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Mencel ML, Bittner GD. Repair of traumatic lesions to the plasmalemma of neurons and other cells: Commonalities, conflicts, and controversies. Front Physiol 2023; 14:1114779. [PMID: 37008019 PMCID: PMC10050709 DOI: 10.3389/fphys.2023.1114779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 02/14/2023] [Indexed: 03/17/2023] Open
Abstract
Neuroscientists and Cell Biologists have known for many decades that eukaryotic cells, including neurons, are surrounded by a plasmalemma/axolemma consisting of a phospholipid bilayer that regulates trans-membrane diffusion of ions (including calcium) and other substances. Cells often incur plasmalemmal damage via traumatic injury and various diseases. If the damaged plasmalemma is not rapidly repaired within minutes, activation of apoptotic pathways by calcium influx often results in cell death. We review publications reporting what is less-well known (and not yet covered in neuroscience or cell biology textbooks): that calcium influx at the lesion sites ranging from small nm-sized holes to complete axonal transection activates parallel biochemical pathways that induce vesicles/membrane-bound structures to migrate and interact to restore original barrier properties and eventual reestablishment of the plasmalemma. We assess the reliability of, and problems with, various measures (e.g., membrane voltage, input resistance, current flow, tracer dyes, confocal microscopy, transmission and scanning electron microscopy) used individually and in combination to assess plasmalemmal sealing in various cell types (e.g., invertebrate giant axons, oocytes, hippocampal and other mammalian neurons). We identify controversies such as plug versus patch hypotheses that attempt to account for currently available data on the subcellular mechanisms of plasmalemmal repair/sealing. We describe current research gaps and potential future developments, such as much more extensive correlations of biochemical/biophysical measures with sub-cellular micromorphology. We compare and contrast naturally occurring sealing with recently-discovered artificially-induced plasmalemmal sealing by polyethylene glycol (PEG) that bypasses all natural pathways for membrane repair. We assess other recent developments such as adaptive membrane responses in neighboring cells following injury to an adjacent cell. Finally, we speculate how a better understanding of the mechanisms involved in natural and artificial plasmalemmal sealing is needed to develop better clinical treatments for muscular dystrophies, stroke and other ischemic conditions, and various cancers.
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Affiliation(s)
- Marshal L. Mencel
- Institute of Cell and Molecular Biology, University of Texas at Austin, Austin, TX, United States
| | - George D. Bittner
- Department of Neuroscience, University of Texas at Austin, Austin, TX, United States
- *Correspondence: George D. Bittner,
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2
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Ammendolia DA, Bement WM, Brumell JH. Plasma membrane integrity: implications for health and disease. BMC Biol 2021; 19:71. [PMID: 33849525 PMCID: PMC8042475 DOI: 10.1186/s12915-021-00972-y] [Citation(s) in RCA: 112] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 02/01/2021] [Indexed: 12/12/2022] Open
Abstract
Plasma membrane integrity is essential for cellular homeostasis. In vivo, cells experience plasma membrane damage from a multitude of stressors in the extra- and intra-cellular environment. To avoid lethal consequences, cells are equipped with repair pathways to restore membrane integrity. Here, we assess plasma membrane damage and repair from a whole-body perspective. We highlight the role of tissue-specific stressors in health and disease and examine membrane repair pathways across diverse cell types. Furthermore, we outline the impact of genetic and environmental factors on plasma membrane integrity and how these contribute to disease pathogenesis in different tissues.
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Affiliation(s)
- Dustin A Ammendolia
- Cell Biology Program, Hospital for Sick Children, 686 Bay Street PGCRL, Toronto, ON, M5G 0A4, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, ON, M5S 1A1, Canada
| | - William M Bement
- Center for Quantitative Cell Imaging and Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - John H Brumell
- Cell Biology Program, Hospital for Sick Children, 686 Bay Street PGCRL, Toronto, ON, M5G 0A4, Canada. .,Department of Molecular Genetics, University of Toronto, Toronto, ON, M5S 1A1, Canada. .,Institute of Medical Science, University of Toronto, Toronto, ON, M5S 1A1, Canada. .,SickKids IBD Centre, Hospital for Sick Children, Toronto, ON, M5G 0A4, Canada.
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3
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Larpin Y, Besançon H, Babiychuk VS, Babiychuk EB, Köffel R. Small Pore-Forming Toxins Different Membrane Area Binding and Ca 2+ Permeability of Pores Determine Cellular Resistance of Monocytic Cells. Toxins (Basel) 2021; 13:toxins13020126. [PMID: 33572185 PMCID: PMC7914786 DOI: 10.3390/toxins13020126] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/27/2021] [Accepted: 02/04/2021] [Indexed: 01/06/2023] Open
Abstract
Pore-forming toxins (PFTs) form multimeric trans-membrane pores in cell membranes that differ in pore channel diameter (PCD). Cellular resistance to large PFTs (>20 nm PCD) was shown to rely on Ca2+ influx activated membrane repair mechanisms. Small PFTs (<2 nm PCD) were shown to exhibit a high cytotoxic activity, but host cell response and membrane repair mechanisms are less well studied. We used monocytic immune cell lines to investigate the cellular resistance and host membrane repair mechanisms to small PFTs lysenin (Eisenia fetida) and aerolysin (Aeromonas hydrophila). Lysenin, but not aerolysin, is shown to induce Ca2+ influx from the extracellular space and to activate Ca2+ dependent membrane repair mechanisms. Moreover, lysenin binds to U937 cells with higher efficiency as compared to THP-1 cells, which is in line with a high sensitivity of U937 cells to lysenin. In contrast, aerolysin equally binds to U937 or THP-1 cells, but in different plasma membrane areas. Increased aerolysin induced cell death of U937 cells, as compared to THP-1 cells, is suggested to be a consequence of cap-like aerolysin binding. We conclude that host cell resistance to small PFTs attack comprises binding efficiency, pore localization, and capability to induce Ca2+ dependent membrane repair mechanisms.
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4
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Badgujar DC, Anil A, Green AE, Surve MV, Madhavan S, Beckett A, Prior IA, Godsora BK, Patil SB, More PK, Sarkar SG, Mitchell A, Banerjee R, Phale PS, Mitchell TJ, Neill DR, Bhaumik P, Banerjee A. Structural insights into loss of function of a pore forming toxin and its role in pneumococcal adaptation to an intracellular lifestyle. PLoS Pathog 2020; 16:e1009016. [PMID: 33216805 PMCID: PMC7717573 DOI: 10.1371/journal.ppat.1009016] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 12/04/2020] [Accepted: 09/24/2020] [Indexed: 12/14/2022] Open
Abstract
The opportunistic pathogen Streptococcus pneumoniae has dual lifestyles: one of an asymptomatic colonizer in the human nasopharynx and the other of a deadly pathogen invading sterile host compartments. The latter triggers an overwhelming inflammatory response, partly driven via pore forming activity of the cholesterol dependent cytolysin (CDC), pneumolysin. Although pneumolysin-induced inflammation drives person-to-person transmission from nasopharynx, the primary reservoir for pneumococcus, it also contributes to high mortality rates, creating a bottleneck that hampers widespread bacterial dissemination, thus acting as a double-edged sword. Serotype 1 ST306, a widespread pneumococcal clone, harbours a non-hemolytic variant of pneumolysin (Ply-NH). Performing crystal structure analysis of Ply-NH, we identified Y150H and T172I as key substitutions responsible for loss of its pore forming activity. We uncovered a novel inter-molecular cation-π interaction, governing formation of the transmembrane β-hairpins (TMH) in the pore state of Ply, which can be extended to other CDCs. H150 in Ply-NH disrupts this interaction, while I172 provides structural rigidity to domain-3, through hydrophobic interactions, inhibiting TMH formation. Loss of pore forming activity enabled improved cellular invasion and autophagy evasion, promoting an atypical intracellular lifestyle for pneumococcus, a finding that was corroborated in in vivo infection models. Attenuation of inflammatory responses and tissue damage promoted tolerance of Ply-NH-expressing pneumococcus in the lower respiratory tract. Adoption of this altered lifestyle may be necessary for ST306 due to its limited nasopharyngeal carriage, with Ply-NH, aided partly by loss of its pore forming ability, facilitating a benign association of SPN in an alternative, intracellular host niche.
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Affiliation(s)
- Dilip C. Badgujar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Anjali Anil
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Angharad E. Green
- Department of Clinical Infection, Microbiology and Immunology, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Manalee Vishnu Surve
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Shilpa Madhavan
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Alison Beckett
- Division of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Ian A. Prior
- Division of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, United Kingdom
| | - Barsa K. Godsora
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Sanket B. Patil
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Prachi Kadam More
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Shruti Guha Sarkar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Andrea Mitchell
- Institute of Microbiology and Infection, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Rinti Banerjee
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Prashant S. Phale
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Timothy J. Mitchell
- Institute of Microbiology and Infection, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Daniel R. Neill
- Department of Clinical Infection, Microbiology and Immunology, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Prasenjit Bhaumik
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Anirban Banerjee
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
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5
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Gottwald EM, Schuh CD, Drücker P, Haenni D, Pearson A, Ghazi S, Bugarski M, Polesel M, Duss M, Landau EM, Kaech A, Ziegler U, Lundby AKM, Lundby C, Dittrich PS, Hall AM. The iron chelator Deferasirox causes severe mitochondrial swelling without depolarization due to a specific effect on inner membrane permeability. Sci Rep 2020; 10:1577. [PMID: 32005861 PMCID: PMC6994599 DOI: 10.1038/s41598-020-58386-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 01/15/2020] [Indexed: 12/13/2022] Open
Abstract
The iron chelator Deferasirox (DFX) causes severe toxicity in patients for reasons that were previously unexplained. Here, using the kidney as a clinically relevant in vivo model for toxicity together with a broad range of experimental techniques, including live cell imaging and in vitro biophysical models, we show that DFX causes partial uncoupling and dramatic swelling of mitochondria, but without depolarization or opening of the mitochondrial permeability transition pore. This effect is explained by an increase in inner mitochondrial membrane (IMM) permeability to protons, but not small molecules. The movement of water into mitochondria is prevented by altering intracellular osmotic gradients. Other clinically used iron chelators do not produce mitochondrial swelling. Thus, DFX causes organ toxicity due to an off-target effect on the IMM, which has major adverse consequences for mitochondrial volume regulation.
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Affiliation(s)
| | - Claus D Schuh
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Patrick Drücker
- Department of Biosystems Science and Engineering, ETH Zurich, Zurich, Switzerland
| | - Dominik Haenni
- Institute of Anatomy, University of Zurich, Zurich, Switzerland.,Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Adam Pearson
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Susan Ghazi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | | | - Michael Duss
- Department of Chemistry, University of Zurich, Zurich, Switzerland
| | - Ehud M Landau
- Department of Chemistry, University of Zurich, Zurich, Switzerland
| | - Andres Kaech
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Urs Ziegler
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Anne K M Lundby
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Carsten Lundby
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Petra S Dittrich
- Department of Biosystems Science and Engineering, ETH Zurich, Zurich, Switzerland
| | - Andrew M Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland. .,Department of Nephrology, University Hospital Zurich, Zurich, Switzerland.
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6
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Larpin Y, Besançon H, Iacovache MI, Babiychuk VS, Babiychuk EB, Zuber B, Draeger A, Köffel R. Bacterial pore-forming toxin pneumolysin: Cell membrane structure and microvesicle shedding capacity determines differential survival of cell types. FASEB J 2019; 34:1665-1678. [PMID: 31914676 DOI: 10.1096/fj.201901737rr] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Revised: 10/14/2019] [Accepted: 11/06/2019] [Indexed: 12/25/2022]
Abstract
Bacterial infectious diseases can lead to death or to serious illnesses. These outcomes are partly the consequence of pore-forming toxins, which are secreted by the pathogenic bacteria (eg, pneumolysin of Streptococcus pneumoniae). Pneumolysin binds to cholesterol within the plasma membrane of host cells and assembles to form trans-membrane pores, which can lead to Ca2+ influx and cell death. Membrane repair mechanisms exist that limit the extent of damage. Immune cells which are essential to fight bacterial infections critically rely on survival mechanisms after detrimental pneumolysin attacks. This study investigated the susceptibility of different immune cell types to pneumolysin. As a model system, we used the lymphoid T-cell line Jurkat, and myeloid cell lines U937 and THP-1. We show that Jurkat T cells are highly susceptible to pneumolysin attack. In contrast, myeloid THP-1 and U937 cells are less susceptible to pneumolysin. In line with these findings, human primary T cells are shown to be more susceptible to pneumolysin attack than monocytes. Differences in susceptibility to pneumolysin are due to (I) preferential binding of pneumolysin to Jurkat T cells and (II) cell type specific plasma membrane repair capacity. Myeloid cell survival is mostly dependent on Ca2+ induced expelling of damaged plasma membrane areas as microvesicles. Thus, in myeloid cells, first-line defense cells in bacterial infections, a potent cellular repair machinery ensures cell survival after pneumolysin attack. In lymphoid cells, which are important at later stages of infections, less efficient repair mechanisms and enhanced toxin binding renders the cells more sensitive to pneumolysin.
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Affiliation(s)
- Yu Larpin
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Hervé Besançon
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Mircea-Ioan Iacovache
- Laboratory of Experimental Morphology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Victoriia S Babiychuk
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Eduard B Babiychuk
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Benoît Zuber
- Laboratory of Experimental Morphology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - Annette Draeger
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
| | - René Köffel
- Department of Cell Biology, Institute of Anatomy, University of Bern, Bern, Switzerland
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7
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Boucher E, Goldin-Blais L, Basiren Q, Mandato CA. Actin dynamics and myosin contractility during plasma membrane repair and restoration: Does one ring really heal them all? CURRENT TOPICS IN MEMBRANES 2019; 84:17-41. [PMID: 31610862 DOI: 10.1016/bs.ctm.2019.07.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In order to survive daily insults, cells have evolved various mechanisms that detect, stabilize and repair damages done to their plasma membrane and cytoskeletal structures. Damage to the PM endangers wounded cells by exposing them to uncontrolled exchanges with the extracellular milieu. The processes and molecular machinery enabling PM repair are therefore at the center of the bulk of the investigations into single-cell repair program. Wounds are repaired by dynamically remodeling the composition and shape of the injured area through exocytosis-mediated release of intracellular membrane components to the wounded area, endocytosis-mediated removal of the injured area, or the shedding of the injury. The wound healing program of Xenopus oocytes and early Drosophila embryos is by contrast, mostly characterized by the rapid formation of a large membrane patch over the wound that eventually fuse with the plasma membrane which restores plasma membrane continuity and lead to the shedding of patch material into the extracellular space. Formation and contraction of actomyosin ring restores normal plasma membrane composition and organizes cytoskeletal repairs. The extend of the contributions of the cytoskeleton to the wound healing program of somatic cells have comparatively received little attention. This review offers a survey of the current knowledge on how actin dynamics, myosin-based contraction and other cytoskeletal structures affects PM and cortical cytoskeleton repair of somatic cells.
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Affiliation(s)
- Eric Boucher
- Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Laurence Goldin-Blais
- Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Quentin Basiren
- Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Craig A Mandato
- Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada.
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8
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Brito C, Cabanes D, Sarmento Mesquita F, Sousa S. Mechanisms protecting host cells against bacterial pore-forming toxins. Cell Mol Life Sci 2019; 76:1319-1339. [PMID: 30591958 PMCID: PMC6420883 DOI: 10.1007/s00018-018-2992-8] [Citation(s) in RCA: 88] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 12/06/2018] [Accepted: 12/10/2018] [Indexed: 12/19/2022]
Abstract
Pore-forming toxins (PFTs) are key virulence determinants produced and secreted by a variety of human bacterial pathogens. They disrupt the plasma membrane (PM) by generating stable protein pores, which allow uncontrolled exchanges between the extracellular and intracellular milieus, dramatically disturbing cellular homeostasis. In recent years, many advances were made regarding the characterization of conserved repair mechanisms that allow eukaryotic cells to recover from mechanical disruption of the PM membrane. However, the specificities of the cell recovery pathways that protect host cells against PFT-induced damage remain remarkably elusive. During bacterial infections, the coordinated action of such cell recovery processes defines the outcome of infected cells and is, thus, critical for our understanding of bacterial pathogenesis. Here, we review the cellular pathways reported to be involved in the response to bacterial PFTs and discuss their impact in single-cell recovery and infection.
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Affiliation(s)
- Cláudia Brito
- i3S-Instituto de Investigação e Inovação em Saúde, IBMC, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135, Porto, Portugal
- Programa Doutoral em Biologia Molecular e Celular (MCbiology), Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Rua Jorge de Viterbo Ferreira 228, 4050-313, Porto, Portugal
| | - Didier Cabanes
- i3S-Instituto de Investigação e Inovação em Saúde, IBMC, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135, Porto, Portugal
| | - Francisco Sarmento Mesquita
- i3S-Instituto de Investigação e Inovação em Saúde, IBMC, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135, Porto, Portugal.
- Global Health Institute, School of Life Science, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
| | - Sandra Sousa
- i3S-Instituto de Investigação e Inovação em Saúde, IBMC, Universidade do Porto, Rua Alfredo Allen, 208, 4200-135, Porto, Portugal.
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9
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Drücker P, Iacovache I, Bachler S, Zuber B, Babiychuk EB, Dittrich PS, Draeger A. Membrane deformation and layer-by-layer peeling of giant vesicles induced by the pore-forming toxin pneumolysin. Biomater Sci 2019; 7:3693-3705. [DOI: 10.1039/c9bm00134d] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Membranes under attack by the pore-forming toxin pneumolysin reveal a hitherto unknown layer-by-layer peeling mechanism and disclose the multilamellar structure.
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Affiliation(s)
- Patrick Drücker
- Department of Biosystems Science and Engineering
- ETH Zurich
- 4058 Basel
- Switzerland
- Department of Cell Biology
| | - Ioan Iacovache
- Laboratory of Experimental Morphology
- Institute of Anatomy
- University of Bern
- 3000 Bern 9
- Switzerland
| | - Simon Bachler
- Department of Biosystems Science and Engineering
- ETH Zurich
- 4058 Basel
- Switzerland
| | - Benoît Zuber
- Laboratory of Experimental Morphology
- Institute of Anatomy
- University of Bern
- 3000 Bern 9
- Switzerland
| | - Eduard B. Babiychuk
- Department of Cell Biology
- Institute of Anatomy
- University of Bern
- 3000 Bern 9
- Switzerland
| | - Petra S. Dittrich
- Department of Biosystems Science and Engineering
- ETH Zurich
- 4058 Basel
- Switzerland
| | - Annette Draeger
- Department of Cell Biology
- Institute of Anatomy
- University of Bern
- 3000 Bern 9
- Switzerland
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