A new antioxidant with alkyl hydroperoxide defense properties in yeast

To isolate new antioxidant genes, we have searched for activities that would rescue the tert-butyl hydroperoxide (t-BOOH)-hypersensitive phenotype of a Saccharomyces cerevisiae strain deleted for the gene encoding the oxidative stress response regulator Skn7. We report the characterization of AHP1, which encodes a 19-kDa protein similar to the AhpC/TSA protein family within a small region encompassing Cys-62 of Ahp1p and the highly conserved N-terminal catalytic AhpC/TSA cysteine. Ahp1p contains a peroxisomal sorting signal, suggesting a peroxisomal localization. AHP1 exerts strong antioxidant protective functions, as demonstrated both by gene overexpression and deletion analyses, and is inducible by peroxides in an Yap1- and Skn7-dependent manner. Similar to yeast Tsa1p, Ahp1p forms a disulfide-linked homodimer upon oxidation and in vivo requires the presence of the thioredoxin system but not of glutathione to perform its antioxidant protective function. Furthermore, in contrast to Tsa1p, which is specific for H2O2, Ahp1p is specific for organic peroxides. Therefore, with respect to substrate specificity, Ahp1p differs from Tsa1p and is similar to prokaryotic alkyl hydroperoxide reductase AhpC. These data suggest that Ahp1p is a yeast orthologue of prokaryotic AhpC and justifies its name of yeast alkyl hydroperoxide reductase.