Membrane Morphology Is Actively Transformed by Covalent Binding of the Protein Atg8 to PE-Lipids |
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Authors: | Roland L Knorr Hitoshi Nakatogawa Yoshinori Ohsumi Reinhard Lipowsky Tobias Baumgart Rumiana Dimova |
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Institution: | 1. Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.; 2. Frontier Research Center, Tokyo Institute of Technology, Yokohama, Japan.; 3. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.; National Institute of Biological Sciences, Beijing, China, |
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Abstract: | Autophagy is a cellular degradation pathway involving the shape transformation of lipid bilayers. During the onset of autophagy, the water-soluble protein Atg8 binds covalently to phosphatdylethanolamines (PEs) in the membrane in an ubiquitin-like reaction coupled to ATP hydrolysis. We reconstituted the Atg8 conjugation system in giant and nm-sized vesicles with a minimal set of enzymes and observed that formation of Atg8-PE on giant vesicles can cause substantial tubulation of membranes even in the absence of Atg12-Atg5-Atg16. Our findings show that ubiquitin-like processes can actively change properties of lipid membranes and that membrane crowding by proteins can be dynamically regulated in cells. Furthermore we provide evidence for curvature sorting of Atg8-PE. Curvature generation and sorting are directly linked to organelle shapes and, thus, to biological function. Our results suggest that a positive feedback exists between the ubiquitin-like reaction and the membrane curvature, which is important for dynamic shape changes of cell membranes, such as those involved in the formation of autophagosomes. |
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