Influence of the Redox Potential of the Primary Quinone Electron Acceptor on Photoinhibition in Photosystem II

• Published in: The Journal of biological chemistry 2007-04, Vol.282 (17), p.12492-12502
• Main Authors: Fufezan, Christian, Gross, Christine M., Sjödin, Martin, Rutherford, A. William, Krieger-Liszkay, Anja, Kirilovsky, Diana
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biochemistry, Molecular Biology; Biophysics; Cyanobacteria - enzymology; Cyanobacteria - genetics; Electron Transport - physiology; Electrons; Kinetics; Life Sciences; Mutation, Missense; Oxidation-Reduction; Photosystem II Protein Complex - genetics; Photosystem II Protein Complex - metabolism; Plastoquinone - metabolism; Singlet Oxygen - metabolism; Thermosynechococcus elongatus
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M610951200

We report the characterization of the effects of the A249S mutation located within the binding pocket of the primary quinone electron acceptor, QA, in the D2 subunit of photosystem II in Thermosynechococcus elongatus. This mutation shifts the redox potential of QA by ∼–60 mV. This mutant provides an opportunity to test the hypothesis, proposed earlier from herbicide-induced redox effects, that photoinhibition (light-induced damage of the photosynthetic apparatus) is modulated by the potential of QA. Thus the influence of the redox potential of QA on photoinhibition was investigated in vivo and in vitro. Compared with the wild-type, the A249S mutant showed an accelerated photoinhibition and an increase in singlet oxygen production. Measurements of thermoluminescence and of the fluorescence yield decay kinetics indicated that the charge-separated state involving QA was destabilized in the A249S mutant. These findings support the hypothesis that a decrease in the redox potential of QA causes an increase in singlet oxygen-mediated photoinhibition by favoring the back-reaction route that involves formation of the reaction center chlorophyll triplet. The kinetics of charge recombination are interpreted in terms of a dynamic structural heterogeneity in photosystem II that results in high and low potential forms of QA. The effect of the A249S mutation seems to reflect a shift in the structural equilibrium favoring the low potential form.