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Structure of photosystem II and substrate binding at room temperature

  • Author(s): Young, ID
  • Ibrahim, M
  • Chatterjee, R
  • Gul, S
  • Fuller, FD
  • Koroidov, S
  • Brewster, AS
  • Tran, R
  • Alonso-Mori, R
  • Kroll, T
  • Michels-Clark, T
  • Laksmono, H
  • Sierra, RG
  • Stan, CA
  • Hussein, R
  • Zhang, M
  • Douthit, L
  • Kubin, M
  • De Lichtenberg, C
  • Vo Pham, L
  • Nilsson, H
  • Cheah, MH
  • Shevela, D
  • Saracini, C
  • Bean, MA
  • Seuffert, I
  • Sokaras, D
  • Weng, TC
  • Pastor, E
  • Weninger, C
  • Fransson, T
  • Lassalle, L
  • Bräuer, P
  • Aller, P
  • Docker, PT
  • Andi, B
  • Orville, AM
  • Glownia, JM
  • Nelson, S
  • Sikorski, M
  • Zhu, D
  • Hunter, MS
  • Lane, TJ
  • Aquila, A
  • Koglin, JE
  • Robinson, J
  • Liang, M
  • Boutet, S
  • Lyubimov, AY
  • Uervirojnangkoorn, M
  • Moriarty, NW
  • Liebschner, D
  • Afonine, PV
  • Waterman, DG
  • Evans, G
  • Wernet, P
  • Dobbek, H
  • Weis, WI
  • Brunger, AT
  • Zwart, PH
  • Adams, PD
  • Zouni, A
  • Messinger, J
  • Bergmann, U
  • Sauter, NK
  • Kern, J
  • Yachandra, VK
  • Yano, J
  • et al.

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© 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. 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 Mn 4 CaO 5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S 0 to S 4), in which S 1 is the dark-stable state and S 3 is the last semi-stable state before O-O bond formation and O 2 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 (S 1), two-flash illuminated (2F; S 3 -enriched), and ammonia-bound two-flash illuminated (2F-NH 3; S 3 -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 S 1 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 Mn 4 CaO 5 cluster in the S 2 and S 3 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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