1
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Teufel R. Oxygen-transfer reactions by enzymatic flavin-N 5 oxygen adducts-Oxidation is not a must. Curr Opin Chem Biol 2024; 80:102464. [PMID: 38739969 DOI: 10.1016/j.cbpa.2024.102464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/16/2024] [Accepted: 04/17/2024] [Indexed: 05/16/2024]
Abstract
Flavoenzymes catalyze numerous redox reactions including the transfer of an O2-derived oxygen atom to organic substrates, while the other one is reduced to water. Investigation of some of these monooxygenases led to a detailed understanding of their catalytic cycle, which involves the flavin-C4α-(hydro)peroxide as hallmark oxygenating species, and newly discovered flavoprotein monooxygenases were generally assumed to operate similarly. However, discoveries in recent years revealed a broader mechanistic versatility, including enzymes that utilize flavin-N5 oxygen adducts for catalysis in the form of the flavin-N5-(hydro)peroxide and the flavin-N5-oxide species. In this review, I will highlight recent developments in that area, including noncanonical flavoenzymes from natural product biosynthesis and sulfur metabolism that provide first insights into the chemical properties of these species. Remarkably, some enzymes may even combine the flavin-N5-peroxide and the flavin-N5-oxide species for consecutive oxygen-transfers to the same substrate and thereby in essence operate as dioxygenases.
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Affiliation(s)
- Robin Teufel
- Pharmaceutical Biology, Department of Pharmaceutical Sciences, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland.
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2
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Cryo-EM structures of Na +-pumping NADH-ubiquinone oxidoreductase from Vibrio cholerae. Nat Commun 2022; 13:4082. [PMID: 35882843 PMCID: PMC9325719 DOI: 10.1038/s41467-022-31718-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 06/29/2022] [Indexed: 11/08/2022] Open
Abstract
The Na+-pumping NADH-ubiquinone oxidoreductase (Na+-NQR) couples electron transfer from NADH to ubiquinone with Na+-pumping, generating an electrochemical Na+ gradient that is essential for energy-consuming reactions in bacteria. Since Na+-NQR is exclusively found in prokaryotes, it is a promising target for highly selective antibiotics. However, the molecular mechanism of inhibition is not well-understood for lack of the atomic structural information about an inhibitor-bound state. Here we present cryo-electron microscopy structures of Na+-NQR from Vibrio cholerae with or without a bound inhibitor at 2.5- to 3.1-Å resolution. The structures reveal the arrangement of all six redox cofactors including a herein identified 2Fe-2S cluster located between the NqrD and NqrE subunits. A large part of the hydrophilic NqrF is barely visible in the density map, suggesting a high degree of flexibility. This flexibility may be responsible to reducing the long distance between the 2Fe-2S centers in NqrF and NqrD/E. Two different types of specific inhibitors bind to the N-terminal region of NqrB, which is disordered in the absence of inhibitors. The present study provides a foundation for understanding the function of Na+-NQR and the binding manner of specific inhibitors.
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3
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Tuz K, Yuan M, Hu Y, Do TTT, Willow SY, DePaolo-Boisvert JA, Fuller JR, Minh DDL, Juárez O. Identification of the riboflavin-cofactor binding site in the Vibrio cholerae ion-pumping NQR complex: A novel structural motif in redox enzymes. J Biol Chem 2022; 298:102182. [PMID: 35752362 PMCID: PMC9293633 DOI: 10.1016/j.jbc.2022.102182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 06/16/2022] [Accepted: 06/18/2022] [Indexed: 11/18/2022] Open
Abstract
The ion-pumping NQR complex is an essential respiratory enzyme in the physiology of many pathogenic bacteria. This enzyme transfers electrons from NADH to ubiquinone through several cofactors, including riboflavin (vitamin B2). NQR is the only enzyme reported that is able to use riboflavin as a cofactor. Moreover, the riboflavin molecule is found as a stable neutral semiquinone radical. The otherwise highly reactive unpaired electron is stabilized via an unknown mechanism. Crystallographic data suggested that riboflavin might be found in a superficially located site in the interface of NQR subunits B and E. However, this location is highly problematic, as the site does not have the expected physiochemical properties. In this work, we have located the riboflavin-binding site in an amphipathic pocket in subunit B, previously proposed to be the entry site of sodium. Here, we show that this site contains absolutely conserved residues, including N200, N203, and D346. Mutations of these residues decrease enzymatic activity and specifically block the ability of NQR to bind riboflavin. Docking analysis and molecular dynamics simulations indicate that these residues participate directly in riboflavin binding, establishing hydrogen bonds that stabilize the cofactor in the site. We conclude that riboflavin is likely bound in the proposed pocket, which is consistent with enzymatic characterizations, thermodynamic studies, and distance between cofactors.
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Affiliation(s)
- Karina Tuz
- Department of Biological Sciences, Illinois Institute of Technology, Chicago IL
| | - Ming Yuan
- Department of Biological Sciences, Illinois Institute of Technology, Chicago IL
| | - Yuyao Hu
- Department of Biological Sciences, Illinois Institute of Technology, Chicago IL
| | - Tien T T Do
- Department of Chemistry, Illinois Institute of Technology, Chicago IL
| | | | | | - James R Fuller
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL
| | - David D L Minh
- Department of Chemistry, Illinois Institute of Technology, Chicago IL
| | - Oscar Juárez
- Department of Biological Sciences, Illinois Institute of Technology, Chicago IL.
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4
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Pompe N, Illarionov B, Fischer M, Bacher A, Weber S. Completing the Picture: Determination of 13C Hyperfine Coupling Constants of Flavin Semiquinone Radicals by Photochemically Induced Dynamic Nuclear Polarization Spectroscopy. J Phys Chem Lett 2022; 13:5160-5167. [PMID: 35658481 DOI: 10.1021/acs.jpclett.2c00919] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
We investigate the electronic structure of flavin semiquinone radicals in terms of their 13C hyperfine coupling constants. Photochemically induced dynamic nuclear polarization (photo-CIDNP) spectroscopy was used to study both the neutral and anionic radical species of flavin mononucleotide (FMN) in bulk aqueous solution. Apart from universally 13C-labeled FMN, partially labeled isotopologues are used to increase sensitivity for nuclei exhibiting very small hyperfine couplings and to cope with spectral overlap. In addition, experimental findings are supported by quantum chemical calculations, and implications for the spin density distribution in free flavin radicals are discussed.
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Affiliation(s)
- Nils Pompe
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Boris Illarionov
- Hamburg School of Food Science, University of Hamburg, 20146 Hamburg, Germany
| | - Markus Fischer
- Hamburg School of Food Science, University of Hamburg, 20146 Hamburg, Germany
| | - Adelbert Bacher
- Department of Chemistry, Technical University of Munich, 85748 Garching, Germany
| | - Stefan Weber
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg im Breisgau, Germany
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5
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Schleicher E, Rein S, Illarionov B, Lehmann A, Al Said T, Kacprzak S, Bittl R, Bacher A, Fischer M, Weber S. Selective 13C labelling reveals the electronic structure of flavocoenzyme radicals. Sci Rep 2021; 11:18234. [PMID: 34521887 PMCID: PMC8440535 DOI: 10.1038/s41598-021-97588-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 08/24/2021] [Indexed: 02/08/2023] Open
Abstract
Flavocoenzymes are nearly ubiquitous cofactors that are involved in the catalysis and regulation of a wide range of biological processes including some light-induced ones, such as the photolyase-mediated DNA repair, magnetoreception of migratory birds, and the blue-light driven phototropism in plants. One of the factors that enable versatile flavin-coenzyme biochemistry and biophysics is the fine-tuning of the cofactor's frontier orbital by interactions with the protein environment. Probing the singly-occupied molecular orbital (SOMO) of the intermediate radical state of flavins is therefore a prerequisite for a thorough understanding of the diverse functions of the flavoprotein family. This may be ultimately achieved by unravelling the hyperfine structure of a flavin by electron paramagnetic resonance. In this contribution we present a rigorous approach to obtaining a hyperfine map of the flavin's chromophoric 7,8-dimethyl isoalloxazine unit at an as yet unprecedented level of resolution and accuracy. We combine powerful high-microwave-frequency/high-magnetic-field electron-nuclear double resonance (ENDOR) with 13C isotopologue editing as well as spectral simulations and density functional theory calculations to measure and analyse 13C hyperfine couplings of the flavin cofactor in DNA photolyase. Our data will provide the basis for electronic structure considerations for a number of flavin radical intermediates occurring in blue-light photoreceptor proteins.
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Affiliation(s)
- Erik Schleicher
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Stephan Rein
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Boris Illarionov
- grid.9026.d0000 0001 2287 2617Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany
| | - Ariane Lehmann
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Tarek Al Said
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Sylwia Kacprzak
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany ,grid.423218.ePresent Address: Bruker BioSpin GmbH, Silberstreifen 4, 76287 Rheinstetten, Germany
| | - Robert Bittl
- grid.14095.390000 0000 9116 4836Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Adelbert Bacher
- grid.6936.a0000000123222966Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany
| | - Markus Fischer
- grid.9026.d0000 0001 2287 2617Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany
| | - Stefan Weber
- grid.5963.9Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
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6
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Willow SY, Yuan M, Juárez O, Minh DDL. Electrostatics and water occlusion regulate covalently-bound flavin mononucleotide cofactors of Vibrio cholerae respiratory complex NQR. Proteins 2021; 89:1376-1385. [PMID: 34091964 DOI: 10.1002/prot.26158] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 05/20/2021] [Accepted: 06/01/2021] [Indexed: 12/20/2022]
Abstract
Proteins like NADH:ubiquinone oxidoreductase (NQR), an essential enzyme and ion pump in the physiology of several pathogenic bacteria, tightly regulate the redox properties of their cofactors. Although flavin mononucleotide (FMN) is fully reduced in aqueous solution, FMN in subunits B and C of NQR exclusively undergo one-electron transitions during its catalytic cycle. Here, we perform ab initio calculations and molecular dynamics simulations to elucidate the mechanisms that regulate the redox state of FMN in NQR. QM/MM calculations show that binding site electrostatics disfavor anionic forms of FMNH2 , but permit a neutral form of the fully reduced flavin. The potential energy surface is unaffected by covalent bonding between FMN and threonine. Molecular dynamics simulations show that the FMN binding sites are inaccessible by water, suggesting that further reductions of the cofactors are limited or prohibited by the availability of water and other proton donors. These findings provide a deeper understanding of the mechanisms used by NQR to regulate electron transfer through the cofactors and perform its physiologic role. They also provide the first, to our knowledge, evidence of the simple concept that proteins regulate flavin redox states via water occlusion.
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Affiliation(s)
- Soohaeng Yoo Willow
- Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois, USA
| | - Ming Yuan
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois, USA
| | - Oscar Juárez
- Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois, USA
| | - David D L Minh
- Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois, USA
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7
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Wörner J, Chen J, Bacher A, Weber S. Non-classical disproportionation revealed by photo-chemically induced dynamic nuclear polarization NMR. MAGNETIC RESONANCE (GOTTINGEN, GERMANY) 2021; 2:281-290. [PMID: 37904753 PMCID: PMC10539781 DOI: 10.5194/mr-2-281-2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Accepted: 04/07/2021] [Indexed: 11/01/2023]
Abstract
Photo-chemically induced dynamic nuclear polarization (photo-CIDNP) was used to observe the light-induced disproportionation reaction of 6,7,8-trimethyllumazine starting out from its triplet state to generate a pair of radicals comprising a one-electron reduced and a one-electron oxidized species. Our evidence is based on the measurement of two marker proton hyperfine couplings, A iso (H(6α )) and A iso (H(8α )), which we correlated to predictions from density functional theory. The ratio of these two hyperfine couplings is reversed in the oxidized and the reduced radical species. Observation of the dismutation reaction is facilitated by the exceptional C-H acidity of the methyl group at position 7 of 6,7,8-trimethyllumazine and the slow proton exchange associated with it, which leads to NMR-distinguishable anionic (TML- ) and neutral (TMLH) protonation forms.
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Affiliation(s)
- Jakob Wörner
- Institute of Physical Chemistry, Albert-Ludwigs-Universität
Freiburg, Freiburg, 79104, Germany
| | - Jing Chen
- Institute of Physical Chemistry, Albert-Ludwigs-Universität
Freiburg, Freiburg, 79104, Germany
| | - Adelbert Bacher
- Department of Chemistry, Technical University of Munich, Garching,
85748, Germany
| | - Stefan Weber
- Institute of Physical Chemistry, Albert-Ludwigs-Universität
Freiburg, Freiburg, 79104, Germany
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8
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Specific chemical modification explores dynamic structure of the NqrB subunit in Na +-pumping NADH-ubiquinone oxidoreductase from Vibrio cholerae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148432. [PMID: 33932367 DOI: 10.1016/j.bbabio.2021.148432] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Accepted: 04/20/2021] [Indexed: 12/28/2022]
Abstract
The Na+-pumping NADH-ubiquinone oxidoreductase (Na+-NQR) is a main ion transporter in many pathogenic bacteria. We previously proposed that N-terminal stretch of the NqrB subunit plays an important role in regulating the ubiquinone reaction at the adjacent NqrA subunit in Vibrio cholerae Na+-NQR. However, since approximately three quarters of the stretch (NqrB-Met1-Pro37) was not modeled in an earlier crystallographic study, its structure and function remain unknown. If we can develop a method that enables pinpoint modification of this stretch by functional chemicals (such as spin probes), it could lead to new ways to investigate the unsettled issues. As the first step to this end, we undertook to specifically attach an alkyne group to a lysine located in the stretch via protein-ligand affinity-driven substitution using synthetic ligands NAS-K1 and NAS-K2. The alkyne, once attached, can serve as an "anchor" for connecting functional chemicals via convenient click chemistry. After a short incubation of isolated Na+-NQR with these ligands, alkyne was predominantly incorporated into NqrB. Proteomic analyses in combination with mutagenesis of predicted target lysines revealed that alkyne attaches to NqrB-Lys22 located at the nonmodeled region of the stretch. This study not only achieved the specific modification initially aimed for but also provided valuable information about positioning of the nonmodeled region. For example, the fact that hydrophobic NAS-Ks come into contact with NqrB-Lys22 suggests that the nonmodeled region may orient toward the membrane phase rather than protruding into cytoplasmic medium. This conformation may be essential for regulating the ubiquinone reaction in the adjacent NqrA.
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9
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Jeong HS, Hong S, Yoo HS, Kim J, Kim Y, Yoon C, Lee SJ, Kim SH. EPR-derived structures of flavin radical and iron-sulfur clusters from Methylosinus sporium 5 reductase. Inorg Chem Front 2021. [DOI: 10.1039/d0qi01334j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic structures of two cofactors, the FAD radical and [2Fe–2S]+ of reduced MMOR from Methylosinus sporium strain 5 were investigated by advanced EPR spectroscopy. The findings provide long overdue detailed structural information of MMOR.
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Affiliation(s)
- Han Sol Jeong
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
| | - Sugyeong Hong
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
| | - Hee Seon Yoo
- Department of Chemistry and Institute of Molecular Biology and Genetics
- Jeonbuk National University
- Jeonju 54896
- Rep. of Korea
| | - Jin Kim
- Department of Chemistry
- Sunchon National University
- Suncheon 57922
- Rep. of Korea
| | - Yujeong Kim
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
| | - Chungwoon Yoon
- Department of Chemistry and Institute of Molecular Biology and Genetics
- Jeonbuk National University
- Jeonju 54896
- Rep. of Korea
| | - Seung Jae Lee
- Department of Chemistry and Institute of Molecular Biology and Genetics
- Jeonbuk National University
- Jeonju 54896
- Rep. of Korea
| | - Sun Hee Kim
- Western Seoul Center
- Korea Basic Science Institute (KBSI)
- Seoul 03759
- Rep. of Korea
- Department of Chemistry and Nano Science
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10
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Beaupre BA, Moran GR. N5 Is the New C4a: Biochemical Functionalization of Reduced Flavins at the N5 Position. Front Mol Biosci 2020; 7:598912. [PMID: 33195440 PMCID: PMC7662398 DOI: 10.3389/fmolb.2020.598912] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 10/05/2020] [Indexed: 12/31/2022] Open
Abstract
For three decades the C4a-position of reduced flavins was the known site for covalency within flavoenzymes. The reactivity of this position of the reduced isoalloxazine ring with the dioxygen ground-state triplet established the C4a as a site capable of one-electron chemistry. Within the last two decades new types of reduced flavin reactivity have been documented. These studies reveal that the N5 position is also a protean site of reactivity, that is capable of nucleophilic attack to form covalent bonds with substrates. In addition, though the precise mechanism of dioxygen reactivity is yet to be definitively demonstrated, it is clear that the N5 position is directly involved in substrate oxygenation in some enzymes. In this review we document the lineage of discoveries that identified five unique modes of N5 reactivity that collectively illustrate the versatility of this position of the reduced isoalloxazine ring.
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Affiliation(s)
- Brett A Beaupre
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
| | - Graham R Moran
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
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11
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Masuya T, Sano Y, Tanaka H, Butler NL, Ito T, Tosaki T, Morgan JE, Murai M, Barquera B, Miyoshi H. Inhibitors of a Na +-pumping NADH-ubiquinone oxidoreductase play multiple roles to block enzyme function. J Biol Chem 2020; 295:12739-12754. [PMID: 32690607 DOI: 10.1074/jbc.ra120.014229] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 07/18/2020] [Indexed: 11/06/2022] Open
Abstract
The Na+-pumping NADH-ubiquinone (UQ) oxidoreductase (Na+-NQR) is present in the respiratory chain of many pathogenic bacteria and is thought to be a promising antibiotic target. Whereas many details of Na+-NQR structure and function are known, the mechanisms of action of potent inhibitors is not well-understood; elucidating the mechanisms would not only advance drug design strategies but might also provide insights on a terminal electron transfer from riboflavin to UQ. To this end, we performed photoaffinity labeling experiments using photoreactive derivatives of two known inhibitors, aurachin and korormicin, on isolated Vibrio cholerae Na+-NQR. The inhibitors labeled the cytoplasmic surface domain of the NqrB subunit including a protruding N-terminal stretch, which may be critical to regulate the UQ reaction in the adjacent NqrA subunit. The labeling was blocked by short-chain UQs such as ubiquinone-2. The photolabile group (2-aryl-5-carboxytetrazole (ACT)) of these inhibitors reacts with nucleophilic amino acids, so we tested mutations of nucleophilic residues in the labeled region of NqrB, such as Asp49 and Asp52 (to Ala), and observed moderate decreases in labeling yields, suggesting that these residues are involved in the interaction with ACT. We conclude that the inhibitors interfere with the UQ reaction in two ways: the first is blocking structural rearrangements at the cytoplasmic interface between NqrA and NqrB, and the second is the direct obstruction of UQ binding at this interfacial area. Unusual competitive behavior between the photoreactive inhibitors and various competitors corroborates our previous proposition that there may be two inhibitor binding sites in Na+-NQR.
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Affiliation(s)
- Takahiro Masuya
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Yuki Sano
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Hinako Tanaka
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | | | | | - Tatsuhiko Tosaki
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Joel E Morgan
- Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Masatoshi Murai
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Blanca Barquera
- Department of Biological Science and.,Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | - Hideto Miyoshi
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
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12
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Brosi R, Illarionov B, Heidinger L, Kim RR, Fischer M, Weber S, Bacher A, Bittl R, Schleicher E. Coupled Methyl Group Rotation in FMN Radicals Revealed by Selective Deuterium Labeling. J Phys Chem B 2020; 124:1678-1690. [PMID: 32011886 DOI: 10.1021/acs.jpcb.9b11331] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Flavin semiquinones are common intermediate redox states in flavoproteins, and thus, knowledge of their electronic structure is essential for fully understanding their chemistry and chemical versatility. In this contribution, we use a combination of high-field electron nuclear double resonance spectroscopy and selective deuterium labeling of flavin mononucleotide (FMN) with subsequent incorporation as cofactor into a variant Avena sativa LOV domain to extract missing traits of the electronic structure of a protein-bound FMN radical. From these experiments, precise values of small proton hyperfine and deuterium nuclear quadrupole couplings could be extracted. Specifically, isotropic hyperfine couplings of -3.34, -0.11, and +0.91 MHz were obtained for the protons H(6), H(9), and H(7α), respectively. These values are discussed in the light of specific protein-cofactor interactions. Furthermore, the temperature behavior of the H(7α) methyl-group rotation elicited by its energy landscape was analyzed in greater detail. Pronounced interplay between the two methyl groups at C(7) and C(8) of FMN could be revealed. Most strikingly, this rotational behavior could be modulated by selective deuterium editing.
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Affiliation(s)
- Richard Brosi
- Fachbereich Physik, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Boris Illarionov
- Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany
| | - Lorenz Heidinger
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Ryu-Ryun Kim
- Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany
| | - Markus Fischer
- Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany
| | - Stefan Weber
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Adelbert Bacher
- Institut für Lebensmittelchemie, Universität Hamburg, Grindelallee 117, 20146 Hamburg, Germany.,Fakultät für Chemie, Technische Universität München, Lichtenbergstr. 4, 80247 Garching, Germany
| | - Robert Bittl
- Fachbereich Physik, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Erik Schleicher
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany
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13
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Pompe N, Chen J, Illarionov B, Panter S, Fischer M, Bacher A, Weber S. Methyl groups matter: Photo-CIDNP characterizations of the semiquinone radicals of FMN and demethylated FMN analogs. J Chem Phys 2019; 151:235103. [PMID: 31864274 DOI: 10.1063/1.5130557] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this contribution, the relative hyperfine couplings are determined for the 1H nuclei of the flavin mononucleotide (FMN) radical in an aqueous environment. In addition, three structural analogs with different methylation patterns are characterized and the influence of the substituents at the isoalloxazine moiety on the electronic structure of the radicals is explored. By exploiting nuclear hyperpolarization generated via the photo-CIDNP (chemically induced dynamic nuclear polarization) effect, it is possible to study the short-lived radical species generated by in situ light excitation. Experimental data are extracted by least-squares fitting and supported by quantum chemical calculations and published values from electron paramagnetic resonance and electron-nuclear double resonance. Furthermore, mechanistic details of the photoreaction of the investigated flavin analogs with l-tryptophan are derived from the photo-CIDNP spectra recorded at different pH values. Thereby, the neutral and anionic radicals of FMN and three structural analogs are, for the first time, characterized in terms of their electronic structure in an aqueous environment.
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Affiliation(s)
- Nils Pompe
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg, Germany
| | - Jing Chen
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg, Germany
| | - Boris Illarionov
- Hamburg School of Food Science, Institute of Food Chemistry, University of Hamburg, 20146 Hamburg, Germany
| | - Sabrina Panter
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg, Germany
| | - Markus Fischer
- Hamburg School of Food Science, Institute of Food Chemistry, University of Hamburg, 20146 Hamburg, Germany
| | - Adelbert Bacher
- Department of Chemistry, Technical University of Munich, 85748 Garching, Germany
| | - Stefan Weber
- Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg, Germany
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14
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Nohr D, Weber S, Schleicher E. EPR spectroscopy on flavin radicals in flavoproteins. Methods Enzymol 2019; 620:251-275. [PMID: 31072489 DOI: 10.1016/bs.mie.2019.03.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Flavin semiquinone redox states are important intermediates in a broad variety of reactions catalyzed by flavoproteins. As paramagnetic states they can be favorably probed by EPR spectroscopy in all its flavors. This review summarizes recent results in the characterization of flavin radicals. On the one hand, flavin radical states, e.g., trapped as reaction intermediates, can be characterized using modern pulsed EPR methods to unravel their electronic structure and to gain information about the surrounding environment and its changes on protein action. On the other hand, short-lived intermediate flavin radical states generated, e.g., photochemically, can be followed by time-resolved EPR, which allows a direct tracking of flavin-dependent reactions with a temporal resolution reaching nanoseconds.
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Affiliation(s)
- Daniel Nohr
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Stefan Weber
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Erik Schleicher
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
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15
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Abstract
Molecular mechanisms of dark-to-light state transitions in flavoprotein photoreceptors have been the subject of intense investigation. Blue-light sensing flavoproteins fall into three general classes that share aspects of their activation processes: LOV domains, BLUF proteins, and cryptochromes. In all cases, light-induced changes in flavin redox, protonation, and bonding states result in hydrogen-bond and conformational rearrangements important for regulation of downstream targets. Physical characterization of these flavoprotein states can provide valuable insights into biological function, but clear conclusions are often challenging to draw owing to complexities of data collection and interpretation. In this chapter, we briefly review the three classes of flavoprotein photoreceptors and provide methods for their recombinant production, reconstitution with flavin cofactor, and characterization. We then relate best practices and special considerations for the application of several types of spectroscopies, redox potential measurements, and X-ray scattering experiments to photosensitive flavoproteins. The methods presented are generally accessible to most laboratories.
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Affiliation(s)
- Estella F Yee
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States
| | | | - Changfan Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States
| | - Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States.
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16
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Muras V, Toulouse C, Fritz G, Steuber J. Respiratory Membrane Protein Complexes Convert Chemical Energy. Subcell Biochem 2019; 92:301-335. [PMID: 31214991 DOI: 10.1007/978-3-030-18768-2_10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The invention of a biological membrane which is used as energy storage system to drive the metabolism of a primordial, unicellular organism represents a key event in the evolution of life. The innovative, underlying principle of this key event is respiration. In respiration, a lipid bilayer with insulating properties is chosen as the site for catalysis of an exergonic redox reaction converting substrates offered from the environment, using the liberated Gibbs free energy (ΔG) for the build-up of an electrochemical H+ (proton motive force, PMF) or Na+ gradient (sodium motive force, SMF) across the lipid bilayer. Very frequently , several redox reactions are performed in a consecutive manner, with the first reaction delivering a product which is used as substrate for the second redox reaction, resulting in a respiratory chain. From today's perspective, the (mostly) unicellular bacteria and archaea seem to be much simpler and less evolved when compared to multicellular eukaryotes. However, they are overwhelmingly complex with regard to the various respiratory chains which permit survival in very different habitats of our planet, utilizing a plethora of substances to drive metabolism. This includes nitrogen, sulfur and carbon compounds which are oxidized or reduced by specialized, respiratory enzymes of bacteria and archaea which lie at the heart of the geochemical N, S and C-cycles. This chapter gives an overview of general principles of microbial respiration considering thermodynamic aspects, chemical reactions and kinetic restraints. The respiratory chains of Escherichia coli and Vibrio cholerae are discussed as models for PMF- versus SMF-generating processes, respectively. We introduce main redox cofactors of microbial respiratory enzymes, and the concept of intra-and interelectron transfer. Since oxygen is an electron acceptor used by many respiratory chains, the formation and removal of toxic oxygen radicals is described. Promising directions of future research are respiratory enzymes as novel bacterial targets, and biotechnological applications relying on respiratory complexes.
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Affiliation(s)
- Valentin Muras
- Institute of Microbiology, University of Hohenheim, Garbenstr. 30, 70599, Stuttgart, Germany
| | - Charlotte Toulouse
- Institute of Microbiology, University of Hohenheim, Garbenstr. 30, 70599, Stuttgart, Germany
| | - Günter Fritz
- Institute of Microbiology, University of Hohenheim, Garbenstr. 30, 70599, Stuttgart, Germany
| | - Julia Steuber
- Institute of Microbiology, University of Hohenheim, Garbenstr. 30, 70599, Stuttgart, Germany.
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17
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Rostas A, Einholz C, Illarionov B, Heidinger L, Said TA, Bauss A, Fischer M, Bacher A, Weber S, Schleicher E. Long-Lived Hydrated FMN Radicals: EPR Characterization and Implications for Catalytic Variability in Flavoproteins. J Am Chem Soc 2018; 140:16521-16527. [PMID: 30412389 DOI: 10.1021/jacs.8b07544] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Until now, FMN/FAD radicals could not be stabilized in aqueous solution or other protic solvents because of rapid and efficient dismutation reactions. In this contribution, a novel system for stabilizing flavin radicals in aqueous solution is reported. Subsequent to trapping FMN in an agarose matrix, light-generated FMN radicals could be produced that were stable for days even under aerobic conditions, and their concentrations were high enough for extensive EPR characterization. All large hyperfine couplings could be extracted by using a combination of continuous-wave EPR and low-temperature ENDOR spectroscopy. To map differences in the electronic structure of flavin radicals, two exemplary proton hyperfine couplings were compared with published values from various neutral and anionic flavoprotein radicals: C(6)H and C(8α)H 3. It turned out that FMN•- in an aqueous environment shows the largest hyperfine couplings, whereas for FMNH• under similar conditions, hyperfine couplings are at the lower end and the values of both vary by up to 30%. This finding demonstrates that protein-cofactor interactions in neutral and anionic flavoprotein radicals can alter their electron spin density in different directions. With this aqueous system that allows the characterization of flavin radicals without protein interactions and that can be extended by using selective isotope labeling, a powerful tool is now at hand to quantify interactions in flavin radicals that modulate the reactivity in different flavoproteins.
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Affiliation(s)
- Arpad Rostas
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Christopher Einholz
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Boris Illarionov
- Hamburg School of Food Science , Institut für Lebensmittelchemie, Universität Hamburg , Grindelallee 117 , 20146 Hamburg , Germany
| | - Lorenz Heidinger
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Tarek Al Said
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Anna Bauss
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Markus Fischer
- Hamburg School of Food Science , Institut für Lebensmittelchemie, Universität Hamburg , Grindelallee 117 , 20146 Hamburg , Germany
| | - Adelbert Bacher
- Department of Chemistry , Technical University of Munich , Lichtenbergstr. 4 , 85747 Garching , Germany
| | - Stefan Weber
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
| | - Erik Schleicher
- Institut für Physikalische Chemie , Albert-Ludwigs-Universität Freiburg , Albertstr. 21 , 79104 Freiburg , Germany
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18
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Robbins JM, Geng J, Barry BA, Gadda G, Bommarius AS. Photoirradiation Generates an Ultrastable 8-Formyl FAD Semiquinone Radical with Unusual Properties in Formate Oxidase. Biochemistry 2018; 57:5818-5826. [PMID: 30226367 DOI: 10.1021/acs.biochem.8b00571] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Formate oxidase (FOX) was previously shown to contain a noncovalently bound 8-formyl FAD (8-fFAD) cofactor. However, both the absorption spectra and the kinetic parameters previously reported for FOX are inconsistent with more recent reports. The ultraviolet-visible (UV-vis) absorption spectrum reported in early studies closely resembles the spectra observed for protein-bound 8-formyl flavin semiquinone species, thus suggesting FOX may be photosensitive. Therefore, the properties of dark and light-exposed FOX were investigated using steady-state kinetics and site-directed mutagenesis analysis along with inductively coupled plasma optical emission spectroscopy, UV-vis absorption spectroscopy, circular dichroism spectroscopy, liquid chromatography and mass spectrometry, and electron paramagnetic resonance (EPR) spectroscopy. Surprisingly, these experimental results demonstrate that FOX is deactivated in the presence of light through generation of an oxygen stable, anionic (red) 8-fFAD semiquinone radical capable of persisting either in an aerobic environment for multiple weeks or in the presence of a strong reducing agent like sodium dithionite. Herein, we study the photoinduced formation of the 8-fFAD semiquinone radical in FOX and report the first EPR spectrum of this radical species. The stability of the 8-fFAD semiquinone radical suggests FOX to be a model enzyme for probing the structural and mechanistic features involved in stabilizing flavin semiquinone radicals. It is likely that the photoinduced formation of a stable 8-fFAD semiquinone radical is a defining characteristic of 8-formyl flavin-dependent enzymes. Additionally, a better understanding of the radical stabilization process may yield a FOX enzyme with more robust activity and broader industrial usefulness.
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Affiliation(s)
- John M Robbins
- School of Chemical and Biomolecular Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332-0100 , United States.,Engineered Biosystems Building (EBB) , Georgia Institute of Technology , Atlanta , Georgia 30332-2000 , United States
| | - Jiafeng Geng
- School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
| | - Bridgette A Barry
- School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
| | - Giovanni Gadda
- Department of Chemistry , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Center for Diagnostics and Therapeutics , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Center for Biotechnology and Drug Design , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Department of Biology , Georgia State University , Atlanta , Georgia 30302-3965 , United States
| | - Andreas S Bommarius
- School of Chemical and Biomolecular Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332-0100 , United States.,Engineered Biosystems Building (EBB) , Georgia Institute of Technology , Atlanta , Georgia 30332-2000 , United States.,School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
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19
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Raba DA, Rosas-Lemus M, Menzer WM, Li C, Fang X, Liang P, Tuz K, Minh DDL, Juárez O. Characterization of the Pseudomonas aeruginosa NQR complex, a bacterial proton pump with roles in autopoisoning resistance. J Biol Chem 2018; 293:15664-15677. [PMID: 30135204 DOI: 10.1074/jbc.ra118.003194] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 08/13/2018] [Indexed: 12/22/2022] Open
Abstract
Pseudomonas aeruginosa is a Gram-negative bacterium responsible for a large number of nosocomial infections. The P. aeruginosa respiratory chain contains the ion-pumping NADH:ubiquinone oxidoreductase (NQR). This enzyme couples the transfer of electrons from NADH to ubiquinone to the pumping of sodium ions across the cell membrane, generating a gradient that drives essential cellular processes in many bacteria. In this study, we characterized P. aeruginosa NQR (Pa-NQR) to elucidate its physiologic function. Our analyses reveal that Pa-NQR, in contrast with NQR homologues from other bacterial species, is not a sodium pump, but rather a completely new form of proton pump. Homology modeling and molecular dynamics simulations suggest that cation selectivity could be determined by the exit ion channels. We also show that Pa-NQR is resistant to the inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO). HQNO is a quinolone secreted by P. aeruginosa during infection that acts as a quorum sensing agent and also has bactericidal properties against other bacteria. Using comparative analysis and computational modeling of the ubiquinone-binding site, we identified the specific residues that confer resistance toward this inhibitor. In summary, our findings indicate that Pa-NQR is a proton pump rather than a sodium pump and is highly resistant against the P. aeruginosa-produced compound HQNO, suggesting an important role in the adaptation against autotoxicity. These results provide a deep understanding of the metabolic role of NQR in P. aeruginosa and provide insight into the structural factors that determine the functional specialization in this family of respiratory complexes.
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Affiliation(s)
| | | | - William M Menzer
- From the Departments of Biological Sciences and.,Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
| | - Chen Li
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
| | - Xuan Fang
- From the Departments of Biological Sciences and
| | | | - Karina Tuz
- From the Departments of Biological Sciences and
| | - David D L Minh
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
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20
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Enzymatic control of dioxygen binding and functionalization of the flavin cofactor. Proc Natl Acad Sci U S A 2018; 115:4909-4914. [PMID: 29686059 DOI: 10.1073/pnas.1801189115] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The reactions of enzymes and cofactors with gaseous molecules such as dioxygen (O2) are challenging to study and remain among the most contentious subjects in biochemistry. To date, it is largely enigmatic how enzymes control and fine-tune their reactions with O2, as exemplified by the ubiquitous flavin-dependent enzymes that commonly facilitate redox chemistry such as the oxygenation of organic substrates. Here we employ O2-pressurized X-ray crystallography and quantum mechanical calculations to reveal how the precise positioning of O2 within a flavoenzyme's active site enables the regiospecific formation of a covalent flavin-oxygen adduct and oxygenating species (i.e., the flavin-N5-oxide) by mimicking a critical transition state. This study unambiguously demonstrates how enzymes may control the O2 functionalization of an organic cofactor as prerequisite for oxidative catalysis. Our work thus illustrates how O2 reactivity can be harnessed in an enzymatic environment and provides crucial knowledge for future rational design of O2-reactive enzymes.
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21
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Martínez JI, Frago S, Lans I, Alonso PJ, García-Rubio I, Medina M. Spin Densities in Flavin Analogs within a Flavoprotein. Biophys J 2017; 110:561-571. [PMID: 26840722 DOI: 10.1016/j.bpj.2015.11.3525] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 10/10/2015] [Accepted: 11/16/2015] [Indexed: 11/26/2022] Open
Abstract
Characterization by electron paramagnetic resonance techniques of several variants of Anabaena flavodoxin, where the naturally occurring FMN cofactor is substituted by different analogs, makes it possible to improve the details of the spin distribution map in the isoallosazine ring in its semiquinone state. The analyzed variants were selected to monitor the effects of intrinsic changes in the flavin ring electronic structure, as well as perturbations in the apoflavodoxin-flavin interaction, on the spin populations. When these effects were analyzed together with the functional properties of the different flavodoxin variants, a relationship between spin population and biochemical parameters, as the reduction potential, could be envisaged.
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Affiliation(s)
- Jesús Ignacio Martínez
- Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza, Consejo Superior de Investigaciones Científicas, Zaragoza, Spain.
| | - Susana Frago
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos, Universidad de Zaragoza, Zaragoza, Spain; Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Isaías Lans
- Grupo de Bioquímica Teórica, Universidad Industrial de Santander, Bucaramanga, Colombia
| | - Pablo Javier Alonso
- Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza, Consejo Superior de Investigaciones Científicas, Zaragoza, Spain
| | - Inés García-Rubio
- Centro Universitario de la Defensa, Zaragoza, Spain; Laboratory of Physical Chemistry, Eidgenössische Technische Hochschule Zürich, Switzerland
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos, Universidad de Zaragoza, Zaragoza, Spain
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22
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Tuz K, Li C, Fang X, Raba DA, Liang P, Minh DDL, Juárez O. Identification of the Catalytic Ubiquinone-binding Site of Vibrio cholerae Sodium-dependent NADH Dehydrogenase: A NOVEL UBIQUINONE-BINDING MOTIF. J Biol Chem 2017; 292:3039-3048. [PMID: 28053088 DOI: 10.1074/jbc.m116.770982] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 12/29/2016] [Indexed: 11/06/2022] Open
Abstract
The sodium-dependent NADH dehydrogenase (Na+-NQR) is a key component of the respiratory chain of diverse prokaryotic species, including pathogenic bacteria. Na+-NQR uses the energy released by electron transfer between NADH and ubiquinone (UQ) to pump sodium, producing a gradient that sustains many essential homeostatic processes as well as virulence factor secretion and the elimination of drugs. The location of the UQ binding site has been controversial, with two main hypotheses that suggest that this site could be located in the cytosolic subunit A or in the membrane-bound subunit B. In this work, we performed alanine scanning mutagenesis of aromatic residues located in transmembrane helices II, IV, and V of subunit B, near glycine residues 140 and 141. These two critical glycine residues form part of the structures that regulate the site's accessibility. Our results indicate that the elimination of phenylalanine residue 211 or 213 abolishes the UQ-dependent activity, produces a leak of electrons to oxygen, and completely blocks the binding of UQ and the inhibitor HQNO. Molecular docking calculations predict that UQ interacts with phenylalanine 211 and pinpoints the location of the binding site in the interface of subunits B and D. The mutagenesis and structural analysis allow us to propose a novel UQ-binding motif, which is completely different compared with the sites of other respiratory photosynthetic complexes. These results are essential to understanding the electron transfer pathways and mechanism of Na+-NQR catalysis.
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Affiliation(s)
- Karina Tuz
- From the Departments of Biological Sciences and
| | - Chen Li
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
| | - Xuan Fang
- From the Departments of Biological Sciences and
| | | | | | - David D L Minh
- Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
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23
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Tan SLJ, Novianti ML, Webster RD. Effects of Low to Intermediate Water Concentrations on Proton-Coupled Electron Transfer (PCET) Reactions of Flavins in Aprotic Solvents and a Comparison with the PCET Reactions of Quinones. J Phys Chem B 2015; 119:14053-64. [PMID: 26447846 DOI: 10.1021/acs.jpcb.5b07534] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The electrochemical reduction mechanisms of 2 synthesized flavins (Flox) were examined in detail in deoxygenated solutions of DMSO containing varying amounts of water, utilizing variable scan rate cyclic voltammetry (ν = 0.1-20 V s(-1)), controlled-potential bulk electrolysis, and UV-vis spectroscopy. Flavin 1, which contains a hydrogen atom at N(3), is capable of donating its proton to other reduced flavin species. After 1e(-) reduction, the initially formed Fl(•-) receives a proton from another Flox to form FlH(•) (and concomitantly produce the deprotonated flavin, Fl(-)), although the equilibrium constant for this process favors the back reaction. Any FlH(•) formed at the electrode surface immediately undergoes another 1e(-) reduction to form FlH(-), which reacts with Fl(-) to form 2 molecules of Fl(•-). Further 1e(-) reduction of Fl(•-) at more negative potentials produces the dianion, Fl(2-), which can also be protonated by another Flox to form FlH(-) and Fl(-). Flavin 2, which is methylated at N(3) (and therefore has no acidic proton), undergoes a simple chemically reversible 1e(-) reduction process in DMSO provided the water content is low (<100 mM). Further 1e(-) reduction of Fl(•-) (from flavin 2) at more negative potentials leads to the dianion, Fl(2-), which is protonated by trace water in solution to form FlH(-), similar to the mechanism of flavin 1 at high scan rates. Addition of sufficient amounts of water to nonaqueous solvents results in protonation of the anion radical species, Fl(•-), for both flavins, causing an increase in the amount of FlH(-) in solution. This behavior contrasts with what is observed for quinones, which are also reduced in two 1e(-) steps in aprotic organic solvents to form the radical anions and dianions, but are able to exist in hydrogen-bonded forms (with trace or added water) without undergoing protonation.
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Affiliation(s)
- Serena L J Tan
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University , 637371, Singapore
| | - Maria L Novianti
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University , 637371, Singapore
| | - Richard D Webster
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University , 637371, Singapore
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24
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Teufel R, Stull F, Meehan MJ, Michaudel Q, Dorrestein PC, Palfey B, Moore BS. Biochemical Establishment and Characterization of EncM's Flavin-N5-oxide Cofactor. J Am Chem Soc 2015; 137:8078-85. [PMID: 26067765 DOI: 10.1021/jacs.5b03983] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ubiquitous flavin-dependent monooxygenases commonly catalyze oxygenation reactions by means of a transient C4a-peroxyflavin. A recent study, however, suggested an unprecedented flavin-oxygenating species, proposed as the flavin-N5-oxide (Fl(N5[O])), as key to an oxidative Favorskii-type rearrangement in the biosynthesis of the bacterial polyketide antibiotic enterocin. This stable superoxidized flavin is covalently tethered to the enzyme EncM and converted into FADH2 (Fl(red)) during substrate turnover. Subsequent reaction of Fl(red) with molecular oxygen restores the postulated Fl(N5[O]) via an unknown pathway. Here, we provide direct evidence for the Fl(N5[O]) species via isotope labeling, proteolytic digestion, and high-resolution tandem mass spectrometry of EncM. We propose that formation of this species occurs by hydrogen-transfer from Fl(red) to molecular oxygen, allowing radical coupling of the formed protonated superoxide and anionic flavin semiquinone at N5, before elimination of water affords the Fl(N5[O]) cofactor. Further biochemical and spectroscopic investigations reveal important features of the Fl(N5[O]) species and the EncM catalytic mechanism. We speculate that flavin-N5-oxides may be intermediates or catalytically active species in other flavoproteins that form the anionic semiquinone and promote access of oxygen to N5.
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Affiliation(s)
- Robin Teufel
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States
| | - Frederick Stull
- ‡Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Michael J Meehan
- §Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
| | - Quentin Michaudel
- ⊥Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Pieter C Dorrestein
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States.,§Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
| | - Bruce Palfey
- ‡Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, United States.,∥Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Bradley S Moore
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States.,§Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
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25
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Tuz K, Mezic KG, Xu T, Barquera B, Juárez O. The Kinetic Reaction Mechanism of the Vibrio cholerae Sodium-dependent NADH Dehydrogenase. J Biol Chem 2015; 290:20009-21. [PMID: 26004776 DOI: 10.1074/jbc.m115.658773] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Indexed: 11/06/2022] Open
Abstract
The sodium-dependent NADH dehydrogenase (Na(+)-NQR) is the main ion transporter in Vibrio cholerae. Its activity is linked to the operation of the respiratory chain and is essential for the development of the pathogenic phenotype. Previous studies have described different aspects of the enzyme, including the electron transfer pathways, sodium pumping structures, cofactor and subunit composition, among others. However, the mechanism of the enzyme remains to be completely elucidated. In this work, we have studied the kinetic mechanism of Na(+)-NQR with the use of steady state kinetics and stopped flow analysis. Na(+)-NQR follows a hexa-uni ping-pong mechanism, in which NADH acts as the first substrate, reacts with the enzyme, and the oxidized NAD leaves the catalytic site. In this conformation, the enzyme is able to capture two sodium ions and transport them to the external side of the membrane. In the last step, ubiquinone is bound and reduced, and ubiquinol is released. Our data also demonstrate that the catalytic cycle involves two redox states, the three- and five-electron reduced forms. A model that gathers all available information is proposed to explain the kinetic mechanism of Na(+)-NQR. This model provides a background to understand the current structural and functional information.
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Affiliation(s)
- Karina Tuz
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
| | - Katherine G Mezic
- the Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Tianhao Xu
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
| | - Blanca Barquera
- the Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Oscar Juárez
- From the Department of Biological Sciences, Illinois Institute of Technology, Chicago, Illinois 60616 and
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26
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Xu J, Eriksson SE, Cebula M, Sandalova T, Hedström E, Pader I, Cheng Q, Myers CR, Antholine WE, Nagy P, Hellman U, Selivanova G, Lindqvist Y, Arnér ESJ. The conserved Trp114 residue of thioredoxin reductase 1 has a redox sensor-like function triggering oligomerization and crosslinking upon oxidative stress related to cell death. Cell Death Dis 2015; 6:e1616. [PMID: 25611390 PMCID: PMC4669772 DOI: 10.1038/cddis.2014.574] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 11/19/2014] [Accepted: 12/03/2014] [Indexed: 12/19/2022]
Abstract
The selenoprotein thioredoxin reductase 1 (TrxR1) has several key roles in cellular redox systems and reductive pathways. Here we discovered that an evolutionarily conserved and surface-exposed tryptophan residue of the enzyme (Trp114) is excessively reactive to oxidation and exerts regulatory functions. The results indicate that it serves as an electron relay communicating with the FAD moiety of the enzyme, and, when oxidized, it facilitates oligomerization of TrxR1 into tetramers and higher multimers of dimers. A covalent link can also be formed between two oxidized Trp114 residues of two subunits from two separate TrxR1 dimers, as found both in cell extracts and in a crystal structure of tetrameric TrxR1. Formation of covalently linked TrxR1 subunits became exaggerated in cells on treatment with the pro-oxidant p53-reactivating anticancer compound RITA, in direct correlation with triggering of a cell death that could be prevented by antioxidant treatment. These results collectively suggest that Trp114 of TrxR1 serves a function reminiscent of an irreversible sensor for excessive oxidation, thereby presenting a previously unrecognized level of regulation of TrxR1 function in relation to cellular redox state and cell death induction.
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Affiliation(s)
- J Xu
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - S E Eriksson
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - M Cebula
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - T Sandalova
- Division of Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - E Hedström
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - I Pader
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - Q Cheng
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - C R Myers
- Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - W E Antholine
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - P Nagy
- Department of Molecular Immunology and Toxicology, National Institute of Oncology, Rath György ut 7-91, 1122, Budapest, Hungary
| | - U Hellman
- Ludwig Institutet for Cancer Research Ltd., Uppsala University BMC, SE-75 124 Uppsala, Sweden
| | - G Selivanova
- Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - Y Lindqvist
- Division of Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
| | - E S J Arnér
- Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-17177 Stockholm, Sweden
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27
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Paulus B, Illarionov B, Nohr D, Roellinger G, Kacprzak S, Fischer M, Weber S, Bacher A, Schleicher E. One Protein, Two Chromophores: Comparative Spectroscopic Characterization of 6,7-Dimethyl-8-ribityllumazine and Riboflavin Bound to Lumazine Protein. J Phys Chem B 2014; 118:13092-105. [DOI: 10.1021/jp507618f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Bernd Paulus
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Boris Illarionov
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
| | - Daniel Nohr
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Guillaume Roellinger
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Sylwia Kacprzak
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Markus Fischer
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
| | - Stefan Weber
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Adelbert Bacher
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
- Chemistry
Department, Technical University Munich, Lichtenbergstrasse 4, 85748 Garching, Germany
| | - Erik Schleicher
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
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28
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Rudolph J, Erbse AH, Behlen LS, Copley SD. A radical intermediate in the conversion of pentachlorophenol to tetrachlorohydroquinone by Sphingobium chlorophenolicum. Biochemistry 2014; 53:6539-49. [PMID: 25238136 PMCID: PMC4204890 DOI: 10.1021/bi5010427] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Pentachlorophenol
(PCP) hydroxylase, the first enzyme in the pathway
for degradation of PCP in Sphingobium chlorophenolicum, is an unusually slow flavin-dependent monooxygenase (kcat = 0.02 s–1) that converts PCP to
a highly reactive product, tetrachlorobenzoquinone (TCBQ). Using stopped-flow
spectroscopy, we have shown that the steps up to and including formation
of TCBQ are rapid (5–30 s–1). Before products
can be released from the active site, the strongly oxidizing TCBQ
abstracts an electron from a donor at the active site, possibly a
cysteine residue, resulting in an off-pathway diradical state that
only slowly reverts to an intermediate capable of completing the catalytic
cycle. TCBQ reductase, the second enzyme in the PCP degradation pathway,
rescues this nonproductive complex via two fast sequential one-electron
transfers. These studies demonstrate how adoption of an ancestral
catalytic strategy for conversion of a substrate with different steric
and electronic properties can lead to subtle yet (literally) radical
changes in enzymatic reaction mechanisms.
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Affiliation(s)
- Johannes Rudolph
- Department of Molecular, Cellular and Developmental Biology and the Cooperative Institute for Research in Environmental Sciences, and ‡Department of Chemistry and Biochemistry, University of Colorado Boulder , Boulder, Colorado 80309, United States
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29
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The sodium pumping NADH:quinone oxidoreductase (Na⁺-NQR), a unique redox-driven ion pump. J Bioenerg Biomembr 2014; 46:289-98. [PMID: 25052842 DOI: 10.1007/s10863-014-9565-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2014] [Accepted: 07/03/2014] [Indexed: 12/15/2022]
Abstract
The Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) is a unique Na(+) pumping respiratory complex found only in prokaryotes, that plays a key role in the metabolism of marine and pathogenic bacteria, including Vibrio cholerae and other human pathogens. Na(+)-NQR is the main entrance for reducing equivalents into the respiratory chain of these bacteria, catalyzing the oxidation of NADH and the reduction of quinone, the free energy of this redox reaction drives the selective translocation of Na(+) across the cell membrane, which energizes key cellular processes. In this review we summarize the unique properties of Na(+)-NQR in terms of its redox cofactor composition, electron transfer reactions and a possible mechanism of coupling and pumping.
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30
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Strickland M, Juárez O, Neehaul Y, Cook DA, Barquera B, Hellwig P. The conformational changes induced by ubiquinone binding in the Na+-pumping NADH:ubiquinone oxidoreductase (Na+-NQR) are kinetically controlled by conserved glycines 140 and 141 of the NqrB subunit. J Biol Chem 2014; 289:23723-33. [PMID: 25006248 DOI: 10.1074/jbc.m114.574640] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Na(+)-pumping NADH:ubiquinone oxidoreductase (Na(+)-NQR) is responsible for maintaining a sodium gradient across the inner bacterial membrane. This respiratory enzyme, which couples sodium pumping to the electron transfer between NADH and ubiquinone, is not present in eukaryotes and as such could be a target for antibiotics. In this paper it is shown that the site of ubiquinone reduction is conformationally coupled to the NqrB subunit, which also hosts the final cofactor in the electron transport chain, riboflavin. Previous work showed that mutations in conserved NqrB glycine residues 140 and 141 affect ubiquinone reduction and the proper functioning of the sodium pump. Surprisingly, these mutants did not affect the dissociation constant of ubiquinone or its analog HQNO (2-n-heptyl-4-hydroxyquinoline N-oxide) from Na(+)-NQR, which indicates that these residues do not participate directly in the ubiquinone binding site but probably control its accessibility. Indeed, redox-induced difference spectroscopy showed that these mutations prevented the conformational change involved in ubiquinone binding but did not modify the signals corresponding to bound ubiquinone. Moreover, data are presented that demonstrate the NqrA subunit is able to bind ubiquinone but with a low non-catalytically relevant affinity. It is also suggested that Na(+)-NQR contains a single catalytic ubiquinone binding site and a second site that can bind ubiquinone but is not active.
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Affiliation(s)
- Madeleine Strickland
- From the Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CNRS Université de Strasbourg, Strasbourg, France, 67000 and
| | - Oscar Juárez
- Department of Biological Sciences, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Yashvin Neehaul
- From the Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CNRS Université de Strasbourg, Strasbourg, France, 67000 and
| | - Darcie A Cook
- Department of Biological Sciences, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Blanca Barquera
- Department of Biological Sciences, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Petra Hellwig
- From the Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CNRS Université de Strasbourg, Strasbourg, France, 67000 and
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31
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Origin and evolution of the sodium -pumping NADH: ubiquinone oxidoreductase. PLoS One 2014; 9:e96696. [PMID: 24809444 PMCID: PMC4014512 DOI: 10.1371/journal.pone.0096696] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 04/11/2014] [Indexed: 11/27/2022] Open
Abstract
The sodium -pumping NADH: ubiquinone oxidoreductase (Na+-NQR) is the main ion pump and the primary entry site for electrons into the respiratory chain of many different types of pathogenic bacteria. This enzymatic complex creates a transmembrane gradient of sodium that is used by the cell to sustain ionic homeostasis, nutrient transport, ATP synthesis, flagellum rotation and other essential processes. Comparative genomics data demonstrate that the nqr operon, which encodes all Na+-NQR subunits, is found in a large variety of bacterial lineages with different habitats and metabolic strategies. Here we studied the distribution, origin and evolution of this enzymatic complex. The molecular phylogenetic analyses and the organizations of the nqr operon indicate that Na+-NQR evolved within the Chlorobi/Bacteroidetes group, after the duplication and subsequent neofunctionalization of the operon that encodes the homolog RNF complex. Subsequently, the nqr operon dispersed through multiple horizontal transfer events to other bacterial lineages such as Chlamydiae, Planctomyces and α, β, γ and δ -proteobacteria. Considering the biochemical properties of the Na+-NQR complex and its physiological role in different bacteria, we propose a detailed scenario to explain the molecular mechanisms that gave rise to its novel redox- dependent sodium -pumping activity. Our model postulates that the evolution of the Na+-NQR complex involved a functional divergence from its RNF homolog, following the duplication of the rnf operon, the loss of the rnfB gene and the recruitment of the reductase subunit of an aromatic monooxygenase.
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32
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Martínez JI, Alonso PJ, García-Rubio I, Medina M. Methyl rotors in flavoproteins. Phys Chem Chem Phys 2014; 16:26203-12. [DOI: 10.1039/c4cp03115f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ENDOR evidence shows that methyl groups in flavin behave as quantum locked rotors.
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Affiliation(s)
- Jesús I. Martínez
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Pablo J. Alonso
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Inés García-Rubio
- Laboratory of Physical Chemistry
- ETH Zurich
- 8093 Zürich, Switzerland
- Centro Universitario de la Defensa
- 50090 Zaragoza, Spain
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI)
- Universidad de Zaragoza
- 50009 Zaragoza, Spain
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33
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Abstract
Flavoproteins often employ radical mechanisms in their enzymatic reactions. This involves paramagnetic species, which can ideally be investigated with electron paramagnetic resonance (EPR) spectroscopy. In this chapter we focus on the example of flavin-based photoreceptors and discuss, how different EPR methods have been used to extract information about the flavin radical's electronic state, its binding pocket, electron-transfer pathways, and about the protein's tertiary and quaternary structure.
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Affiliation(s)
- Richard Brosi
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, Berlin, 14195, Germany,
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34
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Hamdane D, Bruch E, Un S, Field M, Fontecave M. Activation of a unique flavin-dependent tRNA-methylating agent. Biochemistry 2013; 52:8949-56. [PMID: 24228791 DOI: 10.1021/bi4013879] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
TrmFO is a tRNA methyltransferase that uses methylenetetrahydrofolate (CH2THF) and flavin adenine dinucleotide hydroquinone as cofactors. We have recently shown that TrmFO from Bacillus subtilis stabilizes a TrmFO-CH2-FADH adduct and an ill-defined neutral flavin radical. The adduct contains a unique N-CH2-S moiety, with a methylene group bridging N5 of the isoalloxazine ring and the sulfur of an active-site cysteine (Cys53). In the absence of tRNA substrate, this species is remarkably stable but becomes catalytically competent for tRNA methylation following tRNA addition using the methylene group as the source of methyl. Here, we demonstrate that this dormant methylating agent can be activated at low pH, and we propose that this process is triggered upon tRNA addition. The reaction proceeds via protonation of Cys53, cleavage of the C-S bond, and generation of a highly reactive [FADH(N5)═CH2]+ iminium intermediate, which is proposed to be the actual tRNA-methylating agent. This mechanism is fully supported by DFT calculations. The radical present in TrmFO is characterized here by optical and EPR/ENDOR spectroscopy approaches together with DFT calculations and is shown to be the one-electron oxidized product of the TrmFO-CH2-FADH adduct. It is also relatively stable, and its decomposition is facilitated by high pH. These results provide new insights into the structure and reactivity of the unique flavin-dependent methylating agent used by this class of enzymes.
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Affiliation(s)
- Djemel Hamdane
- Laboratoire de Chimie des Processus Biologiques, CNRS-FRE 3488, Collège De France , 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
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35
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Hamdane D, Argentini M, Cornu D, Golinelli-Pimpaneau B, Fontecave M. FAD/folate-dependent tRNA methyltransferase: flavin as a new methyl-transfer agent. J Am Chem Soc 2012; 134:19739-45. [PMID: 23157377 DOI: 10.1021/ja308145p] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RNAs contain structurally and functionally important modified nucleosides. Methylation, the most frequent RNA modification in all living organisms, mostly relies on SAM (S-adenosylmethionine)-dependent methyltransferases. TrmFO was recently discovered as a unique tRNA methyltransferase using instead methylenetetrahydrofolate and reduced flavin adenine dinucleotide (FAD) as essential cofactors, but its mechanism has remained elusive. Here, we report that TrmFO carries an active tRNA-methylating agent and characterize it as an original enzyme-methylene-FAD covalent adduct by mass spectrometry and a combination of spectroscopic and biochemical methods. Our data support a novel tRNA methylating mechanism.
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Affiliation(s)
- Djemel Hamdane
- Laboratoire de Chimie des Processus Biologiques, CNRS-FRE 3488, Collège De France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France.
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36
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Verkhovsky MI, Bogachev AV, Pivtsov AV, Bertsova YV, Fedin MV, Bloch DA, Kulik LV. Sodium-dependent movement of covalently bound FMN residue(s) in Na(+)-translocating NADH:quinone oxidoreductase. Biochemistry 2012; 51:5414-21. [PMID: 22697411 DOI: 10.1021/bi300322n] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR) is a component of respiratory electron-transport chain of various bacteria generating redox-driven transmembrane electrochemical Na(+) potential. We found that the change in Na(+) concentration in the reaction medium has no effect on the thermodynamic properties of prosthetic groups of Na(+)-NQR from Vibrio harveyi, as was revealed by the anaerobic equilibrium redox titration of the enzyme's EPR spectra. On the other hand, the change in Na(+) concentration strongly alters the EPR spectral properties of the radical pair formed by the two anionic semiquinones of FMN residues bound to the NqrB and NqrC subunits (FMN(NqrB) and FMN(NqrC)). Using data obtained by pulse X- and Q-band EPR as well as by pulse ENDOR and ELDOR spectroscopy, the interspin distance between FMN(NqrB) and FMN(NqrC) was found to be 15.3 Å in the absence and 20.4 Å in the presence of Na(+), respectively. Thus, the distance between the covalently bound FMN residues can vary by about 5 Å upon changes in Na(+) concentration. Using these results, we propose a scheme of the sodium potential generation by Na(+)-NQR based on the redox- and sodium-dependent conformational changes in the enzyme.
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Affiliation(s)
- Michael I Verkhovsky
- Department of Molecular Energetics of Microorganisms, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia
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37
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Juárez O, Neehaul Y, Turk E, Chahboun N, DeMicco JM, Hellwig P, Barquera B. The role of glycine residues 140 and 141 of subunit B in the functional ubiquinone binding site of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. J Biol Chem 2012; 287:25678-85. [PMID: 22645140 DOI: 10.1074/jbc.m112.366088] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)-pumping NADH:quinone oxidoreductase (Na(+)-NQR) is the main entrance for electrons into the respiratory chain of many marine and pathogenic bacteria. The enzyme accepts electrons from NADH and donates them to ubiquinone, and the free energy released by this redox reaction is used to create an electrochemical gradient of sodium across the cell membrane. Here we report the role of glycine 140 and glycine 141 of the NqrB subunit in the functional binding of ubiquinone. Mutations at these residues altered the affinity of the enzyme for ubiquinol. Moreover, mutations in residue NqrB-G140 almost completely abolished the electron transfer to ubiquinone. Thus, NqrB-G140 and -G141 are critical for the binding and reaction of Na(+)-NQR with its electron acceptor, ubiquinone.
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Affiliation(s)
- Oscar Juárez
- Department of Biology, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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38
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Martínez JI, Alonso PJ, Medina M. The electronic structure of the neutral isoalloxazine semiquinone within Anabaena flavodoxin: new insights from HYSCORE experiments. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 218:153-162. [PMID: 22446506 DOI: 10.1016/j.jmr.2012.02.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 02/11/2012] [Accepted: 02/18/2012] [Indexed: 05/31/2023]
Abstract
A complete study of Anabaena flavodoxin in the neutral semiquinone state by means of the EPR pulse technique HYSCORE is here presented. The results provide new information about the hyperfine interactions of the unpaired electronic spin and the nuclei in the isoalloxazine ring. This allows a better knowledge of the electronic structure of the neutral flavin radical within the protein. Combination of these results with other previously obtained by using other EPR related techniques allowed producing a very precise mapping of the flavin spin distribution in the neutral semiquinone state. This information can be very useful for determining the relationship between the electronic structure and mechanisms in flavoproteins. An experimental protocol for measuring the electronic structure details available to date is suggested.
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Affiliation(s)
- Jesús I Martínez
- Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas, Facultad de Ciencias, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain.
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39
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Tan SLJ, Webster RD. Electrochemically Induced Chemically Reversible Proton-Coupled Electron Transfer Reactions of Riboflavin (Vitamin B2). J Am Chem Soc 2012; 134:5954-64. [DOI: 10.1021/ja300191u] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Serena L. J. Tan
- Division of Chemistry
and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Richard D. Webster
- Division of Chemistry
and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
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40
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Insights into the mechanism of electron transfer and sodium translocation of the Na(+)-pumping NADH:quinone oxidoreductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1817:1823-32. [PMID: 22465856 DOI: 10.1016/j.bbabio.2012.03.017] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 03/13/2012] [Accepted: 03/15/2012] [Indexed: 11/22/2022]
Abstract
Na(+)-NQR is a unique energy-transducing complex, widely distributed among marine and pathogenic bacteria. It converts the energy from the oxidation of NADH and the reduction of quinone into an electrochemical Na(+)-gradient that can provide energy for the cell. Na(+)-NQR is not homologous to any other respiratory protein but is closely related to the RNF complex. In this review we propose that sodium pumping in Na(+)-NQR is coupled to the redox reactions by a novel mechanism, which operates at multiple sites, is indirect and mediated by conformational changes of the protein. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).
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41
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Nishiura H, Kumagai J, Kashino G, Okada T, Tano K, Watanabe M. The bystander effect is a novel mechanism of UVA-induced melanogenesis. Photochem Photobiol 2011; 88:389-97. [PMID: 22091933 DOI: 10.1111/j.1751-1097.2011.01046.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We successfully identified the bystander effect in B16 murine melanoma cells exposed to UVA irradiation. The effect was identified based on melanogenesis following the medium transfer of the B16 cells, which had been cultured for 24 h after being exposed to UVA irradiation, to nonirradiated cells (bystander cells). Our confirmation study of the functional mechanism of bystander cells confirmed the reduced levels of mitochondrial membrane potential 1-4 h after the medium transfer. In addition, we observed increased levels of intracellular oxidation after 9-12 h, and the generation of melanin radicals, including long-lived radicals, 24 h after medium transfer. Further analysis of bystander factors revealed that the administration of EGTA treatment at the time of medium transfer led to an inhibition of melanogenesis and to neutralization of the mitochondrial membrane potential level, as well as to the restoration of intracellular oxidation levels to those of controls. The results demonstrated that the UVA irradiation bystander effect in B16 cells, as indicated by melanogenesis, was induced by the increase in intracellular oxidation due to the mitochondrial activity of calcium ions, which were among the bystander factors involved in the increase.
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Affiliation(s)
- Hideki Nishiura
- Division of Radiation Life Science, Department of Radiation Life Science and Radiation Medical Science, Kyoto University Research Reactor Institute, Sennan-gun, Osaka, Japan
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42
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Juárez O, Shea ME, Makhatadze GI, Barquera B. The role and specificity of the catalytic and regulatory cation-binding sites of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. J Biol Chem 2011; 286:26383-90. [PMID: 21652714 DOI: 10.1074/jbc.m111.257873] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)-translocating NADH:quinone oxidoreductase is the entry site for electrons into the respiratory chain and the main sodium pump in Vibrio cholerae and many other pathogenic bacteria. In this work, we have employed steady-state and transient kinetics, together with equilibrium binding measurements to define the number of cation-binding sites and characterize their roles in the enzyme. Our results show that sodium and lithium ions stimulate enzyme activity, and that Na(+)-NQR enables pumping of Li(+), as well as Na(+) across the membrane. We also confirm that the enzyme is not able to translocate other monovalent cations, such as potassium or rubidium. Although potassium is not used as a substrate, Na(+)-NQR contains a regulatory site for this ion, which acts as a nonessential activator, increasing the activity and affinity for sodium. Rubidium can bind to the same site as potassium, but instead of being activated, enzyme turnover is inhibited. Activity measurements in the presence of both sodium and lithium indicate that the enzyme contains at least two functional sodium-binding sites. We also show that the binding sites are not exclusively responsible for ion selectivity, and other steps downstream in the mechanism also play a role. Finally, equilibrium-binding measurements with (22)Na(+) show that, in both its oxidized and reduced states, Na(+)-NQR binds three sodium ions, and that the affinity for sodium is the same for both of these states.
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Affiliation(s)
- Oscar Juárez
- Department of Biology and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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Hamdane D, Guerineau V, Un S, Golinelli-Pimpaneau B. A catalytic intermediate and several flavin redox states stabilized by folate-dependent tRNA methyltransferase from Bacillus subtilis. Biochemistry 2011; 50:5208-19. [PMID: 21561081 DOI: 10.1021/bi1019463] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The flavoprotein TrmFO catalyzes the C5 methylation of uridine 54 in the TΨC loop of tRNAs using 5,10-methylenetetrahydrofolate (CH(2)THF) as a methylene donor and FAD as a reducing agent. Here, we report biochemical and spectroscopic studies that unravel the remarkable capability of Bacillus subtilis TrmFO to stabilize, in the presence of oxygen, several flavin-reduced forms, including an FADH(•) radical, and a catalytic intermediate endowed with methylating activity. The FADH(•) radical was characterized by high-field electron paramagnetic resonance and electron nuclear double-resonance spectroscopies. Interestingly, the enzyme exhibited tRNA methylation activity in the absence of both an added carbon donor and an external reducing agent, indicating that a reaction intermediate, containing presumably CH(2)THF and FAD hydroquinone, is present in the freshly purified enzyme. Isolation by acid treatment, under anaerobic conditions, of noncovalently bound molecules, followed by mass spectrometry analysis, confirmed the presence in TrmFO of nonmodified FAD. Addition of formaldehyde to the purified enzyme protects the reduced flavins from decay by probably preventing degradation of CH(2)THF. The absence of air-stable reduced FAD species during anaerobic titration of oxidized TrmFO, performed in the absence or presence of added CH(2)THF, argues against their thermodynamic stabilization but rather implicates their kinetic trapping by the enzyme. Altogether, the unexpected isolation of a stable catalytic intermediate suggests that the flavin-binding pocket of TrmFO is a highly insulated environment, diverting the reduced FAD present in this intermediate from uncoupled reactions.
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Affiliation(s)
- Djemel Hamdane
- Centre de Recherche de Gif, CNRS, 91198 Gif-sur-Yvette, France
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Fadeeva MS, Bertsova YV, Verkhovsky MI, Bogachev AV. Site-directed mutagenesis of conserved cysteine residues in NqrD and NqrE subunits of Na+-translocating NADH:quinone oxidoreductase. BIOCHEMISTRY (MOSCOW) 2011; 73:123-9. [DOI: 10.1134/s0006297908020028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Pauwels E, Declerck R, Verstraelen T, De Sterck B, Kay CWM, Van Speybroeck V, Waroquier M. Influence of Protein Environment on the Electron Paramagnetic Resonance Properties of Flavoprotein Radicals: A QM/MM Study. J Phys Chem B 2010; 114:16655-65. [DOI: 10.1021/jp109763t] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ewald Pauwels
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Reinout Declerck
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Toon Verstraelen
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Bart De Sterck
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Christopher W. M. Kay
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Veronique Van Speybroeck
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Michel Waroquier
- Center for Molecular Modeling, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium QCMM - alliance Ghent-Brussels, Belgium, and Institute of Structural and Molecular Biology and London Centre for Nanotechnology, University College London, Gower Street, London WC1E 6BT, United Kingdom
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Stoll S, Ozarowski A, Britt RD, Angerhofer A. Atomic hydrogen as high-precision field standard for high-field EPR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 207:158-63. [PMID: 20813570 PMCID: PMC2956851 DOI: 10.1016/j.jmr.2010.08.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 06/08/2010] [Accepted: 08/06/2010] [Indexed: 05/05/2023]
Abstract
We introduce atomic hydrogen trapped in an octaisobutylsilsesquioxane nanocage (H@iBuT₈) as a new molecular high-precision magnetic field standard for high-field EPR spectroscopy of organic radicals and other systems with signals around g=2. Its solid-state EPR spectrum consists of two 0.2 mT wide lines separated by about 51 mT and centered at g≈2. The isotropic g factor is 2.00294(3) and essentially temperature independent. The isotropic ¹H hyperfine coupling constant is 1416.8(2) MHz below 70 K and decreases slightly with increasing temperature to 1413.7(1) MHz at room temperature. The spectrum of the standard does not overlap with those of most organic radicals, and it can be easily prepared and is stable at room temperature.
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Affiliation(s)
- Stefan Stoll
- Department of Chemistry, University of California, One Shields Ave, Davis, California 95616, USA
| | - Andrew Ozarowski
- National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA
| | - R. David Britt
- Department of Chemistry, University of California, One Shields Ave, Davis, California 95616, USA
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Stoll S, NejatyJahromy Y, Woodward JJ, Ozarowski A, Marletta MA, Britt RD. Nitric oxide synthase stabilizes the tetrahydrobiopterin cofactor radical by controlling its protonation state. J Am Chem Soc 2010; 132:11812-23. [PMID: 20669954 DOI: 10.1021/ja105372s] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Nitric oxide synthase (NOS), a homodimeric enzyme with a flavin reductase domain and a P450-type heme-containing oxygenase domain, catalyzes the formation of NO from L-arginine, NADPH, and O(2) in a two-step reaction sequence. In the first step, a tetrahydrobiopterin (H(4)B) cofactor bound near one of the heme propionate groups acts as an electron donor to the P450-type heme active site, yielding a one-electron oxidized radical that is subsequently re-reduced. In solution, H(4)B undergoes two-electron oxidation, showing that the enzyme significantly alters the proton- and electron-transfer properties of the cofactor. Multifrequency EPR and ENDOR spectroscopy were used to determine magnetic parameters, and from them the (de)protonation state of the H(4)B radical in the oxygenase domain dimer of inducible NO synthase that was trapped by rapid freeze quench. From 9.5 and 330-416 GHz EPR and from 34 GHz (1)H ENDOR spectroscopy, the g tensor of the radical and the hyperfine tensors of several N and H nuclei in the radical were obtained. Density functional theory calculations at the PBE0/EPR-II level for H(4)B radical models predict different spin density distributions and g and hyperfine tensors for different protonation states. Comparison of the predicted and experimental values leads to the conclusion that the radical is cationic H(4)B(*+), suggesting that NOS stabilizes this protonated form to utilize the cofactor in a unique dual one-electron redox role, where it can deliver an electron to the active site for reductive oxygen activation and also remove an electron from the active site to generate NO and not NO(-). The protein environment also prevents further oxidation and subsequent loss of function of the cofactor, thus enabling the enzyme to perform the unusual catalytic one-electron chemistry.
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Affiliation(s)
- Stefan Stoll
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, USA
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Energy transducing redox steps of the Na+-pumping NADH:quinone oxidoreductase from Vibrio cholerae. Proc Natl Acad Sci U S A 2010; 107:12505-10. [PMID: 20616050 DOI: 10.1073/pnas.1002866107] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Na(+)-NQR is a unique respiratory enzyme that couples the free energy of electron transfer reactions to electrogenic pumping of sodium across the cell membrane. This enzyme is found in many marine and pathogenic bacteria where it plays an analogous role to the H(+)-pumping complex I. It has generally been assumed that the sodium pump of Na(+)-NQR operates on the basis of thermodynamic coupling between reduction of a single redox cofactor and the binding of sodium at a nearby site. In this study, we have defined the coupling to sodium translocation of individual steps in the redox reaction of Na(+)-NQR. Sodium uptake takes place in the reaction step in which an electron moves from the 2Fe-2S center to FMN(C), while the translocation of sodium across the membrane dielectric (and probably its release into the external medium) occurs when an electron moves from FMN(B) to riboflavin. This argues against a single-site coupling model because the redox steps that drive these two parts of the sodium pumping process do not have any redox cofactor in common. The significance of these results for the mechanism of coupling is discussed, and we proposed that Na(+)-NQR operates through a novel mechanism based on kinetic coupling, mediated by conformational changes.
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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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