Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10795407 | Biochimica et Biophysica Acta (BBA) - Bioenergetics | 2015 | 10 Pages |
Abstract
Cytb559 in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Roles for Cytb559 remain elusive. In Thermosynechococcus elongatus, taking advantage of the robustness of the PSII variant with PsbA3 as the D1 subunit (WT*3), 4 mutants were designed hoping to get mutants nevertheless the obligatory phototrophy of this cyanobacterium. In two of them, an axial histidine ligand of the haem-iron was substituted for either a methionine, PsbE/H23M, which could be potentially a ligand or for an alanine, PsbE/H23A, which cannot. In the other mutants, PsbE/Y19F and PsbE/T26P, the environment around PsbE/H23 was expected to be modified. From EPR, MALDI-TOF and O2 evolution activity measurements, the following results were obtained: Whereas the PsbE/H23M and PsbE/H23A mutants assemble only an apo-Cytb559 the steady-state level of active PSII was comparable to that in WT*3. The lack of the haem or, in PsbE/T26P, conversion of the high-potential into a lower potential form, slowed-down the recovery rate of the O2 activity after high-light illumination but did not affect the photoinhibition rate. This resulted in the following order for the steady-state level of active PSII centers under high-light conditions: PsbE/H23M â PsbE/H23A < < PsbE/Y19F â¤Â PsbE/T26P â¤Â WT*3. These data show i) that the haem has no structural role provided that PsbE and PsbF are present, ii) a lack of correlation between the rate of photoinhibition and the Em of the haem and iii) that the holo-Cytb559 favors the recovery of a functional enzyme upon photoinhibition.
Keywords
Cytb559MALDI-TOFPPBQChl monomer of P680 on the D1 or D2 side, respectivelyPD1 and PD243HPSIIChlPheoD1DCBQPheophytinP6802,6-dichloro-p-benzoquinoneStreptomycinspectinomycinChlorophyllcytcytochromePhotoinhibitionPhotosystem IImatrix-assisted laser desorption/ionization-time of flightMeSChloramphenicolprimary quinone acceptorsecondary quinone acceptor
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Authors
Miwa Sugiura, Makoto Nakamura, Kazumi Koyama, Alain Boussac,