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Hards K, Adolph C, Harold LK, McNeil MB, Cheung CY, Jinich A, Rhee KY, Cook GM. Two for the price of one: Attacking the energetic-metabolic hub of mycobacteria to produce new chemotherapeutic agents. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 152:35-44. [PMID: 31733221 DOI: 10.1016/j.pbiomolbio.2019.11.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Accepted: 11/12/2019] [Indexed: 12/25/2022]
Abstract
Cellular bioenergetics is an area showing promise for the development of new antimicrobials, antimalarials and cancer therapy. Enzymes involved in central carbon metabolism and energy generation are essential mediators of bacterial physiology, persistence and pathogenicity, lending themselves natural interest for drug discovery. In particular, succinate and malate are two major focal points in both the central carbon metabolism and the respiratory chain of Mycobacterium tuberculosis. Both serve as direct links between the citric acid cycle and the respiratory chain due to the quinone-linked reactions of succinate dehydrogenase, fumarate reductase and malate:quinone oxidoreductase. Inhibitors against these enzymes therefore hold the promise of disrupting two distinct, but essential, cellular processes at the same time. In this review, we discuss the roles and unique adaptations of these enzymes and critically evaluate the role that future inhibitors of these complexes could play in the bioenergetics target space.
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Affiliation(s)
- Kiel Hards
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, 1042, Auckland, New Zealand.
| | - Cara Adolph
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand
| | - Liam K Harold
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, 1042, Auckland, New Zealand
| | - Matthew B McNeil
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, 1042, Auckland, New Zealand
| | - Chen-Yi Cheung
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand
| | - Adrian Jinich
- Division of Infectious Diseases, Weill Department of Medicine, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Kyu Y Rhee
- Division of Infectious Diseases, Weill Department of Medicine, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Gregory M Cook
- Department of Microbiology and Immunology, School of Biomedical Sciences, University of Otago, 9054, Dunedin, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, 1042, Auckland, New Zealand.
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2
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Hards K, Rodriguez SM, Cairns C, Cook GM. Alternate quinone coupling in a new class of succinate dehydrogenase may potentiate mycobacterial respiratory control. FEBS Lett 2019; 593:475-486. [DOI: 10.1002/1873-3468.13330] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2019] [Accepted: 01/16/2019] [Indexed: 11/09/2022]
Affiliation(s)
- Kiel Hards
- Department of Microbiology and Immunology University of Otago Dunedin New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery The University of Auckland New Zealand
| | | | - Charlotte Cairns
- Department of Microbiology and Immunology University of Otago Dunedin New Zealand
| | - Gregory M. Cook
- Department of Microbiology and Immunology University of Otago Dunedin New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery The University of Auckland New Zealand
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3
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Taylor AJ, Kelly DJ. The function, biogenesis and regulation of the electron transport chains in Campylobacter jejuni: New insights into the bioenergetics of a major food-borne pathogen. Adv Microb Physiol 2019; 74:239-329. [PMID: 31126532 DOI: 10.1016/bs.ampbs.2019.02.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Campylobacter jejuni is a zoonotic Epsilonproteobacterium that grows in the gastrointestinal tract of birds and mammals, and is the most frequent cause of food-borne bacterial gastroenteritis worldwide. As an oxygen-sensitive microaerophile, C. jejuni has to survive high environmental oxygen tensions, adapt to oxygen limitation in the host intestine and resist host oxidative attack. Despite its small genome size, C. jejuni is a versatile and metabolically active pathogen, with a complex and highly branched set of respiratory chains allowing the use of a wide range of electron donors and alternative electron acceptors in addition to oxygen, including fumarate, nitrate, nitrite, tetrathionate and N- or S-oxides. Several novel enzymes participate in these electron transport chains, including a tungsten containing formate dehydrogenase, a Complex I that uses flavodoxin and not NADH, a periplasmic facing fumarate reductase and a cytochrome c tetrathionate reductase. This review presents an updated description of the composition and bioenergetics of these various respiratory chains as they are currently understood, including recent work that gives new insights into energy conservation during electron transport to various alternative electron acceptors. The regulation of synthesis and assembly of the electron transport chains is also discussed. A deeper appreciation of the unique features of the respiratory systems of C. jejuni may be helpful in informing strategies to control this important pathogen.
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Affiliation(s)
- Aidan J Taylor
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - David J Kelly
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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Koehn J, Magallanes ES, Peters BJ, Beuning CN, Haase AA, Zhu MJ, Rithner CD, Crick DC, Crans DC. A Synthetic Isoprenoid Lipoquinone, Menaquinone-2, Adopts a Folded Conformation in Solution and at a Model Membrane Interface. J Org Chem 2018; 83:275-288. [PMID: 29168636 PMCID: PMC5759649 DOI: 10.1021/acs.joc.7b02649] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Indexed: 11/29/2022]
Abstract
Menaquinones (naphthoquinones, MK) are isoprenoids that play key roles in the respiratory electron transport system of some prokaryotes by shuttling electrons between membrane-bound protein complexes acting as electron acceptors and donors. Menaquinone-2 (MK-2), a truncated MK, was synthesized, and the studies presented herein characterize the conformational and chemical properties of the hydrophobic MK-2 molecule. Using 2D NMR spectroscopy, we established for the first time that MK-2 has a folded conformation defined by the isoprenyl side-chain folding back over the napthoquinone in a U-shape, which depends on the specific environmental conditions found in different solvents. We used molecular mechanics to illustrate conformations found by the NMR experiments. The measured redox potentials of MK-2 differed in three organic solvents, where MK-2 was most easily reduced in DMSO, which may suggest a combination of solvent effect (presumably in part because of differences in dielectric constants) and/or conformational differences of MK-2 in different organic solvents. Furthermore, MK-2 was found to associate with the interface of model membranes represented by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles. MK-2 adopts a slightly different U-shaped conformation within reverse micelles compared to within solution, which is in sharp contrast to the extended conformations illustrated in literature for MKs.
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Affiliation(s)
- Jordan
T. Koehn
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Estela S. Magallanes
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Benjamin J. Peters
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Cheryle N. Beuning
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Allison A. Haase
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Michelle J. Zhu
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Christopher D. Rithner
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Dean C. Crick
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
| | - Debbie C. Crans
- Chemistry
Department, Cell and Molecular Biology Program,
and Microbiology, Immunology,
and Pathology Department, Colorado State
University, Fort Collins, Colorado 80523, United States
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5
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Hards K, Cook GM. Targeting bacterial energetics to produce new antimicrobials. Drug Resist Updat 2018; 36:1-12. [DOI: 10.1016/j.drup.2017.11.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 10/25/2017] [Accepted: 10/31/2017] [Indexed: 12/31/2022]
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6
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Lancaster CRD, Betz YM, Heit S, Lafontaine MA. Transmembrane Electron and Proton Transfer in Diheme-Containing Succinate : Quinone Oxidoreductases. Isr J Chem 2017. [DOI: 10.1002/ijch.201600139] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- C. Roy D. Lancaster
- Department of Structural Biology; Center of Human and Molecular Biology (ZHMB); Saarland University; Faculty of Medicine Building 60 D-66421 Homburg (Saar) Germany
| | - Yamila M. Betz
- Department of Structural Biology; Center of Human and Molecular Biology (ZHMB); Saarland University; Faculty of Medicine Building 60 D-66421 Homburg (Saar) Germany
| | - Sabine Heit
- Department of Structural Biology; Center of Human and Molecular Biology (ZHMB); Saarland University; Faculty of Medicine Building 60 D-66421 Homburg (Saar) Germany
| | - Michael A. Lafontaine
- Department of Structural Biology; Center of Human and Molecular Biology (ZHMB); Saarland University; Faculty of Medicine Building 60 D-66421 Homburg (Saar) Germany
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7
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Abstract
The emergence and spread of drug-resistant pathogens and our inability to develop new antimicrobials to overcome resistance has inspired scientists to consider new targets for drug development. Cellular bioenergetics is an area showing promise for the development of new antimicrobials, particularly in the discovery of new anti-tuberculosis drugs where several new compounds have entered clinical trials. In this review, we have examined the bioenergetics of various bacterial pathogens, highlighting the versatility of electron donor and acceptor utilisation and the modularity of electron transport chain components in bacteria. In addition to re-examining classical concepts, we explore new literature that reveals the intricacies of pathogen energetics, for example, how Salmonella enterica and Campylobacter jejuni exploit host and microbiota to derive powerful electron donors and sinks; the strategies Mycobacterium tuberculosis and Pseudomonas aeruginosa use to persist in lung tissues; and the importance of sodium energetics and electron bifurcation in the chemiosmotic anaerobe Fusobacterium nucleatum. A combination of physiological, biochemical, and pharmacological data suggests that, in addition to the clinically-approved target F1Fo-ATP synthase, NADH dehydrogenase type II, succinate dehydrogenase, hydrogenase, cytochrome bd oxidase, and menaquinone biosynthesis pathways are particularly promising next-generation drug targets. The realisation of cellular energetics as a rich target space for the development of new antimicrobials will be dependent upon gaining increased understanding of the energetic processes utilised by pathogens in host environments and the ability to design bacterial-specific inhibitors of these processes.
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8
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Lancaster CRD. The di-heme family of respiratory complex II enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:679-87. [PMID: 23466335 DOI: 10.1016/j.bbabio.2013.02.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2012] [Revised: 02/22/2013] [Accepted: 02/22/2013] [Indexed: 01/28/2023]
Abstract
The di-heme family of succinate:quinone oxidoreductases is of particular interest, because its members support electron transfer across the biological membranes in which they are embedded. In the case of the di-heme-containing succinate:menaquinone reductase (SQR) from Gram-positive bacteria and other menaquinone-containing bacteria, this results in an electrogenic reaction. This is physiologically relevant in that it allows the transmembrane electrochemical proton potential Δp to drive the endergonic oxidation of succinate by menaquinone. In the case of the reverse reaction, menaquinol oxidation by fumarate, catalysed by the di-heme-containing quinol:fumarate reductase (QFR), evidence has been obtained that this electrogenic electron transfer reaction is compensated by proton transfer via a both novel and essential transmembrane proton transfer pathway ("E-pathway"). Although the reduction of fumarate by menaquinol is exergonic, it is obviously not exergonic enough to support the generation of a Δp. This compensatory "E-pathway" appears to be required by all di-heme-containing QFR enzymes and results in the overall reaction being electroneutral. In addition to giving a brief overview of progress in the characterization of other members of this diverse family, this contribution summarizes key evidence and progress in identifying constituents of the "E-pathway" within the framework of the crystal structure of the QFR from the anaerobic epsilon-proteobacterium Wolinella succinogenes at 1.78Å resolution. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.
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Affiliation(s)
- C Roy D Lancaster
- Department of Structural Biology, Saarland University, Homburg, Germany.
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9
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Al-Attar S, de Vries S. Energy transduction by respiratory metallo-enzymes: From molecular mechanism to cell physiology. Coord Chem Rev 2013. [DOI: 10.1016/j.ccr.2012.05.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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10
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Herzog E, Gu W, Juhnke H, Haas A, Mäntele W, Simon J, Helms V, Lancaster C. Hydrogen-bonded networks along and bifurcation of the E-pathway in quinol:fumarate reductase. Biophys J 2012; 103:1305-14. [PMID: 22995503 PMCID: PMC3446689 DOI: 10.1016/j.bpj.2012.07.037] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Revised: 07/24/2012] [Accepted: 07/25/2012] [Indexed: 02/06/2023] Open
Abstract
The E-pathway of transmembrane proton transfer has been demonstrated previously to be essential for catalysis by the diheme-containing quinol:fumarate reductase (QFR) of Wolinella succinogenes. Two constituents of this pathway, Glu-C180 and heme b(D) ring C (b(D)-C-) propionate, have been validated experimentally. Here, we identify further constituents of the E-pathway by analysis of molecular dynamics simulations. The redox state of heme groups has a crucial effect on the connectivity patterns of mobile internal water molecules that can transiently support proton transfer from the b(D)-C-propionate to Glu-C180. The short H-bonding paths formed in the reduced states can lead to high proton conduction rates and thus provide a plausible explanation for the required opening of the E-pathway in reduced QFR. We found evidence that the b(D)-C-propionate group is the previously postulated branching point connecting proton transfer to the E-pathway from the quinol-oxidation site via interactions with the heme b(D) ligand His-C44. An essential functional role of His-C44 is supported experimentally by site-directed mutagenesis resulting in its replacement with Glu. Although the H44E variant enzyme retains both heme groups, it is unable to catalyze quinol oxidation. All results obtained are relevant to the QFR enzymes from the human pathogens Campylobacter jejuni and Helicobacter pylori.
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Affiliation(s)
- Elena Herzog
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
- Department of Structural Biology, Center of Human and Molecular Biology, Institute of Biophysics, Faculty of Medicine, Saarland University, Homburg, Germany
| | - Wei Gu
- Center for Bioinformatics and Center of Human and Molecular Biology, Saarland University, Saarbrücken, Germany
| | - Hanno D. Juhnke
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Alexander H. Haas
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Werner Mäntele
- Institute of Biophysics, J. W. Goethe University, Frankfurt am Main, Germany
| | - Jörg Simon
- Institute of Molecular Biosciences, J. W. Goethe University, Frankfurt am Main, Germany
| | - Volkhard Helms
- Center for Bioinformatics and Center of Human and Molecular Biology, Saarland University, Saarbrücken, Germany
| | - C. Roy D. Lancaster
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
- Department of Structural Biology, Center of Human and Molecular Biology, Institute of Biophysics, Faculty of Medicine, Saarland University, Homburg, Germany
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11
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Iverson TM. Catalytic mechanisms of complex II enzymes: a structural perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:648-57. [PMID: 22995215 DOI: 10.1016/j.bbabio.2012.09.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 09/07/2012] [Accepted: 09/10/2012] [Indexed: 11/25/2022]
Abstract
Over a decade has passed since the elucidation of the first X-ray crystal structure of any complex II homolog. In the intervening time, the structures of five additional integral-membrane complex II enzymes and three homologs of the soluble domain have been determined. These structures have provided a framework for the analysis of enzymological studies of complex II superfamily enzymes, and have contributed to detailed proposals for reaction mechanisms at each of the two enzyme active sites, which catalyze dicarboxylate and quinone oxidoreduction, respectively. This review focuses on how structural data have augmented our understanding of catalysis by the superfamily. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.
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Affiliation(s)
- T M Iverson
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232-6600, USA.
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12
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Limited reversibility of transmembrane proton transfer assisting transmembrane electron transfer in a dihaem-containing succinate:quinone oxidoreductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:593-600. [PMID: 19254686 DOI: 10.1016/j.bbabio.2009.02.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 02/17/2009] [Accepted: 02/18/2009] [Indexed: 11/20/2022]
Abstract
Membrane protein complexes can support both the generation and utilisation of a transmembrane electrochemical proton potential (Deltap), either by supporting transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by supporting transmembrane proton transfer. The first mechanism has been unequivocally demonstrated to be operational for Deltap-dependent catalysis of succinate oxidation by quinone in the case of the dihaem-containing succinate:menaquinone reductase (SQR) from the Gram-positive bacterium Bacillus licheniformis. This is physiologically relevant in that it allows the transmembrane potential Deltap to drive the endergonic oxidation of succinate by menaquinone by the dihaem-containing SQR of Gram-positive bacteria. In the case of a related but different respiratory membrane protein complex, the dihaem-containing quinol:fumarate reductase (QFR) of the epsilon-proteobacterium Wolinella succinogenes, evidence has been obtained that both mechanisms are combined, so as to facilitate transmembrane electron transfer by proton transfer via a both novel and essential compensatory transmembrane proton transfer pathway ("E-pathway"). Although the reduction of fumarate by menaquinol is exergonic, it is obviously not exergonic enough to support the generation of a Deltap. This compensatory "E-pathway" appears to be required by all dihaem-containing QFR enzymes and results in the overall reaction being electroneutral. However, here we show that the reverse reaction, the oxidation of succinate by quinone, as catalysed by W. succinogenes QFR, is not electroneutral. The implications for transmembrane proton transfer via the E-pathway are discussed.
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13
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Simon J, van Spanning RJ, Richardson DJ. The organisation of proton motive and non-proton motive redox loops in prokaryotic respiratory systems. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1480-90. [DOI: 10.1016/j.bbabio.2008.09.008] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 09/08/2008] [Accepted: 09/09/2008] [Indexed: 10/21/2022]
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14
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Electroneutral and electrogenic catalysis by dihaem-containing succinate:quinone oxidoreductases. Biochem Soc Trans 2008; 36:996-1000. [DOI: 10.1042/bst0360996] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Membrane protein complexes can support both the generation and utilization of a transmembrane electrochemical proton potential (Δp), either by supporting transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by supporting transmembrane proton transfer. Regarding the first mechanism, this has been unequivocally demonstrated to be operational for Δp-dependent catalysis of succinate oxidation by quinone in the case of the dihaem-containing SQR (succinate:menaquinone reductase) from the Gram-positive bacterium Bacillus licheniformis. This is physiologically relevant in that it allows the transmembrane Δp to drive the endergonic oxidation of succinate by menaquinone by the dihaem-containing SQR of Gram-positive bacteria. In the case of a related but different respiratory membrane protein complex, the dihaem-containing QFR (quinol:fumarate reductase) of the ϵ-proteobacterium Wolinella succinogenes, evidence has been obtained indicating that both mechanisms are combined, so as to facilitate transmembrane electron transfer by proton transfer via a both novel and essential compensatory transmembrane proton transfer pathway (‘E-pathway’). This is necessary because, although the reduction of fumarate by menaquinol is exergonic, it is obviously not exergonic enough to support the generation of a Δp. This compensatory E-pathway appears to be required by all dihaem-containing QFR enzymes and the conservation of the essential acidic residue on transmembrane helix V (Glu-C180 in W. succinogenes QFR) is a useful key for the sequence-based discrimination of these QFR enzymes from the dihaem-containing SQR enzymes.
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Tomasiak TM, Cecchini G, Iverson TM. Succinate as Donor; Fumarate as Acceptor. EcoSal Plus 2007; 2. [PMID: 26443593 DOI: 10.1128/ecosal.3.2.6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Indexed: 06/05/2023]
Abstract
Succinate and fumarate are four-carbon dicarboxylates that differ in the identity of their central bond (single or double). The oxidoreduction of these small molecules plays a central role in both aerobic and anaerobic respiration. During aerobic respiration, succinate is oxidized, donating two reducing equivalents, while in anaerobic respiration, fumarate is reduced, accepting two reducing equivalents. Two related integral membrane Complex II superfamily members catalyze these reactions, succinate:ubiquinone oxidoreductase (SQR) and fumarate:menaquinol oxidoreductase (QFR). The structure, function, and regulation of these integral-membrane enzymes are summarized here. The overall architecture of these Complex II enzymes has been found to consist of four subunits: two integral membrane subunits, and a soluble domain consisting of an iron-sulfur protein subunit, and a flavoprotein subunit. This architecture provides a scaffold that houses one active site in the membrane and another in the soluble milieu, making a linear electron transfer chain that facilities shuttling of reducing equivalents between the two active sites. A combination of kinetic measurements, mutagenesis, electron paramagnetic resonance spectroscopy, UV/Vis spectroscopy, and x-ray crystallography have suggested mechanisms for succinate:fumarate interconversion, electron transfer, and quinone:quinol interconversion. Of particular interest are the structural details that control directionality and make SQR and QFR primed for preferential catalysis each in different favored directions.
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