Calpain

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. 3D structures of calpain Updated on 31-May-2025 CAP small subunit 1aj5 – rCAP domain VI – rat 1dvi - rCAP domain VI + Ca 1np8 – rCAP residues 87-245 - Cd 1alv, 1nx2 - pCAP domain VI + Ca – pig 1alw, 1nx3 - pCAP domain VI + Ca+ inhibitor 1nx0 - pCAP domain VI + Ca+ Calpastatin peptide + small molecule inhibitor peptide 1nx1 - pCAP domain VI + Ca+ Calpastatin peptide CAP1 1kxr, 1tlo, 1qxp - rCAP protease domain + Ca 1tl9 - rCAP protease domain + Ca+ leupeptin inhibitor 2g8e, 2g8j, 2nqg, 2nqi, 2r9c, 2r9f - rCAP protease domain + Ca+ inhibitor 2ary - hCAP protease domain + Ca – human 1zcm - hCAP protease domain (mutant) + Ca+ inhibitor CAP2 1mdw – rCAP2 protease core domain I and II (mutant) + Ca 1df0, 1u5i – rCAP small subunit domain VI + rCAP2 large subunit 3df0 - hCAP small subunit + hCAP2 large subunit + Calpastatin + Ca 3bow - rCAP small subunit + rCAP2 large subunit + Calpastatin + Ca 1kfu, 1kfx – hCAP small subunit + hCAP2 large subunit CAP7 2qfe - hCAP C2-like domain CAP8 2nqa - hCAP protease domain + Ca+ leupeptin inhibitor CAP9 1ziv – hCAP catalytic domain 2p0r - hCAP protease domain + Ca+ leupeptin inhibitor CAP13 2i7a – hCAP domain IV + Ca

spinqualitylabelsall models Human calpain1 large subunit complex with inhibitor and Ca+2 ions (green) (PDB entry 1zcm) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image