Ubiquitin-like modifier involved in autophagosomes formation. Participates in membrane fusion events that take place in the secretory pathway (By similarity). By Legionella pneumophila infection. The C-terminal 3 residues of atg8 are removed by atg4 to expose Gly-119 at the C-terminus. This Gly-119 forms then a thioester bond with the 'Cys-563' of atg7 (E1-like activating enzyme) before being transferred to the 'Cys-288' of atg3 (the specific E2 conjugating enzyme), in order to be finally amidated with phosphatidylethanolamine. This lipid modification anchors atg8 to membranes and can be reversed by atg4, releasing soluble atg8 (By similarity). Belongs to the ATG8 family.