Cysteine Protease ATG4A (ATG4A) is a cytoplasmic protein that belongs to the peptidase C54 family. ATG4A is widely expressed in many tissues at a low level, but the highest expression is observed in skeletal muscle and brain. ATG4A is a cysteine protease required for autophagy; it cleaves the C-terminal part of MAP1LC3, GABARAPL2 or GABARAP. ATG4A is inhibited by N-ethylmaleimide. It is suggested that ATG4A has a significant role in suppressing various cancers.