1
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Guo Y, He L, Ding Y, Kloo L, Pantazis DA, Messinger J, Sun L. Closing Kok's cycle of nature's water oxidation catalysis. Nat Commun 2024; 15:5982. [PMID: 39013902 PMCID: PMC11252165 DOI: 10.1038/s41467-024-50210-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 07/03/2024] [Indexed: 07/18/2024] Open
Abstract
The Mn4CaO5(6) cluster in photosystem II catalyzes water splitting through the Si state cycle (i = 0-4). Molecular O2 is formed and the natural catalyst is reset during the final S3 → (S4) → S0 transition. Only recently experimental breakthroughs have emerged for this transition but without explicit information on the S0-state reconstitution, thus the progression after O2 release remains elusive. In this report, our molecular dynamics simulations combined with density functional calculations suggest a likely missing link for closing the cycle, i.e., restoring the first catalytic state. Specifically, the formation of closed-cubane intermediates with all hexa-coordinate Mn is observed, which would undergo proton release, water dissociation, and ligand transfer to produce the open-cubane structure of the S0 state. Thereby, we theoretically identify the previously unknown structural isomerism in the S0 state that acts as the origin of the proposed structural flexibility prevailing in the cycle, which may be functionally important for nature's water oxidation catalysis.
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Affiliation(s)
- Yu Guo
- Center of Artificial Photosynthesis for Solar Fuels and Department of Chemistry, School of Science, Westlake University, Hangzhou, 310024, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, 310024, China
| | - Lanlan He
- Center of Artificial Photosynthesis for Solar Fuels and Department of Chemistry, School of Science, Westlake University, Hangzhou, 310024, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, 310024, China
| | - Yunxuan Ding
- Center of Artificial Photosynthesis for Solar Fuels and Department of Chemistry, School of Science, Westlake University, Hangzhou, 310024, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, 310024, China
| | - Lars Kloo
- Department of Chemistry, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-10044, Stockholm, Sweden
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, 45470, Germany
| | - Johannes Messinger
- Department of Plant Physiology, Umeå University, Linnaeus väg 6 (KBC huset), SE-90187, Umeå, Sweden
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University, SE-75120, Uppsala, Sweden
| | - Licheng Sun
- Center of Artificial Photosynthesis for Solar Fuels and Department of Chemistry, School of Science, Westlake University, Hangzhou, 310024, China.
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, 310024, China.
- Division of Solar Energy Conversion and Catalysis at Westlake University, Zhejiang Baima Lake Laboratory Co., Ltd., Hangzhou, 310000, Zhejiang, China.
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2
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Krysiak S, Burda K. The Effect of Removal of External Proteins PsbO, PsbP and PsbQ on Flash-Induced Molecular Oxygen Evolution and Its Biphasicity in Tobacco PSII. Curr Issues Mol Biol 2024; 46:7187-7218. [PMID: 39057069 PMCID: PMC11276211 DOI: 10.3390/cimb46070428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2024] [Revised: 06/30/2024] [Accepted: 07/02/2024] [Indexed: 07/28/2024] Open
Abstract
The oxygen evolution within photosystem II (PSII) is one of the most enigmatic processes occurring in nature. It is suggested that external proteins surrounding the oxygen-evolving complex (OEC) not only stabilize it and provide an appropriate ionic environment but also create water channels, which could be involved in triggering the ingress of water and the removal of O2 and protons outside the system. To investigate the influence of these proteins on the rate of oxygen release and the efficiency of OEC function, we developed a measurement protocol for the direct measurement of the kinetics of oxygen release from PSII using a Joliot-type electrode. PSII-enriched tobacco thylakoids were used in the experiments. The results revealed the existence of slow and fast modes of oxygen evolution. This observation is model-independent and requires no specific assumptions about the initial distribution of the OEC states. The gradual removal of exogenous proteins resulted in a slowdown of the rapid phase (~ms) of O2 release and its gradual disappearance while the slow phase (~tens of ms) accelerated. The role of external proteins in regulating the biphasicity and efficiency of oxygen release is discussed based on observed phenomena and current knowledge.
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Affiliation(s)
| | - Kvetoslava Burda
- Faculty of Physics and Applied Computer Science, AGH University of Krakow, al. Mickiewicza 30, 30-059 Krakow, Poland;
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3
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Pavlou A, Styring S, Mamedov F. The S 1 to S 2 and S 2 to S 3 state transitions in plant photosystem II: relevance to the functional and structural heterogeneity of the water oxidizing complex. PHOTOSYNTHESIS RESEARCH 2024:10.1007/s11120-024-01096-4. [PMID: 38662327 DOI: 10.1007/s11120-024-01096-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 03/18/2024] [Indexed: 04/26/2024]
Abstract
In Photosystem II, light-induced water splitting occurs via the S state cycle of the CaMn4O5-cluster. To understand the role of various possible conformations of the CaMn4O5-cluster in this process, the temperature dependence of the S1 → S2 and S2 → S3 state transitions, induced by saturating laser flashes, was studied in spinach photosystem II membrane preparations under different conditions. The S1 → S2 transition temperature dependence was shown to be much dependent on the type of the cryoprotectant and presence of 3.5% methanol, resulting in the variation of transition half-inhibition temperature by 50 K. No similar effect was observed for the S2 → S3 state transition, for which we also show that both the low spin g = 2.0 multiline and high spin g = 4.1 EPR configurations of the S2 state advance with similar efficiency to the S3 state, both showing a transition half-inhibition temperature of 240 K. This was further confirmed by following the appearance of the Split S3 EPR signal. The results are discussed in relevance to the functional and structural heterogeneity of the water oxidizing complex intermediates in photosystem II.
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Affiliation(s)
- Andrea Pavlou
- Molecular Biomimetics, Department of Chemistry-Ångström, Uppsala University, P.O. Box 523, 751 20, Uppsala, Sweden
| | - Stenbjörn Styring
- Molecular Biomimetics, Department of Chemistry-Ångström, Uppsala University, P.O. Box 523, 751 20, Uppsala, Sweden
| | - Fikret Mamedov
- Molecular Biomimetics, Department of Chemistry-Ångström, Uppsala University, P.O. Box 523, 751 20, Uppsala, Sweden.
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4
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Drosou M, Pantazis DA. Comprehensive Evaluation of Models for Ammonia Binding to the Oxygen Evolving Complex of Photosystem II. J Phys Chem B 2024; 128:1333-1349. [PMID: 38299511 PMCID: PMC10875651 DOI: 10.1021/acs.jpcb.3c06304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 01/08/2024] [Accepted: 01/17/2024] [Indexed: 02/02/2024]
Abstract
The identity and insertion pathway of the substrate oxygen atoms that are coupled to dioxygen by the oxygen-evolving complex (OEC) remains a central question toward understanding Nature's water oxidation mechanism. In several studies, ammonia has been used as a small "water analogue" to elucidate the pathway of substrate access to the OEC and to aid in determining which of the oxygen ligands of the tetramanganese cluster are substrates for O-O bond formation. On the basis of structural and spectroscopic investigations, five first-sphere binding modes of ammonia have been suggested, involving either substitution of an existing H2O/OH-/O2- group or addition as an extra ligand to a metal ion of the Mn4CaO5 cluster. Some of these modes, specifically the ones involving substitution, have already been subject to spectroscopy-oriented quantum chemical investigations, whereas more recent suggestions that postulate the addition of ammonia have not been examined so far with quantum chemistry for their agreement with spectroscopic data. Herein, we use a common structural framework and theoretical methodology to evaluate structural models of the OEC that represent all proposed modes of first-sphere ammonia interaction with the OEC in its S2 state. Criteria include energetic, magnetic, kinetic, and spectroscopic properties compared against available experimental EPR, ENDOR, ESEEM, and EDNMR data. Our results show that models featuring ammonia replacing one of the two terminal water ligands on Mn4 align best with experimental data, while they definitively exclude substitution of a bridging μ-oxo ligand as well as incorporation of ammonia as a sixth ligand on Mn1 or Mn4.
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Affiliation(s)
- Maria Drosou
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr 45470, Germany
- Inorganic
Chemistry Laboratory, National and Kapodistrian
University of Athens, Panepistimiopolis, Zografou 15771, Greece
| | - Dimitrios A. Pantazis
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr 45470, Germany
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5
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Drosou M, Comas-Vilà G, Neese F, Salvador P, Pantazis DA. Does Serial Femtosecond Crystallography Depict State-Specific Catalytic Intermediates of the Oxygen-Evolving Complex? J Am Chem Soc 2023; 145:10604-10621. [PMID: 37137865 DOI: 10.1021/jacs.3c00489] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Recent advances in serial femtosecond crystallography (SFX) of photosystem II (PSII), enabled by X-ray free electron lasers (XFEL), provided the first geometric models of distinct intermediates in the catalytic S-state cycle of the oxygen-evolving complex (OEC). These models are obtained by flash-advancing the OEC from the dark-stable state (S1) to more oxidized intermediates (S2 and S3), eventually cycling back to the most reduced S0. However, the interpretation of these models is controversial because geometric parameters within the Mn4CaO5 cluster of the OEC do not exactly match those expected from coordination chemistry for the spectroscopically verified manganese oxidation states of the distinct S-state intermediates. Here we focus on the first catalytic transition, S1 → S2, which represents a one-electron oxidation of the OEC. Combining geometric and electronic structure criteria, including a novel effective oxidation state approach, we analyze existing 1-flash (1F) SFX-XFEL crystallographic models that should depict the S2 state of the OEC. We show that the 1F/S2 equivalence is not obvious, because the Mn oxidation states and total unpaired electron counts encoded in these models are not fully consistent with those of a pure S2 state and with the nature of the S1 → S2 transition. Furthermore, the oxidation state definition in two-flashed (2F) structural models is practically impossible to elucidate. Our results advise caution in the extraction of electronic structure information solely from the literal interpretation of crystallographic models and call for re-evaluation of structural and mechanistic interpretations that presume exact correspondence of such models to specific catalytic intermediates of the OEC.
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Affiliation(s)
- Maria Drosou
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany
| | - Gerard Comas-Vilà
- Institute of Computational Chemistry and Catalysis, Chemistry Department, University of Girona, Montilivi Campus, Girona, Catalonia 17003, Spain
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany
| | - Pedro Salvador
- Institute of Computational Chemistry and Catalysis, Chemistry Department, University of Girona, Montilivi Campus, Girona, Catalonia 17003, Spain
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany
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6
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Lubitz W, Pantazis DA, Cox N. Water oxidation in oxygenic photosynthesis studied by magnetic resonance techniques. FEBS Lett 2023; 597:6-29. [PMID: 36409002 DOI: 10.1002/1873-3468.14543] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 11/14/2022] [Accepted: 11/15/2022] [Indexed: 11/23/2022]
Abstract
The understanding of light-induced biological water oxidation in oxygenic photosynthesis is of great importance both for biology and (bio)technological applications. The chemically difficult multistep reaction takes place at a unique protein-bound tetra-manganese/calcium cluster in photosystem II whose structure has been elucidated by X-ray crystallography (Umena et al. Nature 2011, 473, 55). The cluster moves through several intermediate states in the catalytic cycle. A detailed understanding of these intermediates requires information about the spatial and electronic structure of the Mn4 Ca complex; the latter is only available from spectroscopic techniques. Here, the important role of Electron Paramagnetic Resonance (EPR) and related double resonance techniques (ENDOR, EDNMR), complemented by quantum chemical calculations, is described. This has led to the elucidation of the cluster's redox and protonation states, the valence and spin states of the manganese ions and the interactions between them, and contributed substantially to the understanding of the role of the protein surrounding, as well as the binding and processing of the substrate water molecules, the O-O bond formation and dioxygen release. Based on these data, models for the water oxidation cycle are developed.
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Affiliation(s)
- Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion, Mülheim/Ruhr, Germany
| | | | - Nicholas Cox
- Research School of Chemistry, Australian National University, Canberra, ACT, Australia
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7
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Sirohiwal A, Pantazis DA. Functional Water Networks in Fully Hydrated Photosystem II. J Am Chem Soc 2022; 144:22035-22050. [PMID: 36413491 PMCID: PMC9732884 DOI: 10.1021/jacs.2c09121] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Water channels and networks within photosystem II (PSII) of oxygenic photosynthesis are critical for enzyme structure and function. They control substrate delivery to the oxygen-evolving center and mediate proton transfer at both the oxidative and reductive endpoints. Current views on PSII hydration are derived from protein crystallography, but structural information may be compromised by sample dehydration and technical limitations. Here, we simulate the physiological hydration structure of a cyanobacterial PSII model following a thorough hydration procedure and large-scale unconstrained all-atom molecular dynamics enabled by massively parallel simulations. We show that crystallographic models of PSII are moderately to severely dehydrated and that this problem is particularly acute for models derived from X-ray free electron laser (XFEL) serial femtosecond crystallography. We present a fully hydrated representation of cyanobacterial PSII and map all water channels, both static and dynamic, associated with the electron donor and acceptor sides. Among them, we describe a series of transient channels and the attendant conformational gating role of protein components. On the acceptor side, we characterize a channel system that is absent from existing crystallographic models but is likely functionally important for the reduction of the terminal electron acceptor plastoquinone QB. The results of the present work build a foundation for properly (re)evaluating crystallographic models and for eliciting new insights into PSII structure and function.
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8
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Imaizumi K, Ifuku K. Binding and functions of the two chloride ions in the oxygen-evolving center of photosystem II. PHOTOSYNTHESIS RESEARCH 2022; 153:135-156. [PMID: 35698013 DOI: 10.1007/s11120-022-00921-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 05/02/2022] [Indexed: 06/15/2023]
Abstract
Light-driven water oxidation in photosynthesis occurs at the oxygen-evolving center (OEC) of photosystem II (PSII). Chloride ions (Cl-) are essential for oxygen evolution by PSII, and two Cl- ions have been found to specifically bind near the Mn4CaO5 cluster in the OEC. The retention of these Cl- ions within the OEC is critically supported by some of the membrane-extrinsic subunits of PSII. The functions of these two Cl- ions and the mechanisms of their retention both remain to be fully elucidated. However, intensive studies performed recently have advanced our understanding of the functions of these Cl- ions, and PSII structures from various species have been reported, aiding the interpretation of previous findings regarding Cl- retention by extrinsic subunits. In this review, we summarize the findings to date on the roles of the two Cl- ions bound within the OEC. Additionally, together with a short summary of the functions of PSII membrane-extrinsic subunits, we discuss the mechanisms of Cl- retention by these extrinsic subunits.
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Affiliation(s)
- Ko Imaizumi
- Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan
| | - Kentaro Ifuku
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan.
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9
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Kalendra V, Reiss KM, Banerjee G, Ghosh I, Baldansuren A, Batista VS, Brudvig GW, Lakshmi KV. Binding of the substrate analog methanol in the oxygen-evolving complex of photosystem II in the D1-N87A genetic variant of cyanobacteria. Faraday Discuss 2022; 234:195-213. [PMID: 35147155 DOI: 10.1039/d1fd00094b] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The solar water-splitting protein complex, photosystem II (PSII), catalyzes one of the most energetically demanding reactions in nature by using light energy to drive a catalyst capable of oxidizing water. The water oxidation reaction is catalyzed at the Mn4Ca-oxo cluster in the oxygen-evolving complex (OEC), which cycles through five light-driven S-state intermediates (S0-S4). A detailed mechanism of the reaction remains elusive as it requires knowledge of the delivery and binding of substrate water in the higher S-state intermediates. In this study, we use two-dimensional (2D) hyperfine sublevel correlation spectroscopy, in conjunction with quantum mechanics/molecular mechanics (QM/MM) and density functional theory (DFT), to probe the binding of the substrate analog, methanol, in the S2 state of the D1-N87A variant of PSII from Synechocystis sp. PCC 6803. The results indicate that the size and specificity of the "narrow" channel is altered in D1-N87A PSII, allowing for the binding of deprotonated 13C-labeled methanol at the Mn4(IV) ion of the catalytic cluster in the S2 state. This has important implications on the mechanistic models for water oxidation in PSII.
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Affiliation(s)
- Vidmantas Kalendra
- Department of Chemistry and Chemical Biology, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA.
| | - Krystle M Reiss
- Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
| | - Gourab Banerjee
- Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
| | - Ipsita Ghosh
- Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
| | - Amgalanbaatar Baldansuren
- Department of Chemistry and Chemical Biology, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA.
| | - Victor S Batista
- Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
| | - Gary W Brudvig
- Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
| | - K V Lakshmi
- Department of Chemistry and Chemical Biology, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA.
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10
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Bigness A, Vaddypally S, Zdilla MJ, Mendoza-Cortes JL. Ubiquity of cubanes in bioinorganic relevant compounds. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2021.214168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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11
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Debus RJ. Alteration of the O 2-Producing Mn 4Ca Cluster in Photosystem II by the Mutation of a Metal Ligand. Biochemistry 2021; 60:3841-3855. [PMID: 34898175 DOI: 10.1021/acs.biochem.1c00504] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The O2-evolving Mn4Ca cluster in photosystem II (PSII) is arranged as a distorted Mn3Ca cube that is linked to a fourth Mn ion (denoted as Mn4) by two oxo bridges. The Mn4 and Ca ions are bridged by residue D1-D170. This is also the only residue known to participate in the high-affinity Mn(II) site that participates in the light-driven assembly of the Mn4Ca cluster. In this study, we use Fourier transform infrared difference spectroscopy to characterize the impact of the D1-D170E mutation. On the basis of analyses of carboxylate and carbonyl stretching modes and the O-H stretching modes of hydrogen-bonded water molecules, we show that this mutation alters the extensive network of hydrogen bonds that surrounds the Mn4Ca cluster in the same manner as that of many other mutations. It also alters the equilibrium between conformers of the Mn4Ca cluster in the dark-stable S1 state so that a high-spin form of the S2 state is produced during the S1-to-S2 transition instead of the low-spin form that gives rise to the S2 state multiline electron paramagnetic resonance signal. The mutation may also change the coordination mode of the carboxylate group at position 170 to unidentate ligation of Mn4. This is the first mutation of a metal ligand in PSII that substantially impacts the spectroscopic signatures of the Mn4Ca cluster without substantially eliminating O2 evolution. The results have significant implications for our understanding of the roles of alternate active/inactive conformers of the Mn4Ca cluster in the mechanism of O2 formation.
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Affiliation(s)
- Richard J Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
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12
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de Lichtenberg C, Kim CJ, Chernev P, Debus RJ, Messinger J. The exchange of the fast substrate water in the S 2 state of photosystem II is limited by diffusion of bulk water through channels - implications for the water oxidation mechanism. Chem Sci 2021; 12:12763-12775. [PMID: 34703563 PMCID: PMC8494045 DOI: 10.1039/d1sc02265b] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 08/31/2021] [Indexed: 12/02/2022] Open
Abstract
The molecular oxygen we breathe is produced from water-derived oxygen species bound to the Mn4CaO5 cluster in photosystem II (PSII). Present research points to the central oxo-bridge O5 as the 'slow exchanging substrate water (Ws)', while, in the S2 state, the terminal water ligands W2 and W3 are both discussed as the 'fast exchanging substrate water (Wf)'. A critical point for the assignment of Wf is whether or not its exchange with bulk water is limited by barriers in the channels leading to the Mn4CaO5 cluster. In this study, we measured the rates of H2 16O/H2 18O substrate water exchange in the S2 and S3 states of PSII core complexes from wild-type (WT) Synechocystis sp. PCC 6803, and from two mutants, D1-D61A and D1-E189Q, that are expected to alter water access via the Cl1/O4 channels and the O1 channel, respectively. We found that the exchange rates of Wf and Ws were unaffected by the E189Q mutation (O1 channel), but strongly perturbed by the D61A mutation (Cl1/O4 channel). It is concluded that all channels have restrictions limiting the isotopic equilibration of the inner water pool near the Mn4CaO5 cluster, and that D61 participates in one such barrier. In the D61A mutant this barrier is lowered so that Wf exchange occurs more rapidly. This finding removes the main argument against Ca-bound W3 as fast substrate water in the S2 state, namely the indifference of the rate of Wf exchange towards Ca/Sr substitution.
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Affiliation(s)
- Casper de Lichtenberg
- Department of Chemistry, Umeå University Linnaeus väg 6 (KBC huset), SE-901 87 Umeå Sweden
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University POB 523 SE-75120 Uppsala Sweden
| | - Christopher J Kim
- Department of Biochemistry, University of California Riverside California 92521 USA
| | - Petko Chernev
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University POB 523 SE-75120 Uppsala Sweden
| | - Richard J Debus
- Department of Biochemistry, University of California Riverside California 92521 USA
| | - Johannes Messinger
- Department of Chemistry, Umeå University Linnaeus väg 6 (KBC huset), SE-901 87 Umeå Sweden
- Molecular Biomimetics, Department of Chemistry - Ångström Laboratory, Uppsala University POB 523 SE-75120 Uppsala Sweden
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13
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Corry TA, O'Malley PJ. S 3 State Models of Nature's Water Oxidizing Complex: Analysis of Bonding and Magnetic Exchange Pathways, Assessment of Experimental Electron Paramagnetic Resonance Data, and Implications for the Water Oxidation Mechanism. J Phys Chem B 2021; 125:10097-10107. [PMID: 34463499 DOI: 10.1021/acs.jpcb.1c04459] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Broken symmetry density functional theory (BS-DFT) calculations on large models of Nature's water oxidizing complex (WOC) are used to investigate the electronic structure and associated magnetic interactions of this key intermediate state. The electronic origins of the ferromagnetic and antiferromagnetic couplings between neighboring Mn ions are investigated and illustrated by using corresponding orbital transformations. Protonation of the O4 and/or O6 atoms leads to large variation in the distribution of spin around the complex with associated changes in its magnetic resonance properties. Models for Sr2+ exchange and methanol addition indicate minor perturbations reflected in slightly altered spin projection coefficients for the Mn1 and Mn2 ions. These are shown to account for the observed changes observed experimentally via electron paramagnetic resonance methods and suggest a reinterpretation of the experimental findings. By comparison with experimental determinations, we show that the spin projections and resulting calculated 55Mn hyperfine couplings support the open cubane form of an oxo (O5)-hydroxo (O6) cluster in all cases with no need to invoke a closed cubane intermediate. The implications of these findings for the water oxidation mechanism are discussed.
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Affiliation(s)
- Thomas A Corry
- Department of Chemistry, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, U.K
| | - Patrick J O'Malley
- Department of Chemistry, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, U.K
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14
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Kaur D, Zhang Y, Reiss KM, Mandal M, Brudvig GW, Batista VS, Gunner MR. Proton exit pathways surrounding the oxygen evolving complex of photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148446. [PMID: 33964279 DOI: 10.1016/j.bbabio.2021.148446] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 04/29/2021] [Accepted: 05/01/2021] [Indexed: 12/17/2022]
Abstract
Photosystem II allows water to be the primary electron source for the photosynthetic electron transfer chain. Water is oxidized to dioxygen at the Oxygen Evolving Complex (OEC), a Mn4CaO5 inorganic core embedded on the lumenal side of PSII. Water-filled channels surrounding the OEC must bring in substrate water molecules, remove the product protons to the lumen, and may transport the product oxygen. Three water-filled channels, denoted large, narrow, and broad, extend from the OEC towards the aqueous surface more than 15 Å away. However, the role of each pathway in the transport in and out of the OEC is yet to be established. Here, we combine Molecular Dynamics (MD), Multi Conformation Continuum Electrostatics (MCCE) and Network Analysis to compare and contrast the three potential proton transfer paths. Hydrogen bond network analysis shows that near the OEC the waters are highly interconnected with similar free energy for hydronium at all locations. The paths diverge as they move towards the lumen. The water chain in the broad channel is better connected than in the narrow and large channels, where disruptions in the network are observed approximately 10 Å from the OEC. In addition, the barrier for hydronium translocation is lower in the broad channel. Thus, a proton released from any location on the OEC can access all paths, but the likely exit to the lumen passes through PsbO via the broad channel.
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Affiliation(s)
- Divya Kaur
- Department of Chemistry, The Graduate Center, City University of New York, New York, NY 10016, United States; Department of Physics, City College of New York, NY 10031, United States
| | - Yingying Zhang
- Department of Physics, City College of New York, NY 10031, United States; Department of Physics, The Graduate Center of the City University of New York, New York, NY 10016, United States
| | - Krystle M Reiss
- Department of Chemistry, Yale University, New Haven, CT 06520, United States
| | - Manoj Mandal
- Department of Physics, City College of New York, NY 10031, United States
| | - Gary W Brudvig
- Department of Chemistry, Yale University, New Haven, CT 06520, United States
| | - Victor S Batista
- Department of Chemistry, Yale University, New Haven, CT 06520, United States
| | - M R Gunner
- Department of Chemistry, The Graduate Center, City University of New York, New York, NY 10016, United States; Department of Physics, City College of New York, NY 10031, United States; Department of Physics, The Graduate Center of the City University of New York, New York, NY 10016, United States.
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15
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Zahariou G, Ioannidis N, Sanakis Y, Pantazis DA. Arrested Substrate Binding Resolves Catalytic Intermediates in Higher-Plant Water Oxidation. Angew Chem Int Ed Engl 2021; 60:3156-3162. [PMID: 33030775 PMCID: PMC7898718 DOI: 10.1002/anie.202012304] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Indexed: 12/05/2022]
Abstract
Among the intermediate catalytic steps of the water-oxidizing Mn4 CaO5 cluster of photosystem II (PSII), the final metastable S3 state is critically important because it binds one substrate and precedes O2 evolution. Herein, we combine X- and Q-band EPR experiments on native and methanol-treated PSII of Spinacia oleracea and show that methanol-treated PSII preparations of the S3 state correspond to a previously uncharacterized high-spin (S=6) species. This is confirmed as a major component also in intact photosynthetic membranes, coexisting with the previously known intermediate-spin conformation (S=3). The high-spin intermediate is assigned to a water-unbound form, with a MnIV3 subunit interacting ferromagnetically via anisotropic exchange with a coordinatively unsaturated MnIV ion. These results resolve and define the structural heterogeneity of the S3 state, providing constraints on the S3 to S4 transition, on substrate identity and delivery pathways, and on the mechanism of O-O bond formation.
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Affiliation(s)
- Georgia Zahariou
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos”Athens15310Greece
| | - Nikolaos Ioannidis
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos”Athens15310Greece
| | - Yiannis Sanakis
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos”Athens15310Greece
| | - Dimitrios A. Pantazis
- Max-Planck-Institut für KohlenforschungKaiser-Wilhelm-Platz 145470Mülheim an der RuhrGermany
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16
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Orio M, Pantazis DA. Successes, challenges, and opportunities for quantum chemistry in understanding metalloenzymes for solar fuels research. Chem Commun (Camb) 2021; 57:3952-3974. [DOI: 10.1039/d1cc00705j] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Overview of the rich and diverse contributions of quantum chemistry to understanding the structure and function of the biological archetypes for solar fuel research, photosystem II and hydrogenases.
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Affiliation(s)
- Maylis Orio
- Aix-Marseille Université
- CNRS
- iSm2
- Marseille
- France
| | - Dimitrios A. Pantazis
- Max-Planck-Institut für Kohlenforschung
- Kaiser-Wilhelm-Platz 1
- 45470 Mülheim an der Ruhr
- Germany
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17
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Marchiori DA, Debus RJ, Britt RD. Pulse EPR Spectroscopic Characterization of the S 3 State of the Oxygen-Evolving Complex of Photosystem II Isolated from Synechocystis. Biochemistry 2020; 59:4864-4872. [PMID: 33319991 DOI: 10.1021/acs.biochem.0c00880] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The S3 state is the last semi-stable state in the water splitting reaction that is catalyzed by the Mn4O5Ca cluster that makes up the oxygen-evolving complex (OEC) of photosystem II (PSII). Recent high-field/frequency (95 GHz) electron paramagnetic resonance (EPR) studies of PSII isolated from the thermophilic cyanobacterium Thermosynechococcus elongatus have found broadened signals induced by chemical modification of the S3 state. These signals are ascribed to an S3 form that contains a five-coordinate MnIV center bridged to a cuboidal MnIV3O4Ca unit. High-resolution X-ray free-electron laser studies of the S3 state have observed the OEC with all-octahedrally coordinated MnIV in what is described as an open cuboid-like cluster. No five-coordinate MnIV centers have been reported in these S3 state structures. Here, we report high-field/frequency (130 GHz) pulse EPR of the S3 state in Synechocystis sp. PCC 6803 PSII as isolated in the presence of glycerol. The S3 state of PSII from Synechocystis exhibits multiple broadened forms (≈69% of the total signal) similar to those seen in the chemically modified S3 centers from T. elongatus. Field-dependent ELDOR-detected nuclear magnetic resonance resolves two classes of 55Mn nuclear spin transitions: one class with small hyperfine couplings (|A| ≈ 1-7 MHz) and another with larger hyperfine couplings (|A| ≈ 100 MHz). These results are consistent with an all-MnIV4 open cubane structure of the S3 state and suggest that the broadened S3 signals arise from a perturbation of Mn4A and/or Mn3B, possibly induced by the presence of glycerol in the as-isolated Synechocystis PSII.
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Affiliation(s)
- David A Marchiori
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
| | - Richard J Debus
- Department of Biochemistry, University of California at Riverside, Riverside, California 92521, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States
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18
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Zahariou G, Ioannidis N, Sanakis Y, Pantazis DA. Arrested Substrate Binding Resolves Catalytic Intermediates in Higher‐Plant Water Oxidation. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202012304] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Georgia Zahariou
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos” Athens 15310 Greece
| | - Nikolaos Ioannidis
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos” Athens 15310 Greece
| | - Yiannis Sanakis
- Institute of Nanoscience & Nanotechnology, NCSR “Demokritos” Athens 15310 Greece
| | - Dimitrios A. Pantazis
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Germany
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19
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Ghosh I, Banerjee G, Reiss K, Kim CJ, Debus RJ, Batista VS, Brudvig GW. D1-S169A substitution of photosystem II reveals a novel S 2-state structure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1861:148301. [PMID: 32860756 DOI: 10.1016/j.bbabio.2020.148301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 08/18/2020] [Accepted: 08/22/2020] [Indexed: 10/23/2022]
Abstract
In photosystem II (PSII), photosynthetic water oxidation occurs at the O2-evolving complex (OEC), a tetramanganese-calcium cluster that cycles through light-induced redox intermediates (S0-S4) to produce oxygen from two substrate water molecules. The OEC is surrounded by a hydrogen-bonded network of amino-acid residues that plays a crucial role in proton transfer and substrate water delivery. Previously, we found that D1-S169 was crucial for water oxidation and its mutation to alanine perturbed the hydrogen-bonding network. In this study, we demonstrate that the activation energy for the S2 to S1 transition of D1-S169A PSII is higher than wild-type PSII with a ~1.7-2.7× slower rate of charge recombination with QA- relative to wild-type PSII. Arrhenius analysis of the decay kinetics shows an Ea of 5.87 ± 1.15 kcal mol-1 for decay back to the S1 state, compared to 0.80 ± 0.13 kcal mol-1 for the wild-type S2 state. In addition, we find that ammonia does not affect the S2-state EPR signal, indicating that ammonia does not bind to the Mn cluster in D1-S169A PSII. Finally, a QM/MM analysis indicates that an additional water molecule binds to the Mn4 ion in place of an oxo ligand O5 in the S2 state of D1-S169A PSII. The altered S2 state of D1-S169A PSII provides insight into the S2➔S3 state transition.
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Affiliation(s)
- Ipsita Ghosh
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
| | - Gourab Banerjee
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
| | - Krystle Reiss
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
| | - Christopher J Kim
- Department of Biochemistry, University of California, Riverside, CA 92521, USA
| | - Richard J Debus
- Department of Biochemistry, University of California, Riverside, CA 92521, USA.
| | - Victor S Batista
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA
| | - Gary W Brudvig
- Department of Chemistry, Yale University, New Haven, CT 06520-8107, USA.
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20
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Kim CJ, Debus RJ. Roles of D1-Glu189 and D1-Glu329 in O2 Formation by the Water-Splitting Mn4Ca Cluster in Photosystem II. Biochemistry 2020; 59:3902-3917. [DOI: 10.1021/acs.biochem.0c00541] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Christopher J. Kim
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Richard J. Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
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21
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Cox N, Pantazis DA, Lubitz W. Current Understanding of the Mechanism of Water Oxidation in Photosystem II and Its Relation to XFEL Data. Annu Rev Biochem 2020; 89:795-820. [DOI: 10.1146/annurev-biochem-011520-104801] [Citation(s) in RCA: 73] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The investigation of water oxidation in photosynthesis has remained a central topic in biochemical research for the last few decades due to the importance of this catalytic process for technological applications. Significant progress has been made following the 2011 report of a high-resolution X-ray crystallographic structure resolving the site of catalysis, a protein-bound Mn4CaOxcomplex, which passes through ≥5 intermediate states in the water-splitting cycle. Spectroscopic techniques complemented by quantum chemical calculations aided in understanding the electronic structure of the cofactor in all (detectable) states of the enzymatic process. Together with isotope labeling, these techniques also revealed the binding of the two substrate water molecules to the cluster. These results are described in the context of recent progress using X-ray crystallography with free-electron lasers on these intermediates. The data are instrumental for developing a model for the biological water oxidation cycle.
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Affiliation(s)
- Nicholas Cox
- Research School of Chemistry, The Australian National University, Canberra ACT 2601, Australia
| | | | - Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion, 45470 Mülheim an der Ruhr, Germany
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22
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Shimada Y, Kitajima-Ihara T, Nagao R, Noguchi T. Role of the O4 Channel in Photosynthetic Water Oxidation as Revealed by Fourier Transform Infrared Difference and Time-Resolved Infrared Analysis of the D1-S169A Mutant. J Phys Chem B 2020; 124:1470-1480. [DOI: 10.1021/acs.jpcb.9b11946] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Yuichiro Shimada
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Tomomi Kitajima-Ihara
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Ryo Nagao
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Takumi Noguchi
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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23
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de Lichtenberg C, Messinger J. Substrate water exchange in the S2 state of photosystem II is dependent on the conformation of the Mn4Ca cluster. Phys Chem Chem Phys 2020; 22:12894-12908. [DOI: 10.1039/d0cp01380c] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The structural flexibility of the Mn4Ca cluster in photosystem II supports the exchange of the central O5 bridge.
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24
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Lubitz W, Chrysina M, Cox N. Water oxidation in photosystem II. PHOTOSYNTHESIS RESEARCH 2019; 142:105-125. [PMID: 31187340 PMCID: PMC6763417 DOI: 10.1007/s11120-019-00648-3] [Citation(s) in RCA: 120] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Accepted: 05/20/2019] [Indexed: 05/18/2023]
Abstract
Biological water oxidation, performed by a single enzyme, photosystem II, is a central research topic not only in understanding the photosynthetic apparatus but also for the development of water splitting catalysts for technological applications. Great progress has been made in this endeavor following the report of a high-resolution X-ray crystallographic structure in 2011 resolving the cofactor site (Umena et al. in Nature 473:55-60, 2011), a tetra-manganese calcium complex. The electronic properties of the protein-bound water oxidizing Mn4OxCa complex are crucial to understand its catalytic activity. These properties include: its redox state(s) which are tuned by the protein matrix, the distribution of the manganese valence and spin states and the complex interactions that exist between the four manganese ions. In this short review we describe how magnetic resonance techniques, particularly EPR, complemented by quantum chemical calculations, have played an important role in understanding the electronic structure of the cofactor. Together with isotope labeling, these techniques have also been instrumental in deciphering the binding of the two substrate water molecules to the cluster. These results are briefly described in the context of the history of biological water oxidation with special emphasis on recent work using time resolved X-ray diffraction with free electron lasers. It is shown that these data are instrumental for developing a model of the biological water oxidation cycle.
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Affiliation(s)
- Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion, Mülheim/Ruhr, Germany
| | - Maria Chrysina
- Max-Planck-Institut für Chemische Energiekonversion, Mülheim/Ruhr, Germany
| | - Nicholas Cox
- Research School of Chemistry, The Australian National University, Canberra, Australia
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25
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Corry TA, O'Malley PJ. Proton Isomers Rationalize the High- and Low-Spin Forms of the S 2 State Intermediate in the Water-Oxidizing Reaction of Photosystem II. J Phys Chem Lett 2019; 10:5226-5230. [PMID: 31429574 DOI: 10.1021/acs.jpclett.9b01372] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A new paradigm for the high- and low-spin forms of the S2 state of nature's water-oxidizing complex in Photosystem II is found. Broken symmetry density functional theory calculations combined with Heisenberg-Dirac-van Vleck spin ladder calculations show that an open cubane form of the water-oxidizing complex changes from a low-spin, S = 1/2, to a high-spin, S = 5/2, form on protonation of the bridging O4 oxo. We show that such models are fully compatible with structural determinations of the S2 state by X-ray free-electron laser crystallography and extended X-ray absorption fine structure and provide a clear rationale for the effect of various treatments on the relative populations of each form observed experimentally in electron paramagnetic resonance studies.
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Affiliation(s)
- Thomas A Corry
- School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom
| | - Patrick J O'Malley
- School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom
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26
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Five-coordinate Mn IV intermediate in the activation of nature's water splitting cofactor. Proc Natl Acad Sci U S A 2019; 116:16841-16846. [PMID: 31391299 DOI: 10.1073/pnas.1817526116] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nature's water splitting cofactor passes through a series of catalytic intermediates (S0-S4) before O-O bond formation and O2 release. In the second last transition (S2 to S3) cofactor oxidation is coupled to water molecule binding to Mn1. It is this activated, water-enriched all MnIV form of the cofactor that goes on to form the O-O bond, after the next light-induced oxidation to S4 How cofactor activation proceeds remains an open question. Here, we report a so far not described intermediate (S3') in which cofactor oxidation has occurred without water insertion. This intermediate can be trapped in a significant fraction of centers (>50%) in (i) chemical-modified cofactors in which Ca2+ is exchanged with Sr2+; the Mn4O5Sr cofactor remains active, but the S2-S3 and S3-S0 transitions are slower than for the Mn4O5Ca cofactor; and (ii) upon addition of 3% vol/vol methanol; methanol is thought to act as a substrate water analog. The S3' electron paramagnetic resonance (EPR) signal is significantly broader than the untreated S3 signal (2.5 T vs. 1.5 T), indicating the cofactor still contains a 5-coordinate Mn ion, as seen in the preceding S2 state. Magnetic double resonance data extend these findings revealing the electronic connectivity of the S3' cofactor is similar to the high spin form of the preceding S2 state, which contains a cuboidal Mn3O4Ca unit tethered to an external, 5-coordinate Mn ion (Mn4). These results demonstrate that cofactor oxidation regulates water molecule insertion via binding to Mn4. The interaction of ammonia with the cofactor is also discussed.
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27
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Krewald V, Neese F, Pantazis DA. Implications of structural heterogeneity for the electronic structure of the final oxygen-evolving intermediate in photosystem II. J Inorg Biochem 2019; 199:110797. [PMID: 31404888 DOI: 10.1016/j.jinorgbio.2019.110797] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/18/2019] [Accepted: 08/01/2019] [Indexed: 10/26/2022]
Abstract
Heterogeneity in intermediate catalytic states of the oxygen-evolving complex (OEC) of Photosystem II is known from a wide range of experimental and theoretical data, but its potential implications for the mechanism of water oxidation remain unexplored. We delineate the consequences of structural heterogeneity for the final step of the catalytic cycle by tracing the evolution of three spectroscopically relevant and structurally distinct components of the last metastable S3 state to the transient O2-evolving S4 state of the OEC. Using quantum chemical calculations, we show that each S3 isomer leads to a different electronic structure formulation for the active S4 state. Crucially, in addition to previously hypothesized Mn(IV)-oxyl species, we establish for the first time, how a genuine Mn(V)-oxo can be obtained in the catalytically active S4 state: this takes the form of a five-coordinate and locally high-spin (SMn = 1) Mn(V) site. This formulation for the S4 state evolves naturally from a preceding S3-state structural intermediate that contains a quasi-trigonal-bipyramidal Mn(IV) ion. The results strongly suggest that water binding in the S3 state is not prerequisite for reaching the oxygen-evolving S4 state of the complex, supporting the notion that both substrates are preloaded at the beginning of the catalytic cycle. This scenario allows true four-electron metal-centered hole accumulation to precede OO bond formation and hence the latter can proceed via a genuine even-electron mechanism. This can occur as intramolecular nucleophilic coupling of two oxo units synchronously with the binding of a water substrate for the next catalytic cycle.
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Affiliation(s)
- Vera Krewald
- Theoretische Chemie, Fachbereich Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 4, 64287 Darmstadt, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.
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28
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Kim CJ, Debus RJ. One of the Substrate Waters for O2 Formation in Photosystem II Is Provided by the Water-Splitting Mn4CaO5 Cluster’s Ca2+ Ion. Biochemistry 2019; 58:3185-3192. [DOI: 10.1021/acs.biochem.9b00418] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Christopher J. Kim
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Richard J. Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
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29
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The S3 State of the Oxygen-Evolving Complex: Overview of Spectroscopy and XFEL Crystallography with a Critical Evaluation of Early-Onset Models for O–O Bond Formation. INORGANICS 2019. [DOI: 10.3390/inorganics7040055] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The catalytic cycle of the oxygen-evolving complex (OEC) of photosystem II (PSII) comprises five intermediate states Si (i = 0–4), from the most reduced S0 state to the most oxidized S4, which spontaneously evolves dioxygen. The precise geometric and electronic structure of the Si states, and hence the mechanism of O–O bond formation in the OEC, remain under investigation, particularly for the final steps of the catalytic cycle. Recent advances in protein crystallography based on X-ray free-electron lasers (XFELs) have produced new structural models for the S3 state, which indicate that two of the oxygen atoms of the inorganic Mn4CaO6 core of the OEC are in very close proximity. This has been interpreted as possible evidence for “early-onset” O–O bond formation in the S3 state, as opposed to the more widely accepted view that the O–O bond is formed in the final state of the cycle, S4. Peroxo or superoxo formation in S3 has received partial support from computational studies. Here, a brief overview is provided of spectroscopic information, recent crystallographic results, and computational models for the S3 state. Emphasis is placed on computational S3 models that involve O–O formation, which are discussed with respect to their agreement with structural information, experimental evidence from various spectroscopic studies, and substrate exchange kinetics. Despite seemingly better agreement with some of the available crystallographic interpretations for the S3 state, models that implicate early-onset O–O bond formation are hard to reconcile with the complete line of experimental evidence, especially with X-ray absorption, X-ray emission, and magnetic resonance spectroscopic observations. Specifically with respect to quantum chemical studies, the inconclusive energetics for the possible isoforms of S3 is an acute problem that is probably beyond the capabilities of standard density functional theory.
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30
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Chrysina M, de Mendonça Silva JC, Zahariou G, Pantazis DA, Ioannidis N. Proton Translocation via Tautomerization of Asn298 During the S 2-S 3 State Transition in the Oxygen-Evolving Complex of Photosystem II. J Phys Chem B 2019; 123:3068-3078. [PMID: 30888175 PMCID: PMC6727346 DOI: 10.1021/acs.jpcb.9b02317] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
![]()
In biological water oxidation, a
redox-active tyrosine residue
(D1-Tyr161 or YZ) mediates electron transfer between the
Mn4CaO5 cluster of the oxygen-evolving complex
and the charge-separation site of photosystem II (PSII), driving the
cluster through progressively higher oxidation states Si (i = 0–4). In contrast to
lower S-states (S0, S1), in higher S-states
(S2, S3) of the Mn4CaO5 cluster, YZ cannot be oxidized at cryogenic temperatures
due to the accumulation of positive charge in the S1 →
S2 transition. However, oxidation of YZ by illumination
of S2 at 77–190 K followed by rapid freezing and
charge recombination between YZ• and
the plastoquinone radical QA•– allows trapping of an S2 variant, the so-called S2trapped state (S2t), that
is capable of forming YZ• at cryogenic
temperature. To identify the differences between the S2 and S2t states, we used the S2tYZ• intermediate as a probe for
the S2t state and followed the S2tYZ•/QA•– recombination kinetics at 10 K using time-resolved electron paramagnetic
resonance spectroscopy in H2O and D2O. The results
show that while S2tYZ•/QA•– recombination can be described
as pure electron transfer occurring in the Marcus inverted region,
the S2t → S2 reversion depends
on proton rearrangement and exhibits a strong kinetic isotope effect.
This suggests that YZ oxidation in the S2t state is facilitated by favorable proton redistribution in
the vicinity of YZ, most likely within the hydrogen-bonded
YZ–His190–Asn298 triad. Computational models
show that tautomerization of Asn298 to its imidic acid form enables
proton translocation to an adjacent asparagine-rich cavity of water
molecules that functions as a proton reservoir and can further participate
in proton egress to the lumen.
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Affiliation(s)
- Maria Chrysina
- Institute of Nanoscience & Nanotechnology , NCSR "Demokritos" , Athens 15310 , Greece.,Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , 45470 Mülheim an der Ruhr , Germany
| | - Juliana Cecília de Mendonça Silva
- Max-Planck-Institut für Chemische Energiekonversion , Stiftstr. 34-36 , 45470 Mülheim an der Ruhr , Germany.,Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1 , 45470 Mülheim an der Ruhr , Germany
| | - Georgia Zahariou
- Institute of Nanoscience & Nanotechnology , NCSR "Demokritos" , Athens 15310 , Greece
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1 , 45470 Mülheim an der Ruhr , Germany
| | - Nikolaos Ioannidis
- Institute of Nanoscience & Nanotechnology , NCSR "Demokritos" , Athens 15310 , Greece
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31
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Abstract
The influence of the environment on the functionality of the oxygen-evolving complex (OEC) of photosystem II has long been a subject of great interest. In particular, various water channels, which could serve as pathways for substrate water diffusion, or proton translocation, are thought to be critical to catalytic performance of the OEC. Here, we address the dynamical nature of hydrogen bonding along the water channels by performing molecular dynamics (MD) simulations of the OEC and its surrounding protein environment in the S1 and S2 states. Through the eigenvector centrality (EC) analysis, we are able to determine the characteristics of the water network and assign potential functions to the major channels, namely that the narrow and broad channels are likely candidates for proton/water transport, while the large channel may serve as a path for larger ions such as chloride and manganese thought to be essential during PSII assembly.
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Ghosh I, Banerjee G, Kim CJ, Reiss K, Batista VS, Debus RJ, Brudvig GW. D1-S169A Substitution of Photosystem II Perturbs Water Oxidation. Biochemistry 2019; 58:1379-1387. [DOI: 10.1021/acs.biochem.8b01184] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Ipsita Ghosh
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Gourab Banerjee
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Christopher J. Kim
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Krystle Reiss
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Victor S. Batista
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Richard J. Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Gary W. Brudvig
- Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
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Affiliation(s)
- Dimitrios A. Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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Yata H, Noguchi T. Mechanism of Methanol Inhibition of Photosynthetic Water Oxidation As Studied by Fourier Transform Infrared Difference and Time-Resolved Infrared Spectroscopies. Biochemistry 2018; 57:4803-4815. [DOI: 10.1021/acs.biochem.8b00596] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Haruna Yata
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Takumi Noguchi
- Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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35
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Kim CJ, Bao H, Burnap RL, Debus RJ. Impact of D1-V185 on the Water Molecules That Facilitate O2 Formation by the Catalytic Mn4CaO5 Cluster in Photosystem II. Biochemistry 2018; 57:4299-4311. [DOI: 10.1021/acs.biochem.8b00630] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Christopher J. Kim
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Han Bao
- Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma 74078, United States
| | - Robert L. Burnap
- Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma 74078, United States
| | - Richard J. Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
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36
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Marchiori DA, Oyala PH, Debus RJ, Stich TA, Britt RD. Structural Effects of Ammonia Binding to the Mn4CaO5 Cluster of Photosystem II. J Phys Chem B 2018; 122:1588-1599. [DOI: 10.1021/acs.jpcb.7b11101] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- David A. Marchiori
- Department
of Chemistry, University of California, Davis, Davis, California 95616, United States
| | - Paul H. Oyala
- Department
of Chemistry, University of California, Davis, Davis, California 95616, United States
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Richard J. Debus
- Department
of Biochemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Troy A. Stich
- Department
of Chemistry, University of California, Davis, Davis, California 95616, United States
| | - R. David Britt
- Department
of Chemistry, University of California, Davis, Davis, California 95616, United States
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37
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Banerjee G, Ghosh I, Kim CJ, Debus RJ, Brudvig GW. Substitution of the D1-Asn 87 site in photosystem II of cyanobacteria mimics the chloride-binding characteristics of spinach photosystem II. J Biol Chem 2017; 293:2487-2497. [PMID: 29263091 DOI: 10.1074/jbc.m117.813170] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Revised: 12/19/2017] [Indexed: 11/06/2022] Open
Abstract
Photoinduced water oxidation at the O2-evolving complex (OEC) of photosystem II (PSII) is a complex process involving a tetramanganese-calcium cluster that is surrounded by a hydrogen-bonded network of water molecules, chloride ions, and amino acid residues. Although the structure of the OEC has remained conserved over eons of evolution, significant differences in the chloride-binding characteristics exist between cyanobacteria and higher plants. An analysis of amino acid residues in and around the OEC has identified residue 87 in the D1 subunit as the only significant difference between PSII in cyanobacteria and higher plants. We substituted the D1-Asn87 residue in the cyanobacterium Synechocystis sp. PCC 6803 (wildtype) with alanine, present in higher plants, or with aspartic acid. We studied PSII core complexes purified from D1-N87A and D1-N87D variant strains to probe the function of the D1-Asn87 residue in the water-oxidation mechanism. EPR spectra of the S2 state and flash-induced FTIR spectra of both D1-N87A and D1-N87D PSII core complexes exhibited characteristics similar to those of wildtype Synechocystis PSII core complexes. However, flash-induced O2-evolution studies revealed a decreased cycling efficiency of the D1-N87D variant, whereas the cycling efficiency of the D1-N87A PSII variant was similar to that of wildtype PSII. Steady-state O2-evolution activity assays revealed that substitution of the D1 residue at position 87 with alanine perturbs the chloride-binding site in the proton-exit channel. These findings provide new insight into the role of the D1-Asn87 site in the water-oxidation mechanism and explain the difference in the chloride-binding properties of cyanobacterial and higher-plant PSII.
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Affiliation(s)
- Gourab Banerjee
- From the Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107 and
| | - Ipsita Ghosh
- From the Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107 and
| | - Christopher J Kim
- the Department of Biochemistry, University of California, Riverside, California 92521
| | - Richard J Debus
- the Department of Biochemistry, University of California, Riverside, California 92521
| | - Gary W Brudvig
- From the Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107 and
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38
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Wang J, Askerka M, Brudvig GW, Batista VS. Crystallographic Data Support the Carousel Mechanism of Water Supply to the Oxygen-Evolving Complex of Photosystem II. ACS ENERGY LETTERS 2017; 2:2299-2306. [PMID: 29057331 PMCID: PMC5644713 DOI: 10.1021/acsenergylett.7b00750] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 09/07/2017] [Indexed: 05/21/2023]
Abstract
Photosystem II (PSII) oxidizes water to produce oxygen through a four-step photocatalytic cycle. Understanding PSII structure-function relations is important for the development of biomimetic photocatalytic systems. The quantum mechanics/molecular mechanics (QM/MM) analysis of substrate water binding to the oxygen-evolving complex (OEC) has suggested a rearrangement of water ligands in a carousel mechanism around a key Mn center. Here, we find that the most recently reported X-ray free-electron laser (XFEL) crystallographic data obtained for the dark-stable S1 state and the doubly flashed S3 state at 2.25 Å resolution support the carousel mechanism. The features in the XFEL data and QM/MM model-simulated difference Fourier maps suggest that water displacement may occur from the so-called "narrow" channel, resulting in binding of a new water molecule to the OEC, and thus provide new insights into the nature of rearrangements of water ligands along the catalytic cycle before O=O bond formation.
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Affiliation(s)
- Jimin Wang
- Department
of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, United States
| | - Mikhail Askerka
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Gary W. Brudvig
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
| | - Victor S. Batista
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520-8107, United States
- E-mail:
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39
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Guo Y, Li H, He LL, Zhao DX, Gong LD, Yang ZZ. Theoretical reflections on the structural polymorphism of the oxygen-evolving complex in the S2 state and the correlations to substrate water exchange and water oxidation mechanism in photosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2017; 1858:833-846. [DOI: 10.1016/j.bbabio.2017.08.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 06/25/2017] [Accepted: 08/02/2017] [Indexed: 11/29/2022]
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40
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Retegan M, Pantazis DA. Differences in the Active Site of Water Oxidation among Photosynthetic Organisms. J Am Chem Soc 2017; 139:14340-14343. [PMID: 28948784 DOI: 10.1021/jacs.7b06351] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The site of biological water oxidation is highly conserved across photosynthetic organisms, but differences of unidentified structural and electronic origin exist between taxonomically discrete clades, revealed by distinct spectroscopic signatures of the oxygen-evolving Mn4CaO5 cluster and variations in active-site accessibility. Comparison of atomistic models of a native cyanobacterial form (Thermosynechococcus vulcanus) and a chimeric spinach-like form of photosystem II allows us to identify the precise atomic-level differences between organisms in the vicinity of the manganese cluster. Substitution of cyanobacterial D1-Asn87 by higher-plant D1-Ala87 is the principal discriminating feature: it drastically rearranges a network of proximal hydrogen bonds, modifying the local architecture of a water channel and the interaction of second coordination shell residues with the manganese cluster. The two variants explain species-dependent differences in spectroscopic properties and in the interaction of substrate analogues with the oxygen-evolving complex, enabling assignment of a substrate delivery channel to the active site.
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Affiliation(s)
- Marius Retegan
- European Synchrotron Radiation Facility , 71 Avenue des Martyrs, 38000 Grenoble, France
| | - Dimitrios A Pantazis
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
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41
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Kim CJ, Debus RJ. Evidence from FTIR Difference Spectroscopy That a Substrate H2O Molecule for O2 Formation in Photosystem II Is Provided by the Ca Ion of the Catalytic Mn4CaO5 Cluster. Biochemistry 2017; 56:2558-2570. [DOI: 10.1021/acs.biochem.6b01278] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Christopher J. Kim
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Richard J. Debus
- Department of Biochemistry, University of California, Riverside, California 92521, United States
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42
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Paul S, Cox N, Pantazis DA. What Can We Learn from a Biomimetic Model of Nature’s Oxygen-Evolving Complex? Inorg Chem 2017; 56:3875-3888. [DOI: 10.1021/acs.inorgchem.6b02777] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Satadal Paul
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, 45470 Mülheim an der Ruhr, Germany
| | - Nicholas Cox
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, 45470 Mülheim an der Ruhr, Germany
- Research School of Chemistry, Australian National University, Canberra ACT 2601, Australia
| | - Dimitrios A. Pantazis
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34−36, 45470 Mülheim an der Ruhr, Germany
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43
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Nagashima H, Mino H. Location of Methanol on the S 2 State Mn Cluster in Photosystem II Studied by Proton Matrix Electron Nuclear Double Resonance. J Phys Chem Lett 2017; 8:621-625. [PMID: 28099021 DOI: 10.1021/acs.jpclett.7b00110] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Proton matrix electron nuclear double resonance (ENDOR) spectroscopy was performed to specify the location of the methanol molecule near the manganese cluster in photosystem II. Comparison of the ENDOR spectra in the presence of CH3OH and CD3OH revealed two pairs of hyperfine couplings, 1.2 MHz for A⊥ and 2.5 MHz for A//, arising from the methyl group in methanol. On the basis of the crystal structure, the possible location of methanol close to the manganese cluster was discussed.
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Affiliation(s)
- Hiroki Nagashima
- Division of Material Science, Graduate School of Science, Nagoya University , Furo-cho, Chikusa-ku, 464-8602 Nagoya, Aichi, Japan
| | - Hiroyuki Mino
- Division of Material Science, Graduate School of Science, Nagoya University , Furo-cho, Chikusa-ku, 464-8602 Nagoya, Aichi, Japan
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44
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Guo Y, He LL, Zhao DX, Gong LD, Liu C, Yang ZZ. How does ammonia bind to the oxygen-evolving complex in the S2state of photosynthetic water oxidation? Theoretical support and implications for the W1 substitution mechanism. Phys Chem Chem Phys 2016; 18:31551-31565. [DOI: 10.1039/c6cp05725j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The mechanistic study shows that NH3substitutes W1 rather than O5 of the OEC in the S2state and leaves in the S4′ state.
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Affiliation(s)
- Yu Guo
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
| | - Lan-Lan He
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
| | - Dong-Xia Zhao
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
| | - Li-Dong Gong
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
| | - Cui Liu
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
| | - Zhong-Zhi Yang
- School of Chemistry and Chemical Engineering
- Liaoning Normal University
- Dalian 116029
- People's Republic of China
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