101
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Read J, Clancy EK, Sarker M, de Antueno R, Langelaan DN, Parmar HB, Shin K, Rainey JK, Duncan R. Reovirus FAST Proteins Drive Pore Formation and Syncytiogenesis Using a Novel Helix-Loop-Helix Fusion-Inducing Lipid Packing Sensor. PLoS Pathog 2015; 11:e1004962. [PMID: 26061049 PMCID: PMC4464655 DOI: 10.1371/journal.ppat.1004962] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Accepted: 05/18/2015] [Indexed: 02/07/2023] Open
Abstract
Pore formation is the most energy-demanding step during virus-induced membrane fusion, where high curvature of the fusion pore rim increases the spacing between lipid headgroups, exposing the hydrophobic interior of the membrane to water. How protein fusogens breach this thermodynamic barrier to pore formation is unclear. We identified a novel fusion-inducing lipid packing sensor (FLiPS) in the cytosolic endodomain of the baboon reovirus p15 fusion-associated small transmembrane (FAST) protein that is essential for pore formation during cell-cell fusion and syncytiogenesis. NMR spectroscopy and mutational studies indicate the dependence of this FLiPS on a hydrophobic helix-loop-helix structure. Biochemical and biophysical assays reveal the p15 FLiPS preferentially partitions into membranes with high positive curvature, and this partitioning is impeded by bis-ANS, a small molecule that inserts into hydrophobic defects in membranes. Most notably, the p15 FLiPS can be functionally replaced by heterologous amphipathic lipid packing sensors (ALPS) but not by other membrane-interactive amphipathic helices. Furthermore, a previously unrecognized amphipathic helix in the cytosolic domain of the reptilian reovirus p14 FAST protein can functionally replace the p15 FLiPS, and is itself replaceable by a heterologous ALPS motif. Anchored near the cytoplasmic leaflet by the FAST protein transmembrane domain, the FLiPS is perfectly positioned to insert into hydrophobic defects that begin to appear in the highly curved rim of nascent fusion pores, thereby lowering the energy barrier to stable pore formation. The fusogenic ortho- and aquareoviruses are the only known nonenveloped viruses that induce syncytium formation. Cell-cell fusion is a virulence determinant of fusogenic reoviruses, and is mediated by a singular family of fusion-associated small transmembrane (FAST) proteins, the smallest known viral fusogens. Unlike their enveloped virus counterparts, reovirus FAST proteins have exceptionally small ectodomains and considerable larger cytoplasmic endodomains, suggesting FAST protein interactions with the cytoplasmic leaflet of the plasma membrane likely play a prominent role in the fusion process. We determined that the baboon reovirus p15 FAST protein endodomain contains a novel type of helix-loop-helix lipid packing sensor that partitions into hydrophobic defects present in highly curved membranes. This fusion-inducing lipid packing sensor (FLiPS) is required for pore formation, and can be functionally replaced by heterologous lipid packing sensors. By masking hydrophobic defects appearing in the highly curved rim of nascent fusion pores, the FliPS would make the forward reaction to pore formation a more energetically favored means of resolving an unstable hemifusion intermediate. These results define a new role for curvature sensing motifs, and reveal how viral fusion proteins can drive pore formation without having to rely on membrane stresses induced by complex refolding of large ectodomains.
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Affiliation(s)
- Jolene Read
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Eileen K. Clancy
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Muzaddid Sarker
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Roberto de Antueno
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - David N. Langelaan
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Hiren B. Parmar
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Kyungsoo Shin
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Jan K. Rainey
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Roy Duncan
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada
- * E-mail:
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102
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Van Lehn RC, Alexander-Katz A. Pathway for insertion of amphiphilic nanoparticles into defect-free lipid bilayers from atomistic molecular dynamics simulations. SOFT MATTER 2015; 11:3165-75. [PMID: 25757187 DOI: 10.1039/c5sm00287g] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Gold nanoparticles (NPs) have been increasingly used in biological applications that involve potential contact with cellular membranes. As a result, it is essential to gain a physical understanding of NP-membrane interactions to guide the design of next-generation bioactive nanoparticles. In previous work, we showed that charged, amphiphilic NPs can fuse with lipid bilayers after contact between protruding solvent-exposed lipid tails and the NP monolayer. Fusion was only observed at the high-curvature edges of large bilayer defects, but not in low-curvature regions where protrusions are rarely observed. Here, we use atomistic molecular dynamics simulations to show that the same NPs can also fuse with low-curvature bilayers in the absence of defects if NP-protrusion contact occurs, generalizing the results of our previous work. Insertion proceeds without applying biasing forces to the NP, driven by the hydrophobic effect, and involves the transient generation of bilayer curvature. We further find that NPs with long hydrophobic ligands can insert a single ligand into the bilayer core in a manner similar to the binding of peripheral proteins. Such anchoring may precede insertion, revealing potential methods for engineering NP monolayers to enhance NP-bilayer fusion in systems with a low likelihood of lipid tail protrusions. These results reveal new pathways for NP-bilayer fusion and provide fundamental insight into behavior at the nano-bio interface.
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Affiliation(s)
- Reid C Van Lehn
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
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103
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Membrane curvature enables N-Ras lipid anchor sorting to liquid-ordered membrane phases. Nat Chem Biol 2015; 11:192-4. [DOI: 10.1038/nchembio.1733] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Accepted: 11/14/2014] [Indexed: 11/08/2022]
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104
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Garten M, Prévost C, Cadart C, Gautier R, Bousset L, Melki R, Bassereau P, Vanni S. Methyl-branched lipids promote the membrane adsorption of α-synuclein by enhancing shallow lipid-packing defects. Phys Chem Chem Phys 2015; 17:15589-97. [DOI: 10.1039/c5cp00244c] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Reconstitution experiments on Giant Unilamellar Vesicles and Molecular Dynamics Simulations indicate that alpha-synuclein binds to neutral flat membranes in the presence of methyl-branched lipids.
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Affiliation(s)
| | | | | | - Romain Gautier
- Institut de Pharmacologie Moléculaire et Cellulaire
- Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique
- UMR 7275
- 06560 Valbonne
- France
| | - Luc Bousset
- CNRS
- Paris Saclay Institute of Neuroscience
- Gif-sur-Yvette
- France
| | - Ronald Melki
- CNRS
- Paris Saclay Institute of Neuroscience
- Gif-sur-Yvette
- France
| | | | - Stefano Vanni
- Institut de Pharmacologie Moléculaire et Cellulaire
- Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique
- UMR 7275
- 06560 Valbonne
- France
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105
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Yang B, Pu M, Khan HM, Friedman L, Reuter N, Roberts MF, Gershenson A. Quantifying transient interactions between Bacillus phosphatidylinositol-specific phospholipase-C and phosphatidylcholine-rich vesicles. J Am Chem Soc 2014; 137:14-7. [PMID: 25517221 PMCID: PMC4304437 DOI: 10.1021/ja508631n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
![]()
Bacillus thuringiensis secretes the virulence
factor phosphatidylinositol-specific phospholipase C (BtPI-PLC), which specifically binds to phosphatidylcholine
(PC) and cleaves GPI-anchored proteins off eukaryotic plasma membranes.
To elucidate how BtPI-PLC searches for GPI-anchored
proteins on the membrane surface, we measured residence times of single
fluorescently labeled proteins on PC-rich small unilamellar vesicles
(SUVs). BtPI-PLC interactions with the SUV surface
are transient with a lifetime of 379 ± 49 ms. These data also
suggest that BtPI-PLC does not directly sense curvature,
but rather prefers to bind to the numerous lipid packing defects in
SUVs. Despite this preference for defects, all-atom molecular dynamics
simulations of BtPI-PLC interacting with PC-rich
bilayers show that the protein is shallowly anchored with the deepest
insertions ∼18 Å above the bilayer center. Membrane partitioning
is mediated, on average, by 41 hydrophobic, 8 hydrogen-bonding, and
2 cation−π (between PC choline headgroups and Tyr residues)
transient interactions with phospholipids. These results lead to a
quantitative model for BtPI-PLC interactions with
cell membranes where protein binding is mediated by lipid packing
defects, possibly near GPI-anchored proteins, and the protein diffuses
on the membrane for ∼100–380 ms, during which time it
may cleave ∼10 GPI-anchored proteins before dissociating. This
combination of short two-dimensional scoots followed by three-dimensional
hops may be an efficient search strategy on two-dimensional surfaces
with obstacles.
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Affiliation(s)
- Boqian Yang
- Department of Biochemistry and Molecular Biology, University of Massachusetts , Amherst, Massachusetts 01003, United States
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106
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Moiset G, López CA, Bartelds R, Syga L, Rijpkema E, Cukkemane A, Baldus M, Poolman B, Marrink SJ. Disaccharides Impact the Lateral Organization of Lipid Membranes. J Am Chem Soc 2014; 136:16167-75. [DOI: 10.1021/ja505476c] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Gemma Moiset
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Cesar A. López
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Rianne Bartelds
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Lukasz Syga
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Egon Rijpkema
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Abhishek Cukkemane
- NMR
Spectroscopy, Bijvoet Center for Biomolecular Research Department
of Chemistry, Faculty of Science, Utrecht University, Padualaan
8, 3584 CH Utrecht, The Netherlands
| | - Marc Baldus
- NMR
Spectroscopy, Bijvoet Center for Biomolecular Research Department
of Chemistry, Faculty of Science, Utrecht University, Padualaan
8, 3584 CH Utrecht, The Netherlands
| | - Bert Poolman
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Siewert J. Marrink
- Groningen
Biomolecular Sciences and Biotechnology Institute and Zernike Institute
for Advanced Materials, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
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107
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Vanni S, Hirose H, Barelli H, Antonny B, Gautier R. A sub-nanometre view of how membrane curvature and composition modulate lipid packing and protein recruitment. Nat Commun 2014; 5:4916. [PMID: 25222832 DOI: 10.1038/ncomms5916] [Citation(s) in RCA: 189] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 08/05/2014] [Indexed: 02/07/2023] Open
Abstract
Two parameters of biological membranes, curvature and lipid composition, direct the recruitment of many peripheral proteins to cellular organelles. Although these traits are often studied independently, it is their combination that generates the unique interfacial properties of cellular membranes. Here, we use a combination of in vivo, in vitro and in silico approaches to provide a comprehensive map of how these parameters modulate membrane adhesive properties. The correlation between the membrane partitioning of model amphipathic helices and the distribution of lipid-packing defects in membranes of different shape and composition explains how macroscopic membrane properties modulate protein recruitment by changing the molecular topography of the membrane interfacial region. Furthermore, our results suggest that the range of conditions that can be obtained in a cellular context is remarkably large because lipid composition and curvature have, under most circumstances, cumulative effects.
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Affiliation(s)
- Stefano Vanni
- 1] Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, UMR 7275, 660 route des Lucioles, 06560 Valbonne, France [2]
| | - Hisaaki Hirose
- 1] Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, UMR 7275, 660 route des Lucioles, 06560 Valbonne, France [2]
| | - Hélène Barelli
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, UMR 7275, 660 route des Lucioles, 06560 Valbonne, France
| | - Bruno Antonny
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, UMR 7275, 660 route des Lucioles, 06560 Valbonne, France
| | - Romain Gautier
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, UMR 7275, 660 route des Lucioles, 06560 Valbonne, France
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108
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Mertins O, Bacellar IOL, Thalmann F, Marques CM, Baptista MS, Itri R. Physical damage on giant vesicles membrane as a result of methylene blue photoirradiation. Biophys J 2014; 106:162-71. [PMID: 24411248 DOI: 10.1016/j.bpj.2013.11.4457] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2013] [Revised: 11/13/2013] [Accepted: 11/18/2013] [Indexed: 02/07/2023] Open
Abstract
In this study we pursue a closer analysis of the photodamage promoted on giant unilamellar vesicles membranes made of dioleoyl-sn-glycero-3-phosphocholine (DOPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), by irradiating methylene blue present in the giant unilamellar vesicles solution. By means of optical microscopy and electro-deformation experiments, the physical damage on the vesicle membrane was followed and the phospholipids oxidation was evaluated in terms of changes in the membrane surface area and permeability. As expected, oxidation modifies structural characteristics of the phospholipids that lead to remarkable membrane alterations. By comparing DOPC- with POPC-made membranes, we observed that the rate of pore formation and vesicle degradation as a function of methylene blue concentration follows a diffusion law in the case of DOPC and a linear variation in the case of POPC. We attributed this scenario to the nucleation process of oxidized species following a diffusion-limited growth regime for DOPC and in the case of POPC a homogeneous nucleation process. On the basis of these premises, we constructed models based on reaction-diffusion equations that fit well with the experimental data. This information shows that the outcome of the photosensitization reactions is critically dependent on the type of lipid present in the membrane.
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Affiliation(s)
- Omar Mertins
- Departamento de Física Aplicada, Instituto de Física, Universidade de São Paulo.
| | - Isabel O L Bacellar
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Fabrice Thalmann
- Institut Charles Sadron, Université de Strasbourg, Centre National de la Recherche Scientifique, Strasbourg, France
| | - Carlos M Marques
- Institut Charles Sadron, Université de Strasbourg, Centre National de la Recherche Scientifique, Strasbourg, France
| | - Maurício S Baptista
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Rosangela Itri
- Departamento de Física Aplicada, Instituto de Física, Universidade de São Paulo.
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109
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Thalhammer A, Bryant G, Sulpice R, Hincha DK. Disordered cold regulated15 proteins protect chloroplast membranes during freezing through binding and folding, but do not stabilize chloroplast enzymes in vivo. PLANT PHYSIOLOGY 2014; 166:190-201. [PMID: 25096979 PMCID: PMC4149706 DOI: 10.1104/pp.114.245399] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Accepted: 08/04/2014] [Indexed: 05/18/2023]
Abstract
Freezing can severely damage plants, limiting geographical distribution of natural populations and leading to major agronomical losses. Plants native to cold climates acquire increased freezing tolerance during exposure to low nonfreezing temperatures in a process termed cold acclimation. This involves many adaptative responses, including global changes in metabolite content and gene expression, and the accumulation of cold-regulated (COR) proteins, whose functions are largely unknown. Here we report that the chloroplast proteins COR15A and COR15B are necessary for full cold acclimation in Arabidopsis (Arabidopsis thaliana). They protect cell membranes, as indicated by electrolyte leakage and chlorophyll fluorescence measurements. Recombinant COR15 proteins stabilize lactate dehydrogenase during freezing in vitro. However, a transgenic approach shows that they have no influence on the stability of selected plastidic enzymes in vivo, although cold acclimation results in increased enzyme stability. This indicates that enzymes are stabilized by other mechanisms. Recombinant COR15 proteins are disordered in water, but fold into amphipathic α-helices at high osmolyte concentrations in the presence of membranes, a condition mimicking molecular crowding induced by dehydration during freezing. X-ray scattering experiments indicate protein-membrane interactions specifically under such crowding conditions. The COR15-membrane interactions lead to liposome stabilization during freezing. Collectively, our data demonstrate the requirement for COR15 accumulation for full cold acclimation of Arabidopsis. The function of these intrinsically disordered proteins is the stabilization of chloroplast membranes during freezing through a folding and binding mechanism, but not the stabilization of chloroplastic enzymes. This indicates a high functional specificity of these disordered plant proteins.
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Affiliation(s)
- Anja Thalhammer
- Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam, Germany (A.T., R.S., D.K.H.); andCentre for Molecular and Nanoscale Physics, School of Applied Sciences, RMIT University, Melbourne 3001, Australia (G.B.)
| | - Gary Bryant
- Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam, Germany (A.T., R.S., D.K.H.); andCentre for Molecular and Nanoscale Physics, School of Applied Sciences, RMIT University, Melbourne 3001, Australia (G.B.)
| | - Ronan Sulpice
- Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam, Germany (A.T., R.S., D.K.H.); andCentre for Molecular and Nanoscale Physics, School of Applied Sciences, RMIT University, Melbourne 3001, Australia (G.B.)
| | - Dirk K Hincha
- Max Planck Institute of Molecular Plant Physiology, D-14476 Potsdam, Germany (A.T., R.S., D.K.H.); andCentre for Molecular and Nanoscale Physics, School of Applied Sciences, RMIT University, Melbourne 3001, Australia (G.B.)
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110
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Pinot M, Vanni S, Pagnotta S, Lacas-Gervais S, Payet LA, Ferreira T, Gautier R, Goud B, Antonny B, Barelli H. Lipid cell biology. Polyunsaturated phospholipids facilitate membrane deformation and fission by endocytic proteins. Science 2014; 345:693-7. [PMID: 25104391 DOI: 10.1126/science.1255288] [Citation(s) in RCA: 241] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Phospholipids (PLs) with polyunsaturated acyl chains are extremely abundant in a few specialized cellular organelles such as synaptic vesicles and photoreceptor discs, but their effect on membrane properties is poorly understood. Here, we found that polyunsaturated PLs increased the ability of dynamin and endophilin to deform and vesiculate synthetic membranes. When cells incorporated polyunsaturated fatty acids into PLs, the plasma membrane became more amenable to deformation by a pulling force and the rate of endocytosis was accelerated, in particular, under conditions in which cholesterol was limiting. Molecular dynamics simulations and biochemical measurements indicated that polyunsaturated PLs adapted their conformation to membrane curvature. Thus, by reducing the energetic cost of membrane bending and fission, polyunsaturated PLs may help to support rapid endocytosis.
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Affiliation(s)
- Mathieu Pinot
- Institut de Pharmacologie Moléculaire et Cellulaire, Université Nice Sophia Antipolis and CNRS, 06560 Valbonne, France. Unité Mixte de Recherche 144, Institut Curie and CNRS, F-75248 Paris, France
| | - Stefano Vanni
- Institut de Pharmacologie Moléculaire et Cellulaire, Université Nice Sophia Antipolis and CNRS, 06560 Valbonne, France
| | - Sophie Pagnotta
- Centre Commun de Microscopie Appliquée, Université Nice Sophia Antipolis, Parc Valrose, 06000 Nice, France
| | - Sandra Lacas-Gervais
- Centre Commun de Microscopie Appliquée, Université Nice Sophia Antipolis, Parc Valrose, 06000 Nice, France
| | - Laurie-Anne Payet
- Signalisation et Transports Ioniques Membranaires, Université de Poitiers and CNRS, Poitiers, France
| | - Thierry Ferreira
- Signalisation et Transports Ioniques Membranaires, Université de Poitiers and CNRS, Poitiers, France
| | - Romain Gautier
- Institut de Pharmacologie Moléculaire et Cellulaire, Université Nice Sophia Antipolis and CNRS, 06560 Valbonne, France
| | - Bruno Goud
- Unité Mixte de Recherche 144, Institut Curie and CNRS, F-75248 Paris, France
| | - Bruno Antonny
- Institut de Pharmacologie Moléculaire et Cellulaire, Université Nice Sophia Antipolis and CNRS, 06560 Valbonne, France.
| | - Hélène Barelli
- Institut de Pharmacologie Moléculaire et Cellulaire, Université Nice Sophia Antipolis and CNRS, 06560 Valbonne, France
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111
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Van Lehn RC, Ricci M, Silva PH, Andreozzi P, Reguera J, Voïtchovsky K, Stellacci F, Alexander-Katz A. Lipid tail protrusions mediate the insertion of nanoparticles into model cell membranes. Nat Commun 2014; 5:4482. [DOI: 10.1038/ncomms5482] [Citation(s) in RCA: 167] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 06/23/2014] [Indexed: 12/30/2022] Open
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112
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Nath S, Dancourt J, Shteyn V, Puente G, Fong WM, Nag S, Bewersdorf J, Yamamoto A, Antonny B, Melia. TJ. Lipidation of the LC3/GABARAP family of autophagy proteins relies on a membrane-curvature-sensing domain in Atg3. Nat Cell Biol 2014; 16:415-24. [PMID: 24747438 PMCID: PMC4111135 DOI: 10.1038/ncb2940] [Citation(s) in RCA: 189] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Accepted: 02/27/2014] [Indexed: 02/07/2023]
Abstract
The components supporting autophagosome growth on the cup-like isolation membrane are likely to be different from those found on closed and maturing autophagosomes. The highly curved rim of the cup may serve as a functionally required surface for transiently associated components of the early acting autophagic machinery. Here we demonstrate that the E2-like enzyme, Atg3, facilitates LC3/GABARAP lipidation only on membranes exhibiting local lipid-packing defects. This activity requires an amino-terminal amphipathic helix similar to motifs found on proteins targeting highly curved intracellular membranes. By tuning the hydrophobicity of this motif, we can promote or inhibit lipidation in vitro and in rescue experiments in Atg3-knockout cells, implying a physiologic role for this stress detection. The need for extensive lipid-packing defects suggests that Atg3 is designed to work at highly curved membranes, perhaps including the limiting edge of the growing phagophore.
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Affiliation(s)
- Sangeeta Nath
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Julia Dancourt
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Vladimir Shteyn
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Gabriella Puente
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Wendy M. Fong
- Departments of Neurology, Pathology and Cell Biology, Columbia University, NY, NY
| | - Shanta Nag
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Joerg Bewersdorf
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
| | - Ai Yamamoto
- Departments of Neurology, Pathology and Cell Biology, Columbia University, NY, NY
| | - Bruno Antonny
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS et université de Nice, France
| | - Thomas J. Melia.
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT
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113
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Wu T, Shi Z, Baumgart T. Mutations in BIN1 associated with centronuclear myopathy disrupt membrane remodeling by affecting protein density and oligomerization. PLoS One 2014; 9:e93060. [PMID: 24755653 PMCID: PMC3995651 DOI: 10.1371/journal.pone.0093060] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2013] [Accepted: 03/02/2014] [Indexed: 11/18/2022] Open
Abstract
The regulation of membrane shapes is central to many cellular phenomena. Bin/Amphiphysin/Rvs (BAR) domain-containing proteins are key players for membrane remodeling during endocytosis, cell migration, and endosomal sorting. BIN1, which contains an N-BAR domain, is assumed to be essential for biogenesis of plasma membrane invaginations (T-tubules) in muscle tissues. Three mutations, K35N, D151N and R154Q, have been discovered so far in the BAR domain of BIN1 in patients with centronuclear myopathy (CNM), where impaired organization of T-tubules has been reported. However, molecular mechanisms behind this malfunction have remained elusive. None of the BIN1 disease mutants displayed a significantly compromised curvature sensing ability. However, two mutants showed impaired membrane tubulation both in vivo and in vitro, and displayed characteristically different behaviors. R154Q generated smaller membrane curvature compared to WT N-BAR. Quantification of protein density on membranes revealed a lower membrane-bound density for R154Q compared to WT and the other mutants, which appeared to be the primary reason for the observation of impaired deformation capacity. The D151N mutant was unable to tubulate liposomes under certain experimental conditions. At medium protein concentrations we found 'budding' structures on liposomes that we hypothesized to be intermediates during the tubulation process except for the D151N mutant. Chemical crosslinking assays suggested that the D151N mutation impaired protein oligomerization upon membrane binding. Although we found an insignificant difference between WT and K35N N-BAR in in vitro assays, depolymerizing actin in live cells allowed tubulation of plasma membranes through the K35N mutant. Our results provide insights into the membrane-involved pathophysiological mechanisms leading to human disease.
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Affiliation(s)
- Tingting Wu
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Zheng Shi
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Tobias Baumgart
- Department of Chemistry, School of Arts & Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
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114
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Chaibva M, Burke KA, Legleiter J. Curvature enhances binding and aggregation of huntingtin at lipid membranes. Biochemistry 2014; 53:2355-65. [PMID: 24670006 DOI: 10.1021/bi401619q] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Huntington disease (HD) is a genetic neurodegenerative disease caused by an expanded polyglutamine (polyQ) domain in the first exon of the huntingtin (Htt) protein, facilitating its aggregation. Htt interacts with a variety of membraneous structures within the cell, and the first 17 amino acids (Nt17) of Htt directly flanking the polyQ domain comprise an amphiphathic α-helix (AH) lipid-binding domain. AHs are also known to detect membrane curvature. To determine if Htt exon 1 preferentially binds curved membranes, in situ atomic force microscopy (AFM) studies were performed. Supported lipid bilayers are commonly used as model membranes for AFM studies of protein aggregation. However, these supported bilayers usually lack curvature. By forming a bilayer on top of silica nanobeads (50 ± 10 nm) deposited on a silicon substrate, model supported lipid bilayers with flat and curved regions were developed for AFM studies. The presence of the bilayer over the beads was validated by continual imaging of the formation of the bilayer, height measurements, and spatially resolved mechanical measurements of the resulting bilayer using scanning probe acceleration microscopy. Interpretation of this data was facilitated by numerical simulations of the entire imaging process. The curved supported bilayers associated with the beads were found to be more compliant than flat supported bilayers, consistent with the altered packing density of lipids caused by the induced curvature. This model bilayer system was exposed to a synthetic truncated Htt exon 1 peptide (Nt17Q35P10KK), and this peptide preferentially accumulated on curved membranes, consistent with the ability of AHs to sense membrane curvature.
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Affiliation(s)
- Maxmore Chaibva
- The C. Eugene Bennett Department of Chemistry, West Virginia University , Morgantown, West Virginia 26505, United States
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115
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Shen W, Hu J, Hu X. Impact of amphiphilic triblock copolymers on stability and permeability of phospholipid/polymer hybrid vesicles. Chem Phys Lett 2014. [DOI: 10.1016/j.cplett.2014.03.057] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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116
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Black JC, Cheney PP, Campbell T, Knowles MK. Membrane curvature based lipid sorting using a nanoparticle patterned substrate. SOFT MATTER 2014; 10:2016-23. [PMID: 24652483 DOI: 10.1039/c3sm52522h] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Cellular membranes contain a variety of shapes that likely act as motifs for sorting lipids and proteins. To understand the sorting that takes place within cells, a continuous, fluid bilayer with regions of membrane curvature was designed and characterized using confocal fluorescence and total internal reflection fluorescence microscopy techniques. A supported lipid bilayer was formed over fluorescently labelled nanoparticles deposited on a glass surface. The lipid composition and membrane shape are separately controlled and the nanoparticle dimensions (d = 40-200 nm) determine the extent of curvature. The bulk membrane is fluid as demonstrated by fluorescence recovery after photobleaching (FRAP) using dye labelled lipids. In bilayers that contain fluorescently labelled, single-tailed lipids, accumulation is observed at regions of curvature, yet the molecules retain fluidity. Using single particle imaging methods, lipids are observed to visit regions of curvature and exchange with the surrounding flat membrane. The nanoparticle patterned substrate described here allows for quantitative measurement of the transient interactions between fluorescently labelled biomolecules and regions of membrane curvature.
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Affiliation(s)
- Joshua C Black
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
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117
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Liang B, Dawidowski D, Ellena JF, Tamm LK, Cafiso DS. The SNARE motif of synaptobrevin exhibits an aqueous-interfacial partitioning that is modulated by membrane curvature. Biochemistry 2014; 53:1485-94. [PMID: 24552121 PMCID: PMC3985803 DOI: 10.1021/bi401638u] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The structure and interfacial association of the full-length vesicle SNARE, synaptobrevin, were compared in four different lipid environments using nuclear magnetic resonance and electron paramagnetic resonance spectroscopy. In micelles, segments of the SNARE motif are helical and associated with the interface. However, the fraction of helix and interfacial association decreases as synaptobrevin is moved from micelle to bicelle to bilayer environments, indicating that the tendency toward interfacial association is sensitive to membrane curvature. In bilayers, the SNARE motif of synaptobrevin transiently associates with the lipid interface, and regions that are helical in micelles are in conformational and environmental exchange in bicelles and bilayers. This work demonstrates that the SNARE motif of synaptobrevin has a significant propensity to form a helix and exchange with the membrane interface prior to SNARE assembly. This transient interfacial association and its sensitivity to membrane curvature are likely to play a role in SNARE recognition events that regulate membrane fusion.
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Affiliation(s)
- Binyong Liang
- Biomolecular Magnetic Resonance Research Core, University of Virginia , P.O. Box 800741, Charlottesville, Virginia 22908, United States
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118
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Chong SSY, Taneva SG, Lee JMC, Cornell RB. The Curvature Sensitivity of a Membrane-Binding Amphipathic Helix Can Be Modulated by the Charge on a Flanking Region. Biochemistry 2014; 53:450-61. [DOI: 10.1021/bi401457r] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Sharon S. Y. Chong
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Svetla G. Taneva
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Joseph M. C. Lee
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
| | - Rosemary B. Cornell
- Department
of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
- Department
of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
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119
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Bissig C, Gruenberg J. ALIX and the multivesicular endosome: ALIX in Wonderland. Trends Cell Biol 2014; 24:19-25. [DOI: 10.1016/j.tcb.2013.10.009] [Citation(s) in RCA: 216] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/29/2013] [Accepted: 10/30/2013] [Indexed: 01/19/2023]
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120
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Insertion of apoLp-III into a lipid monolayer is more favorable for saturated, more ordered, acyl-chains. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:482-92. [PMID: 24099741 DOI: 10.1016/j.bbamem.2013.09.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Revised: 09/20/2013] [Accepted: 09/25/2013] [Indexed: 11/22/2022]
Abstract
Neutral lipid transport in mammals is complicated involving many types of apolipoprotein. The exchangeable apolipoproteins mediate the transfer of hydrophobic lipids between tissues and particles, and bind to cell surface receptors. Amphipathic α-helices form a common structural motif that facilitates their lipid binding and exchangeability. ApoLp-III, the only exchangeable apolipoprotein found in insects, is a model amphipathic α-helix bundle protein and its three dimensional structure and function mimics that of the mammalian proteins apoE and apoAI. Even the intracellular exchangeable lipid droplet protein TIP47/perilipin 3 contains an α-helix bundle domain with high structural similarity to that of apoE and apoLp-III. Here, we investigated the interaction of apoLp-III from Locusta migratoria with lipid monolayers. Consistent with earlier work we find that insertion of apoLp-III into fluid lipid monolayers is highest for diacylglycerol. We observe a preference for saturated and more highly ordered lipids, suggesting a new mode of interaction for amphipathic α-helix bundles. X-ray reflectivity shows that apoLp-III unfolds at a hydrophobic interface and flexible loops connecting the amphipathic α-helices stay in solution. X-ray diffraction indicates that apoLp-III insertion into diacylglycerol monolayers induces additional ordering of saturated acyl-chains. These results thus shed important new insight into the protein-lipid interactions of a model exchangeable apolipoprotein with significant implications for its mammalian counterparts.
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121
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Voth GA. New and notable: key new insights into membrane targeting by proteins. Biophys J 2013; 104:517-9. [PMID: 23442902 DOI: 10.1016/j.bpj.2012.12.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Accepted: 12/13/2012] [Indexed: 10/27/2022] Open
Affiliation(s)
- Gregory A Voth
- Department of Chemistry, Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois, USA.
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122
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Vanni S, Vamparys L, Gautier R, Drin G, Etchebest C, Fuchs PFJ, Antonny B. Amphipathic lipid packing sensor motifs: probing bilayer defects with hydrophobic residues. Biophys J 2013; 104:575-84. [PMID: 23442908 DOI: 10.1016/j.bpj.2012.11.3837] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 10/15/2012] [Accepted: 11/16/2012] [Indexed: 11/18/2022] Open
Abstract
Sensing membrane curvature allows fine-tuning of complex reactions that occur at the surface of membrane-bound organelles. One of the most sensitive membrane curvature sensors, the Amphipathic Lipid Packing Sensor (ALPS) motif, does not seem to recognize the curved surface geometry of membranes per se; rather, it recognizes defects in lipid packing that arise from membrane bending. In a companion paper, we show that these defects can be mimicked by introducing conical lipids in a flat lipid bilayer, in agreement with experimental observations. Here, we use molecular-dynamics (MD) simulations to characterize ALPS binding to such lipid bilayers. The ALPS motif recognizes lipid-packing defects by a conserved mechanism: peptide partitioning is driven by the insertion of hydrophobic residues into large packing defects that are preformed in the bilayer. This insertion induces only minor modifications in the statistical distribution of the free packing defects. ALPS insertion is severely hampered when monounsaturated lipids are replaced by saturated lipids, leading to a decrease in packing defects. We propose that the hypersensitivity of ALPS motifs to lipid packing defects results from the repetitive use of hydrophobic insertions along the monotonous ALPS sequence.
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Affiliation(s)
- Stefano Vanni
- Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia-Antipolis and Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7275, Valbonne, France
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123
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Popova AV, Hincha DK. Interactions of the amphiphiles arbutin and tryptophan with phosphatidylcholine and phosphatidylethanolamine bilayers in the dry state. BMC BIOPHYSICS 2013; 6:9. [PMID: 23879885 PMCID: PMC3726346 DOI: 10.1186/2046-1682-6-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Accepted: 04/17/2013] [Indexed: 11/10/2022]
Abstract
BACKGROUND Water is essential for life, but some organisms can survive complete desiccation, while many more survive partial dehydration during drying or freezing. The function of some protective molecules, such as sugars, has been extensively studied, but much less is known about the effects of amphiphiles such as flavonoids and other aromatic compounds. Amphiphiles may be largely soluble under fully hydrated conditions, but will partition into membranes upon removal of water. Little is known about the effects of amphiphiles on membrane stability and how amphiphile structure and function are related. Here, we have used two of the most intensively studied amphiphiles, tryptophan (Trp) and arbutin (Arb), along with their isolated hydrophilic moieties glycine (Gly) and glucose (Glc) to better understand structure-function relationships in amphiphile-membrane interactions in the dry state. RESULTS Fourier-transform infrared (FTIR) spectroscopy was used to measure gel-to-liquid crystalline phase transition temperatures (Tm) of liposomes formed from phosphatidylcholine and phosphatidylethanolamine in the presence of the different additives. In anhydrous samples, both Glc and Arb strongly depressed Tm, independent of lipid composition, while Gly had no measurable effect. Trp, on the other hand, either depressed or increased Tm, depending on lipid composition. We found no evidence for strong interactions of any of the compounds with the lipid carbonyl or choline groups, while all additives except Gly seemed to interact with the phosphate groups. In the case of Arb and Glc, this also had a strong effect on the sugar OH vibrations in the FTIR spectra. In addition, vibrations from the hydrophobic indole and phenol moieties of Trp and Arb, respectively, provided evidence for interactions with the lipid bilayers. CONCLUSIONS The two amphiphiles Arb and Trp interact differently with dry bilayers. The interactions of Arb are dominated by contributions of the Glc moiety, while the indole governs the effects of Trp. In addition, only Trp-membrane interactions showed a strong influence of lipid composition. Further investigations, using the large structural diversity of plant amphiphiles will help to understand how their structure determines the interaction with membranes and how that influences their biological functions, for example under freezing or dehydration conditions.
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Affiliation(s)
- Antoaneta V Popova
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam, Germany.
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124
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Ouberai MM, Wang J, Swann MJ, Galvagnion C, Guilliams T, Dobson CM, Welland ME. α-Synuclein senses lipid packing defects and induces lateral expansion of lipids leading to membrane remodeling. J Biol Chem 2013; 288:20883-20895. [PMID: 23740253 DOI: 10.1074/jbc.m113.478297] [Citation(s) in RCA: 156] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
There is increasing evidence for the involvement of lipid membranes in both the functional and pathological properties of α-synuclein (α-Syn). Despite many investigations to characterize the binding of α-Syn to membranes, there is still a lack of understanding of the binding mode linking the properties of lipid membranes to α-Syn insertion into these dynamic structures. Using a combination of an optical biosensing technique and in situ atomic force microscopy, we show that the binding strength of α-Syn is related to the specificity of the lipid environment (the lipid chemistry and steric properties within a bilayer structure) and to the ability of the membranes to accommodate and remodel upon the interaction of α-Syn with lipid membranes. We show that this interaction results in the insertion of α-Syn into the region of the headgroups, inducing a lateral expansion of lipid molecules that can progress to further bilayer remodeling, such as membrane thinning and expansion of lipids out of the membrane plane. We provide new insights into the affinity of α-Syn for lipid packing defects found in vesicles of high curvature and in planar membranes with cone-shaped lipids and suggest a comprehensive model of the interaction between α-Syn and lipid bilayers. The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking.
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Affiliation(s)
- Myriam M Ouberai
- From the Nanoscience Centre, Department of Engineering, University of Cambridge, Cambridge CB3 0FF, United Kingdom,.
| | - Juan Wang
- the Farfield Group Ltd., Biolin Scientific, Voyager, Chicago Avenue, Manchester M90 3DQ, United Kingdom, and
| | - Marcus J Swann
- the Farfield Group Ltd., Biolin Scientific, Voyager, Chicago Avenue, Manchester M90 3DQ, United Kingdom, and
| | - Celine Galvagnion
- the Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Tim Guilliams
- the Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Christopher M Dobson
- the Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Mark E Welland
- From the Nanoscience Centre, Department of Engineering, University of Cambridge, Cambridge CB3 0FF, United Kingdom
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125
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Bouvet S, Golinelli-Cohen MP, Contremoulins V, Jackson CL. Targeting of the Arf-GEF GBF1 to lipid droplets and Golgi membranes. J Cell Sci 2013; 126:4794-805. [DOI: 10.1242/jcs.134254] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Lipid droplet metabolism and secretory pathway trafficking both require activation of the Arf1 small G protein. The spatio-temporal regulation of Arf1 activation is mediated by guanine nucleotide exchange factors (GEFs) of the GBF and BIG families, but the mechanisms of their localization to multiple sites within cells are poorly understood. Here we show that GBF1 has a lipid-binding domain (HDS1) immediately downstream of the catalytic Sec7 domain, which mediates association with both lipid droplets and Golgi membranes in cells, and with bilayer liposomes and artificial droplets in vitro. An amphipathic helix within HDS1 is necessary and sufficient for lipid binding, both in vitro and in cells. The HDS1 domain of GBF1 is stably associated with lipid droplets in cells, and the catalytic Sec7 domain inhibits this potent lipid droplet binding capacity. Additional sequences upstream of the Sec7 domain-HDS1 tandem are required for localization to Golgi membranes. This mechanism provides insight into crosstalk between lipid droplet function and secretory trafficking.
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