The multi-functional SNARE protein Ykt6 in autophagosomal fusion processes

Autophagy is a degradative pathway in which cytosolic material is enwrapped within double membrane vesicles, so-called autophagosomes, and delivered to lytic organelles. SNARE (Soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins are key to drive membrane fusion of the autophagosome and the lytic organelles, called lysosomes in higher eukaryotes or vacuoles in plants and yeast. Therefore, the identification of functional SNARE complexes is central for understanding fusion processes and their regulation. The SNARE proteins Syntaxin 17, SNAP29 and Vamp7/VAMP8 are responsible for the fusion of autophagosomes with lysosomes in higher eukaryotes. Recent studies reported that the R-SNARE Ykt6 is an additional SNARE protein involved in autophagosome-lytic organelle fusion in yeast, Drosophila, and mammals. These current findings point to an evolutionarily conserved role of Ykt6 in autophagosome-related fusion events. Here, we briefly summarize the principal mechanisms of autophagosome-lytic organelle fusion, with a special focus on Ykt6 to highlight some intrinsic features of this unusual SNARE protein.