TAILIEUCHUNG - Báo cáo khóa học: The function of D1-H332 in Photosystem II electron transport studied by thermoluminescence and chlorophyll fluorescence in site-directed mutants of Synechocystis 6803

The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxi-dizing complex (Ferreira, ., Iverson, ., Maghlaoui, K., Barber, J. & Iwata, S. (2004) Science303, 1831–1838). However, its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of theD1-H333E,D1-H332DandD1-H332Smutationson the electron transport of Photosystem II in intact cells of the cyanobacteriumSynechocystis6803 | Eur. J. Biochem. 271 3523-3532 2004 FEBS 2004 doi The function of D1-H332 in Photosystem II electron transport studied by thermoluminescence and chlorophyll fluorescence in site-directed mutants of Synechocystis 6803 Yagut Allahverdiyeva1 Zsuzsanna Deak1 Andras Szilard1 Bruce A. Diner2 Peter J. Nixon3 and Imre Vass1 Institute of Plant Biology Biological Research Center Szeged Hungary 2CR D Experimental Station . du Pont de Nemours and Co. Wilmington DE USA 3Department of Biological Sciences Imperial College London UK The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxidizing complex Ferreira . Iverson . Maghlaoui K. Barber J. Iwata S. 2004 Science 303 1831-1838 . However its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of the D1-H333E D1-H332D and D1-H332S mutations onthe electron transport of Photosystem II in intact cells of the cyanobacterium Synechocystis 6803. Although the mutants are not photoautotrophic they all show flash-induced thermoluminescence and chlorophyll fluorescence which originate from the S2QA- and S2QB- recombinations demonstrating that charge stabilization takes place in the water oxidizing complex. However the conversion of S2 to higher S states is inhibited and the energetic stability of the S2Qa charge pair is increased by 75 50 and 7 mV in the D1-H332D D1-H332E and D1-H332S mutants respectively. This is most probably caused by a decrease of Em S2 S1 . Concomitantly the rate of electron donation from Mn to Tyr-Z during the S1 to S2 transition is slowed down relative to the wild type 350- and 60-fold in the D1-H332E and D1-H332D mutants respectively but remains essentially unaffected in D1-H332S. A further effect of the D1-H332E and D1-H332D mutations is the retardation of the QA to QB electron transfer step as an indirect .

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