Cysteine thiol modifications—Oxidative (eu)stress perspective

Cysteine and methionine are two out of twenty common amino acids containing sulfur. In contrast to the thioeter form of sulfur in methionine, the thiol group of cysteine is highly reactive and prone to posttranslational modifications (modifications by chemicals, metabolites, or oxidation). Therefore, although cysteines are under-represented in proteins, their unique chemistry modulates protein functions and governs biological processes in all kingdoms. Cysteine modifications are widely associated with an abnormal cellular redox status. However, the detailed mechanisms of the interaction have not yet been elucidated. In this chapter, we aim to reconcile the impact of thiol modifications on the overall redox status. We review the impact of most abundant cysteine modifications on cellular reactive oxygen species (ROS) producers and their modulation by oxidants. Finally, on the basis of the knockout models, we try out inferring the impact of cysteines modification of redox status. We conclude that thiol modifications should be considered as an indicator of increased redox status and compensatory mechanisms to maintain the appropriate balance.