Protein conformational changes of the oxidative stress sensor, SoxR, upon redox changes of the [2Fe-2S] cluster probed with ultraviolet resonance Raman spectroscopy.

The [2Fe-2S] transcription factor, SoxR, a member of the MerR family, functions as a bacterial sensor of oxidative stress in Escherichia coli. SoxR is activated by reversible one-electron oxidation of the [2Fe-2S] cluster and enhances the production of various antioxidant proteins through the SoxRS regulon. Ultraviolet resonance Raman (UVRR) spectroscopic analysis of SoxR revealed conformational changes upon reduction of the [2Fe-2S] cluster in the absence and presence of promoter oligonucleotide. UVRR spectra reflected the environmental or structural changes of Trp following reduction. Notably, the environment around Trp91 contacting the [2Fe-2S] cluster was altered to become more hydrophilic, whereas that around Trp98 exhibited a small change to become more hydrophobic. In addition, changes in cation-π interactions between the [2Fe-2S] cluster and Trp91 were suggested. On the other hand, the environment around Tyr was barely affected by the [2Fe-2S] reduction. Binding of the promoter oligonucleotide triggered changes in Tyr located in the DNA-binding domain, but not Trp. Furthermore, conformational changes induced upon reduction of DNA-bound SoxR were not significantly different from those of DNA-free SoxR.