title: Residues that influence in vivo and in vitro CbbR function in Rhodobacter sphaeroides and identification of a specific region critical for co-inducer recognition.
abstract: CbbR is a LysR-type transcriptional regulator (LTTR) that is required to activate transcription of the cbb operons, responsible for CO2 fixation, in Rhodobacter sphaeroides. LTTR proteins often require a co-inducer to regulate transcription. Previous studies suggested that ribulose 1,5-bisphosphate (RuBP) is a positive effector for CbbR function in this organism. In the current study, RuBP was found to increase the electrophoretic mobility of the CbbR/cbb(I) promoter complex. To define and analyse the co-inducer recognition region of CbbR, constitutively active mutant CbbR proteins were isolated. Under growth conditions that normally maintain transcriptionally inactive cbb operons, the mutant CbbR proteins activated transcription. Fourteen of the constitutively active mutants resulted from a single amino acid substitution. One mutant was derived from amino acid substitutions at two separate residues that appeared to act synergistically. Different mutant proteins showed both sensitivity and insensitivity to RuBP and residues that conferred constitutive transcriptional activity could be highlighted on a three-dimensional model, with several residues unique to CbbR shown to be at locations critical to LTTR function. Many of the constitutive residues clustered in or near two specific loops in the LTTR tertiary structure, corresponding to a proposed site of co-inducer binding.
authors.affiliation: Department of Microbiology and Plant Molecular Biology/Biotechnology Program, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292, USA.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Dangel
authors.forename: Janet L
authors.initials: JL
authors.lastname: Gibson
authors.forename: Anita P
authors.initials: AP
authors.lastname: Janssen
authors.forename: F Robert
authors.initials: FR
authors.lastname: Tabita
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004351:Drug Resistance / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter / Q000235:genetics; D009154:Mutation; D009876:Operon / Q000235:genetics; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012242:Rhodobacter sphaeroides / Q000235:genetics* / Q000378:metabolism*; D012274:Ribulosephosphates / Q000494:pharmacology; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012274:Ribulosephosphates; D014157:Transcription Factors; C072714:cfxR protein, bacteria; C001933:ribulose-1,5 diphosphate; D001616:beta-Galactosidase