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Open Access Publications from the University of California

Structure of photosystem II and substrate binding at room temperature.

  • Author(s): Young, Iris D;
  • Ibrahim, Mohamed;
  • Chatterjee, Ruchira;
  • Gul, Sheraz;
  • Fuller, Franklin;
  • Koroidov, Sergey;
  • Brewster, Aaron S;
  • Tran, Rosalie;
  • Alonso-Mori, Roberto;
  • Kroll, Thomas;
  • Michels-Clark, Tara;
  • Laksmono, Hartawan;
  • Sierra, Raymond G;
  • Stan, Claudiu A;
  • Hussein, Rana;
  • Zhang, Miao;
  • Douthit, Lacey;
  • Kubin, Markus;
  • de Lichtenberg, Casper;
  • Long Vo, Pham;
  • Nilsson, Håkan;
  • Cheah, Mun Hon;
  • Shevela, Dmitriy;
  • Saracini, Claudio;
  • Bean, Mackenzie A;
  • Seuffert, Ina;
  • Sokaras, Dimosthenis;
  • Weng, Tsu-Chien;
  • Pastor, Ernest;
  • Weninger, Clemens;
  • Fransson, Thomas;
  • Lassalle, Louise;
  • Bräuer, Philipp;
  • Aller, Pierre;
  • Docker, Peter T;
  • Andi, Babak;
  • Orville, Allen M;
  • Glownia, James M;
  • Nelson, Silke;
  • Sikorski, Marcin;
  • Zhu, Diling;
  • Hunter, Mark S;
  • Lane, Thomas J;
  • Aquila, Andy;
  • Koglin, Jason E;
  • Robinson, Joseph;
  • Liang, Mengning;
  • Boutet, Sébastien;
  • Lyubimov, Artem Y;
  • Uervirojnangkoorn, Monarin;
  • Moriarty, Nigel W;
  • Liebschner, Dorothee;
  • Afonine, Pavel V;
  • Waterman, David G;
  • Evans, Gwyndaf;
  • Wernet, Philippe;
  • Dobbek, Holger;
  • Weis, William I;
  • Brunger, Axel T;
  • Zwart, Petrus H;
  • Adams, Paul D;
  • Zouni, Athina;
  • Messinger, Johannes;
  • Bergmann, Uwe;
  • Sauter, Nicholas K;
  • Kern, Jan;
  • Yachandra, Vittal K;
  • Yano, Junko
  • et al.

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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.

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