title: Redox properties of the Rhodobacter sphaeroides transcriptional regulatory proteins PpsR and AppA.
abstract: Redox properties of the photosynthetic gene repressor PpsR and the blue-light photoreceptor/antirepressor AppA from Rhodobacter sphaeroides have been characterized. Redox titrations of PpsR reveal the presence of a two-electron couple, with an E (m) value of -320 mV at pH 7.0, which is likely to arise from the reversible conversion of two cysteine thiols to a disulfide. This E (m) value is very much more negative than the E (m) = -180 mV value measured previously at pH 7.0 for the disulfide/dithiol couple in CrtJ, the homolog for PpsR in the closely related bacterium Rhodobacter capsulatus. AppA, a flavin-containing blue-light receptor that is also involved in the regulation of gene expression in R. sphaeroides, contains multiple cysteines in its C-terminal region, two of which function as a redox-active dithiol/disulfide couple with an E (m) value of -325 mV at pH 7.0 in the dark. Titrations of this dithiol/disulfide couple in illuminated samples of AppA indicate that the E (m) value of this disulfide/dithiol couple is -315 mV at pH 7.0, identical to the value obtained for AppA in the dark within the combined experimental uncertainties of the two measurements. The E (m) values of AppA and PpsR demonstrate that these proteins are thermodynamically capable of electron transfer for their activity as an anti-repressor/repressor in R. sphaeroides.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA.
authors.forename: S-K
authors.initials: SK
authors.lastname: Kim
authors.forename: J T
authors.initials: JT
authors.lastname: Mason
authors.forename: D B
authors.initials: DB
authors.lastname: Knaff
authors.forename: C E
authors.initials: CE
authors.lastname: Bauer
authors.forename: A T
authors.initials: AT
authors.lastname: Setterdahl
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005420:Flavoproteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D010084:Oxidation-Reduction; D012097:Repressor Proteins / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: C116785:AppA protein, Rhodobacter sphaeroides; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D012097:Repressor Proteins