Department of Cell Biology, University of Groningen, University Medical Center Groningen, Groningen, Netherlands.
Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Osnabrück, Germany.
J Cell Biol. 2018 Aug 6;217(8):2743-2763. doi: 10.1083/jcb.201710116. Epub 2018 May 30.
The autophagy-related (Atg) proteins play a key role in the formation of autophagosomes, the hallmark of autophagy. The function of the cluster composed by Atg2, Atg18, and transmembrane Atg9 is completely unknown despite their importance in autophagy. In this study, we provide insights into the molecular role of these proteins by identifying and characterizing Atg2 point mutants impaired in Atg9 binding. We show that Atg2 associates to autophagosomal membranes through lipid binding and independently from Atg9. Its interaction with Atg9, however, is key for Atg2 confinement to the growing phagophore extremities and subsequent association of Atg18. Assembly of the Atg9-Atg2-Atg18 complex is important to establish phagophore-endoplasmic reticulum (ER) contact sites. In turn, disruption of the Atg2-Atg9 interaction leads to an aberrant topological distribution of both Atg2 and ER contact sites on forming phagophores, which severely impairs autophagy. Altogether, our data shed light in the interrelationship between Atg9, Atg2, and Atg18 and highlight the possible functional relevance of the phagophore-ER contact sites in phagophore expansion.
自噬相关（Atg）蛋白在自噬体的形成中起着关键作用，自噬体是自噬的标志。尽管 Atg2、Atg18 和跨膜 Atg9 组成的簇在自噬中非常重要，但它们的功能完全未知。在这项研究中，我们通过鉴定和表征 Atg9 结合受损的 Atg2 点突变体，深入了解了这些蛋白质的分子作用。我们表明，Atg2 通过脂质结合与自噬体膜相关联，而不依赖于 Atg9。然而，它与 Atg9 的相互作用对于 Atg2 局限于不断增长的吞噬体末端以及随后 Atg18 的关联是关键的。Atg9-Atg2-Atg18 复合物的组装对于建立吞噬体-内质网（ER）接触位点很重要。反过来，破坏 Atg2-Atg9 相互作用会导致形成的吞噬体上 Atg2 和 ER 接触位点的异常拓扑分布，严重损害自噬。总之，我们的数据阐明了 Atg9、Atg2 和 Atg18 之间的相互关系，并强调了吞噬体-ER 接触位点在吞噬体扩展中的可能功能相关性。
