Alterations in the activity of the yeast peroxidase Tsa1 upon modification by alkylating agents
Cells have evolved a range of defense mechanisms to handle exposure to environmental toxins, including reactive oxidants and electrophiles. In Saccharomyces cerevisiae, the thioredoxin peroxidase Tsa1 is implicated in the antioxidant response. Tsa1 possesses two catalytic cysteine residues that undergo disulfide bond formation to detoxify oxidants, residues that also make the protein prone to modification by electrophiles. In the presence of the electrophilic protein cross-linkers divinyl sulfone and diethyl acetylenedicarboxylate, recombinant Tsa1 cross-links to itself in a thiol-dependent manner as mutating its active site cysteine residues to alanine does not permit cross-linking to occur. Pre-treatment with the electrophile N-ethylmaleimide to modify active site Cys residues inhibits disulfide bond formation in the presence of H2O2, suggesting that alkylation inhibits Tsa1 peroxidase activity. While the primary function of Tsa1 as a peroxidase is inhibited by electrophiles, cells lacking the TSA1 gene are hypersensitive to these molecules. Tsa1 possesses another function as a high molecular weight (HMW) chaperone, and this function may protect cells against damage by electrophiles. While preliminary results suggest that Tsa1 does not function as a molecular chaperone following electrophilic modification, continued work is necessary to confirm results in vitro and in treated cells.
© Copyright 2012 Haley A. Brown