Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1837, Issue 1, Pages 159-166Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2013.09.013
Keywords
Ca-depleted Photosystem II; Mn4Ca; Distorted Mn3CaO4 cubane; Sr-substituted photosystem II; Overreduced state
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Funding
- JST PRESTO program
- Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan [22740276, 25107517]
- Takeda Science Foundation
- Grants-in-Aid for Scientific Research [25107517] Funding Source: KAKEN
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In the crystal structure of Photosystem II (PSII) analyzed at a resolution of 1.9 angstrom, most of the bond lengths between Mn and O atoms in the oxygen-evolving Mn4Ca cluster are 1.8-2.1 angstrom. On the other hand, the Mn1 - 05 bond in the Mn3CaO4 cubane region of the Mn4Ca cluster is significantly elongated to 2.6 angstrom. Using a quantum mechanical/molecular mechanical approach, we investigated factors that are responsible for distortion of the Mn3CaO4 cubane. Removal of Ca led to shortening the Mn1 - 05 bond by 0.2 angstrom; however, Mn1 - 05 remained significantly elongated, at >2.5 angstrom. Conversely, removal of Mn4 significantly shortens the Mn1 - 05 distance by 0.5 A to 22 angstrom, resulting in a more symmetric cubane shape. These results suggest that Mn4, not Ca, is predominantly responsible for distortion of the Mn3CaO4 cubane. It was not the Ca component that was responsible for the existence of the two S2 conformers but two different Mn oxidation states (Mn1, Mn2, Mn3, M4) = (III, IV, IV, IV) and (IV, IV, IV, III); they were interconvertible by translocation of the 05 atom along the Mn1-O5-Mn4 axis. Depletion of Ca resulted in rearrangement of the H-bond network near TyrZ, which proceeds via a chloride ion (Cl-1 pathway). This may explain why Ca depletion inhibits the S2 to S3 transition, the same process that can also be inhibited by Cl- depletion. (C) 2013 Elsevier B.V. All rights reserved.
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