ATG8, also known as GABARAPL1, is a ubiquitin-like protein that has a crystal structure. ATG8 consists of a 5-stranded β-sheet, which is enclosed by two α-helices at one side and one α-helix at the other side and exhibits a conserved GABARAP domain. It functions in the formation of autophagosomal membranes. The transient conjugation of ATG8 to the autophagosomal membrane through a ubiquitin-like conjugation system is essential for autophagy in eukaryotes. Autophagy is induced upon nutrient depletion or rapamycin treatment and leads to the response of more than 30 autophagy-related (ATG) genes known so far, including ATG8.