SoxS

SoxS is a bacterial transcription factor that functions in the oxidative stress response as part of the SoxRS regulatory system, best characterized in Escherichia coli and other Gram-negative bacteria. It acts as a central activator that coordinates the expression of a broad set of genes to counteract reactive oxygen species.

The two-component-like mechanism begins with SoxR, a redox-sensitive regulator containing an iron-sulfur cluster. In response to superoxide and other redox-active compounds, SoxR becomes oxidized and induces the expression of soxS. The SoxS protein then binds to promoter regions of a large group of genes, the SoxRS regulon, and activates their transcription. This creates a rapid, concerted response to oxidative stress.

The SoxRS regulon includes genes involved in detoxification and repair of oxidative damage, such as antioxidant enzymes, redox maintenance proteins, and components of membrane transport systems. Target genes can also affect cell envelope permeability and efflux, helping limit the influx of harmful compounds and promote survival under stress. The exact targets and magnitude of the response vary among species, reflecting differences in regulatory networks.

In addition to protecting against endogenous and exogenous oxidative stress, the SoxRS system can influence pathogenicity and antibiotic tolerance by enabling bacteria to withstand host immune defenses and certain antimicrobial agents. SoxS thereby serves as a key regulatory node linking redox state to broad cellular defenses.