Regulation of metabolism, stress response, and sod1 activity by cytosolic thioredoxins in yeast depends on growth phase

Reactive Oxygen Species (ROS) can be harmful compounds that can cause damage to macromolecules like lipids, proteins, and DNA when their levels exceed cellular defense mechanisms. Cells have protection and ROS detoxification systems, including thioredoxin and glutaredoxin systems, to counteract oxidative stress. The role of cytosolic thioredoxin system (cTRX) was investigated in different growth phases using a mutant strain lacking both TRX1 and TRX2. The mutant showed a defect in survival during the non-dividing state or stationary phase. The levels of glutathione, an antioxidant, in the mutants were higher in both total and reduced glutathione, indicating an increase in oxidative response. The mutant also showed an increase in protein-bound glutathione, suggesting a compensatory mechanism to counter balance oxidative stress. Proteomic analysis revealed changes in the expression of various proteins in the absence of cytosolic thioredoxins. Upregulated proteins in both exponential and stationary phases were mainly related to oxidative stress response and metabolism. Down- regulated proteins in both phases were associated with glycerol metabolism, glycolysis, and ATP synthesis. These changes indicated a compensatory response to redox imbalance caused by the absence of cytosolic thioredoxins. Further analysis focused on the reversible oxidation of cysteine residues in proteins. Several proteins were identified with cysteines susceptible to reversible oxidation, and their oxidation status was affected by the absence of cytosolic thioredoxins. Notably, cysteine 146 of cytosolic Superoxide Dismutase 1 (Sod1) was more oxidized in growth phase, while oxidation of ribosomal proteins was seen only in exponential phase. Overall, this study provides insights into the role of cytosolic thioredoxin system in growth, aging, in maintaining redox balance, protecting against oxidative stress as well as its impact on SOD1 activity and glutathionylation.