title: Assembly of oxygen-evolving Photosystem II efficiently occurs with the apo-Cytb559 but the holo-Cytb559 accelerates the recovery of a functional enzyme upon photoinhibition.
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≈PsbE/H23A<< PsbE/Y19F≤PsbE/T26P≤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.
authors.affiliation: Proteo-Science Research Center, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan; Department of Chemistry, Graduate School of Science and Technology, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan; PRESTO, Japan Science and Technology Agency (JST), 4-1-8, Honcho, Kawauchi, Saitama 332-0012, Japan. Electronic address: miwa.sugiura@ehime-u.ac.jp.
authors.forename: Miwa
authors.initials: M
authors.lastname: Sugiura
authors.affiliation: Department of Chemistry, Graduate School of Science and Technology, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Proteo-Science Research Center, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Koyama
authors.affiliation: iBiTec-S, CNRS UMR 8221, CEA Saclay, 91191 Gif-sur-Yvette, France. Electronic address: alain.boussac@cea.fr.
authors.forename: Alain
authors.initials: A
authors.lastname: Boussac
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003573:Cytochrome b Group / Q000737:chemistry* / Q000502:physiology; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000502:physiology
chemical_list: D003573:Cytochrome b Group; D045332:Photosystem II Protein Complex; C019313:cytochrome b559; D010100:Oxygen
keywords: Cytb(559); Haem axial ligands; Photoinhibition; Photosystem II