Calpains (CAP) are calcium-dependent cysteine proteases. The CAP family contains 14 members. CAP is a heterodimer containing a small28kDa regulatory subunit which is identical for all CAPs and a large 80kDa catalytic subunit. The best characterized CAPs are CAP1 (or mu-CAP) and CAP2 (or M-CAP). CAP7 is atypical CAP that lacks a penta-EF-hand domain. CAP8 and CAP9 are involved in the mucosal defense against stress-induced gastropathies. CAP9 has been identified as the tumor suppressor for gastric cancer. CAP13 is expressed in testis and lungs. CAPs are regulated by Ca+2 concentration, phosphorylation and calpastatin.
