trxA

trxA is the gene symbol used in many bacteria to denote thioredoxin A (TrxA), a small cytosolic redox protein that helps maintain cellular redox balance. The gene is conserved across diverse bacteria, including Escherichia coli and Bacillus species.

TrxA belongs to the thioredoxin family. It is a small, soluble protein (~12 kDa) characterized by a thioredoxin fold and a conserved active-site motif, CGPC. In the reduced form, the two cysteines form a dithiol; oxidation forms a disulfide that is recycled by thioredoxin reductase (TrxB) using NADPH.

Functionally, TrxA acts as an electron donor for disulfide bond reduction in a range of substrate proteins, aiding proper folding and activity. It participates in DNA synthesis through ribonucleotide reductase, helps counter oxidative damage, and serves as a general regulator of the cytosolic redox environment. It can be reduced by TrxB or analogs in different species.

Genomic context varies by species. In many bacteria trxA is located near trxB and other redox genes; expression is typically constitutive but can be modulated under oxidative stress in some organisms. There may be multiple thioredoxins in a genome, with trxA representing the canonical, cytosolic form.

Applications and significance: In biotechnology, TrxA is widely used as a fusion tag to promote solubility and proper folding of recombinant proteins in Escherichia coli. As a model redox protein, it provides insights into disulfide bond formation and thiol-disulfide exchange reactions.