Regulation of thioredoxin peroxidase activity by C-terminal truncation

Thioredoxin peroxidase is a member of peroxiredoxin (Prx) family, which uses a thioredoxin (Trx) as an immediate electron donor for the reduction of peroxide. We have identified C-terminal truncated TPx from Schizosaccharomyces pombe and also have found the truncated form is significantly tenacious against the inactivation of H2O2 than the intact form. Peroxidase assay of a series of recombinant C-terminal truncation mutants (Delta192, Delta191, Delta188, Delta184, Delta176, and Delta165) revealed that TPx could be inactivated (Delta192), reactivated (Delta191-Delta176) and reinactivated (Delta165) by serial truncation from C-terminus. We did not find any significant kinetic difference among reactivated forms; however, distinctive loss of affinity to H2O2 (K(m) = 5 microM) than that of the intact form (<<5 microM, undeterminable) was monitored. Characterization of a series of Lys(191) point mutants manifested that the loss of affinity caused by a deprivation of positive charge born in Lys(191) and the loss of affinity resulted in the resistibility to H2O2. Disk inhibition assay with S. pombe cells overexpressing wild-type, Delta192 and Delta191 mutants evidenced that the truncated forms functioning in vitro as well as in vivo.