Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 19, Pages 7690-7695Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1300817110
Keywords
oxygen-evolving complex; proton-coupled electron transfer; reaction center evolution; controlling electron transfer rate; hydrogen bond direction switching
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Funding
- Japan Science and Technology Agency Precursory Research for Embryonic Science and Technology program
- Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan [22740276]
- Special Coordination Fund for Promoting Science and Technology of the MEXT
- Takeda Science Foundation
- Sumitomo Foundation
- Wolfson Merit Award of the Royal Society
- Grants-in-Aid for Scientific Research [22740276] Funding Source: KAKEN
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Using quantum mechanics/molecular mechanics calculations and the 1.9-angstrom crystal structure of Photosystem II [Umena Y, Kawakami K, Shen J-R, Kamiya N (2011) Nature 473(7345):55-60], we investigated the H-bonding environment of the redox-active tyrosine D (TyrD) and obtained insights that help explain its slow redox kinetics and the stability of TyrD(.). The water molecule distal to TyrD, located similar to 4 angstrom away from the phenolic O of TyrD, corresponds to the presence of the tyrosyl radical state. The water molecule proximal to TyrD, in H-bonding distance to the phenolic O of TyrD, corresponds to the presence of the unoxidized tyrosine. The H+ released on oxidation of TyrD is transferred to the proximal water, which shifts to the distal position, triggering a concerted proton transfer pathway involving D2-Arg180 and a series of waters, through which the proton reaches the aqueous phase at D2-His61. The water movement linked to the ejection of the proton from the hydrophobic environment near TyrD makes oxidation slow and quasiirreversible, explaining the great stability of the TyrD(.). A symmetry-related proton pathway associated with tyrosine Z is pointed out, and this is associated with one of the Cl- sites. This may represent a proton pathway functional in the water oxidation cycle.
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