Site-specific mutagenesis of yeast 2-Cys peroxiredoxin improves heat or oxidative stress tolerance by enhancing its chaperone or peroxidase function

Yeast peroxiredoxin II (yPrxII) is an antioxidant enzyme that plays a protective role against the damage caused by reactive oxygen species (ROS) in Saccharomyces cerevisiae. This enzyme consists of 196 amino acids containing 2-Cys Prx with highly conserved two active cysteine residues at positions 48 and 171. The yPrxII has dual enzymatic functions as a peroxidase and molecular chaperone. To understand the effect of additional cysteine residues on dual functions of yPrxII, S79C-yPrxII and S109C-yPrxII, the substitution of Ser with Cys residue at 79 and 109 positions, respectively, was generated. S109C-yPrxII and S79C-yPrxII showed 3.7- and 2.7-fold higher chaperone and peroxidase activity, respectively, than the wild type (WT). The improvement in enzyme activity was found to be closely associated with structural changes in proteins. S109C-yPrxII had increased beta-sheet in its secondary structure and formed high-molecular-weight (HMW) as well as low-molecular-weight (LMW) complexes, but S79C-yPrxII formed only LMW complexes. HMW complexes predominantly exhibited a chaperone function, and LMW complexes showed a peroxidase function. In addition, transgenic yeast cells over-expressing Cys-substituted yPrxII showed greater tolerance against heat and oxidative stress compared to WT-yPrxII.