Function of redox-active tyrosine in photosystem II.
Water oxidation at photosystem II Mn-cluster is mediated by the redox-active tyrosine Y(Z). We calculated the redox potential (E(m)) of Y(Z) and its symmetrical counterpart Y(D), by solving the linearized Poisson-Boltzmann equation. The calculated E(m)(Y( )/Y(-)) were +926 mV/+694 mV for Y(Z)/Y(D) with the Mn-cluster in S2 state. Together with the asymmetric position of the Mn-cluster relative to Y(Z/D), differences in H-bond network between Y(Z) (Y(Z)/D1-His(190)/D1-Asn(298)) and Y(D) (Y(D)/D2-His(189)/D2-Arg(294)/CP47-Glu(364)) are crucial for E(m)(Y(Z/D)). When D1-His(190) is protonated, corresponding to a thermally activated state, the calculated E(m)(Y(Z)) was +1216 mV, which is as high as the E(m) for P(D1/D2). We observed deprotonation at CP43-Arg(357) upon S-state transition, which may suggest its involvement in the proton exit pathway. E(m)(Y(D)) was affected by formation of P(D2)(+) (but not P(D1)(+)) and sensitive to the protonation state of D2-Arg(180). This points to an electrostatic link between Y(D) and P(D2).
Ishikita
Hiroshi
H
Institute of Chemistry and Biochemistry, Free University of Berlin, Berlin, Germany.
Knapp
Ernst-Walter
EW
D008345:Manganese / Q000737:chemistry; D008433:Mathematics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011522:Protons; D055672:Static Electricity; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D045332:Photosystem II Protein Complex; D011522:Protons; D014867:Water; D014443:Tyrosine; D008345:Manganese