Calcium-regulated non-lysosomal thiol-protease which catalyze limited proteolysis of substrates involved in cytoskeletal remodeling and signal transduction. Broad endopeptidase specificity. Binds 3 Ca(2+) ions. Activated by micromolar concentrations of calcium and inhibited by calpastatin. Heterodimer of large (catalytic) and a small (regulatory) subunit. Translocates to the plasma membrane upon Ca(2+) binding. Ubiquitously expressed. The N-terminus is blocked. Belongs to the peptidase C2 family. This protein was previously thought to be M-calpain but has since been found to be an intermediate form between the M and Mu types.