Environment of TyrZ in photosystem II from Thermosynechococcus elongatus in which PsbA2 is the D1 protein |
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Authors: | Sugiura Miwa Ogami Shogo Kusumi Mai Un Sun Rappaport Fabrice Boussac Alain |
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Affiliation: | Cell-Free Science and Technology Research Center, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan. miwa.sugiura@ehime-u.ac.jp |
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Abstract: | The main cofactors that determine the photosystem II (PSII) oxygen evolutionactivity are borne by the D1 and D2 subunits. In the cyanobacteriumThermosynechococcus elongatus, there are threepsbA genes coding for D1. Among the 344 residuesconstituting D1, there are 21 substitutions between PsbA1 and PsbA3, 31 betweenPsbA1 and PsbA2, and 27 between PsbA2 and PsbA3. Here, we present the firststudy of PsbA2-PSII. Using EPR and UV-visible time-resolved absorptionspectroscopy, we show that: (i) the time-resolved EPR spectrum of TyrZ• in the(S3TyrZ•)′ is slightly modified; (ii) the split EPR signalarising from TyrZ• in the (S2TyrZ•)′ state induced by near-infraredillumination at 4.2 K of the S3TyrZ state is significantlymodified; and (iii) the slow phases of P680+⋅ reduction by TyrZ areslowed down from the hundreds of μs time range to the ms time range,whereas both the S1TyrZ• → S2TyrZ andthe S3TyrZ• → S0TyrZ + O2transition kinetics remained similar to those in PsbA(1/3)-PSII. These resultsshow that the geometry of the TyrZ phenol and its environment, likelythe Tyr-O···H···Nϵ-His bonding,are modified in PsbA2-PSII when compared with PsbA(1/3)-PSII. They also point tothe dynamics of the proton-coupled electron transfer processes associated withthe oxidation of TyrZ being affected. From sequence comparison, wepropose that the C144P and P173M substitutions in PsbA2-PSIIversus PsbA(1/3)-PSII, respectively located upstream of theα-helix bearing TyrZ and between the two α-helicesbearing TyrZ and its hydrogen-bonded partner, His-190, areresponsible for these changes. |
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Keywords: | Bioenergetics Bioenergetics/Electron Transfer Complex Cyanobacteria Electron Paramagnetic Resonance (EPR) Electron Transfer Photosynthesis Photosystem II PsbA Protein Hydrogen Bond Tyrosine Radical |
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