The glutathione system maintains the thiol redox balance in the mitochondria, but not in the cytosol, of fission yeastd Item

The thioredoxin ang glutathione (GSH)-glutaredoxin electron donor pathways provide a reducing environment to the cell and maintain homeostasis of numerous redox reactions. The abundant tripeptide GSH has multiple roles, including redox buffering, detoxification, peroxide scavenging and iron-sulfur cluster assembly. GSH reductase maintains GSH reduced, and it is essential in most organisms. Fission yeast cells lacking Pgr1 exhibit severe pleiotropic defects. We used multiple approaches to unravel the compartment-specific roles of Pgr1, the GSH reductase of fission yeast. Our findings confirm that Pgr1 had dual cytosolic and mitochondrial localization. Mitochondrial homeostasis was severely impaired in Δ<i>pgr1</i> cells and most of these defects were restored by expression of an exclusively mitochondrial Pgr1 isoform. As expected, the cytosol of Δ<i>pgr1 </i>cells showed low ratio of reduced-to-oxidized GSH. However, this did not significantly affect peroxiredoxin-dependent hydrogen peroxide scavenging, suggesting a minimal role, if any, of GSH in cytosolic thiol reduction. The transcriptome of Δ<i>pgr1</i> cells revealed signatures of oxidative stress and iron deprivation, suggesting that the GSH-containing sensor of iron starvation, the glutaredoxin Grx4, is also a sensor of GSH oxidation. In the mitochondria, Pgr1 not only provided the GSH electron donor for the glutaredoxin-based pathway but also recycled mitochondrial Trx2, thereby contributing to thiol redox homeostasis in the matrix. In conclusion, GSH reductase is essential for maintaining a balanced redox environment in the mitochondria by recycling Trx2, Grx2 and the GSH-containing Grx5, and therefore contributes to the processes of iron-sulfur cluster assembly and respiration, while controlling Grx4 dynamics in the cytosol.