Autophagy protein ATG5 is involved in autophagic vesicle formation. It is conjugated with ATG12, acting as an E3-like ubiquitin enzyme required for lipidation of ATG8 family proteins and their association to the vesicle membranes. ATG5 comprises two ubiquitin-like domains (UblA and UblB) that flank a helix-rich domain. This domain represents the alpha-helical bundle region (HBR) of AT5 which consists of three alpha helices [1,2]. This region contains the Lys residue required for conjugation with ATG12 [1].

1: Structure of the human ATG12~ATG5 conjugate required for LC3 lipidation in autophagy. Otomo C, Metlagel Z, Takaesu G, Otomo T; Nat Struct Mol Biol. 2013;20:59-66. PMID:23202584

2: Structure of Atg5.Atg16, a complex essential for autophagy. Matsushita M, Suzuki NN, Obara K, Fujioka Y, Ohsumi Y, Inagaki F; J Biol Chem. 2007;282:6763-6772. PMID:17192262