The calpain system has been detected in every vertebrate tissue examined, and has been suggested to play a regulatory role in cellular protein metabolism. This regulatory role may have important implications in platelet aggregation and pathologies associated with altered calcium homeostasis and protein metabolism such as ischemic cell injury and degenerative diseases. Inhibitors of calpain have been shown to block dexamethasone and low-level irradiation induced apoptosis in thymocytes suggesting that calpain has a regulatory or mechanistic role in apoptotic cell death. Calpastatin, a specific endogenous inhibitor of calpain, has a predicted molecular weight of ~77 kDa and an internal repeat of four homologous domains which allow it to inhibit multiple calpain molecules simultaneously. It functions by binding to calpain when calpain binds calcium. When calpastatin is subjected to proteolytic digestion, fragments of calpastatin as small as 15 kDa still retain inhibitory activity.
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Protein Aliases: Calpain inhibitor; Calpastatin; calpastatin type III; Sperm BS-17 component
Gene Aliases: BS-17; CAST; PLACK