title: SoxR, a [2Fe-2S] transcription factor, is active only in its oxidized form.
abstract: SoxR protein is known to function both as a sensor and as a transcriptional activator for a superoxide response regulon in Escherichia coli. The activity of SoxR was tested by its ability to enable the transcription of its target gene, soxS, in vitro. The activity of the oxidized form was lost when its [2Fe-2S] clusters were reduced by dithionite under anaerobic conditions, and it was rapidly restored by autooxidation. This result is consistent with the hypothesis that induction of the regulon is effected by the univalent oxidation of the Fe-S centers of SoxR. In vivo, this oxidation may be caused by an alteration of the redox balance of electron chain intermediates that normally maintains soxR in an inactive, reduced state. Oxidized SoxR was about twice as effective as reduced SoxR in protecting the soxS operator from endonucleolytic cleavage. However, this difference could not account for a greater than 50-fold difference in their activities and therefore could not support a model in which oxidation activates SoxR by enabling it to bind to DNA. NADPH, ferredoxin, flavodoxin, or ferredoxin (flavodoxin):NADP+ reductase could not reduce SoxR directly in vitro at a measurable rate. The midpoint potential for SoxR was measured at -283 mV.
authors.affiliation: Department of Pathology, University of Michigan Medical School, Ann Arbor 48109-0602, USA.
authors.forename: P
authors.initials: P
authors.lastname: Gaudu
authors.forename: B
authors.initials: B
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005288:Ferredoxins / Q000378:metabolism; D005418:Flavodoxin / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D047908:Intracellular Signaling Peptides and Proteins; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011494:Protein Kinases; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018085:Regulon; D015183:Restriction Mapping; D013481:Superoxides; D015534:Trans-Activators; D014157:Transcription Factors / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D005288:Ferredoxins; D005418:Flavodoxin; D047908:Intracellular Signaling Peptides and Proteins; D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C028640:fructose-induced HPr-like protein, bacteria; D013481:Superoxides; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli; D011494:Protein Kinases; C488924:fruB protein, E coli