In yeast the cytoplasmic cysteine protease Atg4 is responsible for activation of Atg8 by removal of its C-terminal extension to expose the glycine residue essential for its subsequent phospholipid (PE) conjugation. Atg4 is also required for the deconjugation of Atg8 from PE at outer surface of autophagosomes and their precursor membranes, a process required for clustering and fusion with lysosomes, resulting in the recycling of Atg8 and destruction of the autophagosome
