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标题：In situ structural analysis reveals membrane shape transitions during autophagosome formation
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作者：Anna Bieber ; Cristina Capitanio ; Philipp S. Erdmann 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：39
DOI：10.1073/pnas.2209823119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance Macroautophagy is a degradation process fundamental for (eukaryotic) cellular homeostasis, in which cytosolic material is engulfed by a double-membrane autophagosome for delivery to a lytic compartment. In this study, we capture transient intermediates of autophagosome biogenesis within yeast cells at previously unattained resolution by correlative cryo-electron tomography (cryo-ET). Our quantitative analysis of autophagic membranes reveals unexpected structural features and shape transitions from open phagophores to closed autophagosomes. We further define the subcellular environment of autophagic structures, uncovering polarized contact sites with specific organelles. These results have direct implications for the membrane sources in autophagy and for the forces inducing phagophore shape, thus highlighting the potential of cryo-ET at the junction of biophysics and cell biology. Autophagosomes are unique organelles that form de novo as double-membrane vesicles engulfing cytosolic material for destruction. Their biogenesis involves membrane transformations of distinctly shaped intermediates whose ultrastructure is poorly understood. Here, we combine cell biology, correlative cryo-electron tomography (cryo-ET), and extensive data analysis to reveal the step-by-step structural progression of autophagosome biogenesis at high resolution directly within yeast cells. The analysis uncovers an unexpectedly thin intermembrane distance that is dilated at the phagophore rim. Mapping of individual autophagic structures onto a timeline based on geometric features reveals a dynamical change of membrane shape and curvature in growing phagophores. Moreover, our tomograms show the organelle interactome of growing autophagosomes, highlighting a polar organization of contact sites between the phagophore and organelles, such as the vacuole and the endoplasmic reticulum (ER). Collectively, these findings have important implications for the contribution of different membrane sources during autophagy and for the forces shaping and driving phagophores toward closure without a templating cargo.
关键词：enautophagycryo-electron tomographyautophagosome biogenesisorganelle contact sitesmembrane structure