1
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Chandra M, Kendall AK, Ford MGJ, Jackson LP. VARP binds SNX27 to promote endosomal supercomplex formation on membranes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.11.603126. [PMID: 39026782 PMCID: PMC11257539 DOI: 10.1101/2024.07.11.603126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
Multiple essential membrane trafficking pathways converge at endosomes to maintain cellular homeostasis by sorting critical transmembrane cargo proteins to the plasma membrane or the trans-Golgi network (TGN). The Retromer heterotrimer (VPS26/VPS35/VPS29 subunits) binds multiple sorting nexin (SNX) proteins on endosomal membranes, but molecular mechanisms regarding formation and regulation of metazoan SNX/Retromer complexes have been elusive. Here, we combine biochemical and biophysical approaches with AlphaFold2 Multimer modeling to identify a direct interaction between the VARP N-terminus and SNX27 PDZ domain. VARP and SNX27 interact with high nanomolar affinity using the binding pocket established for PDZ binding motif (PDZbm) cargo. Specific point mutations in VARP abrogate the interaction in vitro. We further establish a full biochemical reconstitution system using purified mammalian proteins to directly and systematically test whether multiple endosomal coat complexes are recruited to membranes to generate tubules. We successfully use purified coat components to demonstrate which combinations of Retromer with SNX27, ESCPE-1 (SNX2/SNX6), or both complexes can remodel membranes containing physiological cargo motifs and phospholipid composition. SNX27, alone and with Retromer, induces tubule formation in the presence of PI(3)P and PDZ cargo motifs. ESCPE-1 deforms membranes enriched with Folch I and CI-MPR cargo motifs, but surprisingly does not recruit Retromer. Finally, we find VARP is required to reconstitute a proposed endosomal "supercomplex" containing SNX27, ESCPE-1, and Retromer on PI(3)P-enriched membranes. These data suggest VARP functions as a key regulator in metazoans to promote cargo sorting out of endosomes.
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Affiliation(s)
- Mintu Chandra
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
| | - Amy K Kendall
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
| | - Marijn G J Ford
- Department of Cell Biology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Lauren P Jackson
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
- Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA
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2
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Gopaldass N, Chen KE, Collins B, Mayer A. Assembly and fission of tubular carriers mediating protein sorting in endosomes. Nat Rev Mol Cell Biol 2024:10.1038/s41580-024-00746-8. [PMID: 38886588 DOI: 10.1038/s41580-024-00746-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/03/2024] [Indexed: 06/20/2024]
Abstract
Endosomes are central protein-sorting stations at the crossroads of numerous membrane trafficking pathways in all eukaryotes. They have a key role in protein homeostasis and cellular signalling and are involved in the pathogenesis of numerous diseases. Endosome-associated protein assemblies or coats collect transmembrane cargo proteins and concentrate them into retrieval domains. These domains can extend into tubular carriers, which then pinch off from the endosomal membrane and deliver the cargoes to appropriate subcellular compartments. Here we discuss novel insights into the structure of a number of tubular membrane coats that mediate the recruitment of cargoes into these carriers, focusing on sorting nexin-based coats such as Retromer, Commander and ESCPE-1. We summarize current and emerging views of how selective tubular endosomal carriers form and detach from endosomes by fission, highlighting structural aspects, conceptual challenges and open questions.
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Affiliation(s)
- Navin Gopaldass
- Department of Immunobiology, University of Lausanne, Epalinges, Switzerland.
| | - Kai-En Chen
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, Queensland, Australia
| | - Brett Collins
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, Queensland, Australia
| | - Andreas Mayer
- Department of Immunobiology, University of Lausanne, Epalinges, Switzerland.
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3
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Overduin M, Bhat R. Recognition and remodeling of endosomal zones by sorting nexins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184305. [PMID: 38408696 DOI: 10.1016/j.bbamem.2024.184305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2023] [Revised: 02/05/2024] [Accepted: 02/18/2024] [Indexed: 02/28/2024]
Abstract
The proteolipid code determines how cytosolic proteins find and remodel membrane surfaces. Here, we investigate how this process works with sorting nexins Snx1 and Snx3. Both proteins form sorting machines by recognizing membrane zones enriched in phosphatidylinositol 3-phosphate (PI3P), phosphatidylserine (PS) and cholesterol. This co-localized combination forms a unique "lipid codon" or lipidon that we propose is responsible for endosomal targeting, as revealed by structures and interactions of their PX domain-based readers. We outline a membrane recognition and remodeling mechanism for Snx1 and Snx3 involving this code element alongside transmembrane pH gradients, dipole moment-guided docking and specific protein-protein interactions. This generates an initial membrane-protein assembly (memtein) that then recruits retromer and additional PX proteins to recruit cell surface receptors for sorting to the trans-Golgi network (TGN), lysosome and plasma membranes. Post-translational modification (PTM) networks appear to regulate how the sorting machines form and operate at each level. The commonalities and differences between these sorting nexins show how the proteolipid code orchestrates parallel flows of molecular information from ribosome emergence to organelle genesis, and illuminates a universally applicable model of the membrane.
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Affiliation(s)
- Michael Overduin
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
| | - Rakesh Bhat
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
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4
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Liao Z, Si T, Kai JJ, Fan J. Mechanism of Membrane Curvature Induced by SNX1: Insights from Molecular Dynamics Simulations. J Phys Chem B 2024; 128:2144-2153. [PMID: 38408890 DOI: 10.1021/acs.jpcb.3c07009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
SNX proteins have been found to induce membrane remodeling to facilitate the generation of transport carriers in endosomal pathways. However, the molecular mechanism of membrane bending and the role of lipids in the bending process remain elusive. Here, we conducted coarse-grained molecular dynamics simulations to investigate the role of the three structural modules (PX, BAR, and AH) of SNX1 and the PI3P lipids in membrane deformation. We observed that the presence of all three domains is essential for SNX1 to achieve a stable membrane deformation. BAR is capable of remodeling the membrane through the charged residues on its concave surface, but it requires PX and AH to establish stable membrane binding. AH penetrates into the lipid membrane, thereby promoting the induction of membrane curvature; however, it is inadequate on its own to maintain membrane bending. PI3P lipids are also indispensable for membrane remodeling, as they play a dominant role in the interactions of lipids with the BAR domain. Our results enhance the comprehension of the molecular mechanism underlying SNX1-induced membrane curvature and help future studies of curvature-inducing proteins.
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Affiliation(s)
- Zhenyu Liao
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077 Hong Kong, China
| | - Ting Si
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077 Hong Kong, China
- Department of Physics, City University of Hong Kong, Kowloon 999077 Hong Kong, China
| | - Ji-Jung Kai
- Department of Mechanical Engineering, City University of Hong Kong, Kowloon 999077 Hong Kong, China
- Centre for Advanced Nuclear Safety and Sustainable Development, City University of Hong Kong, Kowloon 999077 Hong Kong, China
| | - Jun Fan
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077 Hong Kong, China
- Department of Mechanical Engineering, City University of Hong Kong, Kowloon 999077 Hong Kong, China
- Centre for Advanced Nuclear Safety and Sustainable Development, City University of Hong Kong, Kowloon 999077 Hong Kong, China
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5
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Zadka Ł, Sochocka M, Hachiya N, Chojdak-Łukasiewicz J, Dzięgiel P, Piasecki E, Leszek J. Endocytosis and Alzheimer's disease. GeroScience 2024; 46:71-85. [PMID: 37646904 PMCID: PMC10828383 DOI: 10.1007/s11357-023-00923-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Accepted: 08/22/2023] [Indexed: 09/01/2023] Open
Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disorder and is the most common cause of dementia. The pathogenesis of AD still remains unclear, including two main hypotheses: amyloid cascade and tau hyperphosphorylation. The hallmark neuropathological changes of AD are extracellular deposits of amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Endocytosis plays an important role in a number of cellular processes including communication with the extracellular environment, nutrient uptake, and signaling by the cell surface receptors. Based on the results of genetic and biochemical studies, there is a link between neuronal endosomal function and AD pathology. Taking this into account, we can state that in the results of previous research, endolysosomal abnormality is an important cause of neuronal lesions in the brain. Endocytosis is a central pathway involved in the regulation of the degradation of amyloidogenic components. The results of the studies suggest that a correlation between alteration in the endocytosis process and associated protein expression progresses AD. In this article, we discuss the current knowledge about endosomal abnormalities in AD.
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Affiliation(s)
- Łukasz Zadka
- Division of Ultrastructural Research, Wroclaw Medical University, 50-368, Wroclaw, Poland
| | - Marta Sochocka
- Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Rudolfa Weigla 12, 53-114, Wroclaw, Poland.
| | - Naomi Hachiya
- Shonan Research Center, Central Glass Co., Ltd, Shonan Health Innovation Park 26-1, Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa, 251-8555, Japan
| | | | - Piotr Dzięgiel
- Department of Histology and Embryology, Wroclaw Medical University, Chałubińskiego 6a, 50-368, Wroclaw, Poland
| | - Egbert Piasecki
- Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Rudolfa Weigla 12, 53-114, Wroclaw, Poland
| | - Jerzy Leszek
- Department of Psychiatry, Wroclaw Medical University, Wybrzeże L. Pasteura 10, 50-367, Wroclaw, Poland
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6
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Pang X, Zhang Y, Park K, Liao Z, Li J, Xu J, Hong MT, Yin G, Zhang T, Wang Y, Egelman EH, Fan J, Park SY, Hsu VW, Sun F. Structural elucidation of how ARF small GTPases induce membrane tubulation for vesicle fission. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.19.572083. [PMID: 38187566 PMCID: PMC10769218 DOI: 10.1101/2023.12.19.572083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
The ADP-Ribosylation Factor (ARF) small GTPases have been found to act in vesicle fission through a direct ability to tubulate membrane. Here, we have used cryo-electron microscopy (EM) to solve the structure of an ARF6 protein lattice assembled on tubulated membrane to 3.9 Å resolution. ARF6 forms tetramers that polymerize into helical arrays to form this lattice. We identify, and confirm functionally, protein contacts critical for this lattice formation. The solved structure also suggests how the ARF amphipathic helix is positioned in the lattice for membrane insertion, and how a GTPase-activating protein (GAP) docks onto the lattice to catalyze ARF-GTP hydrolysis in completing membrane fission. As ARF1 and ARF6 are structurally conserved, we have also modeled ARF1 onto the ARF6 lattice, which has allowed us to pursue the reconstitution of Coat Protein I (COPI) vesicles to confirm more definitively that the ARF lattice acts in vesicle fission. Our findings are notable for having achieved the first detailed glimpse of how a small GTPase bends membrane and having provided a molecular understanding of how an ARF protein acts in vesicle fission.
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Affiliation(s)
- Xiaoyun Pang
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- Equal contribution
| | - Yan Zhang
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- Equal contribution
| | - Kunyou Park
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
- Equal contribution
| | - Zhenyu Liao
- City University of Hong Kong, Hong Kong, China
| | - Jian Li
- Division of Rheumatology, Inflammation and Immunity, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, MA 02115 USA
| | - Jiashu Xu
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- School of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Minh-Triet Hong
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Guoliang Yin
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- School of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Tongming Zhang
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Yaoyu Wang
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia, VA 22908 USA
| | - Jun Fan
- City University of Hong Kong, Hong Kong, China
| | - Seung-Yeol Park
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, Republic of Korea
| | - Victor W Hsu
- Division of Rheumatology, Inflammation and Immunity, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, MA 02115 USA
| | - Fei Sun
- National Key Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- School of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Center for Biological Imaging, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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7
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Lopez-Robles C, Scaramuzza S, Astorga-Simon EN, Ishida M, Williamson CD, Baños-Mateos S, Gil-Carton D, Romero-Durana M, Vidaurrazaga A, Fernandez-Recio J, Rojas AL, Bonifacino JS, Castaño-Díez D, Hierro A. Architecture of the ESCPE-1 membrane coat. Nat Struct Mol Biol 2023; 30:958-969. [PMID: 37322239 PMCID: PMC10352136 DOI: 10.1038/s41594-023-01014-7] [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: 10/13/2022] [Accepted: 05/05/2023] [Indexed: 06/17/2023]
Abstract
Recycling of membrane proteins enables the reuse of receptors, ion channels and transporters. A key component of the recycling machinery is the endosomal sorting complex for promoting exit 1 (ESCPE-1), which rescues transmembrane proteins from the endolysosomal pathway for transport to the trans-Golgi network and the plasma membrane. This rescue entails the formation of recycling tubules through ESCPE-1 recruitment, cargo capture, coat assembly and membrane sculpting by mechanisms that remain largely unknown. Herein, we show that ESCPE-1 has a single-layer coat organization and suggest how synergistic interactions between ESCPE-1 protomers, phosphoinositides and cargo molecules result in a global arrangement of amphipathic helices to drive tubule formation. Our results thus define a key process of tubule-based endosomal sorting.
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Affiliation(s)
| | | | | | - Morié Ishida
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Chad D Williamson
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | | | - David Gil-Carton
- CIC bioGUNE, Derio, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, Spain
- BREM Basque Resource for Electron Microscopy, Leioa, Spain
| | - Miguel Romero-Durana
- Barcelona Supercomputing Center (BSC), Barcelona, Spain
- Instituto de Ciencias de la Vid y del Vino (ICVV), CSIC-Universidad de La Rioja-Gobierno de La Rioja, Logroño, Spain
| | | | - Juan Fernandez-Recio
- Barcelona Supercomputing Center (BSC), Barcelona, Spain
- Instituto de Ciencias de la Vid y del Vino (ICVV), CSIC-Universidad de La Rioja-Gobierno de La Rioja, Logroño, Spain
| | | | - Juan S Bonifacino
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
| | - Daniel Castaño-Díez
- BioEM Lab, Biozentrum, University of Basel, Basel, Switzerland.
- Instituto Biofisika (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain.
| | - Aitor Hierro
- CIC bioGUNE, Derio, Spain.
- Ikerbasque, Basque Foundation for Science, Bilbao, Spain.
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8
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Simonetti B, Daly JL, Cullen PJ. Out of the ESCPE room: Emerging roles of endosomal SNX-BARs in receptor transport and host-pathogen interaction. Traffic 2023; 24:234-250. [PMID: 37089068 PMCID: PMC10768393 DOI: 10.1111/tra.12885] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 02/22/2023] [Accepted: 03/28/2023] [Indexed: 04/25/2023]
Abstract
Several functions of the human cell, such as sensing nutrients, cell movement and interaction with the surrounding environment, depend on a myriad of transmembrane proteins and their associated proteins and lipids (collectively termed "cargoes"). To successfully perform their tasks, cargo must be sorted and delivered to the right place, at the right time, and in the right amount. To achieve this, eukaryotic cells have evolved a highly organized sorting platform, the endosomal network. Here, a variety of specialized multiprotein complexes sort cargo into itineraries leading to either their degradation or their recycling to various organelles for further rounds of reuse. A key sorting complex is the Endosomal SNX-BAR Sorting Complex for Promoting Exit (ESCPE-1) that promotes the recycling of an array of cargos to the plasma membrane and/or the trans-Golgi network. ESCPE-1 recognizes a hydrophobic-based sorting motif in numerous cargoes and orchestrates their packaging into tubular carriers that pinch off from the endosome and travel to the target organelle. A wide range of pathogens mimic this sorting motif to hijack ESCPE-1 transport to promote their invasion and survival within infected cells. In other instances, ESCPE-1 exerts restrictive functions against pathogens by limiting their replication and infection. In this review, we discuss ESCPE-1 assembly and functions, with a particular focus on recent advances in the understanding of its role in membrane trafficking, cellular homeostasis and host-pathogen interaction.
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Affiliation(s)
- Boris Simonetti
- Charles River Laboratories, Discovery House, Quays Office ParkConference Avenue, PortisheadBristolUK
| | - James L. Daly
- Department of Infectious DiseasesSchool of Immunology and Microbial Sciences, Guy's Hospital, King's College LondonLondonUK
| | - Peter J. Cullen
- School of Biochemistry, Faculty of Life Sciences, Biomedical Sciences BuildingUniversity of BristolBristolUK
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9
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Huang J, Tiu AC, Jose PA, Yang J. Sorting nexins: role in the regulation of blood pressure. FEBS J 2023; 290:600-619. [PMID: 34847291 PMCID: PMC9149145 DOI: 10.1111/febs.16305] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 10/13/2021] [Accepted: 11/29/2021] [Indexed: 02/06/2023]
Abstract
Sorting nexins (SNXs) are a family of proteins that regulate cellular cargo sorting and trafficking, maintain intracellular protein homeostasis, and participate in intracellular signaling. SNXs are also important in the regulation of blood pressure via several mechanisms. Aberrant expression and dysfunction of SNXs participate in the dysregulation of blood pressure. Genetic studies show a correlation between SNX gene variants and the response to antihypertensive drugs. In this review, we summarize the progress in SNX-mediated regulation of blood pressure, discuss the potential role of SNXs in the pathophysiology and treatment of hypertension, and propose novel strategies for the medical therapy of hypertension.
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Affiliation(s)
- Juan Huang
- Department of Clinical Nutrition, The Third Affiliated Hospital of Chongqing Medical University, Chongqing 410020, P.R. China
| | - Andrew C. Tiu
- Department of Medicine, Einstein Medical Center Philadelphia, Philadelphia, PA 19141, USA
| | - Pedro A. Jose
- Division of Renal Diseases & Hypertension, Department of Medicine, and Department of Physiology and Pharmacology, The George Washington University School of Medicine & Health Sciences, Washington, DC 20052, USA
| | - Jian Yang
- Department of Clinical Nutrition, The Third Affiliated Hospital of Chongqing Medical University, Chongqing 410020, P.R. China
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10
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Gopaldass N, De Leo MG, Courtellemont T, Mercier V, Bissig C, Roux A, Mayer A. Retromer oligomerization drives SNX-BAR coat assembly and membrane constriction. EMBO J 2023; 42:e112287. [PMID: 36644906 PMCID: PMC9841331 DOI: 10.15252/embj.2022112287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 11/02/2022] [Accepted: 11/02/2022] [Indexed: 01/17/2023] Open
Abstract
Proteins exit from endosomes through tubular carriers coated by retromer, a complex that impacts cellular signaling, lysosomal biogenesis and numerous diseases. The coat must overcome membrane tension to form tubules. We explored the dynamics and driving force of this process by reconstituting coat formation with yeast retromer and the BAR-domain sorting nexins Vps5 and Vps17 on oriented synthetic lipid tubules. This coat oligomerizes bidirectionally, forming a static tubular structure that does not exchange subunits. High concentrations of sorting nexins alone constrict membrane tubes to an invariant radius of 19 nm. At lower concentrations, oligomers of retromer must bind and interconnect the sorting nexins to drive constriction. Constricting less curved membranes into tubes, which requires more energy, coincides with an increased surface density of retromer on the sorting nexin layer. Retromer-mediated crosslinking of sorting nexins at variable densities may thus tune the energy that the coat can generate to deform the membrane. In line with this, genetic ablation of retromer oligomerization impairs endosomal protein exit in yeast and human cells.
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Affiliation(s)
- Navin Gopaldass
- Department of ImmunobiologyUniversity of LausanneEpalingesSwitzerland
| | | | | | - Vincent Mercier
- Department of BiochemistryUniversity of GenevaGenevaSwitzerland
| | - Christin Bissig
- Department of ImmunobiologyUniversity of LausanneEpalingesSwitzerland
| | - Aurélien Roux
- Department of BiochemistryUniversity of GenevaGenevaSwitzerland
- Swiss National Centre for Competence in Research Program Chemical BiologyGenevaSwitzerland
| | - Andreas Mayer
- Department of ImmunobiologyUniversity of LausanneEpalingesSwitzerland
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11
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Kozlov MM, Taraska JW. Generation of nanoscopic membrane curvature for membrane trafficking. Nat Rev Mol Cell Biol 2023; 24:63-78. [PMID: 35918535 DOI: 10.1038/s41580-022-00511-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/20/2022] [Indexed: 11/09/2022]
Abstract
Curved membranes are key features of intracellular organelles, and their generation involves dynamic protein complexes. Here we describe the fundamental mechanisms such as the hydrophobic insertion, scaffolding and crowding mechanisms these proteins use to produce membrane curvatures and complex shapes required to form intracellular organelles and vesicular structures involved in endocytosis and secretion. For each mechanism, we discuss its cellular functions as well as the underlying physical principles and the specific membrane properties required for the mechanism to be feasible. We propose that the integration of individual mechanisms into a highly controlled, robust process of curvature generation often relies on the assembly of proteins into coats. How cells unify and organize the curvature-generating factors at the nanoscale is presented for three ubiquitous coats central for membrane trafficking in eukaryotes: clathrin-coated pits, caveolae, and COPI and COPII coats. The emerging theme is that these coats arrange and coordinate curvature-generating factors in time and space to dynamically shape membranes to accomplish membrane trafficking within cells.
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Affiliation(s)
- Michael M Kozlov
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
| | - Justin W Taraska
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
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12
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Shortill SP, Frier MS, Wongsangaroonsri P, Davey M, Conibear E. The VINE complex is an endosomal VPS9-domain GEF and SNX-BAR coat. eLife 2022; 11:77035. [PMID: 35938928 PMCID: PMC9507130 DOI: 10.7554/elife.77035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 08/05/2022] [Indexed: 11/18/2022] Open
Abstract
Membrane trafficking pathways perform important roles in establishing and maintaining the endosomal network. Retrograde protein sorting from the endosome is promoted by conserved SNX-BAR-containing coat complexes including retromer which enrich cargo at tubular microdomains and generate transport carriers. In metazoans, retromer cooperates with VARP, a conserved VPS9-domain GEF, to direct an endosomal recycling pathway. The function of the yeast VARP homolog Vrl1 has been overlooked due to an inactivating mutation found in commonly studied strains. Here, we demonstrate that Vrl1 has features of a SNX-BAR coat protein and forms an obligate complex with Vin1, the paralog of the retromer SNX-BAR protein Vps5. Unique features in the Vin1 N-terminus allow Vrl1 to distinguish it from Vps5, thereby forming a complex that we have named VINE. The VINE complex occupies endosomal tubules and redistributes a conserved mannose 6-phosphate receptor-like protein from endosomes. We also find that membrane recruitment by Vin1 is essential for Vrl1 GEF activity, suggesting that VINE is a multifunctional coat complex that regulates trafficking and signaling events at the endosome. All healthy cells have a highly organized interior: different compartments with specialized roles are in different places, and in order to do their jobs properly, proteins need to be in the right place. Endosomes are membrane-bound compartments that act as transport hubs where proteins are sorted into small vesicles and delivered to other parts of the cell. Two groups of proteins regulate this transport: the first group, known as VPS9 GEFs, switches on the enzymes that recruit the second group of proteins, called the sorting nexins. This second group is responsible for forming the transport vesicles via which proteins are distributed all over the cell. Defects in protein sorting can lead to various diseases, including neurodegenerative conditions such as Parkinson’s disease and juvenile amyotrophic lateral sclerosis. Scientists often use budding yeast cells to study protein sorting, because these cells are similar to human cells, but easier to grow in large numbers and examine in the laboratory. Previous work showed that a yeast protein called Vrl1 is equivalent to a VPS9 GEF from humans called VARP. However, Vrl1 only exists in wild forms of budding yeast, and not in laboratory strains of the organism. Therefore, researchers had not studied Vrl1 in detail, and its roles remained unclear. To learn more about Vrl1, Shortill et al. started by re-introducing the protein into laboratory strains of budding yeast and observing what happened to protein sorting in these cells. Like VARP, Vrl1 was found in the endosomes of budding yeast. However, biochemical experiments revealed that, while human VARP binds to a protein called retromer, Vrl1 does not bind to the equivalent protein in yeast. Instead, Vrl1 itself has features of both the VPS9 GEFs and the sorting nexins. Shortill et al. also found that Vrl1 interacted with a different protein in the sorting nexin family called Vin1. In the absence of Vrl1, Vin1 was found floating around the cell, but once Vrl1 was re-introduced into the budding yeast, Vin1 relocated to the endosomes. Vrl1 uses its VPS9 GEF part to move itself to the endosome membrane, and Vin1 controls this movement, highlighting the interdependence between the two proteins. Once they are at the endosome together, Vrl1 and Vin1 help redistribute proteins to other parts of the cell. This study suggests that, like VARP, Vrl1 cooperates with sorting nexins to transport proteins. Since many previous experiments about protein sorting were carried out in yeast cells lacking Vrl1, it is possible that this process was overlooked despite its potential importance. These new findings could also help other researchers investigating how endosomes and protein sorting work, or do not work, in the context of neurodegenerative diseases.
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Affiliation(s)
- Shawn P Shortill
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Mia S Frier
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
| | | | - Michael Davey
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Elizabeth Conibear
- Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, Canada
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