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Biophys. J. BioFAST: First Published March 2, 2006. doi:10.1529/biophysj.105.076984
© 2006 by the Biophysical Society.

A more recent version of this article appeared on June 1, 2006.
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BIOPHYSICAL THEORY AND MODELING

Function of redox-active tyrosine in photosystem II

Hiroshi Ishikita 1 and Ernst Walter Knapp 2*

1 Free University of Berlin
2 Freie Universitat Berlin

* To whom correspondence should be addressed. E-mail: knapp{at}chemie.fu-berlin.de.

Submitted on November 1, 2005
Revised on December 4, 2005
Accepted on 2 February 2006


  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 PD2+ (but not PD1+) and sensitive to the protonation state of D2-Arg180. This points to an electrostatic link between YD and PD2.

Key Words: CP43-Arg357, Poisson-Boltzmann, YZ/YD redox potential, electron transfer, pKa computation, proton exit pathway




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Copyright © 2006 by the Biophysical Society.