Both M-calpain and m-calpain are ubiquitously expressed in mammalian cells, and are countered by the endogenous calpain inhibitor, calpastatin. Other calpain family members (calpain-3, calpain-5, calpain-9, etc) have more limited tissue distribution, and perhaps different functions. The calpain family members consist of a common small subunit (Calpain-S1), and a large variable subunit. It is not clear that all calpains form heterodimers with a small subunit, but calpain-S1 is known to form a heterodimer with calpain-1 and also with calpain-2. Calpain S2 was recently discovered, and initial studies indicate that both small subunits may act as chaperonins to help with folding, or accessory proteins to help localize the calpains. Domains in the small subunit include the amino terminal domain-V (a glycine-rich sequence that is removed on activation of calpain, shorter in calpain-S2 than in calpain S1) and domain-VI, the calcium binding, EF hand domain.
CAPNS2; calpain, small subunit 2; calpain small subunit 2; CSS2; calcium-dependent protease small subunit 2; MGC12536; MGC14804; MGC12536, MGC14804,CAPNS2