FUNCTION: Cysteine protease required for autophagy, which cleaves the C-terminal part of either MAP1LC3, GABARAPL2 or GABARAP, allowing the liberation of form I. A subpopulation of form I is subsequently converted to a smaller form (form II). Form II, with a revealed C-terminal glycine, is considered to be the phosphatidylethanolamine (PE)-conjugated form, and has the capacity for the binding to autophagosomes. ENZYME REGULATION: Inhibited by N-ethylmaleimide. SUBCELLULAR LOCATION: Cytoplasm (Probable). ALTERNATIVE PRODUCTS: 5 named isoforms produced by alternative splicing. TISSUE SPECIFICITY: Mainly expressed in the skeletal muscle, followed by brain, heart, liver and pancreas. SIMILARITY: Belongs to the peptidase C54 family.