Functional analysis of SoxR residues affecting transduction of oxidative stress signals into gene expression.
SoxR protein, a member of the MerR family of transcriptional activators, mediates a global oxidative stress response in Escherichia coli. Upon oxidation or nitrosylation of its [2Fe-2S] centers SoxR activates its target gene, soxS, by mediating a structural transition in the promoter DNA that stimulates initiation by RNA polymerase. We explored the molecular basis of this signal transduction by analyzing mutant SoxR proteins defective in responding to oxidative stress signals in vivo.We have confirmed that the DNA binding domain of SoxR is highly conserved compared with other MerR family proteins and functions in a similar manner to activate transcription. Several mutations in the dimerization domain of SoxR disrupted intersubunit communication, and the resulting proteins were unable to propagate redox signals to the soxS promoter. Mutations scattered throughout the polypeptide yielded proteins that were under-responsive to in vivo redox signals, which indicates that the redox properties of the [2Fe-2S] centers are influenced by global protein structure. These findings indicate that SoxR functions as a redox-responsive molecular switch in which subunit interactions transduce a subtle alteration in oxidation state into a profound change in DNA structure.
Department of Genetics and Complex Diseases, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Monica
M
Chander
Bruce
B
Demple
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D009154:Mutation; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011487:Protein Conformation; D016415:Sequence Alignment; D015398:Signal Transduction; D014157:Transcription Factors / Q000737:chemistry* / Q000502:physiology; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C070724:SoxR protein, Bacteria