The endoplasmic reticulum (ER) is selectively degraded by autophagy (ER-phagy) through proteins called ER-phagy receptors. In Saccharomyces cerevisiae, Atg40 acts as an ER-phagy receptor to sequester ER fragments into autophagosomes by binding Atg8 on forming autophagosomal membranes. During ER-phagy, parts of the ER are morphologically rearranged, fragmented, and loaded into autophagosomes, but the mechanism remains poorly understood. Here we find that Atg40 molecules assemble in the ER membrane concurrently with autophagosome formation via multivalent interaction with Atg8. Atg8-mediated super-assembly of Atg40 generates highly-curved ER regions, depending on its reticulon-like domain, and supports packing of these regions into autophagosomes. Moreover, tight binding of Atg40 to Atg8 is achieved by a short helix C-terminal to the Atg8-family interacting motif, and this feature is also observed for mammalian ER-phagy receptors. Thus, this study significantly advances our understanding of the mechanisms of ER-phagy and also provides insights into organelle fragmentation in selective autophagy of other organelles.

内质网（ER）通过自噬（ER-噬菌体）通过称为ER-噬菌体受体的蛋白质选择性降解。在酿酒酵母中Atg40通过结合Atg8形成自噬体膜而充当ER吞噬受体，将ER片段隔离到自噬体中。在内质网吞噬过程中，内质网的一部分在形态上重新排列，片段化并加载到自噬体中，但其机理仍知之甚少。在这里，我们发现Atg40分子通过与Atg8的多价相互作用在ER膜中组装并与自噬体形成同时发生。Atg8介导的Atg40超级组装体会根据其网状样结构域生成高度弯曲的ER区，并支持将这些区包装成自噬体。此外，Atg40与Atg8的紧密结合是通过Atg8家族相互作用基序的短螺旋C末端实现的，对于哺乳动物ER吞噬受体也可以观察到此特征。从而，