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Function of Redox-Active Tyrosine in Photosystem II

Authors
  • Hiroshi Ishikita
  • Ernst-Walter Knapp
Publisher
Biophysical Society
Publication Date
Mar 02, 2006
Source
PMC
Keywords
License
Unknown

Abstract

Water oxidation at photosystem II Mn-cluster is mediated by the redox-active tyrosine YZ. We calculated the redox potential (Em) of YZ and its symmetrical counterpart YD, by solving the linearized Poisson-Boltzmann equation. The calculated Em(Y˙/Y−) were +926 mV/+694 mV for YZ/YD with the Mn-cluster in S2 state. Together with the asymmetric position of the Mn-cluster relative to YZ/D, differences in H-bond network between YZ (YZ/D1-His190/D1-Asn298) and YD (YD/D2-His189/D2-Arg294/CP47-Glu364) are crucial for Em(YZ/D). When D1-His190 is protonated, corresponding to a thermally activated state, the calculated Em(YZ) was +1216 mV, which is as high as the Em for PD1/D2. We observed deprotonation at CP43-Arg357 upon S-state transition, which may suggest its involvement in the proton exit pathway. Em(YD) was affected by formation of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{P}}_{{\mathrm{D}}2}^{+}\end{equation*}\end{document} (but not \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{P}}_{{\mathrm{D}}1}^{+}\end{equation*}\end{document}) and sensitive to the protonation state of D2-Arg180. This points to an electrostatic link between YD and PD2.

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