title: Cytochrome c550 in the cyanobacterium Thermosynechococcus elongatus: study of redox mutants.
abstract: Cytochrome c(550) is one of the extrinsic Photosystem II subunits in cyanobacteria and red algae. To study the possible role of the heme of the cytochrome c(550) we constructed two mutants of Thermosynechococcus elongatus in which the residue His-92, the sixth ligand of the heme, was replaced by a Met or a Cys in order to modify the redox properties of the heme. The H92M and H92C mutations changed the midpoint redox potential of the heme in the isolated cytochrome by +125 mV and -30 mV, respectively, compared with the wild type. The binding-induced increase of the redox potential observed in the wild type and the H92C mutant was absent in the H92M mutant. Both modified cytochromes were more easily detachable from the Photosystem II compared with the wild type. The Photosystem II activity in cells was not modified by the mutations suggesting that the redox potential of the cytochrome c(550) is not important for Photosystem II activity under normal growth conditions. A mutant lacking the cytochrome c(550) was also constructed. It showed a lowered affinity for Cl(-) and Ca(2+) as reported earlier for the cytochrome c(550)-less Synechocystis 6803 mutant, but it showed a shorter lived S(2)Q(B)(-) state, rather than a stabilized S(2) state and rapid deactivation of the enzyme in the dark, which were characteristic of the Synechocystis mutant. It is suggested that the latter effects may be caused by loss (or weaker binding) of the other extrinsic proteins rather than a direct effect of the absence of the cytochrome c(550).
authors.affiliation: Service de Bioénergétique, Departement Biologie Joliot-Curie, URA Consejo Superior de Investigaciones Cientificas 2096, CEA Saclay, 91191 Gif sur Yvette, France. diana.kirilovsky@cea.fr
authors.forename: Diana
authors.initials: D
authors.lastname: Kirilovsky
authors.forename: Mercedes
authors.initials: M
authors.lastname: Roncel
authors.forename: Alain
authors.initials: A
authors.lastname: Boussac
authors.forename: Adjélé
authors.initials: A
authors.lastname: Wilson
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Zurita
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Ducruet
authors.forename: Hervé
authors.initials: H
authors.lastname: Bottin
authors.forename: Miwa
authors.initials: M
authors.lastname: Sugiura
authors.forename: José M
authors.initials: JM
authors.lastname: Ortega
authors.forename: A William
authors.initials: AW
authors.lastname: Rutherford
mesh_terms: D002118:Calcium / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry; D003574:Cytochrome c Group / Q000737:chemistry / Q000502:physiology*; D004247:DNA / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D006358:Hot Temperature; D008024:Ligands; D008715:Methionine / Q000737:chemistry; D008957:Models, Genetic; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D046939:Synechocystis / Q000378:metabolism; D013696:Temperature; D020524:Thylakoids / Q000737:chemistry; D013997:Time Factors
chemical_list: D003574:Cytochrome c Group; D008024:Ligands; D006418:Heme; D006639:Histidine; D002713:Chlorine; D004247:DNA; C031732:cytochrome C-550; D008715:Methionine; D003545:Cysteine; D010100:Oxygen; D002118:Calcium