Non-canonical role of the SNARE protein Ykt6 in autophagosome-lysosome fusion

• Published in: PLoS genetics Vol. 14; no. 4; p. e1007359
• Main Authors: Takáts, Szabolcs, Glatz, Gábor, Szenci, Győző, Boda, Attila, Horváth, Gábor V, Hegedűs, Krisztina, Kovács, Attila L, Juhász, Gábor
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 25.04.2018; Public Library of Science (PLoS)
• Subjects: Amino acids; Animals; Animals, Genetically Modified; Autophagosomes - physiology; Autophagy; Binding Sites; Biology and Life Sciences; Developmental biology; Drosophila; Drosophila melanogaster - genetics; Drosophila melanogaster - physiology; Drosophila Proteins - genetics; Drosophila Proteins - physiology; Funding; Fusion protein; Golgi apparatus; Insects; Lysosomes; Lysosomes - physiology; Medicine and Health Sciences; Membrane fusion; Membrane Fusion - genetics; Membrane Fusion - physiology; Models, Biological; Multiprotein Complexes - genetics; Multiprotein Complexes - physiology; Observations; Palmitoylation; Phagosomes; Proteins; Qa-SNARE Proteins - genetics; Qa-SNARE Proteins - physiology; R-SNARE Proteins - genetics; R-SNARE Proteins - physiology; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Research and Analysis Methods; SNAP receptors; SNARE Proteins - genetics; SNARE Proteins - physiology; Hungary
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1007359

The autophagosomal SNARE Syntaxin17 (Syx17) forms a complex with Snap29 and Vamp7/8 to promote autophagosome-lysosome fusion via multiple interactions with the tethering complex HOPS. Here we demonstrate that, unexpectedly, one more SNARE (Ykt6) is also required for autophagosome clearance in Drosophila. We find that loss of Ykt6 leads to large-scale accumulation of autophagosomes that are unable to fuse with lysosomes to form autolysosomes. Of note, loss of Syx5, the partner of Ykt6 in ER-Golgi trafficking does not prevent autolysosome formation, pointing to a more direct role of Ykt6 in fusion. Indeed, Ykt6 localizes to lysosomes and autolysosomes, and forms a SNARE complex with Syx17 and Snap29. Interestingly, Ykt6 can be outcompeted from this SNARE complex by Vamp7, and we demonstrate that overexpression of Vamp7 rescues the fusion defect of ykt6 loss of function cells. Finally, a point mutant form with an RQ amino acid change in the zero ionic layer of Ykt6 protein that is thought to be important for fusion-competent SNARE complex assembly retains normal autophagic activity and restores full viability in mutant animals, unlike palmitoylation or farnesylation site mutant Ykt6 forms. As Ykt6 and Vamp7 are both required for autophagosome-lysosome fusion and are mutually exclusive subunits in a Syx17-Snap29 complex, these data suggest that Vamp7 is directly involved in membrane fusion and Ykt6 acts as a non-conventional, regulatory SNARE in this process.