title: The redox state of the [2Fe-2S] clusters in SoxR protein regulates its activity as a transcription factor.
abstract: SoxR protein is a redox-responsive transcription factor that governs a regulon of oxidative stress and antibiotic resistance genes in Escherichia coli. Purified SoxR contains oxidized [2Fe-2S] clusters and stimulates in vitro transcription of its target gene soxS up to 100-fold. SoxR transcriptional activity, but not DNA binding, is completely dependent on the [2Fe-2S] clusters; apo-SoxR prepared in vitro binds the soxS promoter with unchanged affinity but does not have transcription activity. Thus, modulation of the SoxR [2Fe-2S] clusters was proposed to control the protein's function in transcription. Here, we provide evidence that SoxR with reduced [2Fe-2S] clusters is inactive. Redox titration of purified SoxR revealed a midpoint potential of -285 +/- 10 mV (pH 7.6). In vitro transcription assays showed that SoxR was inactivated when the [2Fe-2S] cluster was reduced (-380 mV), and full activity was restored upon reoxidation (+100 mV). The results suggest that one-electron oxidation and reduction of the [2Fe-2S] cluster regulate SoxR transcriptional activity.
authors.affiliation: Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115, USA. demple@mbcrr.harvard.edu
authors.forename: H
authors.initials: H
authors.lastname: Ding
authors.forename: E
authors.initials: E
authors.lastname: Hidalgo
authors.forename: B
authors.initials: B
authors.lastname: Demple
mesh_terms: D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D010084:Oxidation-Reduction; D010957:Plasmids / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D014157:Transcription Factors; C070724:SoxR protein, Bacteria