Date: 19 Aug 2011

Protein Oxidative Modifications

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Proteins are molecules especially susceptible to oxidative modifications owing to their abundance and reactivity to radicals. Amongst the protein oxidative (redox) changes, carbonylation of the molecules represents an irreversible process that leads to the lost of protein functionality. The bulk of carbonylated proteins are produced as a result of metal oxidative stress induction in plants. In addition, metal ions-catalyzed oxidation (MCO) systems have been used especially for the introduction of carbonyl groups in the protein molecules in vitro. The mechanism underlying protein carbonylation for redox active metals is the direct catalysis of reactive oxygen species (ROS) generation, while metals considered redox inactive act in decreasing the antioxidant defence system. Despite the fact that protein carbonylation is associated with general and random processes; recent advances indicate a great degree of selectivity in the protein oxidation process. In turn, there are proteins, such as catalase, that respond to metal-induced oxidative stress by regulating the translation of isoforms and thus inducing the synthesis of new subunits less sensitive to oxidation. Further, the intracellular level of oxidized proteins is the product of a balance between the rate of oxidation and the rate of degradation of proteins. Metals can alter plant cell capacity for removing damaged proteins. As part of the proteolytic system, the 20S proteasome is responsible for the proteolysis of the carbonylated proteins. The 20S proteasome activity is regulated through oxidative modification of the proteasome itself, where a moderate 20S protein oxidation increases its activity, but a severe oxidative condition decreases it, concomitantly producing oxidized protein accumulation. The widespread occurrence of protein modifications and regulated proteolysis, as well as the existence of regenerative mechanisms of oxidative modifications, is presented.