Calpains () are a family of calcium-dependent, non-lysosomal cysteine proteases (proteolytic enzymes) expressed ubiquitously in mammals and many other organisms. Calpains constitute the C2 family of protease clan CA in the MEROPS database. The calpain proteolytic system includes the calpain proteases, the small regulatory subunit (CAPNS1 (former CAPN4, a.k.a. 30K)), and the endogenous calpain-specific inhibitor, calpastatin. Historical background The history of calpain originates during the mi… (More on Calpain)