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Pantazis DA. Clues to how water splits during photosynthesis. Nature 2023; 617:468-469. [PMID: 37138059 DOI: 10.1038/d41586-023-01388-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
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2
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Greife P, Schönborn M, Capone M, Assunção R, Narzi D, Guidoni L, Dau H. The electron-proton bottleneck of photosynthetic oxygen evolution. Nature 2023; 617:623-628. [PMID: 37138082 DOI: 10.1038/s41586-023-06008-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Accepted: 03/23/2023] [Indexed: 05/05/2023]
Abstract
Photosynthesis fuels life on Earth by storing solar energy in chemical form. Today's oxygen-rich atmosphere has resulted from the splitting of water at the protein-bound manganese cluster of photosystem II during photosynthesis. Formation of molecular oxygen starts from a state with four accumulated electron holes, the S4 state-which was postulated half a century ago1 and remains largely uncharacterized. Here we resolve this key stage of photosynthetic O2 formation and its crucial mechanistic role. We tracked 230,000 excitation cycles of dark-adapted photosystems with microsecond infrared spectroscopy. Combining these results with computational chemistry reveals that a crucial proton vacancy is initally created through gated sidechain deprotonation. Subsequently, a reactive oxygen radical is formed in a single-electron, multi-proton transfer event. This is the slowest step in photosynthetic O2 formation, with a moderate energetic barrier and marked entropic slowdown. We identify the S4 state as the oxygen-radical state; its formation is followed by fast O-O bonding and O2 release. In conjunction with previous breakthroughs in experimental and computational investigations, a compelling atomistic picture of photosynthetic O2 formation emerges. Our results provide insights into a biological process that is likely to have occurred unchanged for the past three billion years, which we expect to support the knowledge-based design of artificial water-splitting systems.
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Affiliation(s)
- Paul Greife
- Department of Physics, Freie Universität, Berlin, Germany
| | | | - Matteo Capone
- Department of Information Engineering, Computer Science and Mathematics, University of L'Aquila, L'Aquila, Italy
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy
| | | | - Daniele Narzi
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy
| | - Leonardo Guidoni
- Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy.
| | - Holger Dau
- Department of Physics, Freie Universität, Berlin, Germany.
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Evidence for the Mn4-Yz Magnetic Interaction in Ca2+- depleted Photosystem II. Polyhedron 2021. [DOI: 10.1016/j.poly.2021.115335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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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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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
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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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Affiliation(s)
- Dimitrios A. Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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Beal NJ, Corry TA, O'Malley PJ. A Comparison of Experimental and Broken Symmetry Density Functional Theory (BS-DFT) Calculated Electron Paramagnetic Resonance (EPR) Parameters for Intermediates Involved in the S 2 to S 3 State Transition of Nature's Oxygen Evolving Complex. J Phys Chem B 2018; 122:1394-1407. [PMID: 29300480 DOI: 10.1021/acs.jpcb.7b10843] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A broken symmetry density functional theory (BS-DFT) magnetic analysis of the S2, S2YZ•, and S3 states of Nature's oxygen evolving complex is performed for both the native Ca and Sr substituted forms. Good agreement with experiment is observed between the tyrosyl calculated g-tensor and 1H hyperfine couplings for the native Ca form. Changes in the hydrogen bonding environment of the tyrosyl radical in S2YZ• caused by Sr substitution lead to notable changes in the calculated g-tensor of the tyrosyl radical. Comparison of calculated and experimental 55Mn hyperfine couplings for the S3 state presently favors an open cubane form of the complex with an additional OH ligand coordinating to MnD. In Ca models, this additional ligation can arise by closed-cubane form deprotonation of the Ca ligand W3 in the S2YZ• state accompanied by spontaneous movement to the vacant Mn coordination site or by addition of an external OH group. For the Sr form, no spontaneous movement of W3 to the vacant Mn coordination site is observed in contrast to the native Ca form, a difference which may lead to the reduced catalytic activity of the Sr substituted form. BS-DFT studies on peroxo models of S3 as indicated by a recent X-ray free electron laser (XFEL) crystallography study give rise to a structural model compatible with experimental data and an S = 3 ground state compatible with EPR studies.
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Affiliation(s)
- Nathan J Beal
- School of Chemistry, The University of Manchester , Manchester M13 9PL, U.K
| | - Thomas A Corry
- School of Chemistry, The University of Manchester , Manchester M13 9PL, U.K
| | - Patrick J O'Malley
- School of Chemistry, The University of Manchester , Manchester M13 9PL, U.K
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Beal NJ, Corry TA, O’Malley PJ. Comparison between Experimental and Broken Symmetry Density Functional Theory (BS-DFT) Calculated Electron Paramagnetic Resonance (EPR) Parameters of the S2 State of the Oxygen-Evolving Complex of Photosystem II in Its Native (Calcium) and Strontium-Substituted Form. J Phys Chem B 2017; 121:11273-11283. [DOI: 10.1021/acs.jpcb.7b09498] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Nathan J. Beal
- School of Chemistry, The University of Manchester, Manchester M13 9PL, United Kingdom
| | - 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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Zahariou G, Ioannidis N. Theoretical study of the EPR spectrum of the S 3TyrZ • metalloradical intermediate state of the O 2-evolving complex of photosystem II. PHOTOSYNTHESIS RESEARCH 2016; 130:417-426. [PMID: 27166961 DOI: 10.1007/s11120-016-0274-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Accepted: 05/03/2016] [Indexed: 05/21/2023]
Abstract
The intermediates trapped during the transitions between the consecutive S-states of the oxygen-evolving complex (OEC) of photosystem II (PSII) contain the free radical TyrZ• interacting magnetically with the Mn-cluster (Mn4Ca). In this paper, we present a theoretical study of the EPR spectrum of the S3TyrZ• metalloradical intermediate state, which has been recently detected in MeOH-containing PSII preparations. For this analysis, we use two different approximations: the first, simpler one, is the point-dipole approach, where the two interacting spins are the S = 1/2 of TyrZ• and the ground spin state of S = 3 of the OEC being in the S3 state. The second approximation is based on previous proposals indicating that the ground spin state (S G = 3) of the S3 state arises from an antiferromagnetic exchange coupling between the S = 9/2 of the Mn(IV)3CaO4 and the S = 3/2 of the external Mn(IV) of the OEC. Under the above assumption, the second approximation involves three interacting spins, denoted S A(Mn(IV)3Ca) = 9/2, S B(Mn(IV)) = 3/2 and S C(TyrZ•) = 1/2. Accordingly, the tyrosine radical is exposed to dipolar interactions with both fragments of the OEC, while an antiferromagnetic exchange coupling within the "3 + 1" structural motif of the OEC is also considered. By application of the first-point-dipole approach, the inter-spin distance that simulates the experimental spectrum is not consistent with the theoretical models that were recently reported for the OEC in the S3 state. Instead, the recent models are consistent with the results of the analysis that is performed by using the second, more detailed, approach.
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Affiliation(s)
- Georgia Zahariou
- Institute of Nanoscience & Nanotechnology, NCSR "Demokritos", 15310, Athens, Greece.
| | - Nikolaos Ioannidis
- Institute of Nanoscience & Nanotechnology, NCSR "Demokritos", 15310, Athens, Greece
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Retegan M, Pantazis DA. Interaction of methanol with the oxygen-evolving complex: atomistic models, channel identification, species dependence, and mechanistic implications. Chem Sci 2016; 7:6463-6476. [PMID: 28451104 PMCID: PMC5355959 DOI: 10.1039/c6sc02340a] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Accepted: 06/28/2016] [Indexed: 12/29/2022] Open
Abstract
Methanol has long being used as a substrate analogue to probe access pathways and investigate water delivery at the oxygen-evolving complex (OEC) of photosystem-II. In this contribution we study the interaction of methanol with the OEC by assembling available spectroscopic data into a quantum mechanical treatment that takes into account the local channel architecture of the active site. The effect on the magnetic energy levels of the Mn4Ca cluster in the S2 state of the catalytic cycle can be explained equally well by two models that involve either methanol binding to the calcium ion of the cluster, or a second-sphere interaction in the vicinity of the "dangler" Mn4 ion. However, consideration of the latest 13C hyperfine interaction data shows that only one model is fully consistent with experiment. In contrast to previous hypotheses, methanol is not a direct ligand to the OEC, but is situated at the end-point of a water channel associated with the O4 bridge. Its effect on magnetic properties of plant PS-II results from disruption of hydrogen bonding between O4 and proximal channel water molecules, thus enhancing superexchange (antiferromagnetic coupling) between the Mn3 and Mn4 ions. The same interaction mode applies to the dark-stable S1 state and possibly to all other states of the complex. Comparison of protein sequences from cyanobacteria and plants reveals a channel-altering substitution (D1-Asn87 versus D1-Ala87) in the proximity of the methanol binding pocket, explaining the species-dependence of the methanol effect. The water channel established as the methanol access pathway is the same that delivers ammonia to the Mn4 ion, supporting the notion that this is the only directly solvent-accessible manganese site of the OEC. The results support the pivot mechanism for water binding at a component of the S3 state and would be consistent with partial inhibition of water delivery by methanol. Mechanistic implications for enzymatic regulation and catalytic progression are discussed.
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Affiliation(s)
- Marius Retegan
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , 45470 Mülheim an der Ruhr , Germany .
| | - Dimitrios A Pantazis
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36 , 45470 Mülheim an der Ruhr , Germany .
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