Characterization of Escherichia coli null mutants for glutaredoxin 2.

Three Escherichia coli glutaredoxins catalyze GSH-disulfide oxidoreductions, but the atypical 24-kDa glutaredoxin 2 (Grx2, grxB gene), in contrast to the 9-kDa glutaredoxin 1 (Grx1, grxA gene) and glutaredoxin 3 (Grx3, grxC gene), is not a hydrogen donor for ribonucleotide reductase. To improve the understanding of glutaredoxin function, a null mutant for grxB (grxB(-)) was constructed and combined with other mutations. Null mutants for grxB or all three glutaredoxin genes were viable in rich and minimal media with little changes in their growth properties. Expression of leaderless alkaline phosphatase showed that Grx1 and Grx2 (but not Grx3) contributed in the reduction of cytosolic protein disulfides. Moreover, Grx1 could catalyze disulfide formation in the oxidizing cytosol of combined null mutants for glutathione reductase and thioredoxin 1. grxB(-) cells were more sensitive to hydrogen peroxide and other oxidants and showed increased carbonylation of intracellular proteins, particularly in the stationary phase. Significant up-regulation of catalase activity was observed in null mutants for thioredoxin 1 and the three glutaredoxins, whereas up-regulation of glutaredoxin activity was observed in catalase-deficient strains with additional defects in the thioredoxin pathway. The expression of catalases is thus interconnected with the thioredoxin/glutaredoxin pathways in the antioxidant response.