Insights into autophagosome biogenesis from structural and biochemical analyses of the ATG2AWIPI4 complex

Abstract

Autophagy is an enigmatic cellular process in which double-membrane autophagic compartments form de novo adjacent to the ER, sequestering cytoplasmic contents within and delivering them to lysosomes. Expansion of the precursor membrane phagophore requires autophagy-related 2 (ATG2), which localizes to the phosphatidylinositol-3-phosphate (PI3P)-enriched ER-phagophore junction. We combined single-particle electron microscopy, chemical cross-linking coupled with mass spectrometry, and biochemical analyses to characterize human ATG2A in complex with the PI3P effector WIPI4.

Differential requirement for ATG2A domains for localization to autophagic membranes and lipid droplets

“…These results are in contrast to the situation in yeast, where PAS localization of Atg18 depends on Atg2 [5,14,35]. Although ATG2s strongly interact with WDR45/WIPI4 [36][37][38], the requirement for ATG2s-WDR45 interaction in ATG2 localization to the isolation membrane remains unclear. Further studies are required to determine the precise hierarchy between ATG2s and WIPIs in mammals.…”

“…During preparation of this manuscript, two groups reported the determination of the structure of the ATG2s-WIPI4 complex by single-particle electron microscopy and showed that the ATG2s have membrane-binding/tethering activity [37,38]. WIPI4 associates with a tip of ATG2, which adopts a rod shape.…”

“…WIPI4 associates with a tip of ATG2, which adopts a rod shape. The N-terminal end of ATG2 is located at the opposite tip [37,38]. Chowdhury et al [38] further suggested that the C-terminal end of ATG2A is also located at the same tip as the N terminus.…”

“…The N-terminal end of ATG2 is located at the opposite tip [37,38]. Chowdhury et al [38] further suggested that the C-terminal end of ATG2A is also located at the same tip as the N terminus. Thus, it is possible that the N-and C-terminal regions regulate binding with different organelles at the same tip, which is opposite to the WIPI-binding tip.…”

“…Thus, it is possible that the N-and C-terminal regions regulate binding with different organelles at the same tip, which is opposite to the WIPI-binding tip. Furthermore, Chowdhury et al [38] also proposed that ATG2A has an AH in amino acids 1723-1819 and this fragment binds to highly curved membranes. Overall, their in vitro results are consistent with our findings in vivo.…”