2. Academic Validation
  3. ATG4 family proteins drive phagophore growth independently of the LC3/GABARAP lipidation system

ATG4 family proteins drive phagophore growth independently of the LC3/GABARAP lipidation system

  • Mol Cell. 2021 May 6;81(9):2013-2030.e9. doi: 10.1016/j.molcel.2021.03.001.
Thanh Ngoc Nguyen 1,  Benjamin Scott Padman 2,  Susanne Zellner 3,  Grace Khuu 2,  Louise Uoselis 2,  Wai Kit Lam 2,  Marvin Skulsuppaisarn 2,  Runa S J Lindblom 2,  Emily M Watts 2,  Christian Behrends 3,  Michael Lazarou 4
Affiliations

Affiliations

  • 1 Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Melbourne, Australia. Electronic address: [email protected].
  • 2 Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Melbourne, Australia.
  • 3 Munich Cluster for Systems Neurology, Medical Faculty, Ludwig-Maximilians-University München, Munich, Germany.
  • 4 Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Melbourne, Australia. Electronic address: [email protected].
PMID: 33773106 DOI: 10.1016/j.molcel.2021.03.001
Abstract

The sequestration of damaged mitochondria within double-membrane structures termed autophagosomes is a key step of PINK1/Parkin Mitophagy. The Atg4 family of proteases are thought to regulate autophagosome formation exclusively by processing the ubiquitin-like ATG8 family (LC3/GABARAPs). We discover that human ATG4s promote autophagosome formation independently of their protease activity and of ATG8 family processing. Atg4 proximity networks reveal a role for ATG4s and their proximity partners, including the immune-disease protein LRBA, in ATG9A vesicle trafficking to mitochondria. Artificial intelligence-directed 3D electron microscopy of phagophores shows that ATG4s promote phagophore-ER contacts during the lipid-transfer phase of autophagosome formation. We also show that ATG8 removal during autophagosome maturation does not depend on Atg4 activity. Instead, ATG4s can disassemble ATG8-protein conjugates, revealing a role for ATG4s as deubiquitinating-like enzymes. These findings establish non-canonical roles of the Atg4 family beyond the ATG8 lipidation axis and provide an AI-driven framework for rapid 3D electron microscopy.

Keywords

ATG4; ATG9a; FIB-SEM; LRBA; PINK1; Parkin; autophagosome; autophagy; mitochondria; mitophagy.

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