LC3 lipidation

LC3 lipidation is the covalent conjugation of the autophagy protein LC3 (microtubule-associated protein 1 light chain 3) to phosphatidylethanolamine (PE) in the phagophore and autophagosome membrane, converting cytosolic LC3-I to the membrane-anchored LC3-II form. The reaction is executed by a ubiquitin-like cascade involving the E1-like enzyme ATG7, the E2-like enzyme ATG3, and the E3-like ATG5-ATG12-ATG16L1 complex, and is dependent on prior phosphatidylinositol 3-phosphate (PI3P) generation by the Beclin-1/VPS34 complex. LC3-II density on autophagosomal membranes recruits selective autophagy receptors such as p62 and NDP52 and is the most widely used proxy for autophagosome abundance; the ratio of LC3-II to LC3-I, measured by immunoblot in the presence and absence of lysosomal inhibitors, is a standard method for estimating autophagic flux.