Insights into autophagosome biogenesis from structural and biochemical analyses of the ATG2A-WIPI4 complex

Proc Natl Acad Sci U S A. 2018 Oct 16;115(42):E9792-E9801. doi: 10.1073/pnas.1811874115. Epub 2018 Sep 5.

Abstract

Autophagy is an enigmatic cellular process in which double-membrane compartments, called "autophagosomes, form de novo adjacent to the endoplasmic reticulum (ER) and package cytoplasmic contents for delivery to lysosomes. Expansion of the precursor membrane phagophore requires autophagy-related 2 (ATG2), which localizes to the 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. ATG2A is a rod-shaped protein that can bridge neighboring vesicles through interactions at each of its tips. WIPI4 binds to one of the tips, enabling the ATG2A-WIPI4 complex to tether a PI3P-containing vesicle to another PI3P-free vesicle. These data suggest that the ATG2A-WIPI4 complex mediates ER-phagophore association and/or tethers vesicles to the ER-phagophore junction, establishing the required organization for phagophore expansion via the transfer of lipid membranes from the ER and/or the vesicles to the phagophore.

Keywords: ATG2; autophagy; chemical cross-linking coupled with mass spectrometry; membrane tethering; single-particle analysis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Autophagosomes / metabolism*
  • Autophagy*
  • Autophagy-Related Proteins / chemistry
  • Autophagy-Related Proteins / metabolism*
  • Endoplasmic Reticulum / metabolism*
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism*
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / metabolism*
  • Phosphatidylinositol Phosphates / chemistry
  • Phosphatidylinositol Phosphates / metabolism*
  • Protein Conformation
  • Sequence Homology

Substances

  • Autophagy-Related Proteins
  • Membrane Proteins
  • Multiprotein Complexes
  • Phosphatidylinositol Phosphates
  • WIPI-1 protein, human
  • phosphatidylinositol 3-phosphate