Department of Biological Sciences, Faculty of Science, National University of Singapore, 14 Science Drive 4, 117543, Singapore, Singapore.
Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597, Singapore.
Nat Commun. 2019 May 3;10(1):2059. doi: 10.1038/s41467-019-10096-1.
Mitophagy is the selective autophagic targeting and removal of dysfunctional mitochondria. While PINK1/Parkin-dependent mitophagy is well-characterized, PINK1/Parkin-independent route is poorly understood. Using structure illumination microscopy (SR-SIM), we demonstrate that the SNARE protein Syntaxin 17 (STX17) initiates mitophagy upon depletion of outer mitochondrial membrane protein Fis1. With proteomics analysis, we identify the STX17-Fis1 interaction, which controls the dynamic shuffling of STX17 between ER and mitochondria. Fis1 loss results in aberrant STX17 accumulation on mitochondria, which exposes the N terminus and promotes self-oligomerization to trigger mitophagy. Mitochondrial STX17 interacts with ATG14 and recruits core autophagy proteins to form mitophagosome, followed by Rab7-dependent mitophagosome-lysosome fusion. Furthermore, Fis1 loss impairs mitochondrial respiration and potentially sensitizes cells to mitochondrial clearance, which is mediated through canonical autophagy machinery, closely linking non-selective macroautophagy to mitochondrial turnover. Our findings uncover a PINK1/Parkin-independent mitophagic mechanism in which outer mitochondrial membrane protein Fis1 regulates mitochondrial quality control.
线粒体自噬是一种选择性的自噬靶向和去除功能失调的线粒体的过程。虽然 PINK1/Parkin 依赖性的线粒体自噬已经得到了很好的描述，但 PINK1/Parkin 非依赖性途径还了解甚少。我们使用结构光照明显微镜（SR-SIM）技术，证明了在耗尽外膜蛋白 Fis1 后，SNARE 蛋白 Syntaxin 17（STX17）会引发线粒体自噬。通过蛋白质组学分析，我们确定了 STX17-Fis1 相互作用，它控制了 STX17 在 ER 和线粒体之间的动态交换。Fis1 的缺失导致 STX17 在线粒体上的异常积累，从而暴露其 N 端并促进自身寡聚化以触发线粒体自噬。线粒体 STX17 与 ATG14 相互作用，并招募核心自噬蛋白形成自噬体，随后通过 Rab7 依赖性自噬体-溶酶体融合。此外，Fis1 的缺失会损害线粒体呼吸，并可能使细胞对线粒体清除敏感，这是通过经典的自噬机制介导的，将非选择性的巨自噬与线粒体周转率紧密联系起来。我们的发现揭示了一种 PINK1/Parkin 非依赖性的线粒体自噬机制，其中外膜蛋白 Fis1 调节线粒体质量控制。
