Calpain (CALP) (EC 18.104.22.168) is an intracellular cysteine protease
whose two isoforms require either mM or _M free Ca2+ for activity.
The large subunit of this heterodimer contains a domain homologous to
sulfhydryl protease and five EF-hand domains at the C- terminus. The
small subunit contains a Gly-rich domain at its N-terminus and five
EF-hands at its C-terminus. In both subunits domains 1 & 2 and 3 & 4
form two lobes. The fifth domains of large and small subunits pair, as
usually found in adjacent EF-hands, to join the two in the heterodimer