[Structure, mechanism and roles of the transcription factor SoxR in bacteria--a review]

The transcription factor SoxR is a typical member of the family of mercury resistance operon regulator (MerR), extensively distributed across several bacterial phyla, such as Proteobacteria, Actinobacteria and Acidobacteria. SoxR, which is initially regarded as a cellular redox sensor, is activated by reversible one-electron oxidation of the [2Fe-2S] cluster and then enhances the expression of its target genes. SoxR responds to the oxidative stress mediated by superoxides in Escherichia coli in a global manner, whereas it coordinates the bacterial community growth adapted to the environment in Pseudomonas aeruginosa by sensing pyocyanin, which is a terminal signaling factor in the quorum sensing network. In this review, we focused on the structure, mechanism and roles of the transcription factor SoxR. Although compelling achievements have been made in recent years, some aspects still remain to be unraveled. A widely accepted mechanism of activation of SoxR has not yet been established or validated. And there is much and urgent call for intensive studies from more taxonomic groups rather than E. coli and P. aeruginosa. With more and more work done on these aspects, one can not only understand SoxR more comprehensively, but also gain deeper insights into the bacterial complex regulation networks, and even achieve milestones in this field.