The Thioredoxin system in bacteria is essential for:
Maintenance of intracellular reducing environment and proper thiol-disulfide balance is crucial for protein function, enzyme activity and protection against oxidative damage that would otherwise cause aggregation. The thioredoxin system consists of small 12 kDa redox-active protein thioredoxin TrxA with highly conserved active site motif WCGPC containing two cysteines, flavoprotein thioredoxin reductase TrxB that transfers electrons from NADPH to oxidized thioredoxin via FAD and target disulfide-containing proteins. During oxidative stress or normal oxidative protein maturation in periplasm, inappropriate intermolecular and intramolecular disulfide bonds form in cytoplasmic proteins. Reduced thioredoxin with dithiol performs nucleophilic attack on aberrant disulfide, forming transient mixed disulfide intermediate then resolving through second cysteine to restore native reduced thiols in target and become oxidized itself. TrxB then re-reduces TrxA using NADPH as electron source, completing cycle. This redox cycle also supplies essential electrons to class I ribonucleotide reductase NrdAB for deoxyribonucleotide synthesis required for DNA precursor supply, to methionine sulfoxide reductases MsrA/MsrB that repair oxidized methionine residues, and to peroxiredoxins that detoxify peroxides, explaining essentiality beyond direct antioxidant defense and distinction from activities that inhibit replication or translation.
Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 21: Thioredoxin System and Disulfide Bond Reduction.