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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Institution: | 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 evolution
activity are borne by the D1 and D2 subunits. In the cyanobacterium
Thermosynechococcus elongatus, there are three
psbA genes coding for D1. Among the 344 residues
constituting D1, there are 21 substitutions between PsbA1 and PsbA3, 31 between
PsbA1 and PsbA2, and 27 between PsbA2 and PsbA3. Here, we present the first
study of PsbA2-PSII. Using EPR and UV-visible time-resolved absorption
spectroscopy, we show that: (i) the time-resolved EPR spectrum of TyrZ? in the
(S3TyrZ?)′ is slightly modified; (ii) the split EPR signal
arising from TyrZ? in the (S2TyrZ?)′ state induced by near-infrared
illumination at 4.2 K of the S3TyrZ state is significantly
modified; and (iii) the slow phases of P680+? reduction by TyrZ are
slowed down from the hundreds of μs time range to the ms time range,
whereas both the S1TyrZ? → S2TyrZ and
the S3TyrZ? → S0TyrZ + O2
transition kinetics remained similar to those in PsbA(1/3)-PSII. These results
show that the geometry of the TyrZ phenol and its environment, likely
the Tyr-O···H···N?-His bonding,
are modified in PsbA2-PSII when compared with PsbA(1/3)-PSII. They also point to
the dynamics of the proton-coupled electron transfer processes associated with
the oxidation of TyrZ being affected. From sequence comparison, we
propose that the C144P and P173M substitutions in PsbA2-PSII
versus PsbA(1/3)-PSII, respectively located upstream of the
α-helix bearing TyrZ and between the two α-helices
bearing TyrZ and its hydrogen-bonded partner, His-190, are
responsible 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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