Glutathiolation signals proteins for ubiquitin‐mediated degradation

Glutathione is known to help provide cells with a reducing environment in order to maintain intracellular proteins in a reduced and functional state. Glutathione also plays a role in dynamic regulation of specific protein functions by reversible glutathiolation of certain proteins in response to oxidative stress. This work studied the role of glutathiolation in controlling the susceptibility of proteins to ubiquitin‐dependent proteolysis. Both γC‐crystallin and carbonic anhydrase III were shown to be highly resistant to proteolysis in their native states. However, they were rapidly degraded by the ubiquitin‐proteasome pathway upon S‐glutathiolation. Other forms of sulfhydryl modifications, such as formation of protein‐protein disulfides or modification by iodoacetamide, also enhanced the proteolysis of γC‐crystallin, but not as efficiently as S‐glutathiolation. Structural analysis revealed that S‐glutathiolation caused reversible subtle conformational changes of these proteins, including a significant increase in protein surface hydrophobicity. The modified protein regained its native conformation and its resistance to proteolysis upon removal of the glutathione moiety. These data indicate that, like phosphorylation, glutathiolation serves a signal for targeting proteins for ubiquitin‐mediated degradation in response to oxidative stress. The glutathiolation‐mediated protein degradation may account for, at least in part, the burst of intracellular proteolysis after a mild oxidative stress in many types of cells.