1
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Murali R, Hemp J, Gennis RB. Evolution of quinol oxidation within the heme‑copper oxidoreductase superfamily. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2022; 1863:148907. [PMID: 35944661 DOI: 10.1016/j.bbabio.2022.148907] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Revised: 07/09/2022] [Accepted: 08/02/2022] [Indexed: 06/15/2023]
Abstract
The heme‑copper oxidoreductase (HCO) superfamily is a large superfamily of terminal respiratory enzymes that are widely distributed across the three domains of life. The superfamily includes biochemically diverse oxygen reductases and nitric oxide reductases that are pivotal in the pathways of aerobic respiration and denitrification. The adaptation of HCOs to use quinol as the electron donor instead of cytochrome c has significant implication for the respiratory flexibility and energetic efficiency of the respiratory chains that include them. In this work, we explore the adaptation of this scaffold to two different electron donors, cytochromes c and quinols, with extensive sequence analysis of these enzymes from publicly available datasets. Our work shows that quinol oxidation evolved independently within the HCO superfamily at least seven times. Enzymes from only two of these independently evolved clades have been biochemically well-characterized. Combining structural modeling with sequence analysis, we identify putative quinol binding sites in each of the novel quinol oxidases. Our analysis of experimental and modeling data suggests that the quinol binding site appears to have evolved at the same structural position within the scaffold more than once.
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Affiliation(s)
- Ranjani Murali
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91106, USA.
| | - James Hemp
- Metrodora Institute, West Valley City, UT, USA 84119.
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA.
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2
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Cryo-EM structures of Escherichia coli cytochrome bo 3 reveal bound phospholipids and ubiquinone-8 in a dynamic substrate binding site. Proc Natl Acad Sci U S A 2021; 118:2106750118. [PMID: 34417297 DOI: 10.1073/pnas.2106750118] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two independent structures of the proton-pumping, respiratory cytochrome bo 3 ubiquinol oxidase (cyt bo 3 ) have been determined by cryogenic electron microscopy (cryo-EM) in styrene-maleic acid (SMA) copolymer nanodiscs and in membrane scaffold protein (MSP) nanodiscs to 2.55- and 2.19-Å resolution, respectively. The structures include the metal redox centers (heme b, heme o 3 , and CuB), the redox-active cross-linked histidine-tyrosine cofactor, and the internal water molecules in the proton-conducting D channel. Each structure also contains one equivalent of ubiquinone-8 (UQ8) in the substrate binding site as well as several phospholipid molecules. The isoprene side chain of UQ8 is clamped within a hydrophobic groove in subunit I by transmembrane helix TM0, which is only present in quinol oxidases and not in the closely related cytochrome c oxidases. Both structures show carbonyl O1 of the UQ8 headgroup hydrogen bonded to D75I and R71I In both structures, residue H98I occupies two conformations. In conformation 1, H98I forms a hydrogen bond with carbonyl O4 of the UQ8 headgroup, but in conformation 2, the imidazole side chain of H98I has flipped to form a hydrogen bond with E14I at the N-terminal end of TM0. We propose that H98I dynamics facilitate proton transfer from ubiquinol to the periplasmic aqueous phase during oxidation of the substrate. Computational studies show that TM0 creates a channel, allowing access of water to the ubiquinol headgroup and to H98I.
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3
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Iwasaki T, Miyajima-Nakano Y, Fukazawa R, Lin MT, Matsushita SI, Hagiuda E, Taguchi AT, Dikanov SA, Oishi Y, Gennis RB. Escherichia coli amino acid auxotrophic expression host strains for investigating protein structure-function relationships. J Biochem 2021; 169:387-394. [PMID: 33289521 DOI: 10.1093/jb/mvaa140] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 11/16/2020] [Indexed: 11/13/2022] Open
Abstract
A set of C43(DE3) and BL21(DE3) Escherichia coli host strains that are auxotrophic for various amino acids is briefly reviewed. These strains require the addition of a defined set of one or more amino acids in the growth medium, and have been specifically designed for overproduction of membrane or water-soluble proteins selectively labelled with stable isotopes, such as 2H, 13C and 15N. The strains described here are available for use and have been deposited into public strain banks. Although they cannot fully eliminate the possibility of isotope dilution and mixing, metabolic scrambling of the different amino acid types can be minimized through a careful consideration of the bacterial metabolic pathways. The use of a suitable auxotrophic expression host strain with an appropriately isotopically labelled growth medium ensures high levels of isotope labelling efficiency as well as selectivity for providing deeper insight into protein structure-function relationships.
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Affiliation(s)
- Toshio Iwasaki
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | - Yoshiharu Miyajima-Nakano
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | - Risako Fukazawa
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | | | - Shin-Ichi Matsushita
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | - Emi Hagiuda
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | - Alexander T Taguchi
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
| | - Sergei A Dikanov
- Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Yumiko Oishi
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Sendagi, Tokyo 113-8602, Japan
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4
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Sarewicz M, Pintscher S, Pietras R, Borek A, Bujnowicz Ł, Hanke G, Cramer WA, Finazzi G, Osyczka A. Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes. Chem Rev 2021; 121:2020-2108. [PMID: 33464892 PMCID: PMC7908018 DOI: 10.1021/acs.chemrev.0c00712] [Citation(s) in RCA: 61] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Indexed: 12/16/2022]
Abstract
This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc1 and b6f (Cytbc1/b6f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc1/b6f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc1/b6f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc1/b6f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.
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Affiliation(s)
- Marcin Sarewicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Sebastian Pintscher
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Rafał Pietras
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Arkadiusz Borek
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Łukasz Bujnowicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
| | - Guy Hanke
- School
of Biological and Chemical Sciences, Queen
Mary University of London, London E1 4NS, U.K.
| | - William A. Cramer
- Department
of Biological Sciences, Purdue University, West Lafayette, Indiana 47907 United States
| | - Giovanni Finazzi
- Laboratoire
de Physiologie Cellulaire et Végétale, Université Grenoble Alpes, Centre National Recherche Scientifique,
Commissariat Energie Atomique et Energies Alternatives, Institut National
Recherche l’agriculture, l’alimentation et l’environnement, 38054 Grenoble Cedex 9, France
| | - Artur Osyczka
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, 30-387 Kraków, Poland
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5
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Melin F, Hellwig P. Redox Properties of the Membrane Proteins from the Respiratory Chain. Chem Rev 2020; 120:10244-10297. [DOI: 10.1021/acs.chemrev.0c00249] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Frederic Melin
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
| | - Petra Hellwig
- Chimie de la Matière Complexe UMR 7140, Laboratoire de Bioelectrochimie et Spectroscopie, CNRS-Université de Strasbourg, 1 rue Blaise Pascal, 67070 Strasbourg, France
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6
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Pintscher S, Wójcik-Augustyn A, Sarewicz M, Osyczka A. Charge polarization imposed by the binding site facilitates enzymatic redox reactions of quinone. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1861:148216. [PMID: 32387188 DOI: 10.1016/j.bbabio.2020.148216] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 04/27/2020] [Accepted: 04/29/2020] [Indexed: 11/19/2022]
Abstract
Quinone reduction site (Qi) of cytochrome bc1 represents one of the canonical sites used to explore the enzymatic redox reactions involving semiquinone (SQ) states. However, the mechanism by which Qi allows the completion of quinone reduction during the sequential transfers of two electrons from the adjacent heme bH and two protons to C1- and C4-carbonyl remains unclear. Here we established that the SQ coupled to an oxidized heme bH is a dominant intermediate of catalytic forward reaction and, contrary to the long-standing assumption, represents a significant population of SQ detected across pH 5-9. The pH dependence of its redox midpoint potential implicated proton exchange with histidine. Complementary quantum mechanical calculations revealed that the SQ anion formed after the first electron transfer undergoes charge and spin polarization imposed by the electrostatic field generated by histidine and the aspartate/lysine pair interacting with the C4- and C1-carbonyl, respectively. This favors a barrierless proton exchange between histidine and the C4-carbonyl, which continues until the second electron reaches the SQi. Inversion of charge polarization facilitates the uptake of the second proton by the C1-carbonyl. Based on these findings we developed a comprehensive scheme for electron and proton transfers at Qi featuring the equilibration between the anionic and neutral states of SQi as means for a leak-proof stabilization of the radical intermediate. The key catalytic role of the initial charge/spin polarization of the SQ anion at the active site, inherent to the proposed mechanism, may also be applicable to the other quinone oxidoreductases.
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Affiliation(s)
- Sebastian Pintscher
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 30387, Poland.
| | - Anna Wójcik-Augustyn
- Department of Computational Biophysics and Bioinformatics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 30387, Poland.
| | - Marcin Sarewicz
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 30387, Poland.
| | - Artur Osyczka
- Department of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 30387, Poland.
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7
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Structure of the cytochrome aa 3 -600 heme-copper menaquinol oxidase bound to inhibitor HQNO shows TM0 is part of the quinol binding site. Proc Natl Acad Sci U S A 2019; 117:872-876. [PMID: 31888984 DOI: 10.1073/pnas.1915013117] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Virtually all proton-pumping terminal respiratory oxygen reductases are members of the heme-copper oxidoreductase superfamily. Most of these enzymes use reduced cytochrome c as a source of electrons, but a group of enzymes have evolved to directly oxidize membrane-bound quinols, usually menaquinol or ubiquinol. All of the quinol oxidases have an additional transmembrane helix (TM0) in subunit I that is not present in the related cytochrome c oxidases. The current work reports the 3.6-Å-resolution X-ray structure of the cytochrome aa 3 -600 menaquinol oxidase from Bacillus subtilis containing 1 equivalent of menaquinone. The structure shows that TM0 forms part of a cleft to accommodate the menaquinol-7 substrate. Crystals which have been soaked with the quinol-analog inhibitor HQNO (N-oxo-2-heptyl-4-hydroxyquinoline) or 3-iodo-HQNO reveal a single binding site where the inhibitor forms hydrogen bonds to amino acid residues shown previously by spectroscopic methods to interact with the semiquinone state of menaquinone, a catalytic intermediate.
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8
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Ding Z, Sun C, Yi SM, Gennis RB, Dikanov SA. The Ubiquinol Binding Site of Cytochrome bo3 from Escherichia coli Accommodates Menaquinone and Stabilizes a Functional Menasemiquinone. Biochemistry 2019; 58:4559-4569. [PMID: 31644263 DOI: 10.1021/acs.biochem.9b00750] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cytochrome bo3, one of three terminal oxygen reductases in the aerobic respiratory chain of Escherichia coli, has been well characterized as a ubiquinol oxidase. The ability of cytochrome bo3 to catalyze the two-electron oxidation of ubiquinol-8 requires the enzyme to stabilize the one-electron oxidized ubisemiquinone species that is a transient intermediate in the reaction. Cytochrome bo3 has been shown recently to also utilize demethylmenaquinol-8 as a substrate that, along with menaquinol-8, replaces ubiquinol-8 when E. coli is grown under microaerobic or anaerobic conditions. In this work, we show that its steady-state turnover with 2,3-dimethyl-1,4-naphthoquinol, a water-soluble menaquinol analogue, is just as efficient as with ubiquinol-1. Using pulsed electron paramagnetic resonance spectroscopy, we demonstrate that the same residues in cytochrome bo3 that stabilize the semiquinone state of ubiquinone also stabilize the semiquinone state of menaquinone, with the hydrogen bond strengths and the distribution of unpaired spin density accommodated for the different substrate. Catalytic function with menaquinol is more tolerant of mutations at the active site than with ubiquinol. A mutation of one of the stabilizing residues (R71H in subunit I) that eliminates the ubiquinol oxidase activity of cytochrome bo3 does not abolish activity with soluble menaquinol analogues.
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Affiliation(s)
- Ziqiao Ding
- Department of Biochemistry , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Chang Sun
- Department of Biochemistry , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Sophia M Yi
- Department of Biochemistry , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Robert B Gennis
- Department of Biochemistry , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.,Center for Biophysics and Computational Biology , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Sergei A Dikanov
- Department of Veterinary Clinical Medicine , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
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9
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Taguchi AT, Evans ED, Dikanov SA, Griffin RG. Convolutional Neural Network Analysis of Two-Dimensional Hyperfine Sublevel Correlation Electron Paramagnetic Resonance Spectra. J Phys Chem Lett 2019; 10:1115-1119. [PMID: 30789745 PMCID: PMC8300483 DOI: 10.1021/acs.jpclett.8b03797] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A machine learning approach is presented for analyzing complex two-dimensional hyperfine sublevel correlation electron paramagnetic resonance (HYSCORE EPR) spectra with the proficiency of an expert spectroscopist. The computer vision algorithm requires no training on experimental data; rather, all of the spin physics required to interpret the spectra are learned from simulations alone. This approach is therefore applicable even when insufficient experimental data exist to train the algorithm. The neural network is demonstrated to be capable of utilizing the full information content of two-dimensional 14N HYSCORE spectra to predict the magnetic coupling parameters and their underlying probability distributions that were previously inaccessible. The predicted hyperfine ( a, T) and 14N quadrupole ( K, η) coupling constants deviate from the previous manual analyses of the experimental spectra on average by 0.11 MHz, 0.09 MHz, 0.19 MHz, and 0.09, respectively.
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Affiliation(s)
- Alexander T. Taguchi
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Ethan D. Evans
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Sergei A. Dikanov
- Department of Veterinary Clinical Medicine, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, United States
| | - Robert G. Griffin
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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10
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Melin F, Sabuncu S, Choi SK, Leprince A, Gennis RB, Hellwig P. Role of the tightly bound quinone for the oxygen reaction of cytochrome
bo
3
oxidase from
Escherichia coli. FEBS Lett 2018; 592:3380-3387. [DOI: 10.1002/1873-3468.13263] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 09/21/2018] [Accepted: 09/24/2018] [Indexed: 01/24/2023]
Affiliation(s)
- Frédéric Melin
- Chimie de la Matière Complexe UMR 7140 Laboratoire de Bioélectrochimie et Spectroscopie CNRS‐Université de Strasbourg France
| | - Sinan Sabuncu
- Chimie de la Matière Complexe UMR 7140 Laboratoire de Bioélectrochimie et Spectroscopie CNRS‐Université de Strasbourg France
| | - Sylvia K. Choi
- Center for Biophysics and Computational Biology University of Illinois Urbana IL USA
- Department of Biochemistry University of Illinois Urbana IL USA
| | - Agathe Leprince
- Chimie de la Matière Complexe UMR 7140 Laboratoire de Bioélectrochimie et Spectroscopie CNRS‐Université de Strasbourg France
| | | | - Petra Hellwig
- Chimie de la Matière Complexe UMR 7140 Laboratoire de Bioélectrochimie et Spectroscopie CNRS‐Université de Strasbourg France
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11
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Dikanov SA, Taguchi AT. Two-Dimensional Pulsed EPR Resolves Hyperfine Coupling Strain in Nitrogen Hydrogen Bond Donors of Semiquinone Intermediates. J Phys Chem B 2018; 122:5205-5211. [DOI: 10.1021/acs.jpcb.8b02511] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Alexander T. Taguchi
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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12
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De Almeida WB, O'Malley PJ. Conformational control of cofactors in nature: The effect of methoxy group orientation on the electronic structure of ubisemiquinone. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2017.12.066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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13
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Taguchi AT, O’Malley PJ, Wraight CA, Dikanov SA. Determination of the Complete Spin Density Distribution in 13C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory. J Phys Chem B 2017; 121:10256-10268. [DOI: 10.1021/acs.jpcb.7b10036] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Alexander T. Taguchi
- Center
for Biophysics and Computational Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Department
of Veterinary Clinical Medicine, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | | | - Colin A. Wraight
- Center
for Biophysics and Computational Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Department
of Biochemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Sergei A. Dikanov
- Department
of Veterinary Clinical Medicine, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
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14
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Seif Eddine M, Biaso F, Arias‐Cartin R, Pilet E, Rendon J, Lyubenova S, Seduk F, Guigliarelli B, Magalon A, Grimaldi S. Probing the Menasemiquinone Binding Mode to Nitrate Reductase A by Selective2H and15N Labeling, HYSCORE Spectroscopy, and DFT Modeling. Chemphyschem 2017; 18:2704-2714. [DOI: 10.1002/cphc.201700571] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/04/2017] [Indexed: 11/05/2022]
Affiliation(s)
| | | | | | - Eric Pilet
- Aix Marseille University, CNRS, BIP Marseille France
- Faculté de Biologie, University Pierre et Marie Curie Paris France
| | - Julia Rendon
- Aix Marseille University, CNRS, BIP Marseille France
| | | | - Farida Seduk
- Aix Marseille University, CNRS, LCB Marseille France
| | | | - Axel Magalon
- Aix Marseille University, CNRS, LCB Marseille France
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15
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Choi SK, Schurig-Briccio L, Ding Z, Hong S, Sun C, Gennis RB. Location of the Substrate Binding Site of the Cytochrome bo 3 Ubiquinol Oxidase from Escherichia coli. J Am Chem Soc 2017; 139:8346-8354. [PMID: 28538096 DOI: 10.1021/jacs.7b03883] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cytochrome bo3 is a respiratory proton-pumping oxygen reductase that is a member of the heme-copper superfamily that utilizes ubiquinol-8 (Q8H2) as a substrate. The current consensus model has Q8H2 oxidized at a low affinity site (QL), passing electrons to a tightly bound quinone cofactor at a high affinity site (QH site) that stabilizes the one-electron reduced ubisemiquinone, facilitating the transfer of electrons to the redox active metal centers where O2 is reduced to water. The current work shows that the Q8 bound to the QH site is more dynamic than previously thought. In addition, mutations of residues at the QH site that do not abolish activity have been re-examined and shown to have properties expected of mutations at the substrate binding site (QL): an increase in the KM of the substrate ubiquinol-1 (up to 4-fold) and an increase in the apparent Ki of the inhibitor HQNO (up to 8-fold). The data suggest that there is only one binding site for ubiquinol in cyt bo3 and that site corresponds to the QH site.
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Affiliation(s)
- Sylvia K Choi
- Center for Biophysics and Quantitative Biology, University of Illinois , Urbana, Illinois 61801, United States.,Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Lici Schurig-Briccio
- Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Ziqiao Ding
- Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Sangjin Hong
- Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Chang Sun
- Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
| | - Robert B Gennis
- Center for Biophysics and Quantitative Biology, University of Illinois , Urbana, Illinois 61801, United States.,Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States
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16
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Choi SK, Lin MT, Ouyang H, Gennis RB. Searching for the low affinity ubiquinone binding site in cytochrome bo 3 from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:366-370. [PMID: 28235459 DOI: 10.1016/j.bbabio.2017.02.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 02/11/2017] [Accepted: 02/14/2017] [Indexed: 11/25/2022]
Abstract
The cytochrome bo3 ubiquinol oxidase is one of three respiratory oxygen reductases in the aerobic respiratory chain of Escherichia coli. The generally accepted model of catalysis assumes that cyt bo3 contains two distinct ubiquinol binding sites: (i) a low affinity (QL) site which is the traditional substrate binding site; and (ii) a high affinity (QH) site where a "permanently" bound quinone acts as a cofactor, taking two electrons from the substrate quinol and passing them one-by-one to the heme b component of the enzyme which, in turn, transfers them to the heme o3/CuB active site. Whereas the residues at the QH site are well defined, the location of the QL site remains unknown. The published X-ray structure does not contain quinone, and substantial amounts of the protein are missing as well. A recent bioinformatics study by Bossis et al. [Biochem J. (2014) 461, 305-314] identified a sequence motif G163EFX3GWX2Y173 as the likely QL site in the family of related quinol oxidases. In the current work, this was tested by site-directed mutagenesis. The results show that these residues are not important for catalytic function and do not define the QL substrate binding site.
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Affiliation(s)
- Sylvia K Choi
- Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, IL 61801, USA
| | - Myat T Lin
- Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, IL 61801, USA
| | - Hanlin Ouyang
- Department of Chemistry, University of Illinois, Urbana, IL 61801, USA
| | - Robert B Gennis
- Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, IL 61801, USA; Department of Chemistry, University of Illinois, Urbana, IL 61801, USA; Department of Biochemistry, University of Illinois, Urbana, IL 61801, USA.
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17
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Sun C, Taguchi AT, Vermaas JV, Beal NJ, O'Malley PJ, Tajkhorshid E, Gennis RB, Dikanov SA. Q-Band Electron-Nuclear Double Resonance Reveals Out-of-Plane Hydrogen Bonds Stabilize an Anionic Ubisemiquinone in Cytochrome bo 3 from Escherichia coli. Biochemistry 2016; 55:5714-5725. [PMID: 27622672 DOI: 10.1021/acs.biochem.6b00669] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The respiratory cytochrome bo3 ubiquinol oxidase from Escherichia coli has a high-affinity ubiquinone binding site that stabilizes the one-electron reduced ubisemiquinone (SQH), which is a transient intermediate during the electron-mediated reduction of O2 to water. It is known that SQH is stabilized by two strong hydrogen bonds from R71 and D75 to ubiquinone carbonyl oxygen O1 and weak hydrogen bonds from H98 and Q101 to O4. In this work, SQH was investigated with orientation-selective Q-band (∼34 GHz) pulsed 1H electron-nuclear double resonance (ENDOR) spectroscopy on fully deuterated cytochrome (cyt) bo3 in a H2O solvent so that only exchangeable protons contribute to the observed ENDOR spectra. Simulations of the experimental ENDOR spectra provided the principal values and directions of the hyperfine (hfi) tensors for the two strongly coupled H-bond protons (H1 and H2). For H1, the largest principal component of the proton anisotropic hfi tensor Tz' = 11.8 MHz, whereas for H2, Tz' = 8.6 MHz. Remarkably, the data show that the direction of the H1 H-bond is nearly perpendicular to the quinone plane (∼70° out of plane). The orientation of the second strong hydrogen bond, H2, is out of plane by ∼25°. Equilibrium molecular dynamics simulations on a membrane-embedded model of the cyt bo3 QH site show that these H-bond orientations are plausible but do not distinguish which H-bond, from R71 or D75, is nearly perpendicular to the quinone ring. Density functional theory calculations support the idea that the distances and geometries of the H-bonds to the ubiquinone carbonyl oxygens, along with the measured proton anisotropic hfi couplings, are most compatible with an anionic (deprotonated) ubisemiquinone.
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Affiliation(s)
- Chang Sun
- Department of Biochemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Alexander T Taguchi
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Josh V Vermaas
- Department of Biochemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Nathan J Beal
- School of Chemistry, The University of Manchester , Manchester M13 9PL, U.K
| | - Patrick J O'Malley
- School of Chemistry, The University of Manchester , Manchester M13 9PL, U.K
| | - Emad Tajkhorshid
- Department of Biochemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Beckman Institute, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Sergei A Dikanov
- Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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18
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Hua C, Baldansuren A, Tuna F, Collison D, D'Alessandro DM. In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn(2+) Coordination Framework. Inorg Chem 2016; 55:7270-80. [PMID: 27419690 DOI: 10.1021/acs.inorgchem.6b00981] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An investigation of the redox-active tris[4-(pyridin-4-yl)phenyl]amine (NPy3) ligand in the solution state and upon its incorporation into the solid-state metal-organic framework (MOF) [Zn(NPy3)(NO2)2·xMeOH·xDMF]n (MeOH = methanol and DMF = N,N-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs.
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Affiliation(s)
- Carol Hua
- School of Chemistry, The University of Sydney , Sydney, New South Wales 2006, Australia
| | - Amgalanbaatar Baldansuren
- School of Chemistry and Photon Science Institute, The University of Manchester , Manchester M13 9PL, United Kingdom
| | - Floriana Tuna
- School of Chemistry and Photon Science Institute, The University of Manchester , Manchester M13 9PL, United Kingdom
| | - David Collison
- School of Chemistry and Photon Science Institute, The University of Manchester , Manchester M13 9PL, United Kingdom
| | - Deanna M D'Alessandro
- School of Chemistry, The University of Sydney , Sydney, New South Wales 2006, Australia
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19
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Abstract
Like most bacteria, Escherichia coli has a flexible and branched respiratory chain that enables the prokaryote to live under a variety of environmental conditions, from highly aerobic to completely anaerobic. In general, the bacterial respiratory chain is composed of dehydrogenases, a quinone pool, and reductases. Substrate-specific dehydrogenases transfer reducing equivalents from various donor substrates (NADH, succinate, glycerophosphate, formate, hydrogen, pyruvate, and lactate) to a quinone pool (menaquinone, ubiquinone, and dimethylmenoquinone). Then electrons from reduced quinones (quinols) are transferred by terminal reductases to different electron acceptors. Under aerobic growth conditions, the terminal electron acceptor is molecular oxygen. A transfer of electrons from quinol to O₂ is served by two major oxidoreductases (oxidases), cytochrome bo₃ encoded by cyoABCDE and cytochrome bd encoded by cydABX. Terminal oxidases of aerobic respiratory chains of bacteria, which use O₂ as the final electron acceptor, can oxidize one of two alternative electron donors, either cytochrome c or quinol. This review compares the effects of different inhibitors on the respiratory activities of cytochrome bo₃ and cytochrome bd in E. coli. It also presents a discussion on the genetics and the prosthetic groups of cytochrome bo₃ and cytochrome bd. The E. coli membrane contains three types of quinones that all have an octaprenyl side chain (C₄₀). It has been proposed that the bo₃ oxidase can have two ubiquinone-binding sites with different affinities. "WHAT'S NEW" IN THE REVISED ARTICLE: The revised article comprises additional information about subunit composition of cytochrome bd and its role in bacterial resistance to nitrosative and oxidative stresses. Also, we present the novel data on the electrogenic function of appBCX-encoded cytochrome bd-II, a second bd-type oxidase that had been thought not to contribute to generation of a proton motive force in E. coli, although its spectral properties closely resemble those of cydABX-encoded cytochrome bd.
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20
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Yi SM, Taguchi AT, Samoilova RI, O'Malley PJ, Gennis RB, Dikanov SA. Plasticity in the High Affinity Menaquinone Binding Site of the Cytochrome aa3-600 Menaquinol Oxidase from Bacillus subtilis. Biochemistry 2015. [PMID: 26196462 DOI: 10.1021/acs.biochem.5b00528] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytochrome aa3-600 is a terminal oxidase in the electron transport pathway that contributes to the electrochemical membrane potential by actively pumping protons. A notable feature of this enzyme complex is that it uses menaquinol as its electron donor instead of cytochrome c when it reduces dioxygen to water. The enzyme stabilizes a menasemiquinone radical (SQ) at a high affinity site that is important for catalysis. One of the residues that interacts with the semiquinone is Arg70. We have made the R70H mutant and have characterized the menasemiquinone radical by advanced X- and Q-band EPR. The bound SQ of the R70H mutant exhibits a strong isotropic hyperfine coupling (a(14)N ≈ 2.0 MHz) with a hydrogen bonded nitrogen. This nitrogen originates from a histidine side chain, based on its quadrupole coupling constant, e(2)qQ/h = 1.44 MHz, typical for protonated imidazole nitrogens. In the wild-type cyt aa3-600, the SQ is instead hydrogen bonded with Nε from the Arg70 side chain. Analysis of the (1)H 2D electron spin echo envelope modulation (ESEEM) spectra shows that the mutation also changes the number and strength of the hydrogen bonds between the SQ and the surrounding protein. Despite the alterations in the immediate environment of the SQ, the R70H mutant remains catalytically active. These findings are in contrast to the equivalent mutation in the close homologue, cytochrome bo3 ubiquinol oxidase from Escherichia coli, where the R71H mutation eliminates function.
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Affiliation(s)
- Sophia M Yi
- §Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Alexander T Taguchi
- †Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.,‡Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Rimma I Samoilova
- ⊥V. V. Voevodsky Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
| | - Patrick J O'Malley
- ∥School of Chemistry, The University of Manchester, Manchester M13 9PL, U.K
| | - Robert B Gennis
- §Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.,†Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Sergei A Dikanov
- ‡Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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21
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Lin MT, Fukazawa R, Miyajima-Nakano Y, Matsushita S, Choi SK, Iwasaki T, Gennis RB. Escherichia coli Auxotroph Host Strains for Amino Acid-Selective Isotope Labeling of Recombinant Proteins. Methods Enzymol 2015; 565:45-66. [DOI: 10.1016/bs.mie.2015.05.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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22
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Hong S, de Almeida W, Taguchi AT, Samoilova R, Gennis RB, O’Malley PJ, Dikanov SA, Crofts AR. The semiquinone at the Qi site of the bc1 complex explored using HYSCORE spectroscopy and specific isotopic labeling of ubiquinone in Rhodobacter sphaeroides via (13)C methionine and construction of a methionine auxotroph. Biochemistry 2014; 53:6022-31. [PMID: 25184535 PMCID: PMC4179594 DOI: 10.1021/bi500654y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 09/02/2014] [Indexed: 11/30/2022]
Abstract
Specific isotopic labeling at the residue or substituent level extends the scope of different spectroscopic approaches to the atomistic level. Here we describe (13)C isotopic labeling of the methyl and methoxy ring substituents of ubiquinone, achieved through construction of a methionine auxotroph in Rhodobacter sphaeroides strain BC17 supplemented with l-methionine with the side chain methyl group (13)C-labeled. Two-dimensional electron spin echo envelope modulation (HYSCORE) was applied to study the (13)C methyl and methoxy hyperfine couplings in the semiquinone generated in situ at the Qi site of the bc1 complex in its membrane environment. The data were used to characterize the distribution of unpaired spin density and the conformations of the methoxy substituents based on density functional theory calculations of (13)C hyperfine tensors in the semiquinone of the geometry-optimized X-ray structure of the bc1 complex (Protein Data Bank entry 1PP9 ) with the highest available resolution. Comparison with other proteins indicates individual orientations of the methoxy groups in each particular case are always different from the methoxy conformations in the anion radical prepared in a frozen alcohol solution. The protocol used in the generation of the methionine auxotroph is more generally applicable and, because it introduces a gene deletion using a suicide plasmid, can be applied repeatedly.
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Affiliation(s)
- Sangjin Hong
- Department
of Biochemistry, University of Illinois
at Urbana-Champaign, Urbana, Illinois 61801, United States
| | | | - Alexander T. Taguchi
- Center
for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Rimma
I. Samoilova
- V.
V. Voevodsky Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russian Federation
| | - Robert B. Gennis
- Department
of Biochemistry, University of Illinois
at Urbana-Champaign, Urbana, Illinois 61801, United States
| | | | - Sergei A. Dikanov
- Department
of Veterinary Clinical Medicine, University
of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Antony R. Crofts
- Department
of Biochemistry, University of Illinois
at Urbana-Champaign, Urbana, Illinois 61801, United States
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23
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Prediction of high- and low-affinity quinol-analogue-binding sites in the aa3 and bo3 terminal oxidases from Bacillus subtilis and Escherichia coli1. Biochem J 2014; 461:305-14. [PMID: 24779955 DOI: 10.1042/bj20140082] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Haem-copper oxidases are the terminal enzymes in both prokaryotic and eukaryotic respiratory chains. They catalyse the reduction of dioxygen to water and convert redox energy into a transmembrane electrochemical proton gradient during their catalytic activity. Haem-copper oxidases show substantial structure similarity, but spectroscopic and biochemical analyses indicate that these enzymes contain diverse prosthetic groups and use different substrates (i.e. cytochrome c or quinol). Owing to difficulties in membrane protein crystallization, there are no definitive structural data about the quinol oxidase physiological substrate-binding site(s). In the present paper, we propose an atomic structure model for the menaquinol:O2 oxidoreductase of Bacillus subtilis (QOx.aa3). Furthermore, a multistep computational approach is used to predict residues involved in the menaquinol/menaquinone binding within B. subtilis QOx.aa3 as well as those involved in quinol/quinone binding within Escherichia coli QOx.bo3. Two specific sequence motifs, R70GGXDX4RXQX3PX3FX[D/N/E/Q]X2HYNE97 and G159GSPX2GWX2Y169 (B. subtilis numbering), were highlighted within QOx from Bacillales. Specific residues within the first and the second sequence motif participate in the high- and low-affinity substrate-binding sites respectively. Using comparative analysis, two analogous motifs, R71GFXDX4RXQX8[Y/F]XPPHHYDQ101 and G163EFX3GWX2Y173 (E. coli numbering) were proposed to be involved in Enterobacteriales/Rhodobacterales/Rhodospirillales QOx high- and low-affinity quinol-derivative-binding sites. Results and models are discussed in the context of the literature.
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24
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Taguchi AT, O'Malley PJ, Wraight CA, Dikanov SA. Conformational differences between the methoxy groups of QA and QB site ubisemiquinones in bacterial reaction centers: a key role for methoxy group orientation in modulating ubiquinone redox potential. Biochemistry 2013; 52:4648-55. [PMID: 23745576 DOI: 10.1021/bi400489b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ubiquinone is an almost universal, membrane-associated redox mediator. Its ability to accept either one or two electrons allows it to function in critical roles in biological electron transport. The redox properties of ubiquinone in vivo are determined by its environment in the binding sites of proteins and by the dihedral angle of each methoxy group relative to the ring plane. This is an attribute unique to ubiquinone among natural quinones and could account for its widespread function with many different redox complexes. In this work, we use the photosynthetic reaction center as a model system for understanding the role of methoxy conformations in determining the redox potential of the ubiquinone/semiquinone couple. Despite the abundance of X-ray crystal structures for the reaction center, quinone site resolution has thus far been too low to provide a reliable measure of the methoxy dihedral angles of the primary and secondary quinones, QA and QB. We performed 2D ESEEM (HYSCORE) on isolated reaction centers with ubiquinones (13)C-labeled at the headgroup methyl and methoxy substituents, and have measured the (13)C isotropic and anisotropic components of the hyperfine tensors. Hyperfine couplings were compared to those derived by DFT calculations as a function of methoxy torsional angle allowing estimation of the methoxy dihedral angles for the semiquinones in the QA and QB sites. Based on this analysis, the orientation of the 2-methoxy groups are distinct in the two sites, with QB more out of plane by 20-25°. This corresponds to an ≈50 meV larger electron affinity for the QB quinone, indicating a substantial contribution to the experimental difference in redox potentials (60-75 mV) of the two quinones. The methods developed here can be readily extended to ubiquinone-binding sites in other protein complexes.
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Affiliation(s)
- Alexander T Taguchi
- Center for Biophysics and Computational Biology, §Department of Biochemistry, and ‡Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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25
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Dikanov SA. Resolving protein-semiquinone interactions by two-dimensional ESEEM spectroscopy. ELECTRON PARAMAGNETIC RESONANCE 2012. [DOI: 10.1039/9781849734837-00103] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- S. A. Dikanov
- University of Illinois at Urbana-Champaign, Department of Veterinary Clinical Medicine 190 MSB, 506 S. Mathews Ave., Urbana IL 61801 USA
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