What’s in an E3: role of highly curved membranes in facilitating LC3–phosphatidylethanolamine conjugation during autophagy

ABSTRACT

During autophagosome formation, ATG3, an E2-like enzyme, catalyzes the transfer of LC3-family proteins (including Atg8 in yeast and LC3- and GABARAP-subfamily members in more complex eukaryotes) from the covalent conjugated ATG3–LC3 intermediate to PE lipids in targeted membranes. A recent study has shown that the catalytically important regions of human ATG3 (hereafter referred to as ATG3), including residues 262 to 277 and 291 to 300, in cooperation with its N-terminal curvature-sensing amphipathic helix (NAH), directly interact with the membrane. These membrane interactions are functionally necessary for in vitro conjugation and in vivo cellular assays. They provide a molecular mechanism for how the membrane curvature-sensitive interaction of the NAH of ATG3 is closely coupled to its conjugase activity. Together, the data are consistent with a model in which the highly curved phagophore rims facilitate the recruitment of the ATG3–LC3 complex and promote the conjugation of LC3 to PE lipids. Mechanistically, the highly curved membranes of the phagophore rims act in much the same manner as classical E3 enzymes in the sumo/ubiquitin system, bringing substrates into proximity and rearranging the catalytic center of ATG3. Future studies will investigate how this multifaceted membrane interaction of ATG3 works with the putative E3 complex, ATG12–ATG5-ATG16L1, to promote LC3–PE conjugation.

KEYWORDS:

• Autophagy
• ATG3
• autophagosome biogenesis
• ATG3-LC3 conjugation
• membrane curvature

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Institutes of Health through R01 GM127730 (FT), R01 GM127954 (HGW), R01 CA222349 (HGW) and Four Diamonds through 4D21_2024_1001 (FT) and 4DIA_153697 (JMF). The NMR instruments used in this project (RRID:SCR_023244) were funded, in part, by the Pennsylvania State University College of Medicine via the Office of the Vice Dean of Research and Graduate Students and the Pennsylvania Department of Health using Tobacco Settlement Funds (CURE). The content is solely the responsibility of the authors and does not necessarily represent the official views of the University or College of Medicine. The Pennsylvania Department of Health specifically disclaims responsibility for any analyses, interpretations, or conclusions.