Electrostatic maturation of the autophagosome.

In macroautophagy, lysosomes fuse with closed autophagosomes but not with unclosed ones. This is achieved, at least in part, by the temporally regulated recruitment of the autophagosomal SNARE STX17 (syntaxin 17) to only mature autophagosomes. However, the molecular mechanism by which STX17 recognizes autophagosomal maturation remains unknown. Our recent study revealed that STX17 recruitment is regulated by the electrostatic interaction between the positively charged C-terminal region of STX17 and the autophagosomal membrane, which becomes negatively charged during maturation due to the accumulation of phosphatidylinositol-4-phosphate (PtdIns4P). Here, we propose an electrostatic maturation model of the autophagosome.