Reactive oxygen species (ROS), beyond the role of toxic by-products of aerobic metabolism, contribute to cell redox homeostasis and are signalling molecules in pathogen defence and abiotic stress tolerance. The putative mechanism of cell responses to ROS is thiol modifications of cysteine residues, which cause changes in protein conformation and activity. These post-translational modifications include generation of disulphide bridges and formation of sulphenic, sulphinic, and sulphonic acids, as well as S-glutathionylation and S-nitrosylation. S-nitrosylation or reversible modification may change the activity of enzymes related to the metabolism of nitric oxide, ROS, and cellular metabolism, whereas S-glutathionylation regulates the activity of proteins that contain in their structure the active cysteine residue, regulates the oxidoreductive pathway of signal transduction, and participates in the regeneration of antioxidant enzymes. Carbonylation, an irreversible, non-enzymatic modification of proteins is the most commonly occurring oxidative protein modification. The formation of carbonyl groups can be linked to abnormal translation, altered chaperone system and responses to stress factors. Carbonylated proteins are marked for proteolysis mediated by different pathways in different cell compartments to counteract the formation of high molecular weight aggregates and accumulation of inactive proteins. However, products of proteolysis of carbonylated proteins could function as secondary ROS messengers that target the cell nucleus.
Part of the book: Basic Principles and Clinical Significance of Oxidative Stress