Metamorphosis by ATG13 and ATG101 in human autophagy initiation

Abstract

Autophagosome biogenesis requires the timely assembly of a complex machinery. However, it is unclear how a putative stable super-complex is assembled and disassembled, and how the different parts cooperate to perform its overall function. To shed light on these questions, we embarked on an effort to biochemically reconstitute the human initiation complexes in vitro with purified full-length components. This approach revealed that all initiation subcomplexes together form a stable super-complex on an interaction platform consisting of ATG9A, ATG13 and ATG101. An unusual metamorphosis of ATG13 and ATG101 creates a rate-limiting step in the assembly of the ATG9A-ATG13-ATG101 complex. Furthermore, the interaction of ATG2A with the ATG9A-ATG13-ATG101 complex and WIPI4 cooperatively enhances both the vesicle tethering and lipid transfer of this complex. It seems likely that the spontaneous self-assembly of the super-complex is inhibited before autophagy initiation, a mechanism where the rate-limiting metamorphosis of ATG13 and ATG101 could play a central regulatory role. Abbreviations ATG, Autophagy-related, HORMA, protein domain named after HOP1-MAD2-REV7; RB1CC1, RB1 inducible coiled-coil 1; ULK, Unc-51-like kinase