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. 2018 Dec 12;99(1):853–892. doi: 10.1152/physrev.00005.2018

FIGURE 5.

FIGURE 5.

Formation of autophagosomes. Activation of the Ulk1/2-Atg13-Fip200 complex by AMP-activated protein kinase (AMPK) initiates the formation of the phagophore through activation of the class III phosphatidylinositol 3-kinase (PI3K) complex composed of Vps34-Vps15-Beclin1-Atg14L. Atg9-positive vesicles contribute membrane to the growing phagophore. The subsequent elongation and closure of the membrane are mediated by two ubiquitin-like conjugation pathways: the Atg5–Atg12 and the microtubule-associated protein 1 light chain 3 (LC3) pathways. 1) The Atg12-Atg5 conjugating system consists of Atg12 (ubiquitin-like module), Atg5 (substrate), Atg7 (E1-like enzyme), and Atg10 (E2-like enzyme). The Atg12–Atg5 conjugate is formed by Atg7 and Atg10. Atg12–Atg5 forms a final complex with Atg16 to form the E3 enzyme for the LC3/Atg8 conjugating system. 2) The LC3 (Atg8) conjugating system consists of LC3 (ubiquitin-like module), Atg4 (a cysteine protease), phosphatidylethanolamine (PE, substrate), Atg7 (E1-like enzyme), Atg3 (E2-like enzyme), and Atg5–Atg12–Atg16 (E3-like enzyme).