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Milić JV, Schneeberger T, Zalibera M, Diederich F, Boudon C, Ruhlmann L. Spectro-electrochemical toolbox for monitoring and controlling quinone-mediated redox-driven molecular gripping. Electrochim Acta 2019. [DOI: 10.1016/j.electacta.2019.04.049] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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2
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Maróti P. Chemical rescue of H + delivery in proton transfer mutants of reaction center of photosynthetic bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:317-324. [PMID: 30707884 DOI: 10.1016/j.bbabio.2019.01.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 12/05/2018] [Accepted: 01/25/2019] [Indexed: 11/27/2022]
Abstract
In the native and most mutant reaction centers of bacterial photosynthesis, the electron transfer is coupled to proton transfer and is rate limiting for the second reduction of QB- → QBH2. In the presence of divalent metal ions (e.g. Cd2+) or in some ("proton transfer") mutants (L210DN/M17DN or L213DN), the proton delivery to QB- is made rate limiting and the properties of the proton pathway can be directly examined. We found that small weak acids and buffers in large concentrations (up to 1 M) were able to rescue the severely impaired proton transfer capability differently depending on the location of the defects: lesions at the protein surface (proton gate H126H/H128H + Cd2+), beneath the surface (M17DN + Cd2+, L210DN/M17DN) or deep inside the protein (L213DN) could be completely, partially or to very small extent recovered, respectively. Small zwitterionic acids (azide/hydrazoic acid) and buffers (tricine) proved to be highly effective rescuers consistent with their enhanced binding affinity and access to any of the proton acceptors (including QB- itself) in the pathway. As a consequence, back titration of the protons at L212Glu could be observed as a pH-dependence of the rate constant of the charge recombination in the presence of azide or formate. Model calculations support the collective influence of the acid cluster on the change of the protonation states upon extension of the cluster with the bound small acid. In proton transfer mutants, the rescuing agents decreased the free energy of activation together with their enthalpic and entropic components. This is in agreement with the hypothesis that they function as protein-penetrating protonophores delivering protons into the chain and select dominating paths out of many alternate routes. We estimate that the proton delivery will be accelerated in one pathway out of 100-200 alternate pathways. The implications for design of the chemical recovery of impaired intra-protein proton transfer pathways in proton transfer mutants are discussed.
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Affiliation(s)
- Péter Maróti
- Institute of Medical Physics, University of Szeged, Hungary.
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3
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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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4
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Milić J, Zalibera M, Talaat D, Nomrowski J, Trapp N, Ruhlmann L, Boudon C, Wenger OS, Savitsky A, Lubitz W, Diederich F. Photoredox-Switchable Resorcin[4]arene Cavitands: Radical Control of Molecular Gripping Machinery via Hydrogen Bonding. Chemistry 2017; 24:1431-1440. [DOI: 10.1002/chem.201704788] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Indexed: 01/10/2023]
Affiliation(s)
- Jovana Milić
- Laboratory of Organic Chemistry; ETH Zurich; Vladimir-Prelog-Weg 3 8093 Zurich Switzerland
| | - Michal Zalibera
- Institute of Physical Chemistry and Chemical Physics; Slovak University of Technology; Radlinského 9 81237 Bratislava Slovakia
- Max Planck Institute for Chemical Energy Conversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - Darius Talaat
- Laboratory of Organic Chemistry; ETH Zurich; Vladimir-Prelog-Weg 3 8093 Zurich Switzerland
| | - Julia Nomrowski
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 4056 Basel Switzerland
| | - Nils Trapp
- Laboratory of Organic Chemistry; ETH Zurich; Vladimir-Prelog-Weg 3 8093 Zurich Switzerland
| | - Laurent Ruhlmann
- Laboratoire d'Électrochimie et Chimie Physique du Corps Solide, Institut de Chimie de Strasbourg; Université de Strasbourg; 4 rue Blaise Pascal, CS 90032 67081 Strasbourg France
| | - Corinne Boudon
- Laboratoire d'Électrochimie et Chimie Physique du Corps Solide, Institut de Chimie de Strasbourg; Université de Strasbourg; 4 rue Blaise Pascal, CS 90032 67081 Strasbourg France
| | - Oliver S. Wenger
- Department of Chemistry; University of Basel; St. Johanns-Ring 19 4056 Basel Switzerland
| | - Anton Savitsky
- Max Planck Institute for Chemical Energy Conversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - Wolfgang Lubitz
- Max Planck Institute for Chemical Energy Conversion; Stiftstrasse 34-36 45470 Mülheim an der Ruhr Germany
| | - François Diederich
- Laboratory of Organic Chemistry; ETH Zurich; Vladimir-Prelog-Weg 3 8093 Zurich Switzerland
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5
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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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6
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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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7
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Taguchi AT, O'Malley PJ, Wraight CA, Dikanov SA. Hydrogen bond network around the semiquinone of the secondary quinone acceptor Q(B) in bacterial photosynthetic reaction centers. J Phys Chem B 2015; 119:5805-14. [PMID: 25885036 DOI: 10.1021/acs.jpcb.5b03434] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
By utilizing a combined pulsed EPR and DFT approach, the high-resolution structure of the QB site semiquinone (SQB) was determined. The development of such a technique is crucial toward an understanding of protein-bound semiquinones on the structural level, as (i) membrane protein crystallography typically results in low resolution structures, and (ii) obtaining protein crystals in the semiquinone form is rarely feasible. The SQB hydrogen bond network was investigated with Q- (∼34 GHz) and X-band (∼9.7 GHz) pulsed EPR spectroscopy on fully deuterated reactions centers from Rhodobacter sphaeroides. Simulations in the SQB g-tensor reference frame provided the principal values and directions of the H-bond proton hyperfine tensors. Three protons were detected, one with an anisotropic tensor component, T = 4.6 MHz, assigned to the histidine NδH of His-L190, and two others with similar anisotropic constants T = 3.2 and 3.0 MHz assigned to the peptide NpH of Gly-L225 and Ile-L224, respectively. Despite the strong similarity in the peptide couplings, all hyperfine tensors were resolved in the Q-band ENDOR spectra. The Euler angles describing the series of rotations that bring the hyperfine tensors into the SQB g-tensor reference frame were obtained by least-squares fitting of the spectral simulations to the ENDOR data. These Euler angles show the locations of the hydrogen bonded protons with respect to the semiquinone. Our geometry optimized model of SQB used in previous DFT work is in strong agreement with the angular constraints from the spectral simulations, providing the foundation for future joint pulsed EPR and DFT semiquinone structural determinations in other proteins.
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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
| | - Patrick J O'Malley
- ⊥School of Chemistry, The University of Manchester, Manchester M13 9PL, U.K
| | - 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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8
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Vermaas JV, Taguchi AT, Dikanov SA, Wraight CA, Tajkhorshid E. Redox potential tuning through differential quinone binding in the photosynthetic reaction center of Rhodobacter sphaeroides. Biochemistry 2015; 54:2104-16. [PMID: 25734689 DOI: 10.1021/acs.biochem.5b00033] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ubiquinone forms an integral part of the electron transport chain in cellular respiration and photosynthesis across a vast number of organisms. Prior experimental results have shown that the photosynthetic reaction center (RC) from Rhodobacter sphaeroides is only fully functional with a limited set of methoxy-bearing quinones, suggesting that specific interactions with this substituent are required to drive electron transport and the formation of quinol. The nature of these interactions has yet to be determined. Through parameterization of a CHARMM-compatible quinone force field and subsequent molecular dynamics simulations of the quinone-bound RC, we have investigated and characterized the interactions of the protein with the quinones in the Q(A) and Q(B) sites using both equilibrium simulation and thermodynamic integration. In particular, we identify a specific interaction between the 2-methoxy group of ubiquinone in the Q(B) site and the amide nitrogen of GlyL225 that we implicate in locking the orientation of the 2-methoxy group, thereby tuning the redox potential difference between the quinones occupying the Q(A) and Q(B) sites. Disruption of this interaction leads to weaker binding in a ubiquinone analogue that lacks a 2-methoxy group, a finding supported by reverse electron transfer electron paramagnetic resonance experiments of the Q(A)⁻Q(B)⁻ biradical and competitive binding assays.
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Affiliation(s)
- Josh V Vermaas
- †Center for Biophysics and Computational Biology, ‡Department of Biochemistry, §Beckman Institute, and ∥Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Alexander T Taguchi
- †Center for Biophysics and Computational Biology, ‡Department of Biochemistry, §Beckman Institute, and ∥Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Sergei A Dikanov
- †Center for Biophysics and Computational Biology, ‡Department of Biochemistry, §Beckman Institute, and ∥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, ‡Department of Biochemistry, §Beckman Institute, and ∥Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Emad Tajkhorshid
- †Center for Biophysics and Computational Biology, ‡Department of Biochemistry, §Beckman Institute, and ∥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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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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10
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Jun D, Saer RG, Madden JD, Beatty JT. Use of new strains of Rhodobacter sphaeroides and a modified simple culture medium to increase yield and facilitate purification of the reaction centre. PHOTOSYNTHESIS RESEARCH 2014; 120:197-205. [PMID: 23765434 DOI: 10.1007/s11120-013-9866-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Accepted: 05/24/2013] [Indexed: 06/02/2023]
Abstract
A new gene expression system was developed in Rhodobacter sphaeroides, replacing a pRK415-based system used previously. The broad host-range IPTG-inducible plasmid pIND4 was used to create the plasmid pIND4-RC1 for expression of the puhA and pufQBALMX genes, encoding the reaction centre (RC) and light-harvesting complex 1 (LH1) proteins. The strain R. sphaeroides ΔRCLH was used to make a knockout of the rshI restriction endonuclease gene, enabling electroporation of DNA into the bacterium; a subsequent knockout of ppsR was made, creating the strain R. sphaeroides RCx lacking this oxygen-sensing repressor of the photosynthesis gene cluster. Using pIND4-RC1, LH1 levels were increased by a factor of about 8 over pRS1 per cell in cultures grown semi-aerobically. In addition, the ppsR knockout allowed for photosynthetic pigment-protein complex synthesis in the presence of high concentrations of molecular oxygen; here, LH1 levels per cell increased by 20 % when grown under high aeration conditions. A new medium (called RLB) is the E. coli medium LB supplemented with MgCl2 and CaCl2, which was found to increase growth rates and final cell culture densities, with an increase of 30 % of LH1 per cell detected in R. sphaeroides RCx(pIND4-RC1) grown in RLB versus LB medium. Furthermore, cell density was about three times greater in RLB compared to semi-aerobic conditions. The combination of all the modifications resulted in an increase of LH1 and RC per mL of culture volume by approximately 35-fold, and a decrease in the length of culture incubation time from about 5 days to ~36 h.
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Affiliation(s)
- D Jun
- Department of Microbiology and Immunology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
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11
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Ashizawa R, Noguchi T. Effects of hydrogen bonding interactions on the redox potential and molecular vibrations of plastoquinone as studied using density functional theory calculations. Phys Chem Chem Phys 2014; 16:11864-76. [DOI: 10.1039/c3cp54742f] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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12
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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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13
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Defining a direction: electron transfer and catalysis in Escherichia coli complex II enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:668-78. [PMID: 23396003 DOI: 10.1016/j.bbabio.2013.01.010] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 01/23/2013] [Accepted: 01/23/2013] [Indexed: 11/24/2022]
Abstract
There are two homologous membrane-bound enzymes in Escherichia coli that catalyze reversible conversion between succinate/fumarate and quinone/quinol. Succinate:ubiquinone reductase (SQR) is a component of aerobic respiratory chains, whereas quinol:fumarate reductase (QFR) utilizes menaquinol to reduce fumarate in a final step of anaerobic respiration. Although, both protein complexes are capable of supporting bacterial growth on either minimal succinate or fumarate media, the enzymes are more proficient in their physiological directions. Here we evaluate factors that may underlie this catalytic bias. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.
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