Thioredoxin 2 is involved in the oxidative stress response in Escherichia coli

Two genes encoding thioredoxin are found on the Escherichia coil genome. Bo th of them are capable of reducing protein disulfide bonds in vivo and in v itro. The catalytic site contains a Cys-X-1-X-2-Cys motif in a so-called th ioredoxin fold. Thioredoxin 2 has two additional pairs of cysteines in a no n-conserved N-terminal domain. This domain does not appear to be important for the function of thioredoxin 2 in donating electrons to ribonucleotide r eductase, 3'-phosphoadenylsulfate-reductase, or the periplasmic disulfide i somerase DsbC. Our results suggests that the two thioredoxins are equivalen t for most of the in vivo functions that were tested. On the other hand, tr anscriptional regulation is different. The expression of trxC is regulated by the transcriptional activator OxyR in response to oxidative stress. Oxid ized OxyR binds directly to the trxC promoter and induces its expression in response to elevated hydrogen peroxide levels or the disruption of one or several of the cytoplasmic redox pathways. Mutants lacking thioredoxins 1 a nd 2 are more resistant to high levels of hydrogen peroxide, whereas they a re more sensitive to diamide, a disulfide bond-inducing agent.