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Kampjut D, Sazanov LA. Structure of respiratory complex I – An emerging blueprint for the mechanism. Curr Opin Struct Biol 2022; 74:102350. [PMID: 35316665 PMCID: PMC7613608 DOI: 10.1016/j.sbi.2022.102350] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 01/25/2022] [Accepted: 02/08/2022] [Indexed: 11/26/2022]
Abstract
Complex I is one of the major respiratory complexes, conserved from bacteria to mammals. It oxidises NADH, reduces quinone and pumps protons across the membrane, thus playing a central role in the oxidative energy metabolism. In this review we discuss our current state of understanding the structure of complex I from various species of mammals, plants, fungi, and bacteria, as well as of several complex I-related proteins. By comparing the structural evidence from these systems in different redox states and data from mutagenesis and molecular simulations, we formulate the mechanisms of electron transfer and proton pumping and explain how they are conformationally and electrostatically coupled. Finally, we discuss the structural basis of the deactivation phenomenon in mammalian complex I.
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2
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Richardson KH, Wright JJ, Šimėnas M, Thiemann J, Esteves AM, McGuire G, Myers WK, Morton JJL, Hippler M, Nowaczyk MM, Hanke GT, Roessler MM. Functional basis of electron transport within photosynthetic complex I. Nat Commun 2021; 12:5387. [PMID: 34508071 PMCID: PMC8433477 DOI: 10.1038/s41467-021-25527-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 08/11/2021] [Indexed: 02/08/2023] Open
Abstract
Photosynthesis and respiration rely upon a proton gradient to produce ATP. In photosynthesis, the Respiratory Complex I homologue, Photosynthetic Complex I (PS-CI) is proposed to couple ferredoxin oxidation and plastoquinone reduction to proton pumping across thylakoid membranes. However, little is known about the PS-CI molecular mechanism and attempts to understand its function have previously been frustrated by its large size and high lability. Here, we overcome these challenges by pushing the limits in sample size and spectroscopic sensitivity, to determine arguably the most important property of any electron transport enzyme - the reduction potentials of its cofactors, in this case the iron-sulphur clusters of PS-CI (N0, N1 and N2), and unambiguously assign them to the structure using double electron-electron resonance. We have thus determined the bioenergetics of the electron transfer relay and provide insight into the mechanism of PS-CI, laying the foundations for understanding of how this important bioenergetic complex functions.
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Affiliation(s)
- Katherine H. Richardson
- grid.4868.20000 0001 2171 1133School of Biological and Chemical Sciences, Queen Mary University of London, London, UK ,grid.7445.20000 0001 2113 8111Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, London, UK
| | - John J. Wright
- grid.4868.20000 0001 2171 1133School of Biological and Chemical Sciences, Queen Mary University of London, London, UK ,grid.14105.310000000122478951Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Cambridge, UK
| | - Mantas Šimėnas
- grid.83440.3b0000000121901201London Centre for Nanotechnology, University College London, London, UK
| | - Jacqueline Thiemann
- grid.5570.70000 0004 0490 981XPlant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Ana M. Esteves
- grid.4868.20000 0001 2171 1133School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Gemma McGuire
- grid.4868.20000 0001 2171 1133School of Biological and Chemical Sciences, Queen Mary University of London, London, UK ,grid.7445.20000 0001 2113 8111Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, London, UK
| | - William K. Myers
- grid.4991.50000 0004 1936 8948Inorganic Chemistry, University of Oxford, Oxford, UK
| | - John J. L. Morton
- grid.83440.3b0000000121901201London Centre for Nanotechnology, University College London, London, UK ,grid.83440.3b0000000121901201Department of Electronic & Electrical Engineering, UCL, London, UK
| | - Michael Hippler
- grid.5949.10000 0001 2172 9288Institute of Plant Biology and Biotechnology, University of Münster, Münster, Germany ,grid.261356.50000 0001 1302 4472Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan
| | - Marc M. Nowaczyk
- grid.5570.70000 0004 0490 981XPlant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Guy T. Hanke
- grid.4868.20000 0001 2171 1133School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Maxie M. Roessler
- grid.7445.20000 0001 2113 8111Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, London, UK
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3
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Kampjut D, Sazanov LA. The coupling mechanism of mammalian respiratory complex I. Science 2020; 370:science.abc4209. [PMID: 32972993 DOI: 10.1126/science.abc4209] [Citation(s) in RCA: 129] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Accepted: 09/08/2020] [Indexed: 12/16/2022]
Abstract
Mitochondrial complex I couples NADH:ubiquinone oxidoreduction to proton pumping by an unknown mechanism. Here, we present cryo-electron microscopy structures of ovine complex I in five different conditions, including turnover, at resolutions up to 2.3 to 2.5 angstroms. Resolved water molecules allowed us to experimentally define the proton translocation pathways. Quinone binds at three positions along the quinone cavity, as does the inhibitor rotenone that also binds within subunit ND4. Dramatic conformational changes around the quinone cavity couple the redox reaction to proton translocation during open-to-closed state transitions of the enzyme. In the induced deactive state, the open conformation is arrested by the ND6 subunit. We propose a detailed molecular coupling mechanism of complex I, which is an unexpected combination of conformational changes and electrostatic interactions.
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Affiliation(s)
- Domen Kampjut
- IST Austria, Am Campus 1, 3400 Klosterneuburg, Austria
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4
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Melin F, Hellwig P. Redox Properties of the Membrane Proteins from the Respiratory Chain. Chem Rev 2020; 120:10244-10297. [DOI: 10.1021/acs.chemrev.0c00249] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Frederic Melin
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
| | - Petra Hellwig
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
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5
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Verkhovskaya M, Belevich N. Fluorescent signals associated with respiratory Complex I revealed conformational changes in the catalytic site. FEMS Microbiol Lett 2020; 366:5530755. [PMID: 31291453 DOI: 10.1093/femsle/fnz155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 07/09/2019] [Indexed: 11/14/2022] Open
Abstract
Fluorescent signals associated with Complex I (NADH:ubiquinone oxidoreductase type I) upon its reduction by NADH without added acceptors and upon NADH:ubiquinone oxidoreduction were studied. Two Complex I-associated redox-dependent signals were observed: with maximum emission at 400 nm (λex = 320 nm) and 526 nm (λex = 450 nm). The 400 nm signal derived from ubiquinol accumulated in Complex I/DDM (n-dodecyl β-D-maltopyranoside) micelles. The 526 nm redox signal unexpectedly derives mainly from FMN (flavin mononucleotide), whose fluorescence in oxidized protein is fully quenched, but arises transiently upon reduction of Complex I by NADH. The paradoxical flare-up of FMN fluorescence is discussed in terms of conformational changes in the catalytic site upon NADH binding. The difficulties in revealing semiquinone fluorescent signal are considered.
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Affiliation(s)
- Marina Verkhovskaya
- Institute of Biotechnology, PO Box 65 (Viikinkaari 1) FIN-00014, University of Helsinki, Finland
| | - Nikolai Belevich
- Institute of Biotechnology, PO Box 65 (Viikinkaari 1) FIN-00014, University of Helsinki, Finland
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6
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Kaila VRI. Long-range proton-coupled electron transfer in biological energy conversion: towards mechanistic understanding of respiratory complex I. J R Soc Interface 2019; 15:rsif.2017.0916. [PMID: 29643224 PMCID: PMC5938582 DOI: 10.1098/rsif.2017.0916] [Citation(s) in RCA: 97] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 03/13/2018] [Indexed: 12/20/2022] Open
Abstract
Biological energy conversion is driven by efficient enzymes that capture, store and transfer protons and electrons across large distances. Recent advances in structural biology have provided atomic-scale blueprints of these types of remarkable molecular machinery, which together with biochemical, biophysical and computational experiments allow us to derive detailed energy transduction mechanisms for the first time. Here, I present one of the most intricate and least understood types of biological energy conversion machinery, the respiratory complex I, and how its redox-driven proton-pump catalyses charge transfer across approximately 300 Å distances. After discussing the functional elements of complex I, a putative mechanistic model for its action-at-a-distance effect is presented, and functional parallels are drawn to other redox- and light-driven ion pumps.
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Affiliation(s)
- Ville R I Kaila
- Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, Garching, Germany
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7
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Tran KN, Niu S, Ichiye T. Reduction potential calculations of the Fe–S clusters in
Thermus thermophilus
respiratory complex I. J Comput Chem 2019; 40:1248-1256. [DOI: 10.1002/jcc.25785] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 12/12/2018] [Accepted: 01/06/2019] [Indexed: 01/12/2023]
Affiliation(s)
- Kelly N. Tran
- Department of ChemistryGeorgetown University Washington District of Columbia, 20057
| | - Shuqiang Niu
- Department of ChemistryGeorgetown University Washington District of Columbia, 20057
| | - Toshiko Ichiye
- Department of ChemistryGeorgetown University Washington District of Columbia, 20057
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8
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Schuller JM, Birrell JA, Tanaka H, Konuma T, Wulfhorst H, Cox N, Schuller SK, Thiemann J, Lubitz W, Sétif P, Ikegami T, Engel BD, Kurisu G, Nowaczyk MM. Structural adaptations of photosynthetic complex I enable ferredoxin-dependent electron transfer. Science 2018; 363:257-260. [PMID: 30573545 DOI: 10.1126/science.aau3613] [Citation(s) in RCA: 127] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Accepted: 12/06/2018] [Indexed: 12/22/2022]
Abstract
Photosynthetic complex I enables cyclic electron flow around photosystem I, a regulatory mechanism for photosynthetic energy conversion. We report a 3.3-angstrom-resolution cryo-electron microscopy structure of photosynthetic complex I from the cyanobacterium Thermosynechococcus elongatus. The model reveals structural adaptations that facilitate binding and electron transfer from the photosynthetic electron carrier ferredoxin. By mimicking cyclic electron flow with isolated components in vitro, we demonstrate that ferredoxin directly mediates electron transfer between photosystem I and complex I, instead of using intermediates such as NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate). A large rate constant for association of ferredoxin to complex I indicates efficient recognition, with the protein subunit NdhS being the key component in this process.
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Affiliation(s)
- Jan M Schuller
- Department of Structural Cell Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
| | - James A Birrell
- Max Planck Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
| | - Hideaki Tanaka
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan.,Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Tsuyoshi Konuma
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Hannes Wulfhorst
- Plant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, 44780 Bochum, Germany.,Daiichi Sankyo Deutschland GmbH, Zielstattstr. 48, 81379 München, Germany
| | - Nicholas Cox
- Max Planck Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany.,Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - Sandra K Schuller
- Gene Center and Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany
| | - Jacqueline Thiemann
- Plant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, 44780 Bochum, Germany
| | - Wolfgang Lubitz
- Max Planck Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
| | - Pierre Sétif
- Institut de Biologie Intégrative de la Cellule (I2BC), IBITECS, CEA, CNRS, Université Paris-Saclay, F-91198 Gif-sur-Yvette, France
| | - Takahisa Ikegami
- Graduate School of Medical Life Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Benjamin D Engel
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Genji Kurisu
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan. .,Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
| | - Marc M Nowaczyk
- Plant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, 44780 Bochum, Germany.
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9
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Identification and characterization two isoforms of NADH:ubiquinone oxidoreductase from the hyperthermophilic eubacterium Aquifex aeolicus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:366-373. [DOI: 10.1016/j.bbabio.2018.02.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 02/18/2018] [Accepted: 02/24/2018] [Indexed: 12/20/2022]
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10
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Abstract
Mitochondria are the power stations of the eukaryotic cell, using the energy released by the oxidation of glucose and other sugars to produce ATP. Electrons are transferred from NADH, produced in the citric acid cycle in the mitochondrial matrix, to oxygen by a series of large protein complexes in the inner mitochondrial membrane, which create a transmembrane electrochemical gradient by pumping protons across the membrane. The flow of protons back into the matrix via a proton channel in the ATP synthase leads to conformational changes in the nucleotide binding pockets and the formation of ATP. The three proton pumping complexes of the electron transfer chain are NADH-ubiquinone oxidoreductase or complex I, ubiquinone-cytochrome c oxidoreductase or complex III, and cytochrome c oxidase or complex IV. Succinate dehydrogenase or complex II does not pump protons, but contributes reduced ubiquinone. The structures of complex II, III and IV were determined by x-ray crystallography several decades ago, but complex I and ATP synthase have only recently started to reveal their secrets by advances in x-ray crystallography and cryo-electron microscopy. The complexes I, III and IV occur to a certain extent as supercomplexes in the membrane, the so-called respirasomes. Several hypotheses exist about their function. Recent cryo-electron microscopy structures show the architecture of the respirasome with near-atomic detail. ATP synthase occurs as dimers in the inner mitochondrial membrane, which by their curvature are responsible for the folding of the membrane into cristae and thus for the huge increase in available surface that makes mitochondria the efficient energy plants of the eukaryotic cell.
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Affiliation(s)
- Joana S Sousa
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Edoardo D'Imprima
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Janet Vonck
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
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11
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Structure and electrochemistry of proteins harboring iron-sulfur clusters of different nuclearities. Part I. [4Fe-4S] + [2Fe-2S] iron-sulfur proteins. J Struct Biol 2017; 200:1-19. [DOI: 10.1016/j.jsb.2017.05.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/25/2017] [Indexed: 01/08/2023]
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12
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Haapanen O, Sharma V. Role of water and protein dynamics in proton pumping by respiratory complex I. Sci Rep 2017; 7:7747. [PMID: 28798393 PMCID: PMC5552823 DOI: 10.1038/s41598-017-07930-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 07/05/2017] [Indexed: 11/29/2022] Open
Abstract
Membrane bound respiratory complex I is the key enzyme in the respiratory chains of bacteria and mitochondria, and couples the reduction of quinone to the pumping of protons across the membrane. Recently solved crystal or electron microscopy structures of bacterial and mitochondrial complexes have provided significant insights into the electron and proton transfer pathways. However, due to large spatial separation between the electron and proton transfer routes, the molecular mechanism of coupling remains unclear. Here, based on atomistic molecular dynamics simulations performed on the entire structure of complex I from Thermus thermophilus, we studied the hydration of the quinone-binding site and the membrane-bound subunits. The data from simulations show rapid diffusion of water molecules in the protein interior, and formation of hydrated regions in the three antiporter-type subunits. An unexpected water-protein based connectivity between the middle of the Q-tunnel and the fourth proton channel is also observed. The protonation-state dependent dynamics of key acidic residues in the Nqo8 subunit suggest that the latter may be linked to redox-coupled proton pumping in complex I. We propose that in complex I the proton and electron transfer paths are not entirely separate, instead the nature of coupling may in part be ‘direct’.
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Affiliation(s)
- Outi Haapanen
- Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Helsinki, Finland.,Department of Physics, Tampere University of Technology, P. O. Box 692, FI-33101, Tampere, Finland
| | - Vivek Sharma
- Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Helsinki, Finland. .,Department of Physics, Tampere University of Technology, P. O. Box 692, FI-33101, Tampere, Finland. .,Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
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13
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Artz JH, Mulder DW, Ratzloff MW, Lubner CE, Zadvornyy OA, LeVan AX, Williams SG, Adams MWW, Jones AK, King PW, Peters JW. Reduction Potentials of [FeFe]-Hydrogenase Accessory Iron-Sulfur Clusters Provide Insights into the Energetics of Proton Reduction Catalysis. J Am Chem Soc 2017. [PMID: 28635269 DOI: 10.1021/jacs.7b02099] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
An [FeFe]-hydrogenase from Clostridium pasteurianum, CpI, is a model system for biological H2 activation. In addition to the catalytic H-cluster, CpI contains four accessory iron-sulfur [FeS] clusters in a branched series that transfer electrons to and from the active site. In this work, potentiometric titrations have been employed in combination with electron paramagnetic resonance (EPR) spectroscopy at defined electrochemical potentials to gain insights into the role of the accessory clusters in catalysis. EPR spectra collected over a range of potentials were deconvoluted into individual components attributable to the accessory [FeS] clusters and the active site H-cluster, and reduction potentials for each cluster were determined. The data suggest a large degree of magnetic coupling between the clusters. The distal [4Fe-4S] cluster is shown to have a lower reduction potential (∼ < -450 mV) than the other clusters, and molecular docking experiments indicate that the physiological electron donor, ferredoxin (Fd), most favorably interacts with this cluster. The low reduction potential of the distal [4Fe-4S] cluster thermodynamically restricts the Fdox/Fdred ratio at which CpI can operate, consistent with the role of CpI in recycling Fdred that accumulates during fermentation. Subsequent electron transfer through the additional accessory [FeS] clusters to the H-cluster is thermodynamically favorable.
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Affiliation(s)
- Jacob H Artz
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
| | - David W Mulder
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Michael W Ratzloff
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Carolyn E Lubner
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Oleg A Zadvornyy
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
| | - Axl X LeVan
- Department of Chemistry and Biochemistry, Montana State University , 224 Chemistry and Biochemistry Building, Bozeman, Montana 59717, United States
| | - S Garrett Williams
- School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States
| | - Michael W W Adams
- B216B Life Sciences Complex, Department of Biochemistry, The University of Georgia , Athens, Georgia 30602, United States
| | - Anne K Jones
- School of Molecular Sciences, Arizona State University , P.O. Box 871604, Tempe, Arizona 85287, United States
| | - Paul W King
- Biosciences Center, National Renewable Energy Laboratory , 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - John W Peters
- Institute of Biological Chemistry, Washington State University , 258 Clark Hall, Pullman, Washington 99163, United States
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14
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Holt PJ, Efremov RG, Nakamaru-Ogiso E, Sazanov LA. Reversible FMN dissociation from Escherichia coli respiratory complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1777-1785. [PMID: 27555334 DOI: 10.1016/j.bbabio.2016.08.008] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/04/2016] [Accepted: 08/17/2016] [Indexed: 12/13/2022]
Abstract
Respiratory complex I transfers electrons from NADH to quinone, utilizing the reaction energy to translocate protons across the membrane. It is a key enzyme of the respiratory chain of many prokaryotic and most eukaryotic organisms. The reversible NADH oxidation reaction is facilitated in complex I by non-covalently bound flavin mononucleotide (FMN). Here we report that the catalytic activity of E. coli complex I with artificial electron acceptors potassium ferricyanide (FeCy) and hexaamineruthenium (HAR) is significantly inhibited in the enzyme pre-reduced by NADH. Further, we demonstrate that the inhibition is caused by reversible dissociation of FMN. The binding constant (Kd) for FMN increases from the femto- or picomolar range in oxidized complex I to the nanomolar range in the NADH reduced enzyme, with an FMN dissociation time constant of ~5s. The oxidation state of complex I, rather than that of FMN, proved critical to the dissociation. Such dissociation is not observed with the T. thermophilus enzyme and our analysis suggests that the difference may be due to the unusually high redox potential of Fe-S cluster N1a in E. coli. It is possible that the enzyme attenuates ROS production in vivo by releasing FMN under highly reducing conditions.
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Affiliation(s)
- Peter J Holt
- MRC Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK
| | - Rouslan G Efremov
- Structural Biology Research Center, VIB, 1050 Brussels, Belgium; Structural Biology Brussels, Vrije Universiteit Brussel (VUB), 1050 Brussels, Belgium
| | - Eiko Nakamaru-Ogiso
- Johnson Research Foundation, Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6059, United States
| | - Leonid A Sazanov
- Institute of Science and Technology Austria, Am Campus 1, A-3400 Klosterneuburg, Austria.
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15
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Berrisford JM, Baradaran R, Sazanov LA. Structure of bacterial respiratory complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:892-901. [PMID: 26807915 DOI: 10.1016/j.bbabio.2016.01.012] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 01/18/2016] [Accepted: 01/20/2016] [Indexed: 12/23/2022]
Abstract
Complex I (NADH:ubiquinone oxidoreductase) plays a central role in cellular energy production, coupling electron transfer between NADH and quinone to proton translocation. It is the largest protein assembly of respiratory chains and one of the most elaborate redox membrane proteins known. Bacterial enzyme is about half the size of mitochondrial and thus provides its important "minimal" model. Dysfunction of mitochondrial complex I is implicated in many human neurodegenerative diseases. The L-shaped complex consists of a hydrophilic arm, where electron transfer occurs, and a membrane arm, where proton translocation takes place. We have solved the crystal structures of the hydrophilic domain of complex I from Thermus thermophilus, the membrane domain from Escherichia coli and recently of the intact, entire complex I from T. thermophilus (536 kDa, 16 subunits, 9 iron-sulphur clusters, 64 transmembrane helices). The 95Å long electron transfer pathway through the enzyme proceeds from the primary electron acceptor flavin mononucleotide through seven conserved Fe-S clusters to the unusual elongated quinone-binding site at the interface with the membrane domain. Four putative proton translocation channels are found in the membrane domain, all linked by the central flexible axis containing charged residues. The redox energy of electron transfer is coupled to proton translocation by the as yet undefined mechanism proposed to involve long-range conformational changes. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.
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Affiliation(s)
| | - Rozbeh Baradaran
- Memorial Sloan-Kettering Cancer Center, 430 E 67th Street, NY 10065, USA
| | - Leonid A Sazanov
- Institute of Science and Technology Austria (IST Austria), Am Campus 1, 3400 Klosterneuburg, Austria.
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16
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Hirst J, Roessler MM. Energy conversion, redox catalysis and generation of reactive oxygen species by respiratory complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:872-83. [PMID: 26721206 PMCID: PMC4893023 DOI: 10.1016/j.bbabio.2015.12.009] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 12/15/2015] [Accepted: 12/16/2015] [Indexed: 12/30/2022]
Abstract
Complex I (NADH:ubiquinone oxidoreductase) is critical for respiration in mammalian mitochondria. It oxidizes NADH produced by the Krebs' tricarboxylic acid cycle and β-oxidation of fatty acids, reduces ubiquinone, and transports protons to contribute to the proton-motive force across the inner membrane. Complex I is also a significant contributor to cellular oxidative stress. In complex I, NADH oxidation by a flavin mononucleotide, followed by intramolecular electron transfer along a chain of iron–sulfur clusters, delivers electrons and energy to bound ubiquinone. Either at cluster N2 (the terminal cluster in the chain) or upon the binding/reduction/dissociation of ubiquinone/ubiquinol, energy from the redox process is captured to initiate long-range energy transfer through the complex and drive proton translocation. This review focuses on current knowledge of how the redox reaction and proton transfer are coupled, with particular emphasis on the formation and role of semiquinone intermediates in both energy transduction and reactive oxygen species production. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt. Current knowledge of the redox reactions catalyzed by complex I is reviewed. Possible quinone reduction pathways are presented. The presence and number of semiquinone intermediates are deliberated. The involvement of cluster N2/semiquinones in coupled proton transfer is discussed. Evidence for reactive oxygen species production by semiquinones is examined.
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Affiliation(s)
- Judy Hirst
- Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, United Kingdom.
| | - Maxie M Roessler
- School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
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17
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Real-time optical studies of respiratory Complex I turnover. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1837:1973-1980. [PMID: 25283488 DOI: 10.1016/j.bbabio.2014.09.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Revised: 08/28/2014] [Accepted: 09/23/2014] [Indexed: 12/16/2022]
Abstract
Reduction of Complex l (NADH:ubiquinone oxidoreductase l) from Escherichia coli by NADH was investigated optically by means of an ultrafast stopped-flow approach. A locally designed microfluidic stopped-flow apparatus with a low volume (0.21Jl) but a long optical path (10 mm) cuvette allowed measurements in the time range from 270 ).IS to seconds. The data acquisition system collected spectra in the visible range every 50 )JS. Analysis of the obtained time-resolved spectral changes upon the reaction of Complex I with NADH revealed three kinetic components with characteristic times of <270 ).IS, 0.45-0.9 ms and 3-6 ms, reflecting reduction of different FeS clusters and FMN. The rate of the major ( T = 0.45-0.9 ms) component was slower than predicted by electron transfer theory for the reduction of all FeS clusters in the intraprotein redox chain. This delay of the reaction was explained by retention of NAD+ in the catalytic site. The fast optical changes in the time range of 0.27- 1.5 ms were not altered significantly in the presence of 1 0-fold excess of NAD+ over NADH. The data obtained on the NuoF E95Q variant of Complex I shows that the single amino acid replacement in the catalytic site caused a strong decrease of NADH binding and/or the hydride transfer from bound NADH to FMN.
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18
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Wikström M, Sharma V, Kaila VRI, Hosler JP, Hummer G. New Perspectives on Proton Pumping in Cellular Respiration. Chem Rev 2015; 115:2196-221. [DOI: 10.1021/cr500448t] [Citation(s) in RCA: 183] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mårten Wikström
- Institute
of Biotechnology, University of Helsinki, Biocenter 3 (Viikinkaari 1), PB
65, Helsinki 00014, Finland
| | - Vivek Sharma
- Department
of Physics, Tampere University of Technology, Korkeakoulunkatu 3, Tampere 33720, Finland
| | - Ville R. I. Kaila
- Department
Chemie, Technische Universität München, Lichtenbergstraße 4, D-85748 Garching, Germany
| | - Jonathan P. Hosler
- Department
of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216, United States
| | - Gerhard Hummer
- Department
of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Straße
3, 60438 Frankfurt
am Main, Germany
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19
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Zanello P. The competition between chemistry and biology in assembling iron–sulfur derivatives. Molecular structures and electrochemistry. Part II. {[Fe2S2](SγCys)4} proteins. Coord Chem Rev 2014. [DOI: 10.1016/j.ccr.2014.08.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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20
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Kriegel S, Uchida T, Osawa M, Friedrich T, Hellwig P. Biomimetic environment to study E. coli complex I through surface-enhanced IR absorption spectroscopy. Biochemistry 2014; 53:6340-7. [PMID: 25225967 DOI: 10.1021/bi500955a] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
In this study complex I was immobilized in a biomimetic environment on a gold layer deposited on an ATR-crystal in order to functionally probe the enzyme against substrates and inhibitors via surface-enhanced IR absorption spectroscopy (SEIRAS) and cyclic voltammetry (CV). To achieve this immobilization, two methods based on the generation of a high affinity self-assembled monolayer (SAM) were probed. The first made use of the affinity of Ni-NTA toward a hexahistidine tag that was genetically engineered onto complex I and the second exploited the affinity of the enzyme toward its natural substrate NADH. Experiments were also performed with complex I reconstituted in lipids. Both approaches have been found to be successful, and electrochemically induced IR difference spectra of complex I were obtained.
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Affiliation(s)
- Sébastien Kriegel
- Laboratoire de bioelectrochimie et spectroscopie, UMR 7140, Chimie de la Matière Complexe, Université de Strasbourg-CNRS , Strasbourg 67000, France
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21
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Robinson JL, Miller RV, Brynildsen MP. Model-driven identification of dosing regimens that maximize the antimicrobial activity of nitric oxide. Metab Eng Commun 2014; 1:12-18. [PMID: 34150500 PMCID: PMC8193240 DOI: 10.1016/j.meteno.2014.08.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2014] [Revised: 08/21/2014] [Accepted: 08/22/2014] [Indexed: 12/26/2022] Open
Abstract
The antimicrobial properties of nitric oxide (NO●) have motivated the design of NO●-releasing materials for the treatment and prevention of infection. The biological activity of NO● is dependent on its delivery rate, suggesting that variable antimicrobial effects can result from identical NO● payloads dosed at different rates. Using a kinetic model of the Escherichia coli NO● biochemical network, we investigated the relationship between NO● delivery rate, payload, and cytotoxicity, as indicated by the duration of respiratory inhibition. At low NO● payloads, the model predicted greater toxicity with rapid delivery, while slower delivery was more effective at higher payloads. These predictions were confirmed experimentally, and exhibited quantitative agreement with measured O2 and NO● concentrations, and durations of respiratory inhibition. These results provide important information on key design parameters in the formulation of NO●-based therapeutics, and highlight the utility of a model-based approach for the analysis of dosing regimens. Antimicrobial activity of NO● was predicted to depend strongly on delivery rate. Fast NO● delivery rates were more effective for low NO● payloads. Slow NO● delivery rates were more effective for high NO● payloads. Kinetic modeling of NO● metabolism correctly predicted the observed dependencies.
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Affiliation(s)
- Jonathan L Robinson
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, USA
| | - Richard V Miller
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Mark P Brynildsen
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, USA.,Department of Molecular Biology, Princeton University, Princeton, NJ, USA
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22
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Verkhovskaya M, Wikström M. Oxidoreduction properties of bound ubiquinone in Complex I from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1837:246-50. [PMID: 24216024 DOI: 10.1016/j.bbabio.2013.11.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 10/31/2013] [Accepted: 11/04/2013] [Indexed: 12/12/2022]
Abstract
The exploration of the redox chemistry of bound ubiquinone during catalysis is a prerequisite for the understanding of the mechanism by which Complex I (nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase) transduces redox energy into an electrochemical proton gradient. Studies of redox dependent changes in the spectrum of Complex I from Escherichia coli in the mid- and near-ultraviolet (UV) and visible areas were performed to identify the spectral contribution, and to determine the redox properties, of the tightly bound ubiquinone. A very low midpoint redox potential (<-300mV) was found for the bound ubiquinone, more than 400mV lower than when dissolved in a phospholipid membrane. This thermodynamic property of bound ubiquinone has important implications for the mechanism by which Complex I catalyzes proton translocation.
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Affiliation(s)
- Marina Verkhovskaya
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014 Helsinki, Finland.
| | - Mårten Wikström
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014 Helsinki, Finland
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23
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Knuuti J, Belevich G, Sharma V, Bloch DA, Verkhovskaya M. A single amino acid residue controls ROS production in the respiratory Complex I from Escherichia coli. Mol Microbiol 2013; 90:1190-200. [PMID: 24325249 DOI: 10.1111/mmi.12424] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/03/2013] [Indexed: 01/08/2023]
Abstract
Reactive oxygen species (ROS) production by respiratory Complex I from Escherichia coli was studied in bacterial membrane fragments and in the isolated and purified enzyme, either solubilized or incorporated in proteoliposomes. We found that the replacement of a single amino acid residue in close proximity to the nicotinamide adenine dinucleotide (NADH)-binding catalytic site (E95 in the NuoF subunit) dramatically increases the reactivity of Complex I towards dioxygen (O2 ). In the E95Q variant short-chain ubiquinones exhibit strong artificial one-electron reduction at the catalytic site, also leading to a stronger increase in ROS production. Two mechanisms can contribute to the observed kinetic effects: (a) a change in the reactivity of flavin mononucleotide (FMN) towards dioxygen at the catalytic site, and (b) a change in the population of the ROS-generating state. We propose the existence of two (closed and open) states of the NAD(+) -bound enzyme as one feature of the substrate-binding site of Complex I. The analysis of the kinetic model of ROS production allowed us to propose that the population of Complex I with reduced FMN is always low in the wild-type enzyme even at low ambient redox potentials, minimizing the rate of reaction with O2 in contrast to E95Q variant.
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Affiliation(s)
- Juho Knuuti
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, PO Box 65 (Viikinkaari 1), FIN-00014, Helsinki, Finland
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24
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Verkhovskaya M, Bloch DA. Energy-converting respiratory Complex I: on the way to the molecular mechanism of the proton pump. Int J Biochem Cell Biol 2012; 45:491-511. [PMID: 22982742 DOI: 10.1016/j.biocel.2012.08.024] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Revised: 08/27/2012] [Accepted: 08/28/2012] [Indexed: 12/16/2022]
Abstract
In respiring organisms the major energy transduction flux employs the transmembrane electrochemical proton gradient as a physical link between exergonic redox reactions and endergonic ADP phosphorylation. Establishing the gradient involves electrogenic, transmembrane H(+) translocation by the membrane-embedded respiratory complexes. Among others, Complex I (NADH:ubiquinone oxidoreductase) is the most structurally complex and functionally enigmatic respiratory enzyme; its molecular mechanism is as yet unknown. Here we highlight recent progress and discuss the catalytic events during Complex I turnover in relation to their role in energy conversion and to the enzyme structure.
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Affiliation(s)
- Marina Verkhovskaya
- Helsinki Bioenergetics Group, Institute of Biotechnology, PO Box 65 (Viikinkaari 1) FIN-00014 University of Helsinki, Finland.
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25
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Verkhovsky M, Bloch DA, Verkhovskaya M. Tightly-bound ubiquinone in the Escherichia coli respiratory Complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1550-6. [DOI: 10.1016/j.bbabio.2012.04.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Revised: 04/23/2012] [Accepted: 04/25/2012] [Indexed: 12/12/2022]
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26
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Bridges HR, Bill E, Hirst J. Mössbauer spectroscopy on respiratory complex I: the iron-sulfur cluster ensemble in the NADH-reduced enzyme is partially oxidized. Biochemistry 2011; 51:149-58. [PMID: 22122402 PMCID: PMC3254188 DOI: 10.1021/bi201644x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
In mitochondria, complex I (NADH:quinone oxidoreductase)
couples
electron transfer to proton translocation across an energy-transducing
membrane. It contains a flavin mononucleotide to oxidize NADH, and
an unusually long series of iron–sulfur (FeS) clusters that
transfer the electrons to quinone. Understanding electron transfer
in complex I requires spectroscopic and structural data to be combined
to reveal the properties of individual clusters and of the ensemble.
EPR studies on complex I from Bos taurus have established
that five clusters (positions 1, 2, 3, 5, and 7 along the seven-cluster
chain extending from the flavin) are (at least partially) reduced
by NADH. The other three clusters, positions 4 and 6 plus a cluster
on the other side of the flavin, are not observed in EPR spectra from
the NADH-reduced enzyme: they may remain oxidized, have unusual or
coupled spin states, or their EPR signals may be too fast relaxing.
Here, we use Mössbauer spectroscopy on 57Fe-labeled
complex I from the mitochondria of Yarrowia lipolytica to show that the cluster ensemble is only partially reduced in the
NADH-reduced enzyme. The three EPR-silent clusters are oxidized, and
only the terminal 4Fe cluster (position 7) is fully reduced. Together
with the EPR analyses, our results reveal an alternating profile of
higher and lower potential clusters between the two active sites in
complex I; they are not consistent with the consensus picture of a
set of isopotential clusters. The implications for intramolecular
electron transfer along the extended chain of cofactors in complex
I are discussed.
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Affiliation(s)
- Hannah R Bridges
- Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Cambridge, CB2 0XY, UK
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27
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Gadicherla AK, Stowe DF, Antholine WE, Yang M, Camara AKS. Damage to mitochondrial complex I during cardiac ischemia reperfusion injury is reduced indirectly by anti-anginal drug ranolazine. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:419-29. [PMID: 22178605 DOI: 10.1016/j.bbabio.2011.11.021] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 11/23/2011] [Accepted: 11/30/2011] [Indexed: 12/19/2022]
Abstract
Ranolazine, an anti-anginal drug, is a late Na(+) channel current blocker that is also believed to attenuate fatty acid oxidation and mitochondrial respiratory complex I activity, especially during ischemia. In this study, we investigated if ranolazine's protective effect against cardiac ischemia/reperfusion (IR) injury is mediated at the mitochondrial level and specifically if respiratory complex I (NADH Ubiquinone oxidoreductase) function is protected. We treated isolated and perfused guinea pig hearts with ranolazine just before 30 min ischemia and then isolated cardiac mitochondria at the end of 30 min ischemia and/or 30 min ischemia followed by 10 min reperfusion. We utilized spectrophotometric and histochemical techniques to assay complex I activity, Western blot analysis for complex I subunit NDUFA9, electron paramagnetic resonance for activity of complex I Fe-S clusters, enzyme linked immuno sorbent assay (ELISA) for determination of protein acetylation, native gel histochemical staining for respiratory supercomplex assemblies, and high pressure liquid chromatography for cardiolipin integrity; cardiac function was measured during IR. Ranolazine treated hearts showed higher complex I activity and greater detectable complex I protein levels compared to untreated IR hearts. Ranolazine treatment also led to more normalized electron transfer via Fe-S centers, supercomplex assembly and cardiolipin integrity. These improvements in complex I structure and function with ranolazine were associated with improved cardiac function after IR. However, these protective effects of ranolazine are not mediated by a direct action on mitochondria, but rather indirectly via cytosolic mechanisms that lead to less oxidation and better structural integrity of complex I.
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Affiliation(s)
- Ashish K Gadicherla
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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28
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Couch V, Popovic D, Stuchebrukhov A. Redox-coupled protonation of respiratory complex I: the hydrophilic domain. Biophys J 2011; 101:431-8. [PMID: 21767496 DOI: 10.1016/j.bpj.2011.05.068] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2010] [Revised: 05/20/2011] [Accepted: 05/25/2011] [Indexed: 11/24/2022] Open
Abstract
Respiratory complex I, NADH:ubiquinone oxidoreductase, is a large and complex integral membrane enzyme found in respiring bacteria and mitochondria. It is responsible in part for generating the proton gradient necessary for ATP production. Complex I serves as both a proton pump and an entry point for electrons into the respiratory chain. Although complex I is one of the most important of the respiratory complexes, it is also one of the least understood, with detailed structural information only recently available. In this study, full-finite-difference Poisson-Boltzmann calculations of the protonation state of respiratory complex I in various redox states are presented. Since complex I couples the oxidation and reduction of the NADH/ubiquinone redox couple to proton translocation, the interaction of the protonation and redox states of the enzyme are of the utmost significance. Various aspects of complex I function are presented, including the redox-Bohr effect, intercofactor interactions, and the effects of both the protein dielectric and inclusion of the membrane.
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Affiliation(s)
- Vernon Couch
- Department of Chemistry, University of California, Davis, California, USA
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29
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Couch V, Stuchebrukhov A. Histidine in continuum electrostatics protonation state calculations. Proteins 2011; 79:3410-9. [PMID: 22072521 DOI: 10.1002/prot.23114] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2010] [Revised: 04/15/2011] [Accepted: 06/08/2011] [Indexed: 11/10/2022]
Abstract
A modification to the standard continuum electrostatics approach to calculate protein pK(a)s, which allows for the decoupling of histidine tautomers within a two-state model, is presented. Histidine with four intrinsically coupled protonation states cannot be easily incorporated into a two-state formalism, because the interaction between the two protonatable sites of the imidazole ring is not purely electrostatic. The presented treatment, based on a single approximation of the interrelation between histidine's charge states, allows for a natural separation of the two protonatable sites associated with the imidazole ring as well as the inclusion of all protonation states within the calculation.
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Affiliation(s)
- Vernon Couch
- Department of Chemistry, University of California, Davis, California 95616, USA
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30
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Michel J, DeLeon-Rangel J, Zhu S, Van Ree K, Vik SB. Mutagenesis of the L, M, and N subunits of Complex I from Escherichia coli indicates a common role in function. PLoS One 2011; 6:e17420. [PMID: 21387012 PMCID: PMC3046159 DOI: 10.1371/journal.pone.0017420] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Accepted: 01/24/2011] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND The membrane arm of Complex I (NADH:ubiquinone oxidoreductase) contains three large, and closely related subunits, which are called L, M, and N in E. coli. These subunits are homologous to components of multi-subunit Na(+)/H(+) antiporters, and so are implicated in proton translocation. METHODOLOGY/PRINCIPAL FINDINGS Nineteen site-specific mutations were constructed at two corresponding positions in each of the three subunits. Two positions were selected in each subunit: L_K169, M_K173, N_K158 and L_Q236, M_H241, N_H224. Membrane vesicles were prepared from all of the resulting mutant strains, and were assayed for deamino-NADH oxidase activity, proton translocation, ferricyanide reductase activity, and sensitivity to capsaicin. Corresponding mutations in the three subunits were found to have very similar effects on all activities measured. In addition, the effect of adding exogenous decylubiquinone on these activities was tested. 50 µM decylubiquinone stimulated both deamino-NADH oxidase activity and proton translocation by wild type membrane vesicles, but was inhibitory towards the same activities by membrane vesicles bearing the lysine substitution at the L236/M241/N224 positions. CONCLUSIONS/SIGNIFICANCE The results show a close correlation with reduced activity among the corresponding mutations, and provide evidence that the L, M, and N subunits have a common role in Complex I.
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Affiliation(s)
- Jose Michel
- Department of Biological Sciences, Southern Methodist University, Dallas,
Texas, United States of America
| | - Jessica DeLeon-Rangel
- Department of Biological Sciences, Southern Methodist University, Dallas,
Texas, United States of America
| | - Shaotong Zhu
- Department of Biological Sciences, Southern Methodist University, Dallas,
Texas, United States of America
| | - Kalie Van Ree
- Department of Biological Sciences, Southern Methodist University, Dallas,
Texas, United States of America
| | - Steven B. Vik
- Department of Biological Sciences, Southern Methodist University, Dallas,
Texas, United States of America
- * E-mail:
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31
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Medvedev ES, Couch VA, Stuchebrukhov AA. Determination of the intrinsic redox potentials of FeS centers of respiratory complex I from experimental titration curves. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:1665-71. [PMID: 20513348 DOI: 10.1016/j.bbabio.2010.05.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 05/17/2010] [Accepted: 05/24/2010] [Indexed: 11/19/2022]
Abstract
Recently, Euro et al. [Biochem. 47, 3185 (2008) ] have reported titration data for seven of nine FeS redox centers of complex I from Escherichiacoli. There is a significant uncertainty in the assignment of the titration data. Four of the titration curves were assigned to N1a, N1b, N6b, and N2 centers; one curve either to N3 or N7; one more either to N4 or N5; and the last one denoted Nx could not be assigned at all. In addition, the assignment of the titration data to the N6b/N6a pair is also uncertain. In this paper, using our calculated interaction energies [Couch et al. BBA 1787, 1266 (2009)], we perform statistical analysis of these data, considering a variety of possible assignments, find the best fit, and determine the intrinsic redox potentials of the centers. The intrinsic potentials could be determined with an uncertainty of less than +/-10 mV at a 95% confidence level for best fit assignments. We also find that the best agreement between theoretical and experimental titration curves is obtained with the N6b-N2 interaction equal to 71+/-14 or 96+/-26 mV depending on the N6b/N6a titration data assignment, which is stronger than was expected and may indicate a close distance of the N2 center to the membrane surface.
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Affiliation(s)
- Emile S Medvedev
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia
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32
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Ransac S, Arnarez C, Mazat JP. The flitting of electrons in complex I: a stochastic approach. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2010; 1797:641-8. [PMID: 20230777 DOI: 10.1016/j.bbabio.2010.03.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2009] [Revised: 02/19/2010] [Accepted: 03/06/2010] [Indexed: 12/12/2022]
Abstract
A stochastic approach based on the Gillespie algorithm is particularly well adapted to describe the time course of the redox reactions that occur inside the respiratory chain complexes because they involve the motion of single electrons between the individual unique redox centres of a given complex. We use this approach to describe the molecular functioning of the peripheral arm of complex I based on its known crystallographic structure and the rate constants of electron tunnelling derived from the Moser and Dutton phenomenological equations. There are several possible electrons pathways but we show that most of them take the route defined by the successive sites and redox centres: NADH+ site-FMN-N3-N1b-N4-N5-N6a-N6b-N2-Q site. However, the electrons do not go directly from NADH towards the ubiquinone molecule. They frequently jump back and forth between neighbouring redox centres with the result that the net flux of electrons through complex I (i.e. net number of electrons reducing a ubiquinone) is far smaller than the number of redox reactions which actually occur. While most of the redox centres are reduced in our simulations the degree of reduction can vary according to the individual midpoint potentials. The high turnover number observed in our simulation seems to indicate that, in the whole complex I, one or several slower step(s) follow(s) the redox reactions involved in the peripheral arm. It also appears that the residence time of FMNH* and SQ* (possible producers of ROS) is low (around 4% and between 1.6% and 5% respectively according to the values of the midpoint potentials). We did not find any evidence for a role of N7 which remains mainly reduced in our simulations. The role of N1a is complex and depends upon its midpoint potential. In all cases its presence slightly decreases the life time of the flavosemiquinone species. These simulations demonstrate the interest of this type of model which links the molecular physico-chemistry of the individual redox reactions to the more global level of the reaction, as is observed experimentally.
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Affiliation(s)
- Stéphane Ransac
- Université de Bordeaux 2, Mitochondrial physiopathology laboratory, INSERM U688, Bordeaux, France
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33
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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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Berrisford JM, Sazanov LA. Structural basis for the mechanism of respiratory complex I. J Biol Chem 2009; 284:29773-83. [PMID: 19635800 PMCID: PMC2785608 DOI: 10.1074/jbc.m109.032144] [Citation(s) in RCA: 187] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Revised: 07/15/2009] [Indexed: 11/06/2022] Open
Abstract
Complex I plays a central role in cellular energy production, coupling electron transfer between NADH and quinone to proton translocation. The mechanism of this highly efficient enzyme is currently unknown. Mitochondrial complex I is a major source of reactive oxygen species, which may be one of the causes of aging. Dysfunction of complex I is implicated in many human neurodegenerative diseases. We have determined several x-ray structures of the oxidized and reduced hydrophilic domain of complex I from Thermus thermophilus at up to 3.1 A resolution. The structures reveal the mode of interaction of complex I with NADH, explaining known kinetic data and providing implications for the mechanism of reactive oxygen species production at the flavin site of complex I. Bound metals were identified in the channel at the interface with the frataxin-like subunit Nqo15, indicating possible iron-binding sites. Conformational changes upon reduction of the complex involve adjustments in the nucleotide-binding pocket, as well as small but significant shifts of several alpha-helices at the interface with the membrane domain. These shifts are likely to be driven by the reduction of nearby iron-sulfur clusters N2 and N6a/b. Cluster N2 is the electron donor to quinone and is coordinated by unique motif involving two consecutive (tandem) cysteines. An unprecedented "on/off switch" (disconnection) of coordinating bonds between the tandem cysteines and this cluster was observed upon reduction. Comparison of the structures suggests a novel mechanism of coupling between electron transfer and proton translocation, combining conformational changes and protonation/deprotonation of tandem cysteines.
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Affiliation(s)
- John M. Berrisford
- From the Medical Research Council Mitochondrial Biology Unit, Cambridge CB2 0XY, United Kingdom
| | - Leonid A. Sazanov
- From the Medical Research Council Mitochondrial Biology Unit, Cambridge CB2 0XY, United Kingdom
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Bogachev AV, Bloch DA, Bertsova YV, Verkhovsky MI. Redox properties of the prosthetic groups of Na(+)-translocating NADH:quinone oxidoreductase. 2. Study of the enzyme by optical spectroscopy. Biochemistry 2009; 48:6299-304. [PMID: 19496622 DOI: 10.1021/bi900525v] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Redox titration of the electronic spectra of the prosthetic groups of the Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) from Vibrio harveyi at different pH values showed five redox transitions corresponding to the four flavin cofactors of the enzyme and one additional transition reflecting oxidoreduction of the [2Fe-2S] cluster. The pH dependence of the measured midpoint redox potentials showed that the two-electron reduction of the FAD located in the NqrF subunit was coupled with the uptake of only one H(+). The one-electron reduction of neutral semiquinone of riboflavin and the formation of anion flavosemiquinone from the oxidized FMN bound to the NqrB subunit were not coupled to any proton uptake. The two sequential one-electron reductions of the FMN residue bound to the NqrC subunit showed pH-independent formation of anion radical in the first step and the formation of fully reduced flavin coupled to the uptake of one H(+) in the second step. All four flavins stayed in the anionic form in the fully reduced enzyme. None of the six redox transitions in Na(+)-NQR showed dependence of its midpoint redox potential on the concentration of sodium ions. A model of the sequence of electron transfer steps in the enzyme is suggested.
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Affiliation(s)
- Alexander V Bogachev
- Department of Molecular Energetics of Microorganisms, A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119992, Russia
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Smirnov AY, Savel'ev SE, Nori F. Diffusion-controlled generation of a proton-motive force across a biomembrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:011916. [PMID: 19658738 DOI: 10.1103/physreve.80.011916] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Indexed: 05/28/2023]
Abstract
Respiration in bacteria involves a sequence of energetically coupled electron and proton transfers creating an electrochemical gradient of protons (a proton-motive force) across the inner bacterial membrane. With a simple kinetic model, we analyze a redox loop mechanism of proton-motive force generation mediated by a molecular shuttle diffusing inside the membrane. This model, which includes six electron-binding and two proton-binding sites, reflects the main features of nitrate respiration in E. coli bacteria. We describe the time evolution of the proton translocation process. We find that the electron-proton electrostatic coupling on the shuttle plays a significant role in the process of energy conversion between electron and proton components. We determine the conditions where the redox loop mechanism is able to translocate protons against the transmembrane voltage gradient above 200 mV with a thermodynamic efficiency of about 37%, in the physiologically important range of temperatures from 250 to 350 K.
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Affiliation(s)
- Anatoly Yu Smirnov
- Advanced Science Institute, The Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama 351-0198, Japan
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Couch VA, Medvedev ES, Stuchebrukhov AA. Electrostatics of the FeS clusters in respiratory complex I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1266-71. [PMID: 19445896 DOI: 10.1016/j.bbabio.2009.05.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 04/29/2009] [Accepted: 05/07/2009] [Indexed: 10/20/2022]
Abstract
Respiratory complex I couples the transfer of electrons from NADH to ubiquinone and the translocation of protons across the mitochondrial membrane. A detailed understanding of the midpoint reduction potentials (E(m)) of each redox center and the factors which influence those potentials are critical in the elucidation of the mechanism of electron transfer in this enzyme. We present accurate electrostatic interaction energies for the iron-sulfur (FeS) clusters of complex I to facilitate the development of models and the interpretation of experiments in connection to electron transfer (ET) in this enzyme. To calculate redox titration curves for the FeS clusters it is necessary to include interactions between clusters, which in turn can be used to refine E(m) values and validate spectroscopic assignments of each cluster. Calculated titration curves for clusters N4, N5, and N6a are discussed. Furthermore, we present some initial findings on the electrostatics of the redox centers of complex I under the influence of externally applied membrane potentials. A means of determining the location of the FeS cofactors within the holo-complex based on electrostatic arguments is proposed. A simple electrostatic model of the protein/membrane system is examined to illustrate the viability of our hypothesis.
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Affiliation(s)
- Vernon A Couch
- Department of Chemistry, University of California, Davis, CA 95616, USA
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Rauhamäki V, Bloch DA, Verkhovsky MI, Wikström M. Active site of cytochrome cbb3. J Biol Chem 2009; 284:11301-8. [PMID: 19252222 PMCID: PMC2670135 DOI: 10.1074/jbc.m808839200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 02/27/2009] [Indexed: 11/06/2022] Open
Abstract
Cytochrome cbb(3) is the most distant member of the heme-copper oxidase family still retaining the following major feature typical of these enzymes: reduction of molecular oxygen to water coupled to proton translocation across the membrane. The thermodynamic properties of the six redox centers, five hemes and a copper ion, in cytochrome cbb(3) from Rhodobacter sphaeroides were studied using optical and EPR spectroscopy. The low spin heme b in the catalytic subunit was shown to have the highest midpoint redox potential (E(m)(,7) +418 mV), whereas the three hemes c in the two other subunits titrated with apparent midpoint redox potentials of +351, +320, and +234 mV. The active site high spin heme b(3) has a very low potential (E(m)(,7) -59 mV) as opposed to the copper center (Cu(B)), which has a high potential (E(m)(,7) +330 mV). The EPR spectrum of the ferric heme b(3) has rhombic symmetry. To explain the origins of the rhombicity, the Glu-383 residue located on the proximal side of heme b(3) was mutated to aspartate and to glutamine. The latter mutation caused a 10 nm blue shift in the optical reduced minus oxidized heme b(3) spectrum, and a dramatic change of the EPR signal toward more axial symmetry, whereas mutation to aspartate had far less severe consequences. These results strongly suggest that Glu-383 is involved in hydrogen bonding to the proximal His-405 ligand of heme b(3), a unique interaction among heme-copper oxidases.
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Affiliation(s)
- Virve Rauhamäki
- Helsinki Bioenergetics Group, Program for Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, P. O. Box 65 (Viikinkaari 1), 00014 Helsinki, Finland.
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Euro L, Belevich G, Wikström M, Verkhovskaya M. High affinity cation-binding sites in Complex I from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1024-8. [PMID: 19261245 DOI: 10.1016/j.bbabio.2009.02.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Revised: 02/18/2009] [Accepted: 02/19/2009] [Indexed: 10/21/2022]
Abstract
Studies on the activity of Complex I from Escherichia coli in the presence of different metal cations revealed at least two high affinity metal-binding sites. Membrane-bound or isolated Complex I was activated by K(+) (apparent binding constant approximately 125 microM) and inhibited by La(3+) (IC(50)= 1 microM). K(+) and La(3+) do not occupy the same site. Possible localization of these metal-binding sites and their implication in catalysis are discussed.
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Affiliation(s)
- Liliya Euro
- Helsinki Bioenergetics Group, Institute of Biotechnology, PO Box 65 (Viikinkaari 1) 00014 University of Helsinki, Finland.
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Zickermann V, Kerscher S, Zwicker K, Tocilescu MA, Radermacher M, Brandt U. Architecture of complex I and its implications for electron transfer and proton pumping. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:574-83. [PMID: 19366614 DOI: 10.1016/j.bbabio.2009.01.012] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Revised: 01/15/2009] [Accepted: 01/15/2009] [Indexed: 11/27/2022]
Abstract
Proton pumping NADH:ubiquinone oxidoreductase (complex I) is the largest and remains by far the least understood enzyme complex of the respiratory chain. It consists of a peripheral arm harbouring all known redox active prosthetic groups and a membrane arm with a yet unknown number of proton translocation sites. The ubiquinone reduction site close to iron-sulfur cluster N2 at the interface of the 49-kDa and PSST subunits has been mapped by extensive site directed mutagenesis. Independent lines of evidence identified electron transfer events during reduction of ubiquinone to be associated with the potential drop that generates the full driving force for proton translocation with a 4H(+)/2e(-) stoichiometry. Electron microscopic analysis of immuno-labelled native enzyme and of a subcomplex lacking the electron input module indicated a distance of 35-60 A of cluster N2 to the membrane surface. Resolution of the membrane arm into subcomplexes showed that even the distal part harbours subunits that are prime candidates to participate in proton translocation because they are homologous to sodium/proton antiporters and contain conserved charged residues in predicted transmembrane helices. The mechanism of redox linked proton translocation by complex I is largely unknown but has to include steps where energy is transmitted over extremely long distances. In this review we compile the available structural information on complex I and discuss implications for complex I function.
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Affiliation(s)
- Volker Zickermann
- Goethe-Universität, Fachbereich Medizin, Molekulare Bioenergetik, ZBC, Theodor-Stern-Kai 7, Haus 26, D-60590 Frankfurt am Main, Germany
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Euro L, Belevich G, Bloch DA, Verkhovsky MI, Wikström M, Verkhovskaya M. The role of the invariant glutamate 95 in the catalytic site of Complex I from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1787:68-73. [PMID: 19061856 DOI: 10.1016/j.bbabio.2008.11.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 11/01/2008] [Accepted: 11/05/2008] [Indexed: 12/01/2022]
Abstract
Replacement of glutamate 95 for glutamine in the NADH- and FMN-binding NuoF subunit of E. coli Complex I decreased NADH oxidation activity 2.5-4.8 times depending on the used electron acceptor. The apparent K(m) for NADH was 5.2 and 10.4 microM for the mutant and wild type, respectively. Analysis of the inhibitory effect of NAD(+) on activity showed that the E95Q mutation caused a 2.4-fold decrease of K(i)(NAD+) in comparison to the wild type enzyme. ADP-ribose, which differs from NAD(+) by the absence of the positively charged nicotinamide moiety, is also a competitive inhibitor of NADH binding. The mutation caused a 7.5-fold decrease of K(i)(ADP-ribose) relative to wild type enzyme. Based on these findings we propose that the negative charge of Glu95 accelerates turnover of Complex I by electrostatic interaction with the negatively charged phosphate groups of the substrate nucleotide during operation, which facilitates release of the product NAD(+). The E95Q mutation was also found to cause a positive shift of the midpoint redox potential of the FMN, from -350 mV to -310 mV, which suggests that the negative charge of Glu95 is also involved in decreasing the midpoint potential of the primary electron acceptor of Complex I.
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Affiliation(s)
- Liliya Euro
- Helsinki Bioenergetics Group, Institute of Biotechnology, University of Helsinki, Finland.
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Reda T, Barker CD, Hirst J. Reduction of the iron-sulfur clusters in mitochondrial NADH:ubiquinone oxidoreductase (complex I) by EuII-DTPA, a very low potential reductant. Biochemistry 2008; 47:8885-93. [PMID: 18651753 DOI: 10.1021/bi800437g] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
NADH:ubiquinone oxidoreductase (complex I) is the first enzyme of the mitochondrial electron transport chain. It contains a flavin mononucleotide to oxidize NADH, and eight iron-sulfur clusters. Seven of them transfer electrons between the flavin and the quinone-binding site, and one is on the opposite side of the flavin. Although most information about their properties is from EPR, the spectra from only five clusters have been observed, and it is difficult to match them to the structurally defined clusters. Here, we analyze complex I from bovine mitochondria reacted with a very low potential reductant, to impose a potential approaching -1 V. We compare the spectra with those from higher potentials and from the 24 kDa subunit and flavoprotein subcomplex, and model the spectra by starting from those with fewer components and building the complexity gradually. Spectrum N1a, from the 24 kDa subunit [2Fe-2S] cluster, is not observed in bovine complex I at any potential. Spectrum N1b, from the 75 kDa subunit [2Fe-2S] cluster, exhibits a lower potential than the N3, N4 and N5 spectra of three [4Fe-4S] clusters. In the lowest potential spectra an N5-type spectrum is observed at unusually high temperature (indicating a significant change to the cluster, or that two clusters have very similar g values), the relaxation rate of N1b increases (indicating that a nearby cluster has become reduced) and a new feature with an apparent g value of 2.16 suggests an interaction between two reduced clusters. The consequences of these observations for electron transfer in complex I are discussed.
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Affiliation(s)
- Torsten Reda
- Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK
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