Subsystem: Peptide methionine sulfoxide reductase
This subsystem's description is:
Free and protein-bound methionine residues are easily oxidized to methionine sulfoxides by various reactive oxygen species. However, the oxidized methionines can be reduced back to methionine by repair enzymes, the methionine sulfoxide reductases (Msrs). Two distinct families of these enzymes, MsrA and MsrB, have evolved for stereospecific reduction of methionine sulfoxide residues in proteins (Kim, et al., 2008). MsrA is specific for the reduction of the S-form of methionine sulfoxide, whereas MsrB is specific for the R-form. Msrs are present in most organisms in all three domains of life, but are absent in some hyperthermophiles, parasites, and organisms with minimal genomes. They have been even found in anaerobic bacteria, where their presence may be due to the role in protein repair and antioxidant defense when transiently exposed to oxygen (Kim et al., 2008). Msrs play a pivotal role in the repair of oxidatively damaged proteins and defend cells from oxidative stress. Therefore, these proteins are viewed as protein repair and antioxidant enzymes. These enzymes have been implicated in regulation of physiological and pathological processes such as aging and neurodegenerative diseases.
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