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Two genes encoding thioredoxin are found on the Escherichia coli genome. Both of them are capable of reducing protein disulfide bonds in vivo and in vitro. The catalytic site contains a Cys-X(1)-X(2)-Cys motif in a so-called thioredoxin fold. Thioredoxin 2 has two additional pairs of cysteines in a non-conserved N-terminal domain. This domain does not appear to be important for the function of thioredoxin 2 in donating electrons to ribonucleotide reductase, 3'-phosphoadenylsulfate-reductase, or the periplasmic disulfide isomerase DsbC. Our results suggests that the two thioredoxins are equivalent for most of the in vivo functions that were tested. On the other hand, transcriptional regulation is different. The expression of trxC is regulated by the transcriptional activator OxyR in response to oxidative stress. Oxidized 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 and 2 are more resistant to high levels of hydrogen peroxide, whereas they are more sensitive to diamide, a disulfide bond-inducing agent.
Ritz et al. (Sat,) studied this question.