectra in 50-μs intervals. By comparing the spectra of reaction steps with the spectra of known redox transitions of individual enzyme cofactors, we were able to identify the chemical nature of most intermediates and the sequence of electron transfer events. A previously unknown spectral transition was detected and assigned to the Cys4[Fe] center reduction. Electron transfer from the [2Fe-2S] cluster to the Cys4[Fe] center and all subsequent steps were markedly accelerated when Na(+) concentration was increased from 20 μM to 25 mM, suggesting coupling of the former step with tight Na(+) binding to or occlusion by the enzyme. An alternating access mechanism was proposed to explain electron transfer between subunits NqrF and NqrC. According to the proposed mechanism, the Cys4[Fe] center is alternatively exposed to either side of the membrane, allowing the [2Fe-2S] cluster of NqrF and the FMN residue of NqrC to alternatively approach the Cys4[Fe] center from different sides of the membrane.
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Affiliation(s)
- Nikolai P Belevich
- Institute of Biotechnology, University of Helsinki, PO Box 65, Viikinkaari 1, FIN-00014, Finland
| | - Yulia V Bertsova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia
| | - Marina L Verkhovskaya
- Institute of Biotechnology, University of Helsinki, PO Box 65, Viikinkaari 1, FIN-00014, Finland
| | - Alexander A Baykov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia
| | - Alexander V Bogachev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119992, Russia.
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8
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Tuz K, Mezic KG, Xu T, Barquera B, Juárez O. The Kinetic Reaction Mechanism of the Vibrio cholerae Sodium-dependent NADH Dehydrogenase. J Biol Chem 2015; 290:20009-21. [PMID: 26004776 DOI: 10.1074/jbc.m115.658773] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Indexed: 11/06/2022] Open
Abstract
The sodium-dependent NADH dehydrogenase (Na(+)-NQR) is the main ion transporter in Vibrio cholerae. Its activity is linked to the operation of the respiratory chain and is essential for the development of the pathogenic phenotype. Previous studies have described different aspects of the enzyme, including the electron transfer pathways, sodium pumping structures, cofactor and subunit composition, among others. However, the mechanism of the enzyme remains to be completely elucidated. In this work, we have studied the kinetic mechanism of Na(+)-NQR with the use of steady state kinetics and stopped flow analysis. Na(+)-NQR follows a hexa-uni ping-pong mechanism, in which NADH acts as the first substrate, reacts with the enzyme, and the oxidized NAD leaves the catalytic site. In this conformation, the enzyme is able to capture two sodium ions and transport them to the external side of the membrane. In the last step, ubiquinone is bound and reduced, and ubiquinol is released. Our data also demonstrate that the catalytic cycle involves two redox states, the three- and five-electron reduced forms. A model that gathers all available information is proposed to explain the kinetic mechanism of Na(+)-NQR. This model provides a background to understand the current structural and functional information.
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Affiliation(s)
- Karina Tuz
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
| | - Katherine G Mezic
- the Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Tianhao Xu
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
| | - Blanca Barquera
- the Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Oscar Juárez
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
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9
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Hreha TN, Mezic KG, Herce HD, Duffy EB, Bourges A, Pryshchep S, Juarez O, Barquera B. Complete topology of the RNF complex from Vibrio cholerae. Biochemistry 2015; 54:2443-55. [PMID: 25831459 DOI: 10.1021/acs.biochem.5b00020] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
RNF is a redox-driven ion (Na(+) and in one case possibly H(+)) transporter present in many prokaryotes. It has been proposed that RNF performs a variety of reactions in different organisms, delivering low-potential reducing equivalents for specific cellular processes. RNF shares strong homology with the Na(+)-pumping respiratory enzyme Na(+)-NQR, although there are significant differences in subunit and redox cofactor composition. Here we report a topological analysis of the six subunits of RNF from Vibrio cholerae. Although individual subunits from other organisms have previously been studied, this is the first complete, experimentally derived, analysis of RNF from any one source. This has allowed us to identify and confirm key properties of RNF. The putative NADH binding site in RnfC is located on the cytoplasmic side of the membrane. FeS centers in RnfB and RnfC are also located on the cytoplasmic side. However, covalently attached FMNs in RnfD and RnfG are both located in the periplasm. RNF also contains a number of acidic residues that correspond to functionally important groups in Na(+)-NQR. The acidic residues involved in Na(+) uptake and many of those implicated in Na(+) translocation are topologically conserved. The topology of RNF closely matches the topology represented in the newly published structure of Na(+)-NQR, consistent with the close relation between the two enzymes. The topology of RNF is discussed in the context of the current structural model of Na(+)-NQR, and the proposed functionality of the RNF complex itself.
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10
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Structure of the V. cholerae Na+-pumping NADH:quinone oxidoreductase. Nature 2015; 516:62-7. [PMID: 25471880 DOI: 10.1038/nature14003] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Accepted: 10/24/2014] [Indexed: 11/08/2022]
Abstract
NADH oxidation in the respiratory chain is coupled to ion translocation across the membrane to build up an electrochemical gradient. The sodium-translocating NADH:quinone oxidoreductase (Na(+)-NQR), a membrane protein complex widespread among pathogenic bacteria, consists of six subunits, NqrA, B, C, D, E and F. To our knowledge, no structural information on the Na(+)-NQR complex has been available until now. Here we present the crystal structure of the Na(+)-NQR complex at 3.5 Å resolution. The arrangement of cofactors both at the cytoplasmic and the periplasmic side of the complex, together with a hitherto unknown iron centre in the midst of the membrane-embedded part, reveals an electron transfer pathway from the NADH-oxidizing cytoplasmic NqrF subunit across the membrane to the periplasmic NqrC, and back to the quinone reduction site on NqrA located in the cytoplasm. A sodium channel was localized in subunit NqrB, which represents the largest membrane subunit of the Na(+)-NQR and is structurally related to urea and ammonia transporters. On the basis of the structure we propose a mechanism of redox-driven Na(+) translocation where the change in redox state of the flavin mononucleotide cofactor in NqrB triggers the transport of Na(+) through the observed channel.
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11
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Shea ME, Mezic KG, Juárez O, Barquera B. A mutation in Na(+)-NQR uncouples electron flow from Na(+) translocation in the presence of K(+). Biochemistry 2014; 54:490-6. [PMID: 25486106 DOI: 10.1021/bi501266e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The sodium-pumping NADH:ubiquinone oxidoreductase (Na(+)-NQR) is a bacterial respiratory enzyme that obtains energy from the redox reaction between NADH and ubiquinone and uses this energy to create an electrochemical Na(+) gradient across the cell membrane. A number of acidic residues in transmembrane helices have been shown to be important for Na(+) translocation. One of these, Asp-397 in the NqrB subunit, is a key residue for Na(+) uptake and binding. In this study, we show that when this residue is replaced with asparagine, the enzyme acquires a new sensitivity to K(+); in the mutant, K(+) both activates the redox reaction and uncouples it from the ion translocation reaction. In the wild-type enzyme, Na(+) (or Li(+)) accelerates turnover while K(+) alone does not activate. In the NqrB-D397N mutant, K(+) accelerates the same internal electron transfer step (2Fe-2S → FMNC) that is accelerated by Na(+). This is the same step that is inhibited in mutants in which Na(+) uptake is blocked. NqrB-D397N is able to translocate Na(+) and Li(+), but when K(+) is introduced, no ion translocation is observed, regardless of whether Na(+) or Li(+) is present. Thus, this mutant, when it turns over in the presence of K(+), is the first, and currently the only, example of an uncoupled Na(+)-NQR. The fact the redox reaction and ion pumping become decoupled from each other only in the presence of K(+) provides a switch that promises to be a useful experimental tool.
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Affiliation(s)
- Michael E Shea
- Department of Biological Sciences and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute , Troy, New York 12180, United States
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12
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The sodium pumping NADH:quinone oxidoreductase (Na⁺-NQR), a unique redox-driven ion pump. J Bioenerg Biomembr 2014; 46:289-98. [PMID: 25052842 DOI: 10.1007/s10863-014-9565-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2014] [Accepted: 07/03/2014] [Indexed: 12/15/2022]
Abstract
The Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) is a unique Na(+) pumping respiratory complex found only in prokaryotes, that plays a key role in the metabolism of marine and pathogenic bacteria, including Vibrio cholerae and other human pathogens. Na(+)-NQR is the main entrance for reducing equivalents into the respiratory chain of these bacteria, catalyzing the oxidation of NADH and the reduction of quinone, the free energy of this redox reaction drives the selective translocation of Na(+) across the cell membrane, which energizes key cellular processes. In this review we summarize the unique properties of Na(+)-NQR in terms of its redox cofactor composition, electron transfer reactions and a possible mechanism of coupling and pumping.
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13
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Vohl G, Nedielkov R, Claussen B, Casutt MS, Vorburger T, Diederichs K, Möller HM, Steuber J, Fritz G. Crystallization and preliminary analysis of the NqrA and NqrC subunits of the Na+-translocating NADH:ubiquinone oxidoreductase from Vibrio cholerae. Acta Crystallogr F Struct Biol Commun 2014; 70:987-92. [PMID: 25005105 PMCID: PMC4089548 DOI: 10.1107/s2053230x14009881] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 05/01/2014] [Indexed: 01/20/2023] Open
Abstract
The Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) from Vibrio cholerae is a membrane protein complex consisting of six different subunits NqrA-NqrF. The major domains of the NqrA and NqrC subunits were heterologously expressed in Escherichia coli and crystallized. The structure of NqrA1-377 was solved in space groups C222₁ and P2₁ by SAD phasing and molecular replacement at 1.9 and 2.1 Å resolution, respectively. NqrC devoid of the transmembrane helix was co-expressed with ApbE to insert the flavin mononucleotide group covalently attached to Thr225. The structure was determined by molecular replacement using apo-NqrC of Parabacteroides distasonis as search model at 1.8 Å resolution.
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Affiliation(s)
- Georg Vohl
- Institute for Neuropathology, University of Freiburg, Breisacher Strasse 64, 79106 Freiburg, Germany
- Hermann-Staudinger-Graduate School, University of Freiburg, Hebelstrasse 27, 79104 Freiburg, Germany
| | - Ruslan Nedielkov
- Department of Chemistry and Research School Chemical Biology, University of Konstanz, Universitätsstrasse 10, Konstanz, 78457, Germany
| | - Björn Claussen
- Hermann-Staudinger-Graduate School, University of Freiburg, Hebelstrasse 27, 79104 Freiburg, Germany
| | - Marco S. Casutt
- Institute for Neuropathology, University of Freiburg, Breisacher Strasse 64, 79106 Freiburg, Germany
| | - Thomas Vorburger
- Department of Microbiology, University of Hohenheim, 70599 Garbenstrasse 30, Stuttgart, Germany
| | - Kay Diederichs
- Department of Chemistry and Research School Chemical Biology, University of Konstanz, Universitätsstrasse 10, Konstanz, 78457, Germany
| | - Heiko M. Möller
- Department of Chemistry and Research School Chemical Biology, University of Konstanz, Universitätsstrasse 10, Konstanz, 78457, Germany
| | - Julia Steuber
- Department of Microbiology, University of Hohenheim, 70599 Garbenstrasse 30, Stuttgart, Germany
| | - Günter Fritz
- Institute for Neuropathology, University of Freiburg, Breisacher Strasse 64, 79106 Freiburg, Germany
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Origin and evolution of the sodium -pumping NADH: ubiquinone oxidoreductase. PLoS One 2014; 9:e96696. [PMID: 24809444 PMCID: PMC4014512 DOI: 10.1371/journal.pone.0096696] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 04/11/2014] [Indexed: 11/27/2022] Open
Abstract
The sodium -pumping NADH: ubiquinone oxidoreductase (Na+-NQR) is the main ion pump and the primary entry site for electrons into the respiratory chain of many different types of pathogenic bacteria. This enzymatic complex creates a transmembrane gradient of sodium that is used by the cell to sustain ionic homeostasis, nutrient transport, ATP synthesis, flagellum rotation and other essential processes. Comparative genomics data demonstrate that the nqr operon, which encodes all Na+-NQR subunits, is found in a large variety of bacterial lineages with different habitats and metabolic strategies. Here we studied the distribution, origin and evolution of this enzymatic complex. The molecular phylogenetic analyses and the organizations of the nqr operon indicate that Na+-NQR evolved within the Chlorobi/Bacteroidetes group, after the duplication and subsequent neofunctionalization of the operon that encodes the homolog RNF complex. Subsequently, the nqr operon dispersed through multiple horizontal transfer events to other bacterial lineages such as Chlamydiae, Planctomyces and α, β, γ and δ -proteobacteria. Considering the biochemical properties of the Na+-NQR complex and its physiological role in different bacteria, we propose a detailed scenario to explain the molecular mechanisms that gave rise to its novel redox- dependent sodium -pumping activity. Our model postulates that the evolution of the Na+-NQR complex involved a functional divergence from its RNF homolog, following the duplication of the rnf operon, the loss of the rnfB gene and the recruitment of the reductase subunit of an aromatic monooxygenase.
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15
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Localization-controlled specificity of FAD:threonine flavin transferases in Klebsiella pneumoniae and its implications for the mechanism of Na(+)-translocating NADH:quinone oxidoreductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:1122-9. [PMID: 24361839 DOI: 10.1016/j.bbabio.2013.12.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 12/04/2013] [Accepted: 12/13/2013] [Indexed: 12/22/2022]
Abstract
The Klebsiella pneumoniae genome contains genes for two putative flavin transferase enzymes (ApbE1 and ApbE2) that add FMN to protein Thr residues. ApbE1, but not ApbE2, has a periplasm-addressing signal sequence. The genome also contains genes for three target proteins with the Dxx(s/t)gAT flavinylation motif: two subunits of Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR), and a 99.5kDa protein, KPK_2907, with a previously unknown function. We show here that KPK_2907 is an active cytoplasmically-localized fumarate reductase. K. pneumoniae cells with an inactivated kpk_2907 gene lack cytoplasmic fumarate reductase activity, while retaining this activity in the membrane fraction. Complementation of the mutant strain with a kpk_2907-containing plasmid resulted in a complete recovery of cytoplasmic fumarate reductase activity. KPK_2907 produced in Escherichia coli cells contains 1mol/mol each of covalently bound FMN, noncovalently bound FMN and noncovalently bound FAD. Lesion in the ApbE1 gene in K. pneumoniae resulted in inactive Na(+)-NQR, but cytoplasmic fumarate reductase activity remained unchanged. On the contrary, lesion in the ApbE2 gene abolished the fumarate reductase but not the Na(+)-NQR activity. Both activities could be restored by transformation of the ApbE1- or ApbE2-deficient K. pneumoniae strains with plasmids containing the Vibrio cholerae apbE gene with or without the periplasm-directing signal sequence, respectively. Our data thus indicate that ApbE1 and ApbE2 bind FMN to Na(+)-NQR and fumarate reductase, respectively, and that, contrary to the presently accepted view, the FMN residues are on the periplasmic side of Na(+)-NQR. A new, "electron loop" mechanism is proposed for Na(+)-NQR, involving an electroneutral Na(+)/electron symport. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.
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16
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Shea ME, Juárez O, Cho J, Barquera B. Aspartic acid 397 in subunit B of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae forms part of a sodium-binding site, is involved in cation selectivity, and affects cation-binding site cooperativity. J Biol Chem 2013; 288:31241-9. [PMID: 24030824 DOI: 10.1074/jbc.m113.510776] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)-pumping NADH:quinone complex is found in Vibrio cholerae and other marine and pathogenic bacteria. NADH:ubiquinone oxidoreductase oxidizes NADH and reduces ubiquinone, using the free energy released by this reaction to pump sodium ions across the cell membrane. In a previous report, a conserved aspartic acid residue in the NqrB subunit at position 397, located in the cytosolic face of this protein, was proposed to be involved in the capture of sodium. Here, we studied the role of this residue through the characterization of mutant enzymes in which this aspartic acid was substituted by other residues that change charge and size, such as arginine, serine, lysine, glutamic acid, and cysteine. Our results indicate that NqrB-Asp-397 forms part of one of the at least two sodium-binding sites and that both size and charge at this position are critical for the function of the enzyme. Moreover, we demonstrate that this residue is involved in cation selectivity, has a critical role in the communication between sodium-binding sites, by promoting cooperativity, and controls the electron transfer step involved in sodium uptake (2Fe-2S → FMNC).
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Affiliation(s)
- Michael E Shea
- From the Department of Biology and Center of Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 121801
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17
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Martínez-Valencia R, Reyes-Cortés G, Ramírez-Díaz MI, Riveros-Rosas H, Cervantes C. Antiparallel membrane topology of paired short-chain chromate transport proteins in Bacillus subtilis. FEMS Microbiol Lett 2012; 336:113-21. [PMID: 22900751 DOI: 10.1111/j.1574-6968.2012.02661.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 08/06/2012] [Accepted: 08/12/2012] [Indexed: 11/27/2022] Open
Abstract
Short-chain monodomain family comprises pairs of membrane proteins of about 200 amino acid residues each that belong to the chromate ion transporter (CHR) superfamily. The short-chain CHR homologous pair Chr3N/Chr3C from Bacillus subtilis strain 168 confers chromate resistance only when both proteins are expressed. Membrane topology of the Chr3N and Chr3C proteins was determined in Escherichia coli by the analysis of translational fusions with reporter enzymes alkaline phosphatase and β-galactosidase. Each short-chain CHR protein was found to consist of five transmembrane segments with antiparallel orientation between them. The C terminus of Chr3N is located in the cytoplasm, whereas the C terminus of Chr3C is located in the periplasm. In silico analyses suggest that this antiparallel arrangement is shared by all protein members of the short-chain CHR3 subfamily and that the two Chr3N/Chr3C proteins might carry out distinct functions for the transport of chromate.
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Affiliation(s)
- Rene Martínez-Valencia
- Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana, Morelia, Michoacán, México
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18
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Lunin VY, Lunina NL, Casutt MS, Knoops K, Schaffitzel C, Steuber J, Fritz G, Baumstark MW. Low-resolution structure determination of Na(+)-translocating NADH:ubiquinone oxidoreductase from Vibrio cholerae by ab initio phasing and electron microscopy. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2012; 68:724-31. [PMID: 22683795 DOI: 10.1107/s0907444912012012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 03/20/2012] [Indexed: 11/10/2022]
Abstract
A low-resolution structure of the Na(+)-translocating NADH:ubiquinone oxidoreductase from the human pathogen Vibrio cholerae was determined by ab initio phasing and independently confirmed by electron microscopy. This multi-subunit membrane-protein complex (molecular weight 210 kDa) generates an Na(+) gradient that is essential for substrate uptake, motility, pathogenicity and efflux of antibiotics. The obtained 16 Å resolution electron density-map revealed an asymmetric particle with a central region of low electron density and a putative detergent region, and allowed the identification of the transmembrane regions of the complex.
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Affiliation(s)
- Vladimir Y Lunin
- Department of Rehabilitative and Preventative Sports Medicine, University of Freiburg, Hugstetter Strasse 55, 79106 Freiburg, Germany
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19
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Insights into the mechanism of electron transfer and sodium translocation of the Na(+)-pumping NADH:quinone oxidoreductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1823-32. [PMID: 22465856 DOI: 10.1016/j.bbabio.2012.03.017] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 03/13/2012] [Accepted: 03/15/2012] [Indexed: 11/22/2022]
Abstract
Na(+)-NQR is a unique energy-transducing complex, widely distributed among marine and pathogenic bacteria. It converts the energy from the oxidation of NADH and the reduction of quinone into an electrochemical Na(+)-gradient that can provide energy for the cell. Na(+)-NQR is not homologous to any other respiratory protein but is closely related to the RNF complex. In this review we propose that sodium pumping in Na(+)-NQR is coupled to the redox reactions by a novel mechanism, which operates at multiple sites, is indirect and mediated by conformational changes of the protein. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).
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20
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Juárez O, Shea ME, Makhatadze GI, Barquera B. The role and specificity of the catalytic and regulatory cation-binding sites of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. J Biol Chem 2011; 286:26383-90. [PMID: 21652714 DOI: 10.1074/jbc.m111.257873] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)-translocating NADH:quinone oxidoreductase is the entry site for electrons into the respiratory chain and the main sodium pump in Vibrio cholerae and many other pathogenic bacteria. In this work, we have employed steady-state and transient kinetics, together with equilibrium binding measurements to define the number of cation-binding sites and characterize their roles in the enzyme. Our results show that sodium and lithium ions stimulate enzyme activity, and that Na(+)-NQR enables pumping of Li(+), as well as Na(+) across the membrane. We also confirm that the enzyme is not able to translocate other monovalent cations, such as potassium or rubidium. Although potassium is not used as a substrate, Na(+)-NQR contains a regulatory site for this ion, which acts as a nonessential activator, increasing the activity and affinity for sodium. Rubidium can bind to the same site as potassium, but instead of being activated, enzyme turnover is inhibited. Activity measurements in the presence of both sodium and lithium indicate that the enzyme contains at least two functional sodium-binding sites. We also show that the binding sites are not exclusively responsible for ion selectivity, and other steps downstream in the mechanism also play a role. Finally, equilibrium-binding measurements with (22)Na(+) show that, in both its oxidized and reduced states, Na(+)-NQR binds three sodium ions, and that the affinity for sodium is the same for both of these states.
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Affiliation(s)
- Oscar Juárez
- Department of Biology and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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21
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Biegel E, Schmidt S, González JM, Müller V. Biochemistry, evolution and physiological function of the Rnf complex, a novel ion-motive electron transport complex in prokaryotes. Cell Mol Life Sci 2011; 68:613-34. [PMID: 21072677 PMCID: PMC11115008 DOI: 10.1007/s00018-010-0555-8] [Citation(s) in RCA: 248] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Revised: 09/30/2010] [Accepted: 10/01/2010] [Indexed: 11/25/2022]
Abstract
Microbes have a fascinating repertoire of bioenergetic enzymes and a huge variety of electron transport chains to cope with very different environmental conditions, such as different oxygen concentrations, different electron acceptors, pH and salinity. However, all these electron transport chains cover the redox span from NADH + H(+) as the most negative donor to oxygen/H(2)O as the most positive acceptor or increments thereof. The redox range more negative than -320 mV has been largely ignored. Here, we have summarized the recent data that unraveled a novel ion-motive electron transport chain, the Rnf complex, that energetically couples the cellular ferredoxin to the pyridine nucleotide pool. The energetics of the complex and its biochemistry, as well as its evolution and cellular function in different microbes, is discussed.
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Affiliation(s)
- Eva Biegel
- Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany
| | - Silke Schmidt
- Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany
| | - José M. González
- Department of Microbiology and Cell Biology, University of La Laguna, 38206 La Laguna, Tenerife Spain
| | - Volker Müller
- Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Max-von-Laue-Str. 9, 60438 Frankfurt, Germany
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22
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Fadeeva MS, Bertsova YV, Verkhovsky MI, Bogachev AV. Site-directed mutagenesis of conserved cysteine residues in NqrD and NqrE subunits of Na+-translocating NADH:quinone oxidoreductase. BIOCHEMISTRY (MOSCOW) 2011; 73:123-9. [DOI: 10.1134/s0006297908020028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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23
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Liu S, Kondo N, Long Y, Xiao D, Iwamoto A, Matsuda Z. Membrane topology analysis of HIV-1 envelope glycoprotein gp41. Retrovirology 2010; 7:100. [PMID: 21118523 PMCID: PMC3012657 DOI: 10.1186/1742-4690-7-100] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Accepted: 11/30/2010] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND The gp41 subunit of the HIV-1 envelope glycoprotein (Env) has been widely regarded as a type I transmembrane protein with a single membrane-spanning domain (MSD). An alternative topology model suggested multiple MSDs. The major discrepancy between the two models is that the cytoplasmic Kennedy sequence in the single MSD model is assigned as the extracellular loop accessible to neutralizing antibodies in the other model. We examined the membrane topology of the gp41 subunit in both prokaryotic and mammalian systems. We attached topological markers to the C-termini of serially truncated gp41. In the prokaryotic system, we utilized a green fluorescent protein (GFP) that is only active in the cytoplasm. The tag protein (HaloTag) and a membrane-impermeable ligand specific to HaloTag was used in the mammalian system. RESULTS In the absence of membrane fusion, both the prokaryotic and mammalian systems (293FT cells) supported the single MSD model. In the presence of membrane fusion in mammalian cells (293CD4 cells), the data obtained seem to support the multiple MSD model. However, the region predicted to be a potential MSD is the highly hydrophilic Kennedy sequence and is least likely to become a MSD based on several algorithms. Further analysis revealed the induction of membrane permeability during membrane fusion, allowing the membrane-impermeable ligand and antibodies to cross the membrane. Therefore, we cannot completely rule out the possible artifacts. Addition of membrane fusion inhibitors or alterations of the MSD sequence decreased the induction of membrane permeability. CONCLUSIONS It is likely that a single MSD model for HIV-1 gp41 holds true even in the presence of membrane fusion. The degree of the augmentation of membrane permeability we observed was dependent on the membrane fusion and sequence of the MSD.
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Affiliation(s)
- Shujun Liu
- China-Japan Joint Laboratory of Structural Virology and Immunology, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, P. R. China
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24
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Casutt MS, Huber T, Brunisholz R, Tao M, Fritz G, Steuber J. Localization and function of the membrane-bound riboflavin in the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae. J Biol Chem 2010; 285:27088-27099. [PMID: 20558724 PMCID: PMC2930708 DOI: 10.1074/jbc.m109.071126] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 06/16/2010] [Indexed: 12/29/2022] Open
Abstract
The sodium ion-translocating NADH:quinone oxidoreductase (Na(+)-NQR) from the human pathogen Vibrio cholerae is a respiratory membrane protein complex that couples the oxidation of NADH to the transport of Na(+) across the bacterial membrane. The Na(+)-NQR comprises the six subunits NqrABCDEF, but the stoichiometry and arrangement of these subunits are unknown. Redox-active cofactors are FAD and a 2Fe-2S cluster on NqrF, covalently attached FMNs on NqrB and NqrC, and riboflavin and ubiquinone-8 with unknown localization in the complex. By analyzing the cofactor content and NADH oxidation activity of subcomplexes of the Na(+)-NQR lacking individual subunits, the riboflavin cofactor was unequivocally assigned to the membrane-bound NqrB subunit. Quantitative analysis of the N-terminal amino acids of the holo-complex revealed that NqrB is present in a single copy in the holo-complex. It is concluded that the hydrophobic NqrB harbors one riboflavin in addition to its covalently attached FMN. The catalytic role of two flavins in subunit NqrB during the reduction of ubiquinone to ubiquinol by the Na(+)-NQR is discussed.
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Affiliation(s)
- Marco S Casutt
- Department of Neuropathology, Breisacherstrasse 64, University of Freiburg, 79106 Freiburg, Germany
| | - Tamara Huber
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - René Brunisholz
- Functional Genomics Centre Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Minli Tao
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Günter Fritz
- Department of Neuropathology, Breisacherstrasse 64, University of Freiburg, 79106 Freiburg, Germany
| | - Julia Steuber
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland.
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25
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Meuric V, Rouillon A, Chandad F, Bonnaure-Mallet M. Putative respiratory chain of Porphyromonas gingivalis. Future Microbiol 2010; 5:717-34. [PMID: 20441545 DOI: 10.2217/fmb.10.32] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The electron transfer chain in Porphyromonas gingivalis, or periodontopathogens, has not yet been characterized. P. gingivalis, a strict anaerobic bacteria and the second colonizer of the oral cavity, is considered to be a major causal agent involved in periodontal diseases. Primary colonizers create a favorable environment for P. gingivalis growth by decreasing oxygen pressure. Oxygen does not appear to be the final electron acceptor of the respiratory chain. Fumarate and cytochrome b have been implicated as major components of the respiratory activity. However, the P. gingivalis genome shows many other enzymes that could be implicated in aerobic or nitrite respiration. Using bioinformatic tools and literature studies of respiratory pathways, the ATP synthesis mechanism from the sodium cycle and nutrients metabolism, the putative respirasome of P. gingivalis has been proposed.
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Affiliation(s)
- Vincent Meuric
- Equipe de Microbiologie, UPRES-EA 1254, Université Européenne de Bretagne, Université de Rennes I, UFR Odontologie, Bâtiment 15, 2 Avenue du Professeur Léon Bernard, 35043 Rennes Cedex, France
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26
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Hobb RI, Tzeng YL, Choudhury BP, Carlson RW, Stephens DS. Requirement of NMB0065 for connecting assembly and export of sialic acid capsular polysaccharides in Neisseria meningitidis. Microbes Infect 2010; 12:476-87. [PMID: 20215001 PMCID: PMC2883662 DOI: 10.1016/j.micinf.2010.02.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2009] [Revised: 02/25/2010] [Accepted: 02/27/2010] [Indexed: 12/20/2022]
Abstract
Capsule expression in Neisseria meningitidis is encoded by the cps locus comprised of genes required for biosynthesis and surface translocation. Located adjacent to the gene encoding the polysialyltransferase in serogroups expressing sialic acid-containing capsule, NMB0065 is likely a member of the cps locus, but it is not found in serogroups A or X that express non-sialic acid capsules. To further understand its role in CPS expression, NMB0065 mutants were created in the serogroups B, C and Y strains. The mutants were as sensitive as unencapsulated strains to killing by normal human serum, despite producing near wild-type levels of CPS. Absence of surface expression of capsule was suggested by increased surface hydrophobicity and confirmed by immunogold electron microscopy, which revealed the presence of large vacuoles containing CPS within the cell. GC-MS and NMR analyses of purified capsule from the mutant revealed no apparent changes in polymer structures and lipid anchors. Mutants of NMB0065 homologues in other sialic acid CPS expressing meningococcal serogroups had similar phenotypes. Thus, NMB0065 (CtrG) is not involved in biosynthesis or lipidation of sialic acid-containing capsule but encodes a protein required for proper coupling of the assembly complex to the membrane transport complex allowing surface expression of CPS.
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Affiliation(s)
- Rhonda I Hobb
- Department of Medicine, Emory University School of Medicine, Atlanta, GA, United States
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27
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Sodium-translocating NADH:quinone oxidoreductase as a redox-driven ion pump. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:738-46. [PMID: 20056102 DOI: 10.1016/j.bbabio.2009.12.020] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2009] [Revised: 12/17/2009] [Accepted: 12/24/2009] [Indexed: 11/20/2022]
Abstract
The Na+-translocating NADH:ubiquinone oxidoreductase (Na+-NQR) is a component of the respiratory chain of various bacteria. This enzyme is an analogous but not homologous counterpart of mitochondrial Complex I. Na+-NQR drives the same chemistry and also uses released energy to translocate ions across the membrane, but it pumps Na+ instead of H+. Most likely the mechanism of sodium pumping is quite different from that of proton pumping (for example, it could not accommodate the Grotthuss mechanism of ion movement); this is why the enzyme structure, subunits and prosthetic groups are completely special. This review summarizes modern knowledge on the structural and catalytic properties of bacterial Na+-translocating NADH:quinone oxidoreductases. The sequence of electron transfer through the enzyme cofactors and thermodynamic properties of those cofactors is discussed. The resolution of the intermediates of the catalytic cycle and localization of sodium-dependent steps are combined in a possible molecular mechanism of sodium transfer by the enzyme.
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28
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Juárez O, Athearn K, Gillespie P, Barquera B. Acid residues in the transmembrane helices of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae involved in sodium translocation. Biochemistry 2009; 48:9516-24. [PMID: 19694431 DOI: 10.1021/bi900845y] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Vibrio cholerae and many other marine and pathogenic bacteria possess a unique respiratory complex, the Na(+)-pumping NADH:quinone oxidoreductase (Na(+)-NQR), which pumps Na(+) across the cell membrane using the energy released by the redox reaction between NADH and ubiquinone. To function as a selective sodium pump, Na(+)-NQR must contain structures that (1) allow the sodium ion to pass through the hydrophobic core of the membrane and (2) provide cation specificity to the translocation system. In other sodium-transporting proteins, the structures that carry out these roles frequently include aspartate and glutamate residues. The negative charge of these residues facilitates binding and translocation of sodium. In this study, we have analyzed mutants of acid residues located in the transmembrane helices of subunits B, D, and E of Na(+)-NQR. The results are consistent with the participation of seven of these residues in the translocation process of sodium. Mutations at NqrB-D397, NqrD-D133, and NqrE-E95 produced a decrease of approximately >or=10-fold in the apparent affinity of the enzyme for sodium (Km(app)(Na+)), which suggests that these residues may form part of a sodium-binding site. Mutation at other residues, including NqrB-E28, NqrB-E144, NqrB-E346, and NqrD-D88, had a strong effect on the quinone reductase activity of the enzyme and its sodium sensitivity, but a weaker effect on the apparent sodium affinity, consistent with a possible role in sodium conductance pathways.
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Affiliation(s)
- Oscar Juárez
- Department of Biology and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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Núñez C, Bogachev AV, Guzmán G, Tello I, Guzmán J, Espín G. The Na+-translocating NADH : ubiquinone oxidoreductase of Azotobacter vinelandii negatively regulates alginate synthesis. Microbiology (Reading) 2009; 155:249-256. [DOI: 10.1099/mic.0.022533-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Azotobacter vinelandii is a nitrogen-fixing soil bacterium that produces the exopolysaccharide alginate. In this report we describe the isolation and characterization of A. vinelandii strain GG4, which carries an nqrE : : Tn5 mutation resulting in alginate overproduction. The nqrE gene encodes a subunit of the Na+-translocating NADH : ubiquinone oxidoreductase (Na+-NQR). As expected, Na+-NQR activity was abolished in mutant GG4. When this strain was complemented with the nqrEF genes this activity was restored and alginate production was reduced to wild-type levels. Na+-NQR may be the main sodium pump of A. vinelandii under the conditions tested (∼2 mM Na+) since no Na+/H+-antiporter activity was detected. Collectively our results indicate that in A. vinelandii the lack of Na+-NQR activity caused the absence of a transmembrane Na+ gradient and an increase in alginate production.
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Affiliation(s)
- Cinthia Núñez
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
| | - Alexander V. Bogachev
- Department of Molecular Energetics of Microorganisms, A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia
| | - Gabriel Guzmán
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
| | - Isaac Tello
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
| | - Josefina Guzmán
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
| | - Guadalupe Espín
- Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Col. Chamilpa, Cuernavaca, Morelos 62210, Mexico
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Juárez O, Nilges MJ, Gillespie P, Cotton J, Barquera B. Riboflavin is an active redox cofactor in the Na+-pumping NADH: quinone oxidoreductase (Na+-NQR) from Vibrio cholerae. J Biol Chem 2008; 283:33162-7. [PMID: 18832377 DOI: 10.1074/jbc.m806913200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Here we present new evidence that riboflavin is present as one of four flavins in Na+-NQR. In particular, we present conclusive evidence that the source of the neutral radical is not one of the FMNs and that riboflavin is the center that gives rise to the neutral flavosemiquinone. The riboflavin is a bona fide redox cofactor and is likely to be the last redox carrier of the enzyme, from which electrons are donated to quinone. We have constructed a double mutant that lacks both covalently bound FMN cofactors (NqrB-T236Y/NqrC-T225Y) and have studied this mutant together with the two single mutants (NqrB-T236Y and NqrC-T225Y) and a mutant that lacks the noncovalently bound FAD in NqrF (NqrF-S246A). The double mutant contains riboflavin and FAD in a 0.6:1 ratio, as the only flavins in the enzyme; noncovalently bound flavins were detected. In the oxidized form, the double mutant exhibits an EPR signal consistent with a neutral flavosemiquinone radical, which is abolished on reduction of the enzyme. The same radical can be observed in the FAD deletion mutant. Furthermore, when the oxidized enzyme reacts with ubiquinol (the reduced form of the usual electron acceptor) in a process that reverses the physiological direction of the electron flow, a single kinetic phase is observed. The kinetic difference spectrum of this process is consistent with one-electron reduction of a neutral flavosemiquinone. The presence of riboflavin in the role of a redox cofactor is thus far unique to Na+-NQR.
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Affiliation(s)
- Oscar Juárez
- Department of Biology, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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31
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Backiel J, Juárez O, Zagorevski DV, Wang Z, Nilges MJ, Barquera B. Covalent binding of flavins to RnfG and RnfD in the Rnf complex from Vibrio cholerae. Biochemistry 2008; 47:11273-84. [PMID: 18831535 DOI: 10.1021/bi800920j] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Enzymes of the Rnf family are believed to be bacterial redox-driven ion pumps, coupling an oxidoreduction process to the translocation of Na+ across the cell membrane. Here we show for the first time that Rnf is a flavoprotein, with FMN covalently bound to threonine-175 in RnfG and a second flavin bound to threonine-187 in RnfD. Rnf subunits D and G are homologous to subunits B and C of Na+-NQR, respectively. Each of these Na+-NQR subunits includes a conserved S(T)GAT motif, with FMN covalently bound to the final threonine. RnfD and RnfG both contain the same motif, suggesting that they bind flavins in a similar way. In order to investigate this, the genes for RnfD and RnfG from Vibrio cholerae were cloned and expressed individually in that organism. In both cases the produced protein fluoresced under UV illumination on an SDS gel, further indicating the presence of flavin. However, analysis of the mutants RnfG-T175L, RnfD-T278L, and RnfD-T187V showed that RnfG-T175 and RnfD-T187 are the likely flavin ligands. This indicates that, in the case of RnfD, the flavin is bound, not to the SGAT sequence but to the final residues of a TMAT sequence, a novel variant of the flavin binding motif. In the case of RnfG, flavin analysis, followed by MALDI-TOF-TOF mass spectrometry, showed that an FMN is covalently attached to threonine-175, the final threonine of the S(T)GAT sequence. Studies by visible, EPR, and ENDOR spectroscopy showed that, upon partial reduction, the isolated RnfG produces a neutral semiquinone intermediate. The semiquinone species disappeared upon full reduction and was not observed in the denatured protein. A topological analysis combining reporter protein fusion and computer predictions indicated that the flavins in RnfG and RnfD are localized in the periplasmic space. In contrast, in NqrC and NqrB the flavins are located in a cytoplasmic loop. This topological analysis suggests that there may be mechanistic differences between the Rnf and Na+-NQR complexes.
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Affiliation(s)
- Julianne Backiel
- Department of Biology and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, 110 Eight Street, Troy, New York 12180, USA
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Tao M, Casutt MS, Fritz G, Steuber J. Oxidant-induced formation of a neutral flavosemiquinone in the Na+-translocating NADH:Quinone oxidoreductase (Na+-NQR) from Vibrio cholerae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:696-702. [PMID: 18454933 DOI: 10.1016/j.bbabio.2008.04.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 03/31/2008] [Accepted: 04/05/2008] [Indexed: 10/22/2022]
Abstract
The Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) from the human pathogen Vibrio cholerae is a respiratory flavo-FeS complex composed of the six subunits NqrA-F. The Na(+)-NQR was produced as His(6)-tagged protein by homologous expression in V. cholerae. The isolated complex contained near-stoichiometric amounts of non-covalently bound FAD (0.78 mol/mol Na(+)-NQR) and riboflavin (0.70 mol/mol Na(+)-NQR), catalyzed NADH-driven Na(+) transport (40 nmol Na(+)min(-1) mg(-1)), and was inhibited by 2-n-heptyl-4-hydroxyquinoline-N-oxide. EPR spectroscopy showed that Na(+)-NQR as isolated contained very low amounts of a neutral flavosemiquinone (10(-3) mol/mol Na(+)-NQR). Reduction with NADH resulted in the formation of an anionic flavosemiquinone (0.10 mol/mol Na(+)-NQR). Subsequent oxidation of the Na(+)-NQR with ubiquinone-1 or O(2) led to the formation of a neutral flavosemiquinone (0.24 mol/mol Na(+)-NQR). We propose that the Na(+)-NQR is fully oxidized in its resting state, and discuss putative schemes of NADH-triggered redox transitions.
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Affiliation(s)
- Minli Tao
- Biochemisches Institut, Universität Zürich, CH-8057 Zürich, Switzerland
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Transmembrane topology of the Acr3 family arsenite transporter from Bacillus subtilis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:963-73. [PMID: 18088595 DOI: 10.1016/j.bbamem.2007.11.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Revised: 11/14/2007] [Accepted: 11/16/2007] [Indexed: 11/21/2022]
Abstract
The transmembrane topology of the Acr3 family arsenite transporter Acr3 from Bacillus subtilis was analysed experimentally using translational fusions with alkaline phosphatase and green fluorescent protein and in silico by topology modelling. Initial topology prediction resulted in two models with 9 and 10 TM helices respectively. 32 fusion constructs were made between truncated forms of acr3 and the reporter genes at 17 different sites throughout the acr3 sequence to discriminate between these models. Nine strong reporter protein signals provided information about the majority of the locations of the cytoplasmic and extracellular loops of Acr3 and showed that both the N- and the C-termini are located in the cytoplasm. Two ambiguous data points indicated the possibility of an alternative 8 helix topology. This possibility was investigated using another 10 fusion variants, but no experimental support for the 8 TM topology was obtained. We therefore conclude that Acr3 has 10 transmembrane helices. Overall, the loops which connect the membrane spanning segments are short, with cytoplasmic loops being somewhat longer than the extracellular loops. The study provides the first ever experimentally derived structural information on a protein of the Acr3 family which constitutes one of the largest classes of arsenite transporters.
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Fadeeva MS, Yakovtseva EA, Belevich GA, Bertsova YV, Bogachev AV. Regulation of expression of Na+ -translocating NADH:quinone oxidoreductase genes in Vibrio harveyi and Klebsiella pneumoniae. Arch Microbiol 2007; 188:341-8. [PMID: 17551713 DOI: 10.1007/s00203-007-0254-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 03/16/2007] [Accepted: 04/28/2007] [Indexed: 10/23/2022]
Abstract
The expression of genes encoding sodium-translocating NADH:quinone oxidoreductase (Na(+)-NQR) was studied in the marine bacterium Vibrio harveyi and in the enterobacterium Klebsiella pneumoniae. It has been shown that such parameters as NaCl concentration, pH value, and presence of an uncoupler in the growth media do not influence significantly the level of nqr expression. However, nqr expression depends on the growth substrates used by these bacteria. Na(+)-NQR is highly repressed in V. harveyi during anaerobic growth, and nqr expression is modulated by electron acceptors and values of their redox potentials. The latter effect was shown to be independent of the ArcAB regulatory system.
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Affiliation(s)
- Maria S Fadeeva
- Department of Molecular Energetics of Microorganisms, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory, Moscow 119992, Russia
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Kerscher S, Dröse S, Zickermann V, Brandt U. The three families of respiratory NADH dehydrogenases. Results Probl Cell Differ 2007; 45:185-222. [PMID: 17514372 DOI: 10.1007/400_2007_028] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Most reducing equivalents extracted from foodstuffs during oxidative metabolism are fed into the respiratory chains of aerobic bacteria and mitochondria by NADH:quinone oxidoreductases. Three families of enzymes can perform this task and differ remarkably in their complexity and role in energy conversion. Alternative or NDH-2-type NADH dehydrogenases are simple one subunit flavoenzymes that completely dissipate the redox energy of the NADH/quinone couple. Sodium-pumping NADH dehydrogenases (Nqr) that are only found in procaryotes contain several flavins and are integral membrane protein complexes composed of six different subunits. Proton-pumping NADH dehydrogenases (NDH-1 or complex I) are highly complicated membrane protein complexes, composed of up to 45 different subunits, that are found in bacteria and mitochondria. This review gives an overview of the origin, structural and functional properties and physiological significance of these three types of NADH dehydrogenase.
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Affiliation(s)
- Stefan Kerscher
- Molecular Bioenergetics Group, Centre of Excellence Macromolecular Complexes, Johann Wolfgang Goethe-Universität, 60590, Frankfurt am Main, Germany
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Lin PC, Türk K, Häse CC, Fritz G, Steuber J. Quinone reduction by the Na+-translocating NADH dehydrogenase promotes extracellular superoxide production in Vibrio cholerae. J Bacteriol 2007; 189:3902-8. [PMID: 17322313 PMCID: PMC1913329 DOI: 10.1128/jb.01651-06] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The pathogenicity of Vibrio cholerae is influenced by sodium ions which are actively extruded from the cell by the Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR). To study the function of the Na(+)-NQR in the respiratory chain of V. cholerae, we examined the formation of organic radicals and superoxide in a wild-type strain and a mutant strain lacking the Na(+)-NQR. Upon reduction with NADH, an organic radical was detected in native membranes by electron paramagnetic resonance spectroscopy which was assigned to ubisemiquinones generated by the Na(+)-NQR. The radical concentration increased from 0.2 mM at 0.08 mM Na(+) to 0.4 mM at 14.7 mM Na(+), indicating that the concentration of the coupling cation influences the redox state of the quinone pool in V. cholerae membranes. During respiration, V. cholerae cells produced extracellular superoxide with a specific activity of 10.2 nmol min(-1) mg(-1) in the wild type compared to 3.1 nmol min(-1) mg(-1) in the NQR deletion strain. Raising the Na(+) concentration from 0.1 to 5 mM increased the rate of superoxide formation in the wild-type V. cholerae strain by at least 70%. Rates of respiratory H(2)O(2) formation by wild-type V. cholerae cells (30.9 nmol min(-1) mg(-1)) were threefold higher than rates observed with the mutant strain lacking the Na(+)-NQR (9.7 nmol min(-1) mg(-1)). Our study shows that environmental Na(+) could stimulate ubisemiquinone formation by the Na(+)-NQR and hereby enhance the production of reactive oxygen species formed during the autoxidation of reduced quinones.
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Affiliation(s)
- Po-Chi Lin
- Biochemisches Institut, Universität Zürich, CH-8057 Zürich, Switzerland
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