1
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Zhang Y, Lin C. Lipid osmosis, membrane tension, and other mechanochemical driving forces of lipid flow. Curr Opin Cell Biol 2024; 88:102377. [PMID: 38823338 PMCID: PMC11193448 DOI: 10.1016/j.ceb.2024.102377] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Revised: 05/12/2024] [Accepted: 05/13/2024] [Indexed: 06/03/2024]
Abstract
Nonvesicular lipid transport among different membranes or membrane domains plays crucial roles in lipid homeostasis and organelle biogenesis. However, the forces that drive such lipid transport are not well understood. We propose that lipids tend to flow towards the membrane area with a higher membrane protein density in a process termed lipid osmosis. This process lowers the membrane tension in the area, resulting in a membrane tension difference called osmotic membrane tension. We examine the thermodynamic basis and experimental evidence of lipid osmosis and osmotic membrane tension. We predict that lipid osmosis can drive bulk lipid flows between different membrane regions through lipid transfer proteins, scramblases, or similar barriers that selectively pass lipids but not membrane proteins. We also speculate on the biological functions of lipid osmosis. Finally, we explore other driving forces for lipid transfer and describe potential methods and systems to further test our theory.
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Affiliation(s)
- Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA.
| | - Chenxiang Lin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA; Nanobiology Institute, Yale University, West Haven, CT 06516, USA; Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA.
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2
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Zhang Y, Lin C. Lipid osmosis, membrane tension, and other mechanochemical driving forces of lipid flow. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.08.574656. [PMID: 38260424 PMCID: PMC10802412 DOI: 10.1101/2024.01.08.574656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Nonvesicular lipid transport among different membranes or membrane domains plays crucial roles in lipid homeostasis and organelle biogenesis. However, the forces that drive such lipid transport are not well understood. We propose that lipids tend to flow towards the membrane area with a higher membrane protein density in a process termed lipid osmosis. This process lowers the membrane tension in the area, resulting in a membrane tension difference called osmotic membrane tension. We examine the thermodynamic basis and experimental evidence of lipid osmosis and osmotic membrane tension. We predict that lipid osmosis can drive bulk lipid flows between different membrane regions through lipid transfer proteins, scramblases, or other similar barriers that selectively pass lipids but not membrane proteins. We also speculate on the biological functions of lipid osmosis. Finally, we explore other driving forces for lipid transfer and describe potential methods and systems to further test our theory.
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Affiliation(s)
- Yongli Zhang
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA
| | - Chenxiang Lin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA
- Nanobiology Institute, Yale University, West Haven, CT 06516, USA
- Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA
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3
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Kotani T, Yasuda Y, Nakatogawa H. Molecular Mechanism of Autophagy, Cytoplasmic Zoning by Lipid Membranes. J Biochem 2024; 175:155-165. [PMID: 37983716 DOI: 10.1093/jb/mvad099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 11/02/2023] [Accepted: 11/06/2023] [Indexed: 11/22/2023] Open
Abstract
Autophagy is a highly conserved intracellular degradation mechanism. The most distinctive feature of autophagy is the formation of double-membrane structures called autophagosomes, which compartmentalize portions of the cytoplasm. The outer membrane of the autophagosome fuses with the vacuolar/lysosomal membrane, leading to the degradation of the contents of the autophagosome. Approximately 30 years have passed since the identification of autophagy-related (ATG) genes and Atg proteins essential for autophagosome formation, and the primary functions of these Atg proteins have been elucidated. These achievements have significantly advanced our understanding of the mechanism of autophagosome formation. This article summarizes our current knowledge on how the autophagosome precursor is generated, and how the membrane expands and seals to complete the autophagosome.
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Affiliation(s)
- Tetsuya Kotani
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, S2-14 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
| | - Yuri Yasuda
- School of Life Science and Technology, Tokyo Institute of Technology, S2-14 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
| | - Hitoshi Nakatogawa
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, S2-14 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
- School of Life Science and Technology, Tokyo Institute of Technology, S2-14 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
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4
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Sakai Y, Takahashi S, Koyama-Honda I, Saito C, Mizushima N. Experimental determination and mathematical modeling of standard shapes of forming autophagosomes. Nat Commun 2024; 15:91. [PMID: 38167876 PMCID: PMC10762205 DOI: 10.1038/s41467-023-44442-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 12/12/2023] [Indexed: 01/05/2024] Open
Abstract
The formation of autophagosomes involves dynamic morphological changes of a phagophore from a flat membrane cisterna into a cup-shaped intermediate and a spherical autophagosome. However, the physical mechanism behind these morphological changes remains elusive. Here, we determine the average shapes of phagophores by statistically investigating three-dimensional electron micrographs of more than 100 phagophores. The results show that the cup-shaped structures adopt a characteristic morphology; they are longitudinally elongated, and the rim is catenoidal with an outwardly recurved shape. To understand these characteristic shapes, we establish a theoretical model of the shape of entire phagophores. The model quantitatively reproduces the average morphology and reveals that the characteristic shape of phagophores is primarily determined by the relative size of the open rim to the total surface area. These results suggest that the seemingly complex morphological changes during autophagosome formation follow a stable path determined by elastic bending energy minimization.
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Affiliation(s)
- Yuji Sakai
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
- Department of Biosystems Science, Institute for Life and Medical Sciences, Kyoto University, Sakyo-ku, Kyoto, 606-8507, Japan.
- Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) Program, RIKEN, Wako, Saitama, 351-0198, Japan.
| | - Satoru Takahashi
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
- Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, 113-8510, Japan
| | - Ikuko Koyama-Honda
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Chieko Saito
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Noboru Mizushima
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
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5
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Tooze SA, Zhang W, Lazzeri G, Gahlot D, Thukral L, Covino R, Nishimura T. Membrane association of the ATG8 conjugation machinery emerges as a key regulatory feature for autophagosome biogenesis. FEBS Lett 2024; 598:107-113. [PMID: 37259601 PMCID: PMC10952647 DOI: 10.1002/1873-3468.14676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2023] [Revised: 05/10/2023] [Accepted: 05/10/2023] [Indexed: 06/02/2023]
Abstract
Autophagy is a highly conserved intracellular pathway that is essential for survival in all eukaryotes. In healthy cells, autophagy is used to remove damaged intracellular components, which can be as simple as unfolded proteins or as complex as whole mitochondria. Once the damaged component is captured, the autophagosome engulfs it and closes, isolating the content from the cytoplasm. The autophagosome then fuses with the late endosome and/or lysosome to deliver its content to the lysosome for degradation. Formation of the autophagosome, sequestration or capture of content, and closure all require the ATG proteins, which constitute the essential core autophagy protein machinery. This brief 'nutshell' will highlight recent data revealing the importance of small membrane-associated domains in the ATG proteins. In particular, recent findings from two parallel studies reveal the unexpected key role of α-helical structures in the ATG8 conjugation machinery and ATG8s. These studies illustrate how unique membrane association modules can control the formation of autophagosomes.
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Affiliation(s)
- Sharon A. Tooze
- Molecular Cell Biology of Autophagy LaboratoryThe Francis Crick InstituteLondonUK
| | - Wenxin Zhang
- Molecular Cell Biology of Autophagy LaboratoryThe Francis Crick InstituteLondonUK
| | | | - Deepanshi Gahlot
- CSIR‐Institute of Genomics and Integrative BiologyNew DelhiIndia
- Academy of Scientific and Innovative Research (AcSIR)GhaziabadIndia
| | - Lipi Thukral
- CSIR‐Institute of Genomics and Integrative BiologyNew DelhiIndia
- Academy of Scientific and Innovative Research (AcSIR)GhaziabadIndia
| | | | - Taki Nishimura
- PRESTO, Japan Science and Technology AgencyTokyoJapan
- Department of Biochemistry and Molecular Biology, Graduate School of MedicineThe University of TokyoJapan
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6
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Puri C, Gratian MJ, Rubinsztein DC. Mammalian autophagosomes form from finger-like phagophores. Dev Cell 2023; 58:2746-2760.e5. [PMID: 37683632 DOI: 10.1016/j.devcel.2023.08.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2023] [Revised: 07/12/2023] [Accepted: 08/09/2023] [Indexed: 09/10/2023]
Abstract
The sequence of morphological intermediates that leads to mammalian autophagosome formation and closure is a crucial yet poorly understood issue. Previous studies have shown that yeast autophagosomes evolve from cup-shaped phagophores with only one closure point, and mammalian studies have inferred that mammalian phagophores also have single openings. Our superresolution microscopy studies in different human cell lines in conditions of basal and nutrient-deprivation-induced autophagy identified autophagosome precursors with multifocal origins that evolved into unexpected finger-like phagophores with multiple openings before becoming more spherical structures. Compatible phagophore structures were observed with whole-mount and conventional electron microscopy. This sequence of events was visualized using advanced SIM2 superresolution live microscopy. The finger-shaped phagophore apertures remained open when ESCRT function was compromised. The efficient closure of autophagic structures is important for their release from the recycling endosome. This has important implications for understanding how autophagosomes form and capture various cargoes.
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Affiliation(s)
- Claudia Puri
- Department of Medical Genetics, University of Cambridge, Cambridge, UK; Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK; UK Dementia Research Institute, Cambridge Biomedical Campus, University of Cambridge, The Keith Peters Building Cambridge, Hills Road, Cambridge CB2 0XY, UK
| | - Matthew J Gratian
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK
| | - David C Rubinsztein
- Department of Medical Genetics, University of Cambridge, Cambridge, UK; Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK; UK Dementia Research Institute, Cambridge Biomedical Campus, University of Cambridge, The Keith Peters Building Cambridge, Hills Road, Cambridge CB2 0XY, UK.
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7
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Kotani T, Sakai Y, Kirisako H, Kakuta C, Kakuta S, Ohsumi Y, Nakatogawa H. A mechanism that ensures non-selective cytoplasm degradation by autophagy. Nat Commun 2023; 14:5815. [PMID: 37726301 PMCID: PMC10509180 DOI: 10.1038/s41467-023-41525-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 09/07/2023] [Indexed: 09/21/2023] Open
Abstract
In autophagy, a membrane cisterna called the isolation membrane expands, bends, becomes spherical, and closes to sequester cytoplasmic constituents into the resulting double-membrane vesicle autophagosome for lysosomal/vacuolar degradation. Here, we discover a mechanism that allows the isolation membrane to expand with a large opening to ensure non-selective cytoplasm sequestration within the autophagosome. A sorting nexin complex that localizes to the opening edge of the isolation membrane plays a critical role in this process. Without the complex, the isolation membrane expands with a small opening that prevents the entry of particles larger than about 25 nm, including ribosomes and proteasomes, although autophagosomes of nearly normal size eventually form. This study sheds light on membrane morphogenesis during autophagosome formation and selectivity in autophagic degradation.
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Affiliation(s)
- Tetsuya Kotani
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan
| | - Yuji Sakai
- Department of Biosystems Science, Institute for Life and Medical Sciences, Kyoto University, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Hiromi Kirisako
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan
| | - Chika Kakuta
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan
| | - Soichiro Kakuta
- Laboratory of Morphology and Image Analysis, Biomedical Research Core Facilities, Juntendo University Graduate School of Medicine, Bunkyo-ku, Tokyo, 113-8421, Japan
| | - Yoshinori Ohsumi
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan
| | - Hitoshi Nakatogawa
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
- School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
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8
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Melia TJ. Growing thin - How bulk lipid transport drives expansion of the autophagosome membrane but not of its lumen. Curr Opin Cell Biol 2023; 83:102190. [PMID: 37385155 PMCID: PMC10528516 DOI: 10.1016/j.ceb.2023.102190] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 05/30/2023] [Accepted: 05/30/2023] [Indexed: 07/01/2023]
Abstract
The key event in macroautophagy is the de novo formation of a new organelle called the autophagosome which when complete, will have captured bits of cytoplasm within its double-membrane structure. Eventual fusion with the lysosome allows this captured material to be degraded back to simple molecules which can be recycled to support cell function during starvation. How autophagosomes form has been a challenging question for over 60 years. This review highlights work that forms the basis for an autophagosome membrane expansion model grounded in protein-mediated lipid transport.
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9
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Dabrowski R, Tulli S, Graef M. Parallel phospholipid transfer by Vps13 and Atg2 determines autophagosome biogenesis dynamics. J Cell Biol 2023; 222:e202211039. [PMID: 37115156 PMCID: PMC10148235 DOI: 10.1083/jcb.202211039] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 03/30/2023] [Accepted: 04/08/2023] [Indexed: 04/29/2023] Open
Abstract
During autophagy, rapid membrane assembly expands small phagophores into large double-membrane autophagosomes. Theoretical modeling predicts that the majority of autophagosomal phospholipids are derived from highly efficient non-vesicular phospholipid transfer (PLT) across phagophore-ER contacts (PERCS). Currently, the phagophore-ER tether Atg2 is the only PLT protein known to drive phagophore expansion in vivo. Here, our quantitative live-cell imaging analysis reveals a poor correlation between the duration and size of forming autophagosomes and the number of Atg2 molecules at PERCS of starving yeast cells. Strikingly, we find that Atg2-mediated PLT is non-rate limiting for autophagosome biogenesis because membrane tether and the PLT protein Vps13 localizes to the rim and promotes the expansion of phagophores in parallel with Atg2. In the absence of Vps13, the number of Atg2 molecules at PERCS determines the duration and size of forming autophagosomes with an apparent in vivo transfer rate of ∼200 phospholipids per Atg2 molecule and second. We propose that conserved PLT proteins cooperate in channeling phospholipids across organelle contact sites for non-rate-limiting membrane assembly during autophagosome biogenesis.
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Affiliation(s)
- Rahel Dabrowski
- Max Planck Research Group of Autophagy and Cellular Ageing, Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Susanna Tulli
- Max Planck Research Group of Autophagy and Cellular Ageing, Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Martin Graef
- Max Planck Research Group of Autophagy and Cellular Ageing, Max Planck Institute for Biology of Ageing, Cologne, Germany
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
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10
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Nishimura T, Lazzeri G, Mizushima N, Covino R, Tooze SA. Unique amphipathic α helix drives membrane insertion and enzymatic activity of ATG3. SCIENCE ADVANCES 2023; 9:eadh1281. [PMID: 37352354 PMCID: PMC10289646 DOI: 10.1126/sciadv.adh1281] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Accepted: 05/22/2023] [Indexed: 06/25/2023]
Abstract
Autophagosome biogenesis requires a localized perturbation of lipid membrane dynamics and a unique protein-lipid conjugate. Autophagy-related (ATG) proteins catalyze this biogenesis on cellular membranes, but the underlying molecular mechanism remains unclear. Focusing on the final step of the protein-lipid conjugation reaction, the ATG8/LC3 lipidation, we show how the membrane association of the conjugation machinery is organized and fine-tuned at the atomistic level. Amphipathic α helices in ATG3 proteins (AHATG3) have low hydrophobicity and contain less bulky residues. Molecular dynamics simulations reveal that AHATG3 regulates the dynamics and accessibility of the thioester bond of the ATG3~LC3 conjugate to lipids, enabling the covalent lipidation of LC3. Live-cell imaging shows that the transient membrane association of ATG3 with autophagic membranes is governed by the less bulky-hydrophobic feature of AHATG3. The unique properties of AHATG3 facilitate protein-lipid bilayer association, leading to the remodeling of the lipid bilayer required for the formation of autophagosomes.
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Affiliation(s)
- Taki Nishimura
- PRESTO, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076, Japan
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
- Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Gianmarco Lazzeri
- Frankfurt Institute for Advanced Studies, Ruth-Moufang-Straße 1, Frankfurt am Main 60438, Germany
- Goethe University, Frankfurt am Main 60438, Germany
| | - Noboru Mizushima
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Roberto Covino
- Frankfurt Institute for Advanced Studies, Ruth-Moufang-Straße 1, Frankfurt am Main 60438, Germany
- Goethe University, Frankfurt am Main 60438, Germany
| | - Sharon A. Tooze
- Molecular Cell Biology of Autophagy Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
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11
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Capitanio C, Bieber A, Wilfling F. How Membrane Contact Sites Shape the Phagophore. CONTACT (THOUSAND OAKS (VENTURA COUNTY, CALIF.)) 2023; 6:25152564231162495. [PMID: 37366413 PMCID: PMC10243513 DOI: 10.1177/25152564231162495] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 02/15/2023] [Accepted: 02/18/2023] [Indexed: 06/28/2023]
Abstract
During macroautophagy, phagophores establish multiple membrane contact sites (MCSs) with other organelles that are pivotal for proper phagophore assembly and growth. In S. cerevisiae, phagophore contacts have been observed with the vacuole, the ER, and lipid droplets. In situ imaging studies have greatly advanced our understanding of the structure and function of these sites. Here, we discuss how in situ structural methods like cryo-CLEM can give unprecedented insights into MCSs, and how they help to elucidate the structural arrangements of MCSs within cells. We further summarize the current knowledge of the contact sites in autophagy, focusing on autophagosome biogenesis in the model organism S. cerevisiae.
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Affiliation(s)
- Cristina Capitanio
- Department of Molecular Machines and
Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
- Aligning Science Across Parkinson's (ASAP)
Collaborative Research Network, Chevy Chase, MD, USA
| | - Anna Bieber
- Department of Molecular Machines and
Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
- Aligning Science Across Parkinson's (ASAP)
Collaborative Research Network, Chevy Chase, MD, USA
| | - Florian Wilfling
- Mechanisms of Cellular Quality Control, Max Planck Institute of Biophysics, Frankfurt a. M., Germany
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12
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Vargas Duarte P, Reggiori F. The Organization and Function of the Phagophore-ER Membrane Contact Sites. CONTACT (THOUSAND OAKS (VENTURA COUNTY, CALIF.)) 2023; 6:25152564231183898. [PMID: 37465355 PMCID: PMC10350784 DOI: 10.1177/25152564231183898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 06/06/2023] [Accepted: 06/06/2023] [Indexed: 07/20/2023]
Abstract
Macroautophagy is characterized by the de novo formation of double-membrane vesicles termed autophagosomes. The precursor structure of autophagosomes is a membrane cistern called phagophore, which elongates through a massive acquisition of lipids until closure. The phagophore establishes membrane-contact sites (MCSs) with the endoplasmic reticulum (ER), where conserved ATG proteins belonging to the ATG9 lipid scramblase, ATG2 lipid transfer and Atg18/WIPI4 β-propeller families concentrate. Several recent in vivo and in vitro studies have uncovered the relevance of these proteins and MCSs in the lipid supply required for autophagosome formation. Although important conceptual advances have been reached, the functional interrelationship between ATG9, ATG2 and Atg18/WIPI4 proteins at the phagophore-ER MCSs and their role in the phagophore expansion are not completely understood. In this review, we describe the current knowledge about the structure, interactions, localizations, and molecular functions of these proteins, with a particular emphasis on the yeast Saccharomyces cerevisiae and mammalian systems.
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Affiliation(s)
| | - Fulvio Reggiori
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
- Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Aarhus C, Denmark
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13
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Takahashi S, Saito C, Koyama-Honda I, Mizushima N. Quantitative 3D correlative light and electron microscopy of organelle association during autophagy. Cell Struct Funct 2022; 47:89-99. [PMID: 36418108 PMCID: PMC10511054 DOI: 10.1247/csf.22071] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 11/03/2022] [Indexed: 11/23/2022] Open
Abstract
In macroautophagy, disk-shaped double-membrane structures called phagophores elongate to form cup-shaped structures, becoming autophagosomes upon closure. These autophagosomes then fuse with lysosomes to become autolysosomes and degrade engulfed material. Autophagosome formation is reported to involve other organelles, including the endoplasmic reticulum (ER) and mitochondria. Organelles are also taken up by autophagosomes as autophagy cargos. However, few studies have performed systematic spatiotemporal analysis of inter-organelle relationships during macroautophagy. Here, we investigated the organelles in contact with phagophores, autophagosomes, and autolysosomes by using three-dimensional correlative light and electron microscopy with array tomography in cells starved 30 min. As previously reported, all phagophores associate with the ER. The surface area of phagophores in contact with the ER decreases gradually as they mature into autophagosomes and autolysosomes. However, the ER still associates with 92% of autophagosomes and 79% of autolysosomes, suggesting that most autophagosomes remain on the ER after closure and even when they fuse with lysosomes. In addition, we found that phagophores form frequently near other autophagic structures, suggesting the presence of potential hot spots for autophagosome formation. We also analyzed the contents of phagophores and autophagosomes and found that the ER is the most frequently engulfed organelle (detected in 65% of total phagophores and autophagosomes). These quantitative three-dimensional ultrastructural data provide insights into autophagosome-organelle relationships during macroautophagy.Key words: 3D-CLEM, autophagosome, electron microscopy, endoplasmic reticulum, lysosome.
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Affiliation(s)
- Satoru Takahashi
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
- Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
| | - Chieko Saito
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Ikuko Koyama-Honda
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Noboru Mizushima
- Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
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14
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Jensen LE, Rao S, Schuschnig M, Cada AK, Martens S, Hummer G, Hurley JH. Membrane curvature sensing and stabilization by the autophagic LC3 lipidation machinery. SCIENCE ADVANCES 2022; 8:eadd1436. [PMID: 36516251 PMCID: PMC9750143 DOI: 10.1126/sciadv.add1436] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 11/10/2022] [Indexed: 05/28/2023]
Abstract
How the highly curved phagophore membrane is stabilized during autophagy initiation is a major open question in autophagosome biogenesis. Here, we use in vitro reconstitution on membrane nanotubes and molecular dynamics simulations to investigate how core autophagy proteins in the LC3 (Microtubule-associated proteins 1A/1B light chain 3) lipidation cascade interact with curved membranes, providing insight into their possible roles in regulating membrane shape during autophagosome biogenesis. ATG12(Autophagy-related 12)-ATG5-ATG16L1 was up to 100-fold enriched on highly curved nanotubes relative to flat membranes. At high surface density, ATG12-ATG5-ATG16L1 binding increased the curvature of the nanotubes. While WIPI2 (WD repeat domain phosphoinositide-interacting protein 2) binding directs membrane recruitment, the amphipathic helix α2 of ATG16L1 is responsible for curvature sensitivity. Molecular dynamics simulations revealed that helix α2 of ATG16L1 inserts shallowly into the membrane, explaining its curvature-sensitive binding to the membrane. These observations show how the binding of the ATG12-ATG5-ATG16L1 complex to the early phagophore rim could stabilize membrane curvature and facilitate autophagosome growth.
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Affiliation(s)
- Liv E. Jensen
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
| | - Shanlin Rao
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Martina Schuschnig
- Department of Biochemistry and Cell Biology, Max Perutz Labs, University of Vienna, Vienna BioCenter, Vienna, Austria
| | - A. King Cada
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
| | - Sascha Martens
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
- Department of Biochemistry and Cell Biology, Max Perutz Labs, University of Vienna, Vienna BioCenter, Vienna, Austria
| | - Gerhard Hummer
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
- Institute of Biophysics, Goethe University Frankfurt, Frankfurt am Main 60438, Germany
| | - James H. Hurley
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA
- California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
- Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA
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15
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Bieber A, Capitanio C, Erdmann PS, Fiedler F, Beck F, Lee CW, Li D, Hummer G, Schulman BA, Baumeister W, Wilfling F. In situ structural analysis reveals membrane shape transitions during autophagosome formation. Proc Natl Acad Sci U S A 2022; 119:e2209823119. [PMID: 36122245 PMCID: PMC9522377 DOI: 10.1073/pnas.2209823119] [Citation(s) in RCA: 40] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 08/09/2022] [Indexed: 11/18/2022] Open
Abstract
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.
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Affiliation(s)
- Anna Bieber
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
| | - Cristina Capitanio
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
| | - Philipp S. Erdmann
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Human Technopole, 20157 Milan, Italy
| | - Fabian Fiedler
- Mechanisms of Cellular Quality Control, Max Planck Institute of Biophysics, 60438 Frankfurt a. M., Germany
| | - Florian Beck
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- CryoEM Technology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Chia-Wei Lee
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Department of Molecular Metabolism, Harvard T. H. Chan School of Public Health, Boston, MA 02115
| | - Delong Li
- Mechanisms of Cellular Quality Control, Max Planck Institute of Biophysics, 60438 Frankfurt a. M., Germany
| | - Gerhard Hummer
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, 60438 Frankfurt a. M., Germany
- Institute of Biophysics, Goethe University Frankfurt, 60438 Frankfurt a. M., Germany
| | - Brenda A. Schulman
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
| | - Florian Wilfling
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
- Aligning Science Across Parkinson’s (ASAP) Collaborative Research Network, Chevy Chase, MD 20815
- Mechanisms of Cellular Quality Control, Max Planck Institute of Biophysics, 60438 Frankfurt a. M., Germany
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16
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Kriegenburg F, Huiting W, van Buuren-Broek F, Zwilling E, Hardenberg R, Mari M, Kraft C, Reggiori F. The lipid flippase Drs2 regulates anterograde transport of Atg9 during autophagy. AUTOPHAGY REPORTS 2022; 1:345-367. [PMID: 38106996 PMCID: PMC7615381 DOI: 10.1080/27694127.2022.2104781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Macroautophagy/autophagy is a conserved catabolic pathway during which cellular material is sequestered within newly formed double-membrane vesicles called autophagosomes and delivered to the lytic compartment of eukaryotic cells for degradation. Autophagosome biogenesis depends on the core autophagy-related (Atg) machinery, and involves a massive supply and remodelling of membranes. To gain insight into the lipid remodelling mechanisms during autophagy, we have systematically investigated whether lipid flippases are required for this pathway in the yeast Saccharomyces cerevisiae. We found that the flippase Drs2, which transfers phosphatidylserine and phosphatidylethanolamine from the lumenal to the cytosolic leaflet of the limiting membrane at the trans-Golgi network, is required for normal progression of autophagy. We also show that Drs2 is important for the trafficking of the core Atg protein Atg9. Atg9 is a transmembrane protein important for autophagosome biogenesis and its anterograde transport from its post-Golgi reservoirs to the site of autophagosome formation is severely impaired in the absence of Drs2. Thus, our results identify a novel autophagy player and highlight that membrane asymmetry regulates early autophagy steps.
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Affiliation(s)
- Franziska Kriegenburg
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104, Freiburg, Germany
- CIBSS - Centre for Integrative Biological Signalling Studies, University of Freiburg, 79104, Freiburg, Germany
| | - Wouter Huiting
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
| | - Fleur van Buuren-Broek
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
| | - Emma Zwilling
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000 Aarhus C, Denmark
| | - Ralph Hardenberg
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
| | - Muriel Mari
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000 Aarhus C, Denmark
| | - Claudine Kraft
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104, Freiburg, Germany
- CIBSS - Centre for Integrative Biological Signalling Studies, University of Freiburg, 79104, Freiburg, Germany
| | - Fulvio Reggiori
- Department of Biomedical Sciences of Cells and Systems, University of Groningen, University medical Centre Groningen, 9713AV Groningen, The Netherlands
- Department of Biomedicine, Aarhus University, Ole Worms Allé 4, 8000 Aarhus C, Denmark
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17
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Molecular regulation of autophagosome formation. Biochem Soc Trans 2022; 50:55-69. [PMID: 35076688 PMCID: PMC9022990 DOI: 10.1042/bst20210819] [Citation(s) in RCA: 40] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 12/21/2021] [Accepted: 01/04/2022] [Indexed: 12/11/2022]
Abstract
Macroautophagy, hereafter autophagy, is a degradative process conserved among eukaryotes, which is essential to maintain cellular homeostasis. Defects in autophagy lead to numerous human diseases, including various types of cancer and neurodegenerative disorders. The hallmark of autophagy is the de novo formation of autophagosomes, which are double-membrane vesicles that sequester and deliver cytoplasmic materials to lysosomes/vacuoles for degradation. The mechanism of autophagosome biogenesis entered a molecular era with the identification of autophagy-related (ATG) proteins. Although there are many unanswered questions and aspects that have raised some controversies, enormous advances have been done in our understanding of the process of autophagy in recent years. In this review, we describe the current knowledge about the molecular regulation of autophagosome formation, with a particular focus on budding yeast and mammalian cells.
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18
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Egea PF. Moving Lipids, by the Numbers. CONTACT 2022; 5. [PMID: 36128030 PMCID: PMC9484574 DOI: 10.1177/25152564221103080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Pascal F. Egea
- Department of Biological Chemistry, School of Medicine, University of California Los Angeles, Los Angeles, USA
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19
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Ohashi Y. Activation Mechanisms of the VPS34 Complexes. Cells 2021; 10:cells10113124. [PMID: 34831348 PMCID: PMC8624279 DOI: 10.3390/cells10113124] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/09/2021] [Accepted: 11/09/2021] [Indexed: 01/18/2023] Open
Abstract
Phosphatidylinositol-3-phosphate (PtdIns(3)P) is essential for cell survival, and its intracellular synthesis is spatially and temporally regulated. It has major roles in two distinctive cellular pathways, namely, the autophagy and endocytic pathways. PtdIns(3)P is synthesized from phosphatidylinositol (PtdIns) by PIK3C3C/VPS34 in mammals or Vps34 in yeast. Pathway-specific VPS34/Vps34 activity is the consequence of the enzyme being incorporated into two mutually exclusive complexes: complex I for autophagy, composed of VPS34/Vps34-Vps15/Vps15-Beclin 1/Vps30-ATG14L/Atg14 (mammals/yeast), and complex II for endocytic pathways, in which ATG14L/Atg14 is replaced with UVRAG/Vps38 (mammals/yeast). Because of its involvement in autophagy, defects in which are closely associated with human diseases such as cancer and neurodegenerative diseases, developing highly selective drugs that target specific VPS34/Vps34 complexes is an essential goal in the autophagy field. Recent studies on the activation mechanisms of VPS34/Vps34 complexes have revealed that a variety of factors, including conformational changes, lipid physicochemical parameters, upstream regulators, and downstream effectors, greatly influence the activity of these complexes. This review summarizes and highlights each of these influences as well as clarifying key questions remaining in the field and outlining future perspectives.
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Affiliation(s)
- Yohei Ohashi
- MRC Laboratory of Molecular Biology, Protein and Nucleic Acid Chemistry Division, Francis Crick Avenue, Cambridge CB2 0QH, UK
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