Abstract
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.
Highlights
We explored the molecular basis of this signal transduction by analyzing mutant SoxR proteins defective in responding to oxidative stress signals in vivo
Mutations scattered throughout the polypeptide yielded proteins that were underresponsive to in vivo redox signals, which indicates that the redox properties of the [2Fe-2S] centers are influenced by global protein structure
When cellular oxidative stress increases, SoxR, a dimeric protein that functions as a redox-responsive genetic switch, mediates transcriptional regulation of the soxRS regulon that encodes resistance to oxidative stress in Escherichia coli and Salmonella enterica [5]
Summary
To better understand the mechanism of gene activation by MerR family members and, in particular, signal transduction via protein iron-sulfur centers, we previously isolated 29 soxR mutant alleles that confer defects in activating soxS expression in response to oxidative or nitrosative stress in vivo [7]. The resulting mutant proteins might suffer from one or a combination of the following defects; inability to make appropriate contacts with the soxS promoter, inability to remodel the promoter and signal RNAP to initiate transcription, loss or destabilization of [2Fe-2S] centers, intact [2Fe-2S] centers that are poorly responsive to redox/nitric oxide signals, inappropriate regulation by cellular reducing systems, and inability to undergo conformational changes to the activated form. In this work we have assessed the specific defects in 19 mutant alleles using a variety of in vitro and in vivo biochemical assays. Viewed in a structural context provided by MerR family proteins, these results underscore the critical effect of global protein conformation on the redox reactivity of the SoxR [2Fe-2S] centers and the role of subunit interactions in the transmission of oxidative stress signals
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
