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Taguchi AT, Wraight CA, Dikanov SA. Influence of Polar Mutations on the Electronic and Structural Properties of QA-· in Bacterial Reaction Centers. J Phys Chem B 2022; 126:6210-6220. [PMID: 35960270 DOI: 10.1021/acs.jpcb.2c04371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Reaction centers from Rhodobacter sphaeroides with residue M265 mutated from isoleucine to threonine, serine, and asparagine (M265IT, M265IS, and M265IN, respectively) in the QA-· state are studied by high-resolution electron spin echo envelope modulation (ESEEM) and electron nuclear double resonance spectroscopy methods to investigate the structural characteristics of these mutants influencing the redox properties of the QA site. All three mutants decrease the redox midpoint potential (Em) of QA by ∼0.1 V, yet the mechanism for this drop in Em is unclear. In this work, we examine (i) the hydrogen bonding interactions between QA-· and residues histidine M219 and alanine M260, (ii) the electron spin density distribution of the semiquinone, and (iii) the orientations of the ubiquinone methoxy substituents. 13C measurements show no significant contribution of methoxy dihedral angles to the observed decrease in Em for the QA mutants. Instead, 14N three-pulse ESEEM data suggest that electrostatic or hydrogen bond formation between the mutated M265 side chain and His-M219 Nδ may be involved in the observed lowering of the QA midpoint potential. For mutant M265IN, analysis of the proton hyperfine couplings reveals a weakened hydrogen bond network, resulting in an altered QA-· spin density distribution. The magnetic resonance study presented here is most consistent with an electrostatic or structural perturbation of the His-M219 Nδ hydrogen bond in these mutants as a mechanism for the ∼0.1 V decrease in QA Em.
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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.,RubrYc Therapeutics, 733 Industrial Road, San Carlos, California 94403, United States
| | - Colin A Wraight
- 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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Méndez-Hernández DD, Baldansuren A, Kalendra V, Charles P, Mark B, Marshall W, Molnar B, Moore TA, Lakshmi KV, Moore AL. HYSCORE and DFT Studies of Proton-Coupled Electron Transfer in a Bioinspired Artificial Photosynthetic Reaction Center. iScience 2020; 23:101366. [PMID: 32738611 PMCID: PMC7394912 DOI: 10.1016/j.isci.2020.101366] [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: 05/17/2020] [Revised: 06/22/2020] [Accepted: 07/10/2020] [Indexed: 11/24/2022] Open
Abstract
The photosynthetic water-oxidation reaction is catalyzed by the oxygen-evolving complex in photosystem II (PSII) that comprises the Mn4CaO5 cluster, with participation of the redox-active tyrosine residue (YZ) and a hydrogen-bonded network of amino acids and water molecules. It has been proposed that the strong hydrogen bond between YZ and D1-His190 likely renders YZ kinetically and thermodynamically competent leading to highly efficient water oxidation. However, a detailed understanding of the proton-coupled electron transfer (PCET) at YZ remains elusive owing to the transient nature of its intermediate states involving YZ⋅. Herein, we employ a combination of high-resolution two-dimensional 14N hyperfine sublevel correlation spectroscopy and density functional theory methods to investigate a bioinspired artificial photosynthetic reaction center that mimics the PCET process involving the YZ residue of PSII. Our results underscore the importance of proximal water molecules and charge delocalization on the electronic structure of the artificial reaction center. Structural factors are critical in the design of artificial photosynthetic systems Correlation between hyperfine couplings of the N atoms and electron spin density Spin density distribution affected by charge delocalization and explicit waters Spin density modulation by electronic coupling as observed with P680 and YZ in PSII
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Affiliation(s)
| | - Amgalanbaatar Baldansuren
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - Vidmantas Kalendra
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - Philip Charles
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - Brian Mark
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - William Marshall
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - Brian Molnar
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
| | - Thomas A Moore
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - K V Lakshmi
- Department of Chemistry and Chemical Biology and The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
| | - Ana L Moore
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA.
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3
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Stamos NA, Ferentinos E, Chrysina M, Raptopoulou CP, Psycharis V, Sanakis Y, Pantazis DA, Kyritsis P, Mitrikas G. Unusual 31P Hyperfine Strain Effects in a Conformationally Flexible Cu(II) Complex Revealed by Two-Dimensional Pulse EPR Spectroscopy. Inorg Chem 2020; 59:3666-3676. [PMID: 32077279 DOI: 10.1021/acs.inorgchem.9b03237] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Strain effects on g and metal hyperfine coupling tensors, A, are often manifested in Electron Paramagnetic Resonance (EPR) spectra of transition metal complexes, as a result of their intrinsic and/or solvent-mediated structural variations. Although distributions of these tensors are quite common and well understood in continuous-wave (cw) EPR spectroscopy, reported strain effects on ligand hyperfine coupling constants are rather scarce. Here we explore the case of a conformationally flexible Cu(II) complex, [Cu{Ph2P(O)NP(O)Ph2-κ2O,O'}2], bearing P atoms in its second coordination sphere and exhibiting two structurally distinct CuO4 coordination spheres, namely a square planar and a tetrahedrally distorted one, as revealed by X-ray crystallography. The Hyperfine Sublevel Correlation (HYSCORE) spectra of this complex exhibit 31P correlation ridges that have unusual inverse or so-called "boomerang" shapes and features that cannot be reproduced by standard simulation procedures assuming only one set of magnetic parameters. Our work shows that a distribution of isotropic hyperfine coupling constants (hfc) spanning a range between negative and positive values is necessary in order to describe in detail the unusual shapes of HYSCORE spectra. By employing DFT calculations we show that these hfc correspond to molecules showing variable distortions from square planar to tetrahedral geometry, and we demonstrate that line shape analysis of such HYSCORE spectra provides new insight into the conformation-dependent spectroscopic response of the spin system under investigation.
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Affiliation(s)
- Nikolaos-Angelos Stamos
- Institute of Nanoscience and Nanotechnology, N.C.S.R. "Demokritos", 15310 Athens, Greece.,Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
| | - Eleftherios Ferentinos
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
| | - Maria Chrysina
- Institute of Nanoscience and Nanotechnology, N.C.S.R. "Demokritos", 15310 Athens, Greece
| | | | - Vassilis Psycharis
- Institute of Nanoscience and Nanotechnology, N.C.S.R. "Demokritos", 15310 Athens, Greece
| | - Yiannis Sanakis
- Institute of Nanoscience and Nanotechnology, N.C.S.R. "Demokritos", 15310 Athens, Greece
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Panayotis Kyritsis
- Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
| | - George Mitrikas
- Institute of Nanoscience and Nanotechnology, N.C.S.R. "Demokritos", 15310 Athens, Greece
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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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