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Structure of photosystem II and substrate binding at room temperature.

ABSTRACT: Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the Mn4CaO5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S0 to S4), in which S1 is the dark-stable state and S3 is the last semi-stable state before O-O bond formation and O2 evolution. A detailed understanding of the O-O bond formation mechanism remains a challenge, and will require elucidation of both the structures of the OEC in the different S-states and the binding of the two substrate waters to the catalytic site. Here we report the use of femtosecond pulses from an X-ray free electron laser (XFEL) to obtain damage-free, room temperature structures of dark-adapted (S1), two-flash illuminated (2F; S3-enriched), and ammonia-bound two-flash illuminated (2F-NH3; S3-enriched) PS II. Although the recent 1.95?Å resolution structure of PS II at cryogenic temperature using an XFEL provided a damage-free view of the S1 state, measurements at room temperature are required to study the structural landscape of proteins under functional conditions, and also for in situ advancement of the S-states. To investigate the water-binding site(s), ammonia, a water analogue, has been used as a marker, as it binds to the Mn4CaO5 cluster in the S2 and S3 states. Since the ammonia-bound OEC is active, the ammonia-binding Mn site is not a substrate water site. This approach, together with a comparison of the native dark and 2F states, is used to discriminate between proposed O-O bond formation mechanisms.

SUBMITTER: Young ID

PROVIDER: S-EPMC5201176 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature

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Structure of photosystem II and substrate binding at room temperature.

Young Iris D ID Ibrahim Mohamed M Chatterjee Ruchira R Gul Sheraz S Fuller Franklin F Koroidov Sergey S Brewster Aaron S AS Tran Rosalie R Alonso-Mori Roberto R Kroll Thomas T Michels-Clark Tara T Laksmono Hartawan H Sierra Raymond G RG Stan Claudiu A CA Hussein Rana R Zhang Miao M Douthit Lacey L Kubin Markus M de Lichtenberg Casper C Long Vo Pham P Nilsson Håkan H Cheah Mun Hon MH Shevela Dmitriy D Saracini Claudio C Bean Mackenzie A MA Seuffert Ina I Sokaras Dimosthenis D Weng Tsu-Chien TC Pastor Ernest E Weninger Clemens C Fransson Thomas T Lassalle Louise L Bräuer Philipp P Aller Pierre P Docker Peter T PT Andi Babak B Orville Allen M AM Glownia James M JM Nelson Silke S Sikorski Marcin M Zhu Diling D Hunter Mark S MS Lane Thomas J TJ Aquila Andy A Koglin Jason E JE Robinson Joseph J Liang Mengning M Boutet Sébastien S Lyubimov Artem Y AY Uervirojnangkoorn Monarin M Moriarty Nigel W NW Liebschner Dorothee D Afonine Pavel V PV Waterman David G DG Evans Gwyndaf G Wernet Philippe P Dobbek Holger H Weis William I WI Brunger Axel T AT Zwart Petrus H PH Adams Paul D PD Zouni Athina A Messinger Johannes J Bergmann Uwe U Sauter Nicholas K NK Kern Jan J Yachandra Vittal K VK Yano Junko J

Nature 20161121 7633

Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the Mn4CaO5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S0 ...[more]

PMID: 27871088

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Project description:Highlights • We derive a model that provides an exact solution to the substrate-water exchange kinetics in a double-conformation system.• This model is used to interpret recently published data for Ca2+- and Sr2+-containing PSII in the S2 state, in which the g = 2.0 and g = 4.1 conformations coexist.• The component concentrations derived from the kinetic model provide an analytic description of the substrate-water exchange kinetics.• Contrary to previous reports, there is no significant effect of substituting Sr2+ for Ca2+ on any of the exchange rate constants.• The exchange rate of the slowly-exchanging water (Ws) in the S2 state g = 4.1 conformation is much faster than that in the g = 2.0 conformation, consistent with the assignment of Ws to W1 or W2 bound as terminal ligands to Mn4. We derive a model that provides an exact solution to the substrate-water exchange kinetics in a double-conformation system and use this model to interpret recently published data for Ca2+- and Sr2+-containing PSII in the S2 state, in which the g = 2.0 and g = 4.1 conformations coexist. The component concentrations derived from the kinetic model provide an analytic description of the substrate-water exchange kinetics, allowing us to more accurately interpret the results. Based on this model and the previously reported data on the S2 state g = 2.0 conformation, we obtain the substrate-water exchange rates of the g = 4.1 conformation and the conformational change rates. Two conclusions are made from the analyses. First, contrary to previous reports, there is no significant effect of substituting Sr2+ for Ca2+ on any of the exchange rate constants. Second, the exchange rate of the slowly-exchanging water (Ws) in the S2 state g = 4.1 conformation is much faster than that in the S2 state g = 2.0 conformation. The second conclusion is consistent with the assignment of Ws to W1 or W2 bound as terminal ligands to Mn4; Mn4 has been proposed to undergo an oxidation state change from Mn(IV) in the g = 2.0 conformation to Mn(III) in the g = 4.1 conformation.

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Structure of photosystem II and substrate binding at room temperature.

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Structure of photosystem II and substrate binding at room temperature.

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