Inhibits the protease activity of CAPN3. Inhibits the protease activity of CAPN3. Interacts (via SIM domains) with SUMO1 and SUMO2 (PubMed:23086935). Interacts with CAPN3 and CTBP1 (PubMed:23707407). Interacts with CAPN3 and CTBP1. Skeletal muscle.