The hairpin-type tail-anchored SNARE syntaxin 17 targets to autophagosomes for fusion with endosomes/lysosomes
- Cell. 2012 Dec 7;151(6):1256-69. doi: 10.1016/j.cell.2012.11.001.
- 1. Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
The lysosome is a degradative organelle, and its fusion with Other organelles is strictly regulated. In contrast to fusion with the late endosome, the mechanisms underlying autophagosome-lysosome fusion remain unknown. Here, we identify syntaxin 17 (Stx17) as the autophagosomal SNARE required for fusion with the endosome/lysosome. Stx17 localizes to the outer membrane of completed autophagosomes but not to the isolation membrane (unclosed intermediate structures); for this reason, the lysosome does not fuse with the isolation membrane. Stx17 interacts with SNAP-29 and the endosomal/lysosomal SNARE VAMP8. Depletion of Stx17 causes accumulation of autophagosomes without degradation. Stx17 has a unique C-terminal hairpin structure mediated by two tandem transmembrane domains containing glycine zipper-like motifs, which is essential for its association with the autophagosomal membrane. These findings reveal a mechanism by which the SNARE protein is available to the completed autophagosome.