Calcium-regulated non-lysosomal thiol-protease. Proteolytically cleaves CTBP1 at 'His-410'. Mediates, with UTP25, the proteasome-independent degradation of p53/TP53. Broad endopeptidase activity. Activated by micromolar concentrations of calcium and inhibited by calpastatin. Homodimer; via EF-hand domain 4. Interacts with TTN/titin. Interacts with CMYA5; this interaction, which results in CMYA5 proteolysis, may protect CAPN3 from autolysis. Interacts with SIMC1. Interacts with UTP25; the interaction is required for CAPN3 translocation to the nucleolus. Belongs to the peptidase C2 family.