Characterization of the oxidative stress response in yeast cells protected by gamma-glutamylcysteine instead of glutathione

Redox homeostasis is achieved by antioxidant systems, involving a large collection of enzymes that scavenge or degrade Reactive Oxygen Species (ROS) produced endogenously at low levels during cell growth. Besides the enzymatic protection against ROS, cells also contain small antioxidant molecules, such as glutathione (GSH). With an intracellular concentration between 1 and 10 mM, GSH is the most abundant non-protein thiol in the cell and is considered as the major redox buffer of the cell. In a previous study, we showed that only scarce amounts of intracellular GSH are required to protect yeast nuclear activities during oxidative stress. Surprisingly, such protection is sufficient for cell survival despite the strong oxidation of cytosolic proteins and the complete inhibition of protein synthesis (Hatem et al., 2014). GSH synthesis is a two-step process involving the gamma-glutamylcysteine (g-GC) synthetase Gsh1, which produces the g-GC intermediate from glutamate and cysteine, and the glutathione synthetase Gsh2, which adds a glycine to g-GC to release the final tripeptide. Deletion of GSH2 leads to yeast cells accumulating abnormal amounts of g-GC. It has been suggested that this molecule could replace GSH during oxidative stress exposure as the viability of ∆gsh2 cells, unable to synthesize GSH, is only mildly affected in oxidative stress conditions. Because our previous study revealed that the antioxidant protection of all cellular components and activities is not strictly required to preserve cell viability during oxidative stress, we decided to better characterize the physiological response of ∆gsh2 cells submitted to hydrogen peroxide treatments. Here we present the main results of this study and discuss the potential role of g-GC in the cellular protection against oxidative injury, compare to GSH.