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Hussein R, Graça A, Forsman J, Aydin AO, Hall M, Gaetcke J, Chernev P, Wendler P, Dobbek H, Messinger J, Zouni A, Schröder WP. Cryo-electron microscopy reveals hydrogen positions and water networks in photosystem II. Science 2024; 384:1349-1355. [PMID: 38900892 DOI: 10.1126/science.adn6541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Accepted: 05/16/2024] [Indexed: 06/22/2024]
Abstract
Photosystem II starts the photosynthetic electron transport chain that converts solar energy into chemical energy and thus sustains life on Earth. It catalyzes two chemical reactions: water oxidation to molecular oxygen and plastoquinone reduction. Coupling of electron and proton transfer is crucial for efficiency; however, the molecular basis of these processes remains speculative owing to uncertain water binding sites and the lack of experimentally determined hydrogen positions. We thus collected high-resolution cryo-electron microscopy data of fully hydrated photosystem II from the thermophilic cyanobacterium Thermosynechococcus vestitus to a final resolution of 1.71 angstroms. The structure reveals several previously undetected partially occupied water binding sites and more than half of the hydrogen and proton positions. This clarifies the pathways of substrate water binding and plastoquinone B protonation.
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Affiliation(s)
- Rana Hussein
- Humboldt-Universität zu Berlin, Department of Biology, D 10099 Berlin, Germany
| | - André Graça
- Department of Chemistry, Umeå University, SE 90187 Umeå, Sweden
- Molecular Biomimetics, Department of Chemistry- Ångström Laboratory, Uppsala University, SE 75120 Uppsala, Sweden
| | - Jack Forsman
- Department of Chemistry, Umeå University, SE 90187 Umeå, Sweden
| | - A Orkun Aydin
- Molecular Biomimetics, Department of Chemistry- Ångström Laboratory, Uppsala University, SE 75120 Uppsala, Sweden
| | - Michael Hall
- Department of Chemistry, Umeå University, SE 90187 Umeå, Sweden
| | - Julia Gaetcke
- Humboldt-Universität zu Berlin, Department of Biology, D 10099 Berlin, Germany
| | - Petko Chernev
- Molecular Biomimetics, Department of Chemistry- Ångström Laboratory, Uppsala University, SE 75120 Uppsala, Sweden
| | - Petra Wendler
- Institute of Biochemistry and Biology, Department of Biochemistry, University of Potsdam, Karl-Liebknecht Strasse 24-25, D 14476, Potsdam-Golm, Germany
| | - Holger Dobbek
- Humboldt-Universität zu Berlin, Department of Biology, D 10099 Berlin, Germany
| | - Johannes Messinger
- Molecular Biomimetics, Department of Chemistry- Ångström Laboratory, Uppsala University, SE 75120 Uppsala, Sweden
- Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Sweden
| | - Athina Zouni
- Humboldt-Universität zu Berlin, Department of Biology, D 10099 Berlin, Germany
| | - Wolfgang P Schröder
- Department of Chemistry, Umeå University, SE 90187 Umeå, Sweden
- Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Sweden
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Khaing EP, Eaton-Rye JJ. Lys264 of the D2 Protein Performs a Dual Role in Photosystem II Modifying Assembly and Electron Transfer through the Quinone-Iron Acceptor Complex. Biochemistry 2023; 62:2738-2750. [PMID: 37606628 DOI: 10.1021/acs.biochem.3c00240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2023]
Abstract
Bicarbonate (HCO3-) binding regulates electron flow between the primary (QA) and secondary (QB) plastoquinone electron acceptors of Photosystem II (PS II). Lys264 of the D2 subunit of PS II contributes to a hydrogen-bond network that stabilizes HCO3- ligation to the non-heme iron in the QA-Fe-QB complex. Using the cyanobacterium Synechocystis sp. PCC 6803, alanine and glutamate were introduced to create the K264A and K264E mutants. Photoautotrophic growth was slowed in K264E cells but not in the K264A strain. Both mutants accumulated an unassembled CP43 precomplex as well as the CP43-lacking RC47 assembly intermediate, indicating weakened binding of the CP43 precomplex to RC47. Assembly was impeded more in K264E cells than in the K264A strain, but K264A cells were more susceptible to high-light-induced photodamage when assayed using PS II-specific electron acceptors. Furthermore, an impaired repair mechanism was observed in the K264A mutant in protein labeling experiments. Unexpectedly, unlike the K264A strain, the K264E mutant displayed inhibited oxygen evolution following high-light exposure when HCO3- was added to support whole chain electron transport. In both mutants, the decay of chlorophyll fluorescence was slowed, indicating impaired electron transfer between QA and QB. Furthermore, the fluorescence decay kinetics in the K264E strain were insensitive to addition of either formate or HCO3-, whereas HCO3--reversible formate-induced inhibition in the K264A mutant was observed. Exchange of plastoquinol with the membrane plastoquinone pool at the QB-binding site was also retarded in both mutants. Hence, D2-Lys264 possesses key roles in both assembly and activity of PS II.
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Affiliation(s)
- Ei Phyo Khaing
- Department of Biochemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
| | - Julian J Eaton-Rye
- Department of Biochemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
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Sugo Y, Tamura H, Ishikita H. Electron Transfer Route between Quinones in Type-II Reaction Centers. J Phys Chem B 2022; 126:9549-9558. [PMID: 36374126 PMCID: PMC9707520 DOI: 10.1021/acs.jpcb.2c05713] [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: 08/10/2022] [Revised: 10/28/2022] [Indexed: 11/16/2022]
Abstract
In photosynthetic reaction centers from purple bacteria (PbRCs) and photosystem II (PSII), the photoinduced charge separation is terminated by an electron transfer between the primary (QA) and secondary (QB) quinones. Here, we investigate the electron transfer route, calculating the superexchange coupling (HQA-QB) for electron transfer from QA to QB in the protein environment. HQA-QB is significantly larger in PbRC than in PSII. In superexchange electron tunneling, the electron transfer via unoccupied molecular orbitals of the nonheme Fe complex (QA → Fe → QB) is pronounced in PbRC, whereas the electron transfer via occupied molecular orbitals (Fe → QB followed by QA → Fe) is pronounced in PSII. The significantly large HQA-QB is caused by a water molecule that donates the H-bond to the ligand Glu-M234 in PbRC. The corresponding water molecule is absent in PSII due to the existence of D1-Tyr246. HQA-QB increases in response to the Ser-L223···QB H-bond formation caused by an extension of the H-bond network, which facilitates charge delocalization over the QB site. This explains the observed discrepancy in the QA-to-QB electron transfer between PbRC and PSII, despite their structural similarity.
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Affiliation(s)
- Yu Sugo
- Department
of Applied Chemistry, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo113-8654, Japan
| | - 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
| | - 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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