ATG12 is a core autophagy-related protein essential for autophagosome formation and cellular homeostasis. Functionally, ATG12 operates as part of the ATG12-ATG5-ATG16L1 conjugate complex, which acts as an E3-like ubiquitin ligase that catalyzes lipidation of LC3 (microtubule-associated protein 1 light chain 3), a critical step in autophagosome biogenesis 1. This complex facilitates phagophore expansion, maturation, and subsequent autophagosome-lysosome fusion 1. ATG12 also functions through interaction with ATG3 to regulate basal autophagy and late endosome trafficking, including exosome secretion and viral budding 2. Beyond canonical autophagy, ATG12 exhibits immune-modulatory roles: it negatively regulates antiviral innate immunity by impairing type I interferon production during VSV infection and is required for hepatitis C virus RNA translation and replication initiation [UniProt/PubMed:17709747, 19666601]. Clinically, ATG12 dysregulation is implicated in Parkinson's disease; functional promoter variants that alter ATG12 transcription have been identified in sporadic PD patients, suggesting impaired autophagy contributes to neurodegeneration 3. Additionally, ATG12 upregulation in pancreatic β-cells under glucocorticoid receptor activation promotes excessive autophagy during glucolipotoxicity, contributing to diabetes pathogenesis 4. These findings establish ATG12 as a multifunctional regulator bridging autophagy, immunity, and metabolic disease.