title: Heterogeneous Rieske proteins in the cytochrome b6f complex of Synechocystis PCC6803?
abstract: The completely sequenced genome of the cyanobacterium Synechocystis PCC6803 contains three open reading frames, petC1, petC2, and petC3, encoding putative Rieske iron-sulfur proteins. After heterologous overexpression, all three gene products have been characterized and shown to be Rieske proteins as typified by sequence analysis and EPR spectroscopy. Two of the overproduced proteins contained already incorporated iron-sulfur clusters, whereas the third one formed unstable aggregates, in which the FeS cluster had to be reconstituted after refolding of the denatured protein. Although EPR spectroscopy showed typical FeS signals for all Rieske proteins, an unusual low midpoint potential was revealed for PetC3 by EPR redox titration. Detailed characterization of Synechocystis membranes indicated that all three Rieske proteins are expressed under physiological conditions. Both for PetC1 and PetC3 the association with the thylakoid membrane was shown, and both could be identified, although in different amounts, in the isolated cytochrome b(6)f complex. The considerably lower redox potential determined for PetC3 indicates heterogeneous cytochrome b(6)f complexes in Synechocystis and suggests still to be established alternative electron transport routes.
authors.affiliation: Lehrstuhl für Biochemie der Pflanzen, Fakultät für Biologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schneider
authors.forename: Sven
authors.initials: S
authors.lastname: Skrzypczak
authors.forename: Stefan
authors.initials: S
authors.lastname: Anemüller
authors.forename: Christian L
authors.initials: CL
authors.lastname: Schmidt
authors.forename: Andreas
authors.initials: A
authors.lastname: Seidler
authors.forename: Matthias
authors.initials: M
authors.lastname: Rögner
mesh_terms: D000595:Amino Acid Sequence; D000458:Cyanobacteria / Q000201:enzymology*; D003573:Cytochrome b Group / Q000378:metabolism*; D045346:Cytochrome b6f Complex; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid
chemical_list: D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; C037989:Rieske iron-sulfur protein; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III