The Z-shaped N-terminal Domain of Atg11 Coordinates Atg9 Recruitment in Selective Autophagy
Macroautophagy is a conserved catabolic process that facilitates the degradation of cellular material by capturing it in double membrane vesicles termed autophagosomes. In Saccharomyces cerevisiae, selective macroautophagy is initiated by the scaffolding protein Atg11. Atg11 recruits the transmembrane protein Atg9, which resides in small vesicles, to autophagic cargo. Atg9 vesicles then fuse, forming the initial membrane sheet that expands into the autophagosomal membrane. While it is known that Atg9 interacts with Atg11 via a set of hydrophobic amino acids in the disordered N-terminus of Atg9, it is unclear how Atg11 mediates this interaction. To gain insight into this unknown aspect of autophagy initiation we utilized a combination of biochemical, structural, and cellular approaches. We demonstrate that the N-terminal domain (NTD) of Atg11 is the primary interaction site for Atg9, but the NTD requires clustering by the C-terminal region of Atg11 for its complete interaction with Atg9. We investigated the structure of the Atg11-NTD using cryo-EM which, in combination with AlphaFold modeling, revealed a positively charged binding pocket within the Atg11-NTD that is essential for Atg9 binding. Mutation of this conserved binding pocket leads to a loss of Atg9 binding in yeast and a reduction in the selective autophagy of mitochondria. Taken together, our results demonstrate the mechanism by which Atg11 recruits Atg9 to autophagy initiation sites.