1
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Kumar A, Thompson B, Gautam R, Tomat E, Huxter V. Temperature-Dependent Spin-Driven Dimerization Determines the Ultrafast Dynamics of a Copper(II)-Bound Tripyrrindione Radical. J Phys Chem Lett 2023; 14:11268-11273. [PMID: 38060441 DOI: 10.1021/acs.jpclett.3c02726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
Radicals and other open-shell molecules play a central role in chemical transformations and redox chemistry. While radicals are often highly reactive, stable radical systems are desirable for a range of potential applications, ranging from materials chemistry and catalysis to spintronics and quantum information. Here we investigate the ultrafast properties of a stable radical system with temperature-dependent spin-tunable properties. This radical complex, Cu(II) hexaethyl tripyrrin-1,14-dione, accommodates unpaired electrons localized on both the copper metal center and the tripyrrolic ligand. The unusual combination of two unpaired electrons and high stability in this radical molecule enable switchable temperature-dependent spin coupling. Two-dimensional electronic spectroscopy measurements of Cu(II) hexaethyl tripyrrin-1,14-dione were collected at room temperature and at 77 K. At room temperature, the molecules are present as monomers and have short picosecond lifetimes. At 77 K, the molecules are present in a dimer form mediated by ferromagnetic and antiferromagnetic coupling. This reversible spin-driven dimerization changes the optical properties of the system, generating long-lived excitonic states.
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Affiliation(s)
- Anshu Kumar
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
| | - Benjamin Thompson
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
- Department of Optical Sciences, University of Arizona, Tucson, Arizona 85721, United States
| | - Ritika Gautam
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Elisa Tomat
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Vanessa Huxter
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
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2
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Saito K, Nishio S, Ishikita H. Interplay of two low-barrier hydrogen bonds in long-distance proton-coupled electron transfer for water oxidation. PNAS NEXUS 2023; 2:pgad423. [PMID: 38130665 PMCID: PMC10733176 DOI: 10.1093/pnasnexus/pgad423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 11/20/2023] [Indexed: 12/23/2023]
Abstract
D1-Tyr161 (TyrZ) forms a low-barrier H-bond with D1-His190 and functions as a redox-active group in photosystem II. When oxidized to the radical form (TyrZ-O•), it accepts an electron from the oxygen-evolving Mn4CaO5 cluster, facilitating an increase in the oxidation state (Sn; n = 0-3). In this study, we investigated the mechanism of how TyrZ-O• drives proton-coupled electron transfer during the S2 to S3 transition using a quantum mechanical/molecular mechanical approach. In response to TyrZ-O• formation and subsequent loss of the low-barrier H-bond, the ligand water molecule at the Ca2+ site (W4) reorients away from TyrZ and donates an H-bond to D1-Glu189 at Mn4 of Mn4CaO5 together with an adjacent water molecule. The H-bond donation to the Mn4CaO5 cluster triggers the release of the proton from the lowest pKa site (W1 at Mn4) along the W1…D1-Asp61 low-barrier H-bond, leading to protonation of D1-Asp61. The interplay of the two low-barrier H-bonds, involving the Ca2+ interface and forming the extended Grotthuss-like network [TyrZ…D1-His190]-[Mn4CaO5]-[W1…D1-Asp61], rather than the direct electrostatic interaction, is likely a basis of the apparent long-distance interaction (11.4 Å) between TyrZ-O• formation and D1-Asp61 protonation.
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Affiliation(s)
- Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan
| | - Shunya Nishio
- Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan
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3
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Bhattacharjee S, Neese F, Pantazis DA. Triplet states in the reaction center of Photosystem II. Chem Sci 2023; 14:9503-9516. [PMID: 37712047 PMCID: PMC10498673 DOI: 10.1039/d3sc02985a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2023] [Accepted: 08/16/2023] [Indexed: 09/16/2023] Open
Abstract
In oxygenic photosynthesis sunlight is harvested and funneled as excitation energy into the reaction center (RC) of Photosystem II (PSII), the site of primary charge separation that initiates the photosynthetic electron transfer chain. The chlorophyll ChlD1 pigment of the RC is the primary electron donor, forming a charge-separated radical pair with the vicinal pheophytin PheoD1 (ChlD1+PheoD1-). To avert charge recombination, the electron is further transferred to plastoquinone QA, whereas the hole relaxes to a central pair of chlorophylls (PD1PD2), subsequently driving water oxidation. Spin-triplet states can form within the RC when forward electron transfer is inhibited or back reactions are favored. This can lead to formation of singlet dioxygen, with potential deleterious effects. Here we investigate the nature and properties of triplet states within the PSII RC using a multiscale quantum-mechanics/molecular-mechanics (QM/MM) approach. The low-energy spectrum of excited singlet and triplet states, of both local and charge-transfer nature, is compared using range-separated time-dependent density functional theory (TD-DFT). We further compute electron paramagnetic resonance properties (zero-field splitting parameters and hyperfine coupling constants) of relaxed triplet states and compare them with available experimental data. Moreover, the electrostatic modulation of excited state energetics and redox properties of RC pigments by the semiquinone QA- is described. The results provide a detailed electronic-level understanding of triplet states within the PSII RC and form a refined basis for discussing primary and secondary electron transfer, charge recombination pathways, and possible photoprotection mechanisms in PSII.
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Affiliation(s)
- Sinjini Bhattacharjee
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr 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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4
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Kanda T, Ishikita H. Redox Potentials of Iron-Sulfur Clusters in Type I Photosynthetic Reaction Centers. J Phys Chem B 2023; 127:4998-5004. [PMID: 37226417 PMCID: PMC10259448 DOI: 10.1021/acs.jpcb.3c01071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 05/10/2023] [Indexed: 05/26/2023]
Abstract
The electron transfer pathways in type I photosynthetic reaction centers, such as photosystem I (PSI) and reaction centers from green sulfur bacteria (GsbRC), are terminated by two Fe4S4 clusters, FA and FB. The protein structures are the basis of understanding how the protein electrostatic environment interacts with the Fe4S4 clusters and facilitates electron transfer. Using the protein structures, we calculated the redox potential (Em) values for FA and FB in PSI and GsbRC, solving the linear Poisson-Boltzmann equation. The FA-to-FB electron transfer is energetically downhill in the cyanobacterial PSI structure, while it is isoenergetic in the plant PSI structure. The discrepancy arises from differences in the electrostatic influences of conserved residues, including PsaC-Lys51 and PsaC-Arg52, located near FA. The FA-to-FB electron transfer is slightly downhill in the GsbRC structure. Em(FA) and Em(FB) exhibit similar levels upon isolation of the membrane-extrinsic PsaC and PscB subunits from the PSI and GsbRC reaction centers, respectively. The binding of the membrane-extrinsic subunit at the heterodimeric/homodimeric reaction center plays a key role in tuning Em(FA) and Em(FB).
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Affiliation(s)
- Tomoki Kanda
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroshi Ishikita
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
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5
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Hayase T, Shimada Y, Mitomi T, Nagao R, Noguchi T. Triplet Delocalization over the Reaction Center Chlorophylls in Photosystem II. J Phys Chem B 2023; 127:1758-1770. [PMID: 36809007 DOI: 10.1021/acs.jpcb.3c00139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
The triplet state of chlorophyll formed by charge recombination in photosystem II (PSII) is a precursor of harmful singlet oxygen. Although main localization of the triplet state on the monomeric chlorophyll, ChlD1, at cryogenic temperatures has been suggested, how the triplet state is delocalized on other chlorophylls remains unclear. Here, we investigated the distribution of the triplet state of chlorophyll in PSII using light-induced Fourier transform infrared (FTIR) difference spectroscopy. Measurements of triplet-minus-singlet FTIR difference spectra with PSII core complexes from cyanobacterial mutants, D1-V157H, D2-V156H, D2-H197A, and D1-H198A, in which the interactions of the 131-keto C═O groups of the reaction center chlorophylls, PD1, PD2, ChlD1, and ChlD2, respectively, were perturbed, identified the 131-keto C═O bands of the individual chlorophylls and showed that the triplet state is delocalized over all of these chlorophylls. It is suggested that the triplet delocalization plays important roles in the photoprotection and photodamage mechanisms in PSII.
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Affiliation(s)
- Taichi Hayase
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Yuichiro Shimada
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Tatsuya Mitomi
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Ryo Nagao
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.,Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan
| | - Takumi Noguchi
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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6
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Mandal M, Saito K, Ishikita H. Substitution of Ca 2+ and changes in the H-bond network near the oxygen-evolving complex of photosystem II. Phys Chem Chem Phys 2023; 25:6473-6480. [PMID: 36785919 DOI: 10.1039/d2cp05036f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Ca2+, which provides binding sites for ligand water molecules W3 and W4 in the Mn4CaO5 cluster, is a prerequisite for O2 evolution in photosystem II (PSII). We report structural changes in the H-bond network and the catalytic cluster itself upon the replacement of Ca2+ with other alkaline earth metals, using a quantum mechanical/molecular mechanical approach. The small radius of Mg2+ makes W3 donate an H-bond to D1-Glu189 in Mg2+-PSII. If an additional water molecule binds at the large surface of Ba2+, it donates H-bonds to D1-Glu189 and the ligand water molecule at the dangling Mn, altering the H-bond network. The potential energy profiles of the H-bond between D1-Tyr161 (TyrZ) and D1-His190 and the interconversion between the open- and closed-cubane S2 conformations remain substantially unaltered upon the replacement of Ca2+. Remarkably, the O5⋯Ca2+ distance is shortest among all O5⋯metal distances irrespective of the radius being larger than that of Mg2+. Furthermore, Ca2+ is the only alkaline earth metal that equalizes the O5⋯metal and O2⋯metal distances and facilitates the formation of the symmetric cubane structure.
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Affiliation(s)
- Manoj Mandal
- Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata 700106, West Bengal, India.
| | - Keisuke Saito
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan. .,Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroshi Ishikita
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan. .,Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
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7
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Kanda T, Ishikita H. Energetic Diversity in the Electron-Transfer Pathways of Type I Photosynthetic Reaction Centers. Biochemistry 2023; 62:934-941. [PMID: 36749324 PMCID: PMC9949227 DOI: 10.1021/acs.biochem.2c00689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 01/08/2023] [Indexed: 02/08/2023]
Abstract
Photosynthetic reaction centers from heliobacteria (HbRC) and green sulfur bacteria (GsbRC) are homodimeric proteins and share a common ancestor with photosystem I (PSI), classified as type I reaction centers. Using the HbRC crystal structure, we calculated the redox potential (Em) values in the electron-transfer branches, solving the linear Poisson-Boltzmann equation and considering the protonation states of all titratable sites in the entire protein-pigment complex. Em(A-1) for bacteriochlorophyll g at the secondary site in HbRC (-1157 mV) is as low as Em(A-1) for chlorophyll a in PSI (-1173 mV). Em(A0/HbRC) is at the same level as Em(A0/GsbRC) and is 200 mV higher than Em(A0/PSI) due to the replacement of PsaA-Trp697/PsaB-Trp677 in PSI with PshA-Arg554 in HbRC. In contrast, Em(FX) for the Fe4S4 cluster in HbRC (-420 mV) is significantly higher than Em(FX) in GsbRC (-719 mV) and PSI (-705 mV) due to the absence of acidic residues that correspond to PscA-Asp634 in GsbRC and PsaB-Asp575 in PSI. It seems likely that type I reaction centers have evolved, adopting (bacterio)chlorophylls suitable for their light environments while maintaining electron-transfer cascades.
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Affiliation(s)
- Tomoki Kanda
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroshi Ishikita
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
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8
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Capone M, Sirohiwal A, Aschi M, Pantazis DA, Daidone I. Alternative Fast and Slow Primary Charge-Separation Pathways in Photosystem II. Angew Chem Int Ed Engl 2023; 62:e202216276. [PMID: 36791234 DOI: 10.1002/anie.202216276] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 01/23/2023] [Accepted: 02/13/2023] [Indexed: 02/17/2023]
Abstract
Photosystem-II (PSII) is a multi-subunit protein complex that harvests sunlight to perform oxygenic photosynthesis. Initial light-activated charge separation takes place at a reaction centre consisting of four chlorophylls and two pheophytins. Understanding the processes following light excitation remains elusive due to spectral congestion, the ultrafast nature, and multi-component behaviour of the charge-separation process. Here, using advanced computational multiscale approaches which take into account the large-scale configurational flexibility of the system, we identify two possible primary pathways to radical-pair formation that differ by three orders of magnitude in their kinetics. The fast (short-range) pathway is dominant, but the existence of an alternative slow (long-range) charge-separation pathway hints at the evolution of redundancy that may serve other purposes, adaptive or protective, related to formation of the unique oxidative species that drives water oxidation in PSII.
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Affiliation(s)
- Matteo Capone
- Department of Physical and Chemical Sciences, University of L'Aquila, via Vetoio (Coppito 1), 67010, L'Aquila, Italy
| | - Abhishek Sirohiwal
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany.,Present Address: Department of Biochemistry and Biophysics, Arrhenius Laboratory, Stockholm University, 10691, Stockholm, Sweden
| | - Massimiliano Aschi
- Department of Physical and Chemical Sciences, University of L'Aquila, via Vetoio (Coppito 1), 67010, L'Aquila, Italy
| | - Dimitrios A Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany
| | - Isabella Daidone
- Department of Physical and Chemical Sciences, University of L'Aquila, via Vetoio (Coppito 1), 67010, L'Aquila, Italy
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9
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Tamura H, Saito K, Nishio S, Ishikita H. Electron-Transfer Route in the Early Oxidation States of the Mn 4CaO 5 Cluster in Photosystem II. J Phys Chem B 2023; 127:205-211. [PMID: 36542840 PMCID: PMC9841979 DOI: 10.1021/acs.jpcb.2c08246] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 12/07/2022] [Indexed: 12/24/2022]
Abstract
The electron transfer from the oxygen-evolving Mn4CaO5 cluster to the electron acceptor D1-Tyr161 (TyrZ) is a prerequisite for water oxidation and O2 evolution. Here, we analyzed the electronic coupling in the rate-limiting electron-transfer transitions using a combined quantum mechanical/molecular mechanical/polarizable continuum model approach. In the S0 to S1 transition, the electronic coupling between the electron-donor Mn3(III) and TyrZ is small (2 meV). In contrast, the electronic coupling between the dangling Mn4(III) and TyrZ is significantly large (172 meV), which suggests that the electron transfer proceeds from Mn3(III) to TyrZ via Mn4(III). In the S1 to S2 transition, the electronic coupling between Mn4(III) and TyrZ is also larger (124 meV) than that between Mn1(III) and TyrZ (1 meV), which favors the formation of the open-cubane S2 conformation with Mn4(IV) over the formation of the closed-cubane S2 conformation with Mn1(IV). In the S0 to S1 and S1 to S2 transitions, the Mn4 d-orbital and the TyrZ π-orbital are hybridized via D1-Asp170, which suggests that D1-Asp170 commonly provides a dominant electron-transfer route.
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Affiliation(s)
- Hiroyuki Tamura
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo153-8904, Japan
| | - Keisuke Saito
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo153-8904, Japan
| | - Shunya Nishio
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo113-8654, Japan
| | - Hiroshi Ishikita
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo113-8654, Japan
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo153-8904, Japan
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10
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Mandal M, Saito K, Ishikita H. Release of a Proton and Formation of a Low-Barrier Hydrogen Bond between Tyrosine D and D2-His189 in Photosystem II. ACS PHYSICAL CHEMISTRY AU 2022; 2:423-429. [PMID: 36855688 PMCID: PMC9955220 DOI: 10.1021/acsphyschemau.2c00019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In photosystem II (PSII), the second-lowest oxidation state (S1) of the oxygen-evolving Mn4CaO5 cluster is the most stable, as the radical form of the redox-active D2-Tyr160 is considered to be a candidate that accepts an electron from the lowest oxidation state (S0) in the dark. Using quantum mechanical/molecular mechanical calculations, we investigated the redox potential (E m) of TyrD and its H-bond partner, D2-His189. The potential energy profile indicates that the release of a proton from the TyrD...D2-His189 pair leads to the formation of a low-barrier H-bond. The E m depends on the H+ position along the low-barrier H-bond, e.g., 680 mV when the H+ is at the D2-His189 moiety and 800 mV when the H+ is at the TyrD moiety, which can explain why TyrD mediates both the S0 to S1 oxidation and the S2 to S1 reduction.
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Affiliation(s)
- Manoj Mandal
- Department
of Chemical, Biological & Macro-Molecular Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata 700106, West Bengal, India
| | - Keisuke Saito
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan,Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroshi Ishikita
- Research
Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan,Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan,. Tel: +81-3-5452-5056. Fax: +81-3-5452-5083
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11
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Yoneda Y, Arsenault EA, Yang SJ, Orcutt K, Iwai M, Fleming GR. The initial charge separation step in oxygenic photosynthesis. Nat Commun 2022; 13:2275. [PMID: 35477708 PMCID: PMC9046298 DOI: 10.1038/s41467-022-29983-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 04/11/2022] [Indexed: 11/09/2022] Open
Abstract
Photosystem II is crucial for life on Earth as it provides oxygen as a result of photoinduced electron transfer and water splitting reactions. The excited state dynamics of the photosystem II-reaction center (PSII-RC) has been a matter of vivid debate because the absorption spectra of the embedded chromophores significantly overlap and hence it is extremely difficult to distinguish transients. Here, we report the two-dimensional electronic-vibrational spectroscopic study of the PSII-RC. The simultaneous resolution along both the visible excitation and infrared detection axis is crucial in allowing for the character of the excitonic states and interplay between them to be clearly distinguished. In particular, this work demonstrates that the mixed exciton-charge transfer state, previously proposed to be responsible for the far-red light operation of photosynthesis, is characterized by the ChlD1+Phe radical pair and can be directly prepared upon photoexcitation. Further, we find that the initial electron acceptor in the PSII-RC is Phe, rather than PD1, regardless of excitation wavelength. The photosystem II reaction center (PSII-RC) is a model system to understand the initial steps of photosynthesis, but its excited state dynamics is difficult to disentangle with most spectroscopic methods. Here the authors perform a two-dimensional electronic-vibrational spectroscopic study of PSII-RC, providing detailed insight into such dynamics and into the mechanism of charge separation.
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Affiliation(s)
- Yusuke Yoneda
- Department of Chemistry, University of California, Berkeley, CA, 94720, United States.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States.,Research Center of Integrative Molecular Systems, Institute for Molecular Science, National Institute of Natural Sciences, Okazaki, Aichi, 444-8585, Japan
| | - Eric A Arsenault
- Department of Chemistry, University of California, Berkeley, CA, 94720, United States.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States.,Kavli Energy Nanoscience Institute at Berkeley, Berkeley, CA, 94720, United States
| | - Shiun-Jr Yang
- Department of Chemistry, University of California, Berkeley, CA, 94720, United States.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States
| | - Kaydren Orcutt
- Department of Chemistry, University of California, Berkeley, CA, 94720, United States.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States
| | - Masakazu Iwai
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States.,Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720, United States
| | - Graham R Fleming
- Department of Chemistry, University of California, Berkeley, CA, 94720, United States. .,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, United States. .,Kavli Energy Nanoscience Institute at Berkeley, Berkeley, CA, 94720, United States.
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12
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Sirohiwal A, Pantazis DA. The Electronic Origin of Far-Red-Light-Driven Oxygenic Photosynthesis. Angew Chem Int Ed Engl 2022; 61:e202200356. [PMID: 35142017 PMCID: PMC9304563 DOI: 10.1002/anie.202200356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Indexed: 12/19/2022]
Abstract
Photosystem‐II uses sunlight to trigger charge separation and catalyze water oxidation. Intrinsic properties of chlorophyll a pigments define a natural “red limit” of photosynthesis at ≈680 nm. Nevertheless, charge separation can be triggered with far‐red photons up to 800 nm, without altering the nature of light‐harvesting pigments. Here we identify the electronic origin of this remarkable phenomenon using quantum chemical and multiscale simulations on a native Photosystem‐II model. We find that the reaction center is preorganized for charge separation in the far‐red region by specific chlorophyll–pheophytin pairs, potentially bypassing the light‐harvesting apparatus. Charge transfer can occur along two distinct pathways with one and the same pheophytin acceptor (PheoD1). The identity of the donor chlorophyll (ChlD1 or PD1) is wavelength‐dependent and conformational dynamics broaden the sampling of the far‐red region by the two charge‐transfer states. The two pathways rationalize spectroscopic observations and underpin designed extensions of the photosynthetically active radiation limit.
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Affiliation(s)
- Abhishek Sirohiwal
- 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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13
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Sirohiwal A, Pantazis DA. The Electronic Origin of Far‐Red‐Light‐Driven Oxygenic Photosynthesis. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202200356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Abhishek Sirohiwal
- 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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14
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Che X, Zhang T, Li H, Zhang L, Liu J. Effect of Hypoxia on Photosystem II of Tropical Seagrass Enhalus acoroides in the Dark. Photochem Photobiol 2021; 98:421-428. [PMID: 34547108 DOI: 10.1111/php.13522] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2021] [Accepted: 09/16/2021] [Indexed: 01/07/2023]
Abstract
Hypoxia induced by eutrophication has become an important factor threatening the survival of coastal life such as Enhalus acoroides. The purpose of the current study was to explore the effect of hypoxia on photosystem II (PSII) of E. acoroides in the dark. The results showed that long-term dark hypoxia damages PSII activity of E. acoroides. The lower the oxygen content and the longer the hypoxic duration, the more seriously PSII was damaged and the less light-independent recovery parts of the damaged PSII. The damage to PSII caused by hypoxia was unrelated to ROS but related to respiration, because the respiration rate decreased with the decrease of oxygen content and PSII activity decreased significantly even at a normal oxygen content after the inhibition of aerobic respiratory pathway. Hypoxia reduced energy fluxes between the antennas and the RCs, and generated many inactive RCs, which significantly reduced the electron transfer efficiency of PSII. Severe hypoxia (2.65 mg L-1 oxygen content) caused chlorophyll degradation. The study demonstrated that hypoxia damages PSII of E. acoroides and inhibits PSII recovery in the dark. We suggested that hypoxia together with other environment stressors would be the key reason for the decline of E. acoroides meadows.
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Affiliation(s)
- Xingkai Che
- CAS and Shandong Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
| | - Tie Zhang
- CAS and Shandong Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Hu Li
- CAS and Shandong Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
| | - Litao Zhang
- CAS and Shandong Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, Shandong, China
| | - Jianguo Liu
- CAS and Shandong Key Laboratory of Experimental Marine Biology, Center for Ocean Mega-Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, Shandong, China
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15
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Electronic Structure of Tyrosyl D Radical of Photosystem II, as Revealed by 2D-Hyperfine Sublevel Correlation Spectroscopy. MAGNETOCHEMISTRY 2021. [DOI: 10.3390/magnetochemistry7090131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The biological water oxidation takes place in Photosystem II (PSII), a multi-subunit protein located in thylakoid membranes of higher plant chloroplasts and cyanobacteria. The catalytic site of PSII is a Mn4Ca cluster and is known as the oxygen evolving complex (OEC) of PSII. Two tyrosine residues D1-Tyr161 (YZ) and D2-Tyr160 (YD) are symmetrically placed in the two core subunits D1 and D2 and participate in proton coupled electron transfer reactions. YZ of PSII is near the OEC and mediates electron coupled proton transfer from Mn4Ca to the photooxidizable chlorophyll species P680+. YD does not directly interact with OEC, but is crucial for modulating the various S oxidation states of the OEC. In PSII from higher plants the environment of YD• radical has been extensively characterized only in spinach (Spinacia oleracea) Mn-depleted non functional PSII membranes. Here, we present a 2D-HYSCORE investigation in functional PSII of spinach to determine the electronic structure of YD• radical. The hyperfine couplings of the protons that interact with the YD• radical are determined and the relevant assignment is provided. A discussion on the similarities and differences between the present results and the results from studies performed in non functional PSII membranes from higher plants and PSII preparations from other organisms is given.
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16
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Tamura H, Saito K, Ishikita H. The origin of unidirectional charge separation in photosynthetic reaction centers: nonadiabatic quantum dynamics of exciton and charge in pigment-protein complexes. Chem Sci 2021; 12:8131-8140. [PMID: 34194703 PMCID: PMC8208306 DOI: 10.1039/d1sc01497h] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/03/2021] [Indexed: 11/21/2022] Open
Abstract
Exciton charge separation in photosynthetic reaction centers from purple bacteria (PbRC) and photosystem II (PSII) occurs exclusively along one of the two pseudo-symmetric branches (active branch) of pigment-protein complexes. The microscopic origin of unidirectional charge separation in photosynthesis remains controversial. Here we elucidate the essential factors leading to unidirectional charge separation in PbRC and PSII, using nonadiabatic quantum dynamics calculations in conjunction with time-dependent density functional theory (TDDFT) with the quantum mechanics/molecular mechanics/polarizable continuum model (QM/MM/PCM) method. This approach accounts for energetics, electronic coupling, and vibronic coupling of the pigment excited states under electrostatic interactions and polarization of whole protein environments. The calculated time constants of charge separation along the active branches of PbRC and PSII are similar to those observed in time-resolved spectroscopic experiments. In PbRC, Tyr-M210 near the accessary bacteriochlorophyll reduces the energy of the intermediate state and drastically accelerates charge separation overcoming the electron-hole interaction. Remarkably, even though both the active and inactive branches in PSII can accept excitons from light-harvesting complexes, charge separation in the inactive branch is prevented by a weak electronic coupling due to symmetry-breaking of the chlorophyll configurations. The exciton in the inactive branch in PSII can be transferred to the active branch via direct and indirect pathways. Subsequently, the ultrafast electron transfer to pheophytin in the active branch prevents exciton back transfer to the inactive branch, thereby achieving unidirectional charge separation.
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Affiliation(s)
- Hiroyuki Tamura
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
| | - Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo 113-8654 Japan
- Research Center for Advanced Science and Technology, The University of Tokyo 4-6-1 Komaba, Meguro-ku Tokyo 153-8904 Japan
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17
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Mitsuhashi K, Tamura H, Saito K, Ishikita H. Nature of Asymmetric Electron Transfer in the Symmetric Pathways of Photosystem I. J Phys Chem B 2021; 125:2879-2885. [DOI: 10.1021/acs.jpcb.0c10885] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Koji Mitsuhashi
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Hiroyuki Tamura
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
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18
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Sakashita N, Ishikita H, Saito K. Rigidly hydrogen-bonded water molecules facilitate proton transfer in photosystem II. Phys Chem Chem Phys 2020; 22:15831-15841. [PMID: 32613215 DOI: 10.1039/d0cp00295j] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
In the water-splitting enzyme photosystem II (PSII), the proton is released from the catalytic site and transferred to the protein bulk surface via the proton-relay mechanism. Proton transfer occurs in a proton-conducting channel consisting of a series of water molecules connected by hydrogen-bonded (H-bonded) chains. The water-transport protein aquaporin (AQP) also contains a water chain with structure similar to that of the PSII proton channel, although the water chain does not transport protons. We compared the PSII proton channel with the AQP water channel from the following standpoints: (1) the energetics of proton transfer based on crystal structures obtained from quantum mechanical/molecular mechanical calculations, and (2) fluctuations in water molecules obtained from molecular dynamics simulations. The results showed that residues facing the channel and acting as H-bonded partners of water molecules predominantly determined the proton-transfer ability. In PSII, the water chain is surrounded by H-bond acceptors (e.g., carbonyl groups), and the water chain transports protons where the water molecules are rigidly fixed. In AQP, the water chain is surrounded by hydrophobic sidechains or H-bond donors (e.g., NH2 groups), and it does not transport protons where the water molecules are flexible and fluctuating.
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Affiliation(s)
- Naoki Sakashita
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan and Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904, Japan.
| | - Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan and Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904, Japan.
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19
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Tsujimura M, Noji T, Saito K, Kojima K, Sudo Y, Ishikita H. Mechanism of absorption wavelength shifts in anion channelrhodopsin-1 mutants. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1862:148349. [PMID: 33248117 DOI: 10.1016/j.bbabio.2020.148349] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 11/05/2020] [Accepted: 11/21/2020] [Indexed: 12/11/2022]
Abstract
Using a quantum mechanical/molecular mechanical approach, we show the mechanisms of how the protein environment of Guillardia theta anion channelrhodopsin-1 (GtACR1) can shift the absorption wavelength. The calculated absorption wavelengths for GtACR1 mutants, M105A, C133A, and C237A are in agreement with experimentally measured wavelengths. Among 192 mutant structures investigated, mutations at Thr101, Cys133, Pro208, and Cys237 are likely to increase the absorption wavelength. In particular, T101A GtACR1 was expressed in HEK293T cells. The measured absorption wavelength is 10 nm higher than that of wild type, consistent with the calculated wavelength. (i) Removal of a polar residue from the Schiff base moiety, (ii) addition of a polar or acidic residue to the β-ionone ring moiety, and (iii) addition of a bulky residue to increase the planarity of the β-ionone and Schiff base moieties are the basis of increasing the absorption wavelength.
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Affiliation(s)
- Masaki Tsujimura
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
| | - Tomoyasu Noji
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan; Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Keisuke Saito
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan; Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Keiichi Kojima
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan
| | - Yuki Sudo
- Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8530, Japan
| | - Hiroshi Ishikita
- Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan; Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
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20
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Sirohiwal A, Neese F, Pantazis DA. Protein Matrix Control of Reaction Center Excitation in Photosystem II. J Am Chem Soc 2020; 142:18174-18190. [PMID: 33034453 PMCID: PMC7582616 DOI: 10.1021/jacs.0c08526] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Indexed: 02/06/2023]
Abstract
Photosystem II (PSII) is a multisubunit pigment-protein complex that uses light-induced charge separation to power oxygenic photosynthesis. Its reaction center chromophores, where the charge transfer cascade is initiated, are arranged symmetrically along the D1 and D2 core polypeptides and comprise four chlorophyll (PD1, PD2, ChlD1, ChlD2) and two pheophytin molecules (PheoD1 and PheoD2). Evolution favored productive electron transfer only via the D1 branch, with the precise nature of primary excitation and the factors that control asymmetric charge transfer remaining under investigation. Here we present a detailed atomistic description for both. We combine large-scale simulations of membrane-embedded PSII with high-level quantum-mechanics/molecular-mechanics (QM/MM) calculations of individual and coupled reaction center chromophores to describe reaction center excited states. We employ both range-separated time-dependent density functional theory and the recently developed domain based local pair natural orbital (DLPNO) implementation of the similarity transformed equation of motion coupled cluster theory with single and double excitations (STEOM-CCSD), the first coupled cluster QM/MM calculations of the reaction center. We find that the protein matrix is exclusively responsible for both transverse (chlorophylls versus pheophytins) and lateral (D1 versus D2 branch) excitation asymmetry, making ChlD1 the chromophore with the lowest site energy. Multipigment calculations show that the protein matrix renders the ChlD1 → PheoD1 charge-transfer the lowest energy excitation globally within the reaction center, lower than any pigment-centered local excitation. Remarkably, no low-energy charge transfer states are located within the "special pair" PD1-PD2, which is therefore excluded as the site of initial charge separation in PSII. Finally, molecular dynamics simulations suggest that modulation of the electrostatic environment due to protein conformational flexibility enables direct excitation of low-lying charge transfer states by far-red light.
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Affiliation(s)
- Abhishek Sirohiwal
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
- Fakultät
für Chemie und Biochemie, Ruhr-Universität
Bochum, 44780 Bochum, 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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21
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A TDDFT investigation of the Photosystem II reaction center: Insights into the precursors to charge separation. Proc Natl Acad Sci U S A 2020; 117:19705-19712. [PMID: 32747579 PMCID: PMC7443915 DOI: 10.1073/pnas.1922158117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Examining the excited states of the Photosystem II reaction center furthers our understanding of available charge separation pathways that lead to successful photosynthesis. Our results comprise the largest complete model of the Photosystem II reaction center to be described using time-dependent density functional theory reported in the literature to date. We reveal the molecular orbitals contributing to the excited states that are precursors to charge separation. We demonstrate that our model can successfully predict the action of specific mutations, a valuable tool for the agricultural industry. These models may also be beneficial in informing the design of artificial photosynthetic complexes as well as enhanced bioengineered photosystems. Photosystem II (PS II) captures solar energy and directs charge separation (CS) across the thylakoid membrane during photosynthesis. The highly oxidizing, charge-separated state generated within its reaction center (RC) drives water oxidation. Spectroscopic studies on PS II RCs are difficult to interpret due to large spectral congestion, necessitating modeling to elucidate key spectral features. Herein, we present results from time-dependent density functional theory (TDDFT) calculations on the largest PS II RC model reported to date. This model explicitly includes six RC chromophores and both the chlorin phytol chains and the amino acid residues <6 Å from the pigments’ porphyrin ring centers. Comparing our wild-type model results with calculations on mutant D1-His-198-Ala and D2-His-197-Ala RCs, our simulated absorption-difference spectra reproduce experimentally observed shifts in known chlorophyll absorption bands, demonstrating the predictive capabilities of this model. We find that inclusion of both nearby residues and phytol chains is necessary to reproduce this behavior. Our calculations provide a unique opportunity to observe the molecular orbitals that contribute to the excited states that are precursors to CS. Strikingly, we observe two high oscillator strength, low-lying states, in which molecular orbitals are delocalized over ChlD1 and PheD1 as well as one weaker oscillator strength state with molecular orbitals delocalized over the P chlorophylls. Both these configurations are a match for previously identified exciton–charge transfer states (ChlD1+PheD1−)* and (PD2+PD1−)*. Our results demonstrate the power of TDDFT as a tool, for studies of natural photosynthesis, or indeed future studies of artificial photosynthetic complexes.
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22
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Acquirement of water-splitting ability and alteration of the charge-separation mechanism in photosynthetic reaction centers. Proc Natl Acad Sci U S A 2020; 117:16373-16382. [PMID: 32601233 PMCID: PMC7368266 DOI: 10.1073/pnas.2000895117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
In photosynthetic reaction centers from purple bacteria (PbRC) and the water-oxidizing enzyme, photosystem II (PSII), charge separation occurs along one of the two symmetrical electron-transfer branches. Here we report the microscopic origin of the unidirectional charge separation, fully considering electron-hole interaction, electronic coupling of the pigments, and electrostatic interaction with the polarizable entire protein environments. The electronic coupling between the pair of bacteriochlorophylls is large in PbRC, forming a delocalized excited state with the lowest excitation energy (i.e., the special pair). The charge-separated state in the active branch is stabilized by uncharged polar residues in the transmembrane region and charged residues on the cytochrome c 2 binding surface. In contrast, the accessory chlorophyll in the D1 protein (ChlD1) has the lowest excitation energy in PSII. The charge-separated state involves ChlD1 •+ and is stabilized predominantly by charged residues near the Mn4CaO5 cluster and the proceeding proton-transfer pathway. It seems likely that the acquirement of water-splitting ability makes ChlD1 the initial electron donor in PSII.
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23
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Mandal M, Kawashima K, Saito K, Ishikita H. Redox Potential of the Oxygen-Evolving Complex in the Electron Transfer Cascade of Photosystem II. J Phys Chem Lett 2020; 11:249-255. [PMID: 31729876 DOI: 10.1021/acs.jpclett.9b02831] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
In photosystem II (PSII), water oxidation occurs in the Mn4CaO5 cluster with the release of electrons via the redox-active tyrosine (TyrZ) to the reaction-center chlorophylls (PD1/PD2). Using a quantum mechanical/molecular mechanical approach, we report the redox potentials (Em) of these cofactors in the PSII protein environment. The Em values suggest that the Mn4CaO5 cluster, TyrZ, and PD1/PD2 form a downhill electron transfer pathway. Em for the first oxidation step, Em(S0/S1), is uniquely low (730 mV) and is ∼100 mV lower than that for the second oxidation step, Em(S1/S2) (830 mV) only when the O4 site of the Mn4CaO5 cluster is protonated in S0. The O4-water chain, which directly forms a low-barrier H-bond with the Mn4CaO5 cluster and mediates proton-coupled electron transfer in the S0 to S1 transition, explains why the second lowest oxidation state, S1, is the most stable and S0 is converted to S1 even in the dark.
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Affiliation(s)
- Manoj Mandal
- Research Center for Advanced Science and Technology , The University of Tokyo , 4-6-1 Komaba , Meguro-ku, Tokyo 153-8904 , Japan
| | - Keisuke Kawashima
- Department of Applied Chemistry , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8654 , Japan
| | - Keisuke Saito
- Research Center for Advanced Science and Technology , The University of Tokyo , 4-6-1 Komaba , Meguro-ku, Tokyo 153-8904 , Japan
- Department of Applied Chemistry , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8654 , Japan
| | - Hiroshi Ishikita
- Research Center for Advanced Science and Technology , The University of Tokyo , 4-6-1 Komaba , Meguro-ku, Tokyo 153-8904 , Japan
- Department of Applied Chemistry , The University of Tokyo , 7-3-1 Hongo , Bunkyo-ku, Tokyo 113-8654 , Japan
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24
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Saito K, Mandal M, Ishikita H. Redox potentials along the redox-active low-barrier H-bonds in electron transfer pathways. Phys Chem Chem Phys 2020; 22:25467-25473. [DOI: 10.1039/d0cp04265j] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Local proton transfer along redox-active low-barrier H-bonds can alter the driving force or electronic coupling for electron transfer, as the redox potential values depend on the H+ position in low-barrier H-bonds.
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Affiliation(s)
- Keisuke Saito
- Research Center for Advanced Science and Technology
- The University of Tokyo
- Tokyo 153-8904
- Japan
- Department of Applied Chemistry
| | - Manoj Mandal
- Research Center for Advanced Science and Technology
- The University of Tokyo
- Tokyo 153-8904
- Japan
| | - Hiroshi Ishikita
- Research Center for Advanced Science and Technology
- The University of Tokyo
- Tokyo 153-8904
- Japan
- Department of Applied Chemistry
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25
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Mechanism of protonation of the over-reduced Mn4CaO5 cluster in photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:148059. [DOI: 10.1016/j.bbabio.2019.148059] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 07/18/2019] [Accepted: 08/02/2019] [Indexed: 01/12/2023]
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26
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Takahashi H, Suzuoka D, Sakuraba S, Morita A. Role of the Photosystem II as an Environment in the Oxidation Free Energy of the Mn Cluster from S 1 to S 2. J Phys Chem B 2019; 123:7081-7091. [PMID: 31282160 DOI: 10.1021/acs.jpcb.9b03831] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The manganese cluster (CaMn4O5) in the photosystem II (PSII) is the reaction center of the light-driven oxidation reaction, which generates the molecular oxygen. In this paper, we address the issue of the effect of the environment on the free energy associated with the oxidation of the Mn cluster in S1 state by conducting the large-scale quantum mechanical/molecular mechanical simulations, which involve the whole of the PSII monomer. It was found by the simulations at the level of the B3LYP functional that the environment surrounding the Mn cluster reduces the vertical oxidation free energy Δμvrt by 64.8 kcal/mol. A decomposition analysis of the free energy Δμvrt revealed that the system composed of peptide chains, ligands, lipids, and potassium ions contributes to lowering of Δμvrt by -98.0 kcal/mol, whereas the solvent water makes an opposite contribution of 38.9 kcal/mol. Reduction of the vertical oxidation free energy directly leads to the lowering of the activation free energy ΔGac for the electron transfer reaction from the Mn cluster in S1 state to the neighboring Tyrz+. Consequently, the electron transfer rate was found to be enhanced by a factor of 1012 by virtue of the influence of the environment.
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Affiliation(s)
- Hideaki Takahashi
- Department of Chemistry, Graduate School of Science , Tohoku University , Sendai , Miyagi 980-8578 , Japan
| | - Daiki Suzuoka
- Department of Chemistry, Graduate School of Science , Tohoku University , Sendai , Miyagi 980-8578 , Japan
| | - Shun Sakuraba
- National Institutes for Quantum and Radiological Science and Technology , Kizugawa , Kyoto 619-0215 , Japan
| | - Akihiro Morita
- Department of Chemistry, Graduate School of Science , Tohoku University , Sendai , Miyagi 980-8578 , Japan.,Element Strategy Initiative for Catalysts and Batteries (ESICB) , Kyoto University , Kyoto 615-8520 , Japan
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27
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Nishimura N, Nakayama S, Horiuchi A, Kumoda M, Miyatake T. Reversible Aggregation of Chlorophyll Derivative Induced by Phase Transition of Lipid. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:7242-7248. [PMID: 31063389 DOI: 10.1021/acs.langmuir.9b00586] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Controlling the supramolecular organization of pigment molecules will provide innovative materials that exhibit variable optical properties. In nature, photosynthetic systems employ chlorophyllous supramolecules in which each pigment molecule is suitably organized in proteins, and their properties are adequately optimized by changing the structures of the surrounding amino acid residues. Here, we report a strategy for varying the aggregation behavior of a chlorophyll derivative by using a phase-transition phenomenon of lipid bilayers. Methyl pyropheophorbide a (MPP) was employed as a chlorophyllous pigment in our artificial system, and synthetic phosphatidylcholines with saturated acyl chain(s) were also used. The MPP molecules successfully accumulated within the lipid bilayer of liposomes without changing the vesicular structure. When the lipid bilayer was in a gel form (under the phase-transition temperature, Tm), the embedded MPP aggregated to yield a dimeric form showing red-shifted absorption bands and circular dichroism signals. When the solutions of MPP-containing liposomes were heated to higher temperatures than their Tm, MPP disaggregated to monomeric form as the absorption spectrum changed into its original fashion in dichloromethane. The reversible thermochromic (dis)aggregation of the MPP molecules had good cyclability. Additional careful examination of the phase transition in the MPP-lipid co-assemblies clarified that the critical temperatures of the MPP (dis)aggregation were in good agreement with the phase-transition temperatures of the pigment-containing bilayers. The reversible MPP aggregation in the lipid bilayers occurred in a wide range of temperatures (around 10-55 °C) by changing the length of the diacyl side chains of phospholipids. The reversible thermochromism of the chlorophyllous system was established by varying the nature of the surrounding lipid bilayer. This study can provide a useful strategy for making variable tetrapyrrolic aggregate systems induced by mild extrinsic stimuli.
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Sirohiwal A, Neese F, Pantazis DA. Microsolvation of the Redox-Active Tyrosine-D in Photosystem II: Correlation of Energetics with EPR Spectroscopy and Oxidation-Induced Proton Transfer. J Am Chem Soc 2019; 141:3217-3231. [PMID: 30666866 PMCID: PMC6728127 DOI: 10.1021/jacs.8b13123] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Photosystem
II (PSII) of oxygenic photosynthesis captures sunlight
to drive the catalytic oxidation of water and the reduction of plastoquinone.
Among the several redox-active cofactors that participate in intricate
electron transfer pathways there are two tyrosine residues, YZ and YD. They are situated in symmetry-related
electron transfer branches but have different environments and play
distinct roles. YZ is the immediate oxidant of the oxygen-evolving
Mn4CaO5 cluster, whereas YD serves
regulatory and protective functions. The protonation states and hydrogen-bond
network in the environment of YD remain debated, while
the role of microsolvation in stabilizing different redox states of
YD and facilitating oxidation or mediating deprotonation,
as well the fate of the phenolic proton, is unclear. Here we present
detailed structural models of YD and its environment using
large-scale quantum mechanical models and all-atom molecular dynamics
of a complete PSII monomer. The energetics of water distribution within
a hydrophobic cavity adjacent to YD are shown to correlate
directly with electron paramagnetic resonance (EPR) parameters such
as the tyrosyl g-tensor, allowing us to map the correspondence
between specific structural models and available experimental observations.
EPR spectra obtained under different conditions are explained with
respect to the mode of interaction of the proximal water with the
tyrosyl radical and the position of the phenolic proton within the
cavity. Our results revise previous models of the energetics and build
a detailed view of the role of confined water in the oxidation and
deprotonation of YD. Finally, the model of microsolvation
developed in the present work rationalizes in a straightforward way
the biphasic oxidation kinetics of YD, offering new structural
insights regarding the function of the radical in biological photosynthesis.
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Affiliation(s)
- Abhishek Sirohiwal
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1 , 45470 Mülheim an der Ruhr , Germany.,Fakultät für Chemie und Biochemie , Ruhr-Universität Bochum , 44780 Bochum , 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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29
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Absorption-energy calculations of chlorophyll a and b with an explicit solvent model. J Photochem Photobiol A Chem 2018. [DOI: 10.1016/j.jphotochem.2017.10.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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30
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Kawashima K, Ishikita H. Energetic insights into two electron transfer pathways in light-driven energy-converting enzymes. Chem Sci 2018; 9:4083-4092. [PMID: 29780537 PMCID: PMC5944228 DOI: 10.1039/c8sc00424b] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/28/2018] [Indexed: 11/21/2022] Open
Abstract
We report Em values of (bacterio-)chlorophylls for one-electron reduction in both electron-transfer branches of PbRC, PSI, and PSII.
We report redox potentials (Em) for one-electron reduction for all chlorophylls in the two electron-transfer branches of water-oxidizing enzyme photosystem II (PSII), photosystem I (PSI), and purple bacterial photosynthetic reaction centers (PbRC). In PSI, Em values for the accessory chlorophylls were similar in both electron-transfer branches. In PbRC, the corresponding Em value was 170 mV less negative in the active L-branch (BL) than in the inactive M-branch (BM), favoring BL˙– formation. This contrasted with the corresponding chlorophylls, ChlD1 and ChlD2, in PSII, where Em(ChlD1) was 120 mV more negative than Em(ChlD2), implying that to rationalize electron transfer in the D1-branch, ChlD1 would need to serve as the primary electron donor. Residues that contributed to Em(ChlD1) < Em(ChlD2) simultaneously played a key role in (i) releasing protons from the substrate water molecules and (ii) contributing to the larger cationic population on the chlorophyll closest to the Mn4CaO5 cluster (PD1), favoring electron transfer from water molecules. These features seem to be the nature of PSII, which needs to possess the proton-exit pathway to use a protonated electron source—water molecules.
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Affiliation(s)
- Keisuke Kawashima
- Department of Applied Chemistry , The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku , Tokyo 113-8654 , Japan .
| | - Hiroshi Ishikita
- Department of Applied Chemistry , The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku , Tokyo 113-8654 , Japan . .,Research Center for Advanced Science and Technology , The University of Tokyo , 4-6-1 Komaba, Meguro-ku , Tokyo 153-8904 , Japan . ; Tel: +81-3-5452-5056
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31
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Narzi D, Coccia E, Manzoli M, Guidoni L. Impact of molecular flexibility on the site energy shift of chlorophylls in Photosystem II. Biophys Chem 2017; 229:93-98. [DOI: 10.1016/j.bpc.2017.06.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Revised: 06/26/2017] [Accepted: 06/26/2017] [Indexed: 01/31/2023]
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Nagao R, Yamaguchi M, Nakamura S, Ueoka-Nakanishi H, Noguchi T. Genetically introduced hydrogen bond interactions reveal an asymmetric charge distribution on the radical cation of the special-pair chlorophyll P680. J Biol Chem 2017; 292:7474-7486. [PMID: 28302724 DOI: 10.1074/jbc.m117.781062] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2017] [Revised: 03/08/2017] [Indexed: 11/06/2022] Open
Abstract
The special-pair chlorophyll (Chl) P680 in photosystem II has an extremely high redox potential (Em ) to enable water oxidation in photosynthesis. Significant positive-charge localization on one of the Chl constituents, PD1 or PD2, in P680+ has been proposed to contribute to this high Em To identify the Chl molecule on which the charge is mainly localized, we genetically introduced a hydrogen bond to the 131-keto C=O group of PD1 and PD2 by changing the nearby D1-Val-157 and D2-Val-156 residues to His, respectively. Successful hydrogen bond formation at PD1 and PD2 in the obtained D1-V157H and D2-V156H mutants, respectively, was monitored by detecting 131-keto C=O vibrations in Fourier transfer infrared (FTIR) difference spectra upon oxidation of P680 and the symmetrically located redox-active tyrosines YZ and YD, and they were simulated by quantum-chemical calculations. Analysis of the P680+/P680 FTIR difference spectra of D1-V157H and D2-V156H showed that upon P680+ formation, the 131-keto C=O frequency upshifts by a much larger extent in PD1 (23 cm-1) than in PD2 (<9 cm-1). In addition, thermoluminescence measurements revealed that the D1-V157H mutation increased the Em of P680 to a larger extent than did the D2-V156H mutation. These results, together with the previous results for the mutants of the His ligands of PD1 and PD2, lead to a definite conclusion that a charge is mainly localized to PD1 in P680<sup/>.
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Affiliation(s)
- Ryo Nagao
- From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Motoki Yamaguchi
- From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Shin Nakamura
- From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Hanayo Ueoka-Nakanishi
- From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Takumi Noguchi
- From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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33
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Hasegawa M, Nagashima H, Minobe R, Tachikawa T, Mino H, Kobori Y. Regulated Electron Tunneling of Photoinduced Primary Charge-Separated State in the Photosystem II Reaction Center. J Phys Chem Lett 2017; 8:1179-1184. [PMID: 28240917 DOI: 10.1021/acs.jpclett.7b00044] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In initial events of the photosynthesis by higher plants, the photosystem II (PSII) generates photoinduced primary charge-separated (CS) state composed of reduced pheophytin (PheoD1-•) and oxidized special pair (P+•) in chlorophyll a (Chla) PD1/PD2 in the D1/D2 heterodimer, ultimately leading to the water oxidation at the oxygen-evolving Mn4CaO5 cluster by P+•. To understand the mechanism of the efficient generation of initially localized CS state (PD1+• PheoD1-•), we have characterized cofactor geometries and electronic coupling of the photoinduced primary CS state in quinone prereduced membrane of PSII from spinach using the time-resolved electron paramagnetic resonance method. It has been revealed that the electronic coupling between the charges is significantly weak in the CS state separated by 1.5 nm, showing the importance of regulated cofactor-cofactor electronic interaction between a vinyl substituent in PheoD1 and an accessory chlorophyll to inhibit the energy-wasting charge recombination after the primary electron-transfer processes.
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Affiliation(s)
- Masashi Hasegawa
- Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
| | - Hiroki Nagashima
- Division of Materials Science (Physics), Graduate School of Science, Nagoya University , Furocho, Chikusa, Nagoya 464-8602, Japan
| | - Reina Minobe
- Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
| | - Takashi Tachikawa
- Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
- Laser Molecular Photoscience Laboratory, Molecular Photoscience Research Center, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
| | - Hiroyuki Mino
- Division of Materials Science (Physics), Graduate School of Science, Nagoya University , Furocho, Chikusa, Nagoya 464-8602, Japan
| | - Yasuhiro Kobori
- Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
- Laser Molecular Photoscience Laboratory, Molecular Photoscience Research Center, Kobe University , 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
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34
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Sugiura M, Ozaki Y, Rappaport F, Boussac A. Corrigendum to "Influence of Histidine-198 of the D1 subunit on the properties of the primary electron donor, P 680 , of photosystem II in Thermosynechococcus elongatus". BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1943-1948. [DOI: 10.1016/j.bbabio.2016.09.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 09/26/2016] [Accepted: 09/28/2016] [Indexed: 11/25/2022]
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35
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Senge MO, MacGowan SA, O'Brien JM. Conformational control of cofactors in nature - the influence of protein-induced macrocycle distortion on the biological function of tetrapyrroles. Chem Commun (Camb) 2016; 51:17031-63. [PMID: 26482230 DOI: 10.1039/c5cc06254c] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Tetrapyrrole-containing proteins are one of the most fundamental classes of enzymes in nature and it remains an open question to give a chemical rationale for the multitude of biological reactions that can be catalyzed by these pigment-protein complexes. There are many fundamental processes where the same (i.e., chemically identical) porphyrin cofactor is involved in chemically quite distinct reactions. For example, heme is the active cofactor for oxygen transport and storage (hemoglobin, myoglobin) and for the incorporation of molecular oxygen in organic substrates (cytochrome P450). It is involved in the terminal oxidation (cytochrome c oxidase) and the metabolism of H2O2 (catalases and peroxidases) and catalyzes various electron transfer reactions in cytochromes. Likewise, in photosynthesis the same chlorophyll cofactor may function as a reaction center pigment (charge separation) or as an accessory pigment (exciton transfer) in light harvesting complexes (e.g., chlorophyll a). Whilst differences in the apoprotein sequences alone cannot explain the often drastic differences in physicochemical properties encountered for the same cofactor in diverse protein complexes, a critical factor for all biological functions must be the close structural interplay between bound cofactors and the respective apoprotein in addition to factors such as hydrogen bonding or electronic effects. Here, we explore how nature can use the same chemical molecule as a cofactor for chemically distinct reactions using the concept of conformational flexibility of tetrapyrroles. The multifaceted roles of tetrapyrroles are discussed in the context of the current knowledge on distorted porphyrins. Contemporary analytical methods now allow a more quantitative look at cofactors in protein complexes and the development of the field is illustrated by case studies on hemeproteins and photosynthetic complexes. Specific tetrapyrrole conformations are now used to prepare bioengineered designer proteins with specific catalytic or photochemical properties.
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Affiliation(s)
- Mathias O Senge
- School of Chemistry, SFI Tetrapyrrole Laboratory, Trinity Biomedical Sciences Institute, Trinity College Dublin, The University of Dublin, 152-160 Pearse Street, Dublin 2, Ireland and Medicinal Chemistry, Institute of Molecular Medicine, Trinity Centre for Health Sciences, Trinity College Dublin, St. James's Hospital, Dublin 8, Ireland.
| | - Stuart A MacGowan
- School of Chemistry, SFI Tetrapyrrole Laboratory, Trinity Biomedical Sciences Institute, Trinity College Dublin, The University of Dublin, 152-160 Pearse Street, Dublin 2, Ireland
| | - Jessica M O'Brien
- Medicinal Chemistry, Institute of Molecular Medicine, Trinity Centre for Health Sciences, Trinity College Dublin, St. James's Hospital, Dublin 8, Ireland.
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36
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Suomivuori CM, Winter NOC, Hättig C, Sundholm D, Kaila VRI. Exploring the Light-Capturing Properties of Photosynthetic Chlorophyll Clusters Using Large-Scale Correlated Calculations. J Chem Theory Comput 2016; 12:2644-51. [DOI: 10.1021/acs.jctc.6b00237] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Carl-Mikael Suomivuori
- Department
of Chemistry, University of Helsinki, P.O. Box 55 (A. I. Virtanens plats
1), FIN-00014 Helsinki, Finland
- Department
Chemie, Technische Universität München, Lichtenbergstraße 4, Garching, Germany
| | - Nina O. C. Winter
- Ruhr-University at Bochum, Universitätsstraße
150, 44801 Bochum, Germany
| | - Christof Hättig
- Ruhr-University at Bochum, Universitätsstraße
150, 44801 Bochum, Germany
| | - Dage Sundholm
- Department
of Chemistry, University of Helsinki, P.O. Box 55 (A. I. Virtanens plats
1), FIN-00014 Helsinki, Finland
| | - Ville R. I. Kaila
- Department
Chemie, Technische Universität München, Lichtenbergstraße 4, Garching, Germany
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37
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Najafpour MM, Renger G, Hołyńska M, Moghaddam AN, Aro EM, Carpentier R, Nishihara H, Eaton-Rye JJ, Shen JR, Allakhverdiev SI. Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures. Chem Rev 2016; 116:2886-936. [PMID: 26812090 DOI: 10.1021/acs.chemrev.5b00340] [Citation(s) in RCA: 332] [Impact Index Per Article: 41.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidation. This catalyst is housed in Photosystem II, a membrane-protein complex that functions as a light-driven water oxidase in oxygenic photosynthesis. Water oxidation is also an important reaction in artificial photosynthesis because it has the potential to provide cheap electrons from water for hydrogen production or for the reduction of carbon dioxide on an industrial scale. The water-oxidizing complex of Photosystem II is a Mn-Ca cluster that oxidizes water with a low overpotential and high turnover frequency number of up to 25-90 molecules of O2 released per second. In this Review, we discuss the atomic structure of the Mn-Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlying mechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration of functional Mn-based model complexes for water oxidation and the issue of Mn complexes decomposing to Mn oxide. We then provide a detailed assessment of the chemistry of Mn oxides by considering how their bulk and nanoscale properties contribute to their effectiveness as water-oxidizing catalysts.
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Affiliation(s)
| | - Gernot Renger
- Institute of Chemistry, Max-Volmer-Laboratory of Biophysical Chemistry, Technical University Berlin , Straße des 17. Juni 135, D-10623 Berlin, Germany
| | - Małgorzata Hołyńska
- Fachbereich Chemie und Wissenschaftliches Zentrum für Materialwissenschaften (WZMW), Philipps-Universität Marburg , Hans-Meerwein-Straße, D-35032 Marburg, Germany
| | | | - Eva-Mari Aro
- Department of Biochemistry and Food Chemistry, University of Turku , 20014 Turku, Finland
| | - Robert Carpentier
- Groupe de Recherche en Biologie Végétale (GRBV), Université du Québec à Trois-Rivières , C.P. 500, Trois-Rivières, Québec G9A 5H7, Canada
| | - Hiroshi Nishihara
- Department of Chemistry, School of Science, The University of Tokyo , 7-3-1, Hongo, Bunkyo-Ku, Tokyo 113-0033, Japan
| | - Julian J Eaton-Rye
- Department of Biochemistry, University of Otago , P.O. Box 56, Dunedin 9054, New Zealand
| | - Jian-Ren Shen
- Photosynthesis Research Center, Graduate School of Natural Science and Technology, Faculty of Science, Okayama University , Okayama 700-8530, Japan.,Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences , Beijing 100093, China
| | - Suleyman I Allakhverdiev
- Controlled Photobiosynthesis Laboratory, Institute of Plant Physiology, Russian Academy of Sciences , Botanicheskaya Street 35, Moscow 127276, Russia.,Institute of Basic Biological Problems, Russian Academy of Sciences , Pushchino, Moscow Region 142290, Russia.,Department of Plant Physiology, Faculty of Biology, M.V. Lomonosov Moscow State University , Leninskie Gory 1-12, Moscow 119991, Russia
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38
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Saito K, Sakashita N, Ishikita H. Energetics of the Proton Transfer Pathway for Tyrosine D in Photosystem II. Aust J Chem 2016. [DOI: 10.1071/ch16248] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The proton transfer pathway for redox active tyrosine D (TyrD) in photosystem II is a hydrogen-bond network that involves D2-Arg180 and a series of water molecules. Using quantum mechanical/molecular mechanical calculations, the detailed properties of the energetics and structural geometries were investigated. The potential-energy profile of all hydrogen bonds along the proton transfer pathway indicates that the overall proton transfer from TyrD is energetically downhill. D2-Arg180 plays a key role in the proton transfer pathway, providing a driving force for proton transfer, maintaining the hydrogen-bond network structure, stabilising P680•+, and thus deprotonating TyrD-OH to TyrD-O•. A hydrophobic environment near TyrD enhances the electrostatic interactions between TyrD and redox active groups, e.g. P680 and the catalytic Mn4CaO5 cluster: the redox states of those groups are linked with the protonation state of TyrD, i.e. release of the proton from TyrD. Thus, the proton transfer pathway from TyrD may ultimately contribute to the conversion of S0 into S1 in the dark in order to stabilise the Mn4CaO5 cluster when the photocycle is interrupted in S0.
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39
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Narzi D, Bovi D, De Gaetano P, Guidoni L. Dynamics of the Special Pair of Chlorophylls of Photosystem II. J Am Chem Soc 2015; 138:257-64. [PMID: 26587662 DOI: 10.1021/jacs.5b10523] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cholophylls are at the basis of the photosynthetic energy conversion mechanisms in algae, plants, and cyanobacteria. In photosystem II, the photoproduced electrons leave a special pair of chlorophylls (namely, P(D1) and P(D2)) that becomes cationic. This oxidizing pair [P(D1),P(D2)](+), in turn, triggers a cascade of oxidative events, eventually leading to water splitting and oxygen evolution. In the present work, using quantum mechanics/molecular mechanics calculations, we investigate the electronic structure and the dynamics of the P(D1)P(D2) special pair in both its oxidized and reduced states. In agreement with previously reported static calculations, the symmetry between the two chlorophylls was found to be broken, the positive charge being preferentially located on P(D1). Nevertheless, this study reveals for the first time that large charge fluctuations occur along dynamics, temporarily inverting the charge preference for the two branches. Finally, a vibrational analysis pinpointed that such charge fluctuations are strongly coupled to specific modes of the special pair.
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40
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Li X, Qin X, Zheng H, Yuan H, Guo Y, Xiao D. Highly efficient electrogenerated chemiluminescence of natural chlorophyll a. Electrochem commun 2015. [DOI: 10.1016/j.elecom.2015.10.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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41
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Kaminskaya OP, Shuvalov VA. Towards an understanding of redox heterogeneity of the photosystem II cytochrome b559 in the native membrane. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 45:129-38. [DOI: 10.1007/s00249-015-1082-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 09/07/2015] [Accepted: 09/16/2015] [Indexed: 11/29/2022]
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42
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Olson TL, Espiritu E, Edwardraja S, Simmons CR, Williams JC, Ghirlanda G, Allen JP. Design of dinuclear manganese cofactors for bacterial reaction centers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:539-547. [PMID: 26392146 DOI: 10.1016/j.bbabio.2015.09.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 09/14/2015] [Indexed: 12/28/2022]
Abstract
A compelling target for the design of electron transfer proteins with novel cofactors is to create a model for the oxygen-evolving complex, a Mn4Ca cluster, of photosystem II. A mononuclear Mn cofactor can be added to the bacterial reaction center, but the addition of multiple metal centers is constrained by the native protein architecture. Alternatively, metal centers can be incorporated into artificial proteins. Designs for the addition of dinuclear metal centers to four-helix bundles resulted in three artificial proteins with ligands for one, two, or three dinuclear metal centers able to bind Mn. The three-dimensional structure determined by X-ray crystallography of one of the Mn-proteins confirmed the design features and revealed details concerning coordination of the Mn center. Electron transfer between these artificial Mn-proteins and bacterial reaction centers was investigated using optical spectroscopy. After formation of a light-induced, charge-separated state, the experiments showed that the Mn-proteins can donate an electron to the oxidized bacteriochlorophyll dimer of modified reaction centers, with the Mn-proteins having additional metal centers being more effective at this electron transfer reaction. Modeling of the structure of the Mn-protein docked to the reaction center showed that the artificial protein likely binds on the periplasmic surface similarly to cytochrome c2, the natural secondary donor. Combining reaction centers with exogenous artificial proteins provides the opportunity to create ligands and investigate the influence of inhomogeneous protein environments on multinuclear redox-active metal centers. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson.
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Affiliation(s)
- Tien L Olson
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
| | - Eduardo Espiritu
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
| | | | - Chad R Simmons
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
| | - JoAnn C Williams
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
| | - Giovanna Ghirlanda
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
| | - James P Allen
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA.
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43
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Chauvet A, Jankowiak R, Kell A, Picorel R, Savikhin S. Does the singlet minus triplet spectrum with major photobleaching band near 680-682 nm represent an intact reaction center of Photosystem II? J Phys Chem B 2014; 119:448-55. [PMID: 25495638 DOI: 10.1021/jp510049k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
We use both frequency- and time-domain low-temperature (5-20 K) spectroscopies to further elucidate the shape and spectral position of singlet minus triplet (triplet-bottleneck) spectra in the reaction centers (RCs) of Photosystem II (PSII) isolated from wild-type Chlamydomonas reinhardtii and spinach. It is shown that the shape of the nonresonant transient hole-burned spectrum in destabilized RCs from C. reinhardtii is very similar to that typically observed for spinach. This suggests that the previously observed difference in transient spectra between RCs from C. reinhardtii and spinach is not due to the sample origin but most likely due to a partial destabilization of the D1 and D2 polypeptides. This supports our previous assignments that destabilized RCs (referred to as RC680) (Acharya, K. et al. J. Phys. Chem. B 2012, 116, 4860-4870), with a major photobleaching band near 680-682 nm and the absence of a photobleaching band near 673 nm, do not represent the intact RC residing within the PSII core complex. Time-resolved absorption difference spectra obtained for partially destabilized RCs of C. reinhardtii and for typical spinach RCs support the above conclusions. The absence of clear photobleaching bands near 673 and 684 nm (where the PD1 chlorophyll and the active pheophytin (PheoD1) contribute, respectively) in picosecond transient absorption spectra in both RCs studied in this work indicates that the cation can move from the primary electron donor (ChlD1) to PD1 (i.e., PD1ChlD1(+)PheoD1(-) → PD1(+)ChlD1PheoD1(-)). Therefore, we suggest that ChlD1 is the major electron donor in usually studied destabilized RCs (with a major photobleaching near 680-682 nm), although the PD1 path (where PD1 serves as the primary electron donor) is likely present in intact RCs, as discussed in Acharya, K. et al. J. Phys. Chem. B 2012, 116, 4860-4870.
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Affiliation(s)
- Adrien Chauvet
- Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States
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Zhang L, Silva DA, Zhang H, Yue A, Yan Y, Huang X. Dynamic protein conformations preferentially drive energy transfer along the active chain of the photosystem II reaction centre. Nat Commun 2014; 5:4170. [PMID: 24954746 PMCID: PMC4083425 DOI: 10.1038/ncomms5170] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 05/20/2014] [Indexed: 11/11/2022] Open
Abstract
One longstanding puzzle concerning photosystem II, a core component of photosynthesis, is that only one of the two symmetric branches in its reaction centre is active in electron transfer. To investigate the effect of the photosystem II environment on the preferential selection of the energy transfer pathway (a prerequisite for electron transfer), we have constructed an exciton model via extensive molecular dynamics simulations and quantum mechanics/molecular mechanics calculations based on a recent X-ray structure. Our results suggest that it is essential to take into account an ensemble of protein conformations to accurately compute the site energies. We identify the cofactor CLA606 of active chain as the most probable site for the energy excitation. We further pinpoint a number of charged protein residues that collectively lower the CLA606 site energy. Our work provides insights into the understanding of molecular mechanisms of the core machinery of the green-plant photosynthesis. Cofactor-mediated energy and electron transfer in photosystem II occurs preferentially through one branch of the reaction centre, despite there being a symmetric path available. Here, the authors use computational methods to determine the influence of protein conformation on this selectivity.
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Affiliation(s)
- Lu Zhang
- Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Daniel-Adriano Silva
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2]
| | - Houdao Zhang
- Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Alexander Yue
- Division of Biomedical Engineering, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - YiJing Yan
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2] Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
| | - Xuhui Huang
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2] Division of Biomedical Engineering, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [3] Centre of Systems Biology and Human Health, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
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Li X, Yuan H, Li L, Xiao D. Electrogenerated chemiluminescence of magnesium chlorophyllin a aqueous solution and its sensitive response to the carcinogen aflatoxin B1. Biosens Bioelectron 2014; 55:350-4. [DOI: 10.1016/j.bios.2013.12.026] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2013] [Revised: 12/02/2013] [Accepted: 12/09/2013] [Indexed: 12/23/2022]
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Saito K, Ishikita H. Influence of the Ca 2+ ion on the Mn 4 Ca conformation and the H-bond network arrangement in Photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:159-66. [DOI: 10.1016/j.bbabio.2013.09.013] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 09/19/2013] [Accepted: 09/24/2013] [Indexed: 01/06/2023]
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Kim HW, Rhee YM. On the pH Dependent Behavior of the Firefly Bioluminescence: Protein Dynamics and Water Content in the Active Pocket. J Phys Chem B 2013; 117:7260-9. [DOI: 10.1021/jp4024553] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Hyun Woo Kim
- Center for Self-Assembly and Complexity, Institute for Basic Science (IBS), Pohang 790-784,
Korea, and Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 790-784,
Korea
| | - Young Min Rhee
- Center for Self-Assembly and Complexity, Institute for Basic Science (IBS), Pohang 790-784,
Korea, and Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang 790-784,
Korea
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Abstract
Using quantum mechanics/molecular mechanics calculations and the 1.9-Å crystal structure of Photosystem II [Umena Y, Kawakami K, Shen J-R, Kamiya N (2011) Nature 473(7345):55-60], we investigated the H-bonding environment of the redox-active tyrosine D (TyrD) and obtained insights that help explain its slow redox kinetics and the stability of TyrD(•). The water molecule distal to TyrD, located ~4 Å away from the phenolic O of TyrD, corresponds to the presence of the tyrosyl radical state. The water molecule proximal to TyrD, in H-bonding distance to the phenolic O of TyrD, corresponds to the presence of the unoxidized tyrosine. The H(+) released on oxidation of TyrD is transferred to the proximal water, which shifts to the distal position, triggering a concerted proton transfer pathway involving D2-Arg180 and a series of waters, through which the proton reaches the aqueous phase at D2-His61. The water movement linked to the ejection of the proton from the hydrophobic environment near TyrD makes oxidation slow and quasiirreversible, explaining the great stability of the TyrD(•). A symmetry-related proton pathway associated with tyrosine Z is pointed out, and this is associated with one of the Cl(-) sites. This may represent a proton pathway functional in the water oxidation cycle.
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Olson TL, Williams JC, Allen JP. Influence of protein interactions on oxidation/reduction midpoint potentials of cofactors in natural and de novo metalloproteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:914-22. [PMID: 23466333 DOI: 10.1016/j.bbabio.2013.02.014] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 02/13/2013] [Accepted: 02/23/2013] [Indexed: 01/14/2023]
Abstract
As discussed throughout this special issue, oxidation and reduction reactions play critical roles in the function of many organisms. In photosynthetic organisms, the conversion of light energy drives oxidation and reduction reactions through the transfer of electrons and protons in order to create energy-rich compounds. These reactions occur in proteins such as cytochrome c, a heme-containing water-soluble protein, the bacteriochlorophyll-containing reaction center, and photosystem II where water is oxidized at the manganese cluster. A critical measure describing the ability of cofactors in proteins to participate in such reactions is the oxidation/reduction midpoint potential. In this review, the basic concepts of oxidation/reduction reactions are reviewed with a summary of the experimental approaches used to measure the midpoint potential of metal cofactors. For cofactors in proteins, the midpoint potential not only depends upon the specific chemical characteristics of cofactors but also upon interactions with the surrounding protein, such as the nature of the coordinating ligands and protein environment. These interactions can be tailored to optimize an oxidation/reduction reaction carried out by the protein. As examples, the midpoint potentials of hemes in cytochromes, bacteriochlorophylls in reaction centers, and the manganese cluster of photosystem II are discussed with an emphasis on the influence that protein interactions have on these potentials. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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Affiliation(s)
- T L Olson
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA
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Abstract
Photosystem II uses light to drive water oxidation and plastoquinone (PQ) reduction. PQ reduction involves two PQ cofactors, Q(A) and Q(B), working in series. Q(A) is a one-electron carrier, whereas Q(B) undergoes sequential reduction and protonation to form Q(B)H(2). Q(B)H(2) exchanges with PQ from the pool in the membrane. Based on the atomic coordinates of the Photosystem II crystal structure, we analyzed the proton transfer (PT) energetics adopting a quantum mechanical/molecular mechanical approach. The potential-energy profile suggests that the initial PT to Q(B)(•-) occurs from the protonated, D1-His252 to Q(B)(•)(-) via D1-Ser264. The second PT is likely to occur from D1-His215 to Q(B)H(-) via an H-bond with an energy profile with a single well, resulting in the formation of Q(B)H(2) and the D1-His215 anion. The pathway for reprotonation of D1-His215(-) may involve bicarbonate, D1-Tyr246 and water in the Q(B) site. Formate ligation to Fe(2+) did not significantly affect the protonation of reduced Q(B), suggesting that formate inhibits Q(B)H(2) release rather than its formation. The presence of carbonate rather than bicarbonate seems unlikely because the calculations showed that this greatly perturbed the potential of the nonheme iron, stabilizing the Fe(3+) state in the presence of Q(B)(•-), a situation not encountered experimentally. H-bonding from D1-Tyr246 and D2-Tyr244 to the bicarbonate ligand of the nonheme iron contributes to the stability of the semiquinones. A detailed mechanistic model for Q(B) reduction is presented.
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