Poster Presentation 11th International Symposium on Autophagy 2025

Interaction network that recruits the Atg2-Atg18 complex to the pre-autophagosomal structure (#108)

Yuri Yasuda 1 2 , Toshiaki Tsuchiya 2 , Takayuki Sekito 3 , Kanae Hitomi 2 , Tetsuya Kotani 1 , Hitoshi Nakatogawa 1 2
  1. Cell Biology Center, Institute of Integrated Research, Institute of Science Tokyo, Yokohama, Kanagawa, Japan
  2. School of Life Science and Technology, Institute of Science Tokyo, Yokohama, Kanagawa, Japan
  3. Graduate School of Agriculture, Faculty of Agriculture, Ehime University, Matsuyama, Ehime, Japan

In autophagy, intracellular components are sequestered into double-membrane vesicles called autophagosomes, which subsequently fuse with the vacuole or lysosome for degradation. In Saccharomyces cerevisiae, the Atg1 protein kinase complex forms a scaffold that recruits other Atg proteins to assemble the pre-autophagosomal structure (PAS). The Atg2–Atg18 complex mediates lipid transfer from the endoplasmic reticulum (ER), which is essential for the expansion of the isolation membrane (or phagophore). The PAS localization of this complex depends on the phosphatidylinositol 3-phosphate (PI3P)-binding ability of Atg18. However, the atg18FTTG mutation, which is defective in PI3P binding, does not completely abolish the PAS localization of the complex. Moreover, PI3P is also present in other intracellular compartments, such as endosomes. These observations suggest that Atg18 binding to PI3P alone is insufficient to achieve specific PAS localization, and that additional interactions contribute to this process.

In this study, we identified an interaction between the Atg2–Atg18 complex and the Atg1 complex, which is mediated by Atg2 and the Atg1 complex subunit Atg29. We further investigated how this interaction relates to Atg18–PI3P binding and the interaction between Atg2 and Atg9, which has been proposed to target the Atg2–Atg18 complex to the isolation membrane edge. Using mutants defective in these interactions, we found that disruption of either the Atg2–Atg29 or Atg2–Atg9 interaction alone had minimal impact on autophagy. However, in the atg18FTTG background, these mutations significantly impaired the PAS localization of Atg2 and reduced autophagic activity. These findings suggest that the PAS localization of the Atg2–Atg18 complex is achieved through a tripartite mechanism involving the Atg2–Atg29, Atg2–Atg9, and Atg18–PI3P interactions.