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Abstract：
The sole proteases of the macroautophagy/autophagy machinery, the ATG4s, contribute to autophagosome formation by cleaving Atg8-family protein members (LC3/GABARAPs) which enables Atg8-family protein lipidation and de-lipidation. Our recent work reveals that ATG4s can also promote phagophore growth independently of their protease activity and of Atg8-family proteins. ATG4s and their proximity partners including ARFIP2 and LRBA function to promote trafficking of ATG9A to mitochondria during PINK1-PRKN mitophagy. Through the development of a 3D electron microscopy framework utilizing FIB-SEM and artificial intelligence (termed AIVE: Artificial Intelligence-directed Voxel Extraction), we show that ATG4s promote ER-phagophore contacts during the lipid-transfer phase of autophagosome biogenesis, which requires ATG2B and ATG9A to support phagophore growth. We also discovered that ATG4s are not essential for removal of Atg8-family proteins from autolysosomes, but they can function as deubiquitinase-like enzymes to counteract the conjugation of Atg8-family proteins to other proteins, a process that we have termed ATG8ylation (also known as LC3ylation). These discoveries demonstrate the duality of the ATG4 family in driving autophagosome formation by functioning as both autophagy proteases and trafficking factors, while simultaneously raising questions about the putative roles of ATG8ylation in cell biology.
摘要：
巨自噬/自噬机制的唯一蛋白酶，ATG4s,通过切割Atg8家族蛋白成员（LC3/GABARAPs）有助于自噬体形成，从而使Atg8家族蛋白脂化和去脂化。我们最近的工作表明，ATG4s也可以独立于其蛋白酶活性和Atg8家族蛋白促进吞噬细胞的生长。ATG4s及其邻近伴侣包括ARFIP2和LRBA在PINK1-PRKN线粒体自噬过程中促进ATG9A向线粒体的运输。通过开发利用FIB-SEM和人工智能的3D电子显微镜框架（称为AIVE：人工智能定向的体素提取），我们表明ATG4s在自噬小体生物发生的脂质转移阶段促进ER-吞噬体接触，这需要ATG2B和ATG9A来支持吞噬体的生长。我们还发现ATG4s对于从自体溶酶体中去除Atg8家族蛋白不是必需的，但它们可以作为去泛素酶类酶来抵消Atg8家族蛋白与其他蛋白的结合，我们称为ATG8化（也称为LC3化）的过程。这些发现证明了ATG4家族通过充当自噬蛋白酶和贩运因子来驱动自噬体形成的双重性。同时提出了关于ATG8化在细胞生物学中的推定作用的问题。
