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Iriondo MN, Etxaniz A, Antón Z, Montes LR, Alonso A. Molecular and mesoscopic geometries in autophagosome generation. A review. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183731. [PMID: 34419487 DOI: 10.1016/j.bbamem.2021.183731] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 08/12/2021] [Accepted: 08/15/2021] [Indexed: 01/18/2023]
Abstract
Autophagy is an essential process in cell self-repair and survival. The centre of the autophagic event is the generation of the so-called autophagosome (AP), a vesicle surrounded by a double membrane (two bilayers). The AP delivers its cargo to a lysosome, for degradation and re-use of the hydrolysis products as new building blocks. AP formation is a very complex event, requiring dozens of specific proteins, and involving numerous instances of membrane biogenesis and architecture, including membrane fusion and fission. Many stages of AP generation can be rationalised in terms of curvature, both the molecular geometry of lipids interpreted in terms of 'intrinsic curvature', and the overall mesoscopic curvature of the whole membrane, as observed with microscopy techniques. The present contribution intends to bring together the worlds of biophysics and cell biology of autophagy, in the hope that the resulting cross-pollination will generate abundant fruit.
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Affiliation(s)
- Marina N Iriondo
- Instituto Biofisika (CSIC, UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48940 Leioa, Spain
| | - Asier Etxaniz
- Instituto Biofisika (CSIC, UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48940 Leioa, Spain
| | - Zuriñe Antón
- Instituto Biofisika (CSIC, UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48940 Leioa, Spain
| | - L Ruth Montes
- Instituto Biofisika (CSIC, UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48940 Leioa, Spain
| | - Alicia Alonso
- Instituto Biofisika (CSIC, UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, 48940 Leioa, Spain.
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2
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Artetxe I, Ugarte-Uribe B, Gil D, Valle M, Alonso A, García-Sáez AJ, Goñi FM. Does Ceramide Form Channels? The Ceramide-Induced Membrane Permeabilization Mechanism. Biophys J 2017; 113:860-868. [PMID: 28834722 DOI: 10.1016/j.bpj.2017.06.071] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 04/10/2017] [Accepted: 06/06/2017] [Indexed: 12/30/2022] Open
Abstract
Ceramide is a sphingolipid involved in several cellular processes, including apoptosis. It has been proposed that ceramide forms large and stable channels in the mitochondrial outer membrane that induce cell death through direct release of cytochrome c. However, this mechanism is still debated because the membrane permeabilizing activity of ceramide remains poorly understood. To determine whether the mechanism of ceramide-induced membrane leakage is consistent with the hypothesis of an apoptotic ceramide channel, we have used here assays of calcein release from liposomes. When assaying liposomes containing sphingomyelin and cholesterol, we observed an overall gradual phenomenon of contents release, together with some all-or-none leakage (at low ceramide concentrations or short times). The presence of channels in the bilayer should cause only an all-or-none leakage. When liposomes poor in sphingomyelin/cholesterol or mimicking the lipid composition of the mitochondrial outer membrane were tested, we did not detect any leakage. In consequence, the hypothesis of formation of large ceramide channels in the membrane is not consistent with our results. Instead we propose that the presence of ceramide in one of the membrane monolayers causes a surface area mismatch between both monolayers, which leads to vesicle collapse. The gradual phenomenon of calcein release would be due to a competition between two ceramide effects; namely, lateral segregation that facilitates permeabilization, and at longer times, trans-bilayer flip-flop that opposes asymmetric lateral segregation and causes a mismatch.
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Affiliation(s)
- Ibai Artetxe
- Biofisika Institute (CSIC, UPV/EHU) and Department of Biochemistry, University of the Basque Country, Leioa, Spain
| | - Begoña Ugarte-Uribe
- Membrane Biophysics, Interfaculty Institute of Biochemistry, Eberhard Karls University Tübingen, Tübingen, Germany
| | - David Gil
- Structural Biology Unit, Center for Cooperative Research in Biosciences, CIC bioGUNE, Derio, Spain
| | - Mikel Valle
- Structural Biology Unit, Center for Cooperative Research in Biosciences, CIC bioGUNE, Derio, Spain
| | - Alicia Alonso
- Biofisika Institute (CSIC, UPV/EHU) and Department of Biochemistry, University of the Basque Country, Leioa, Spain
| | - Ana J García-Sáez
- Membrane Biophysics, Interfaculty Institute of Biochemistry, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Félix M Goñi
- Biofisika Institute (CSIC, UPV/EHU) and Department of Biochemistry, University of the Basque Country, Leioa, Spain.
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3
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Casas J, Ibarguren M, Álvarez R, Terés S, Lladó V, Piotto SP, Concilio S, Busquets X, López DJ, Escribá PV. G protein-membrane interactions II: Effect of G protein-linked lipids on membrane structure and G protein-membrane interactions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1526-1535. [PMID: 28411171 DOI: 10.1016/j.bbamem.2017.04.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 03/21/2017] [Accepted: 04/09/2017] [Indexed: 10/19/2022]
Abstract
G proteins often bear myristoyl, palmitoyl and isoprenyl moieties, which favor their association with the membrane and their accumulation in G Protein Coupled Receptor-rich microdomains. These lipids influence the biophysical properties of membranes and thereby modulate G protein binding to bilayers. In this context, we showed here that geranylgeraniol, but neither myristate nor palmitate, increased the inverted hexagonal (HII) phase propensity of phosphatidylethanolamine-containing membranes. While myristate and palmitate preferentially associated with phosphatidylcholine membranes, geranylgeraniol favored nonlamellar-prone membranes. In addition, Gαi1 monomers had a higher affinity for lamellar phases, while Gβγ and Gαβγ showed a marked preference for nonlamellar prone membranes. Moreover, geranylgeraniol enhanced the binding of G protein dimers and trimers to phosphatidylethanolamine-containing membranes, yet it decreased that of monomers. By contrast, both myristate and palmitate increased the Gαi1 preference for lamellar membranes. Palmitoylation reinforced the binding of the monomer to PC membranes and myristoylation decreased its binding to PE-enriched bilayer. Finally, binding of dimers and trimers to lamellar-prone membranes was decreased by palmitate and myristate, but it was increased in nonlamellar-prone bilayers. These results demonstrate that co/post-translational G protein lipid modifications regulate the membrane lipid structure and that they influence the physico-chemical properties of membranes, which in part explains why G protein subunits sort to different plasma membrane domains. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
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Affiliation(s)
- Jesús Casas
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain
| | - Maitane Ibarguren
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain; Lipopharma Therapeutics, S.L., ParcBit, 07121 Palma de Mallorca, Spain
| | - Rafael Álvarez
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain
| | - Silvia Terés
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain; Lipopharma Therapeutics, S.L., ParcBit, 07121 Palma de Mallorca, Spain
| | - Victoria Lladó
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain
| | - Stefano P Piotto
- Department of Pharmacy, University of Salerno, Via Ponte don Melillo, 84084 Fisciano, SA, Italy
| | - Simona Concilio
- Department of Industrial Engineering, University of Salerno, Via Ponte don Melillo, 84084 Fisciano, SA, Italy
| | - Xavier Busquets
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain
| | - David J López
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain; Lipopharma Therapeutics, S.L., ParcBit, 07121 Palma de Mallorca, Spain.
| | - Pablo V Escribá
- Laboratory of Molecular Cell Biomedicine, Department of Biology, University of the Balearic Islands, E-07122 Palma de Mallorca, Spain
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Ahyayauch H, Sot J, Collado MI, Huarte N, Requejo-Isidro J, Alonso A, Goñi FM. End-product diacylglycerol enhances the activity of PI-PLC through changes in membrane domain structure. Biophys J 2016; 108:1672-1682. [PMID: 25863059 DOI: 10.1016/j.bpj.2015.02.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 01/28/2015] [Accepted: 02/12/2015] [Indexed: 11/25/2022] Open
Abstract
Diacylglycerol (DAG)-induced activation of phosphatidylinositol-phospholipase C (PI-PLC) was studied with vesicles containing PI, either pure or in mixtures with dimyristoyl phosphatidylcholine, distearoyl phosphatidylcholine, sphingomyelin, or galactosylceramide, used as substrates. At 22°C, DAG at 33 mol % increased PI-PLC activity in all of the mixtures, but not in pure PI bilayers. DAG also caused an overall decrease in diphenylhexatriene fluorescence polarization (decreased molecular order) in all samples, and increased overall enzyme binding. Confocal fluorescence microscopy of giant unilamellar vesicles of all of the compositions under study, with or without DAG, and quantitative evaluation of the phase behavior using Laurdan generalized polarization, and of enzyme binding to the various domains, indicated that DAG activates PI-PLC whenever it can generate fluid domains to which the enzyme can bind with high affinity. In the specific case of PI/dimyristoyl phosphatidylcholine bilayers at 22°C, DAG induced/increased enzyme binding and activation, but no microscopic domain separation was observed. The presence of DAG-generated nanodomains, or of DAG-induced lipid packing defects, is proposed instead for this system. In PI/galactosylceramide mixtures, DAG may exert its activation role through the generation of small vesicles, which PI-PLC is known to degrade at higher rates. In general, our results indicate that global measurements obtained using fluorescent probes in vesicle suspensions in a cuvette are not sufficient to elucidate DAG effects that take place at the domain level. The above data reinforce the idea that DAG functions as an important physical agent in regulating membrane and cell properties.
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Affiliation(s)
- Hasna Ahyayauch
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain; Institut Supérieur des Professions Infirmières et des Techniques de Santé, Rabat, Morocco
| | - Jesús Sot
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain
| | - M Isabel Collado
- SGiker, Servicios Generales de Investigación UPV/EHU, Bizkaia, Spain
| | - Nerea Huarte
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain
| | - José Requejo-Isidro
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain
| | - Alicia Alonso
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain
| | - Félix M Goñi
- Unidad de Biofísica (CSIC, UPV/EHU), Universidad del País Vasco, Bilbao, Spain; Departamento de Bioquímica, Universidad del País Vasco, Bilbao, Spain.
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Jewell SA, Titball RW, Huyet J, Naylor CE, Basak AK, Gologan P, Winlove CP, Petrov PG. Clostridium perfringensα-toxin interaction with red cells and model membranes. SOFT MATTER 2015; 11:7748-7761. [PMID: 26303814 DOI: 10.1039/c5sm00876j] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The effects of Clostridium perfringensα-toxin on host cells have previously been studied extensively but the biophysical processes associated with toxicity are poorly understood. The work reported here shows that the initial interaction between the toxin and lipid membrane leads to measurable changes in the physical properties and morphology of the membrane. A Langmuir monolayer technique was used to assess the response of different lipid species to toxin. Sphingomyelin and unsaturated phosphatidylcholine showed the highest susceptibility to toxin lypolitic action, with a two stage response to the toxin (an initial, rapid hydrolysis stage followed by the insertion and/or reorganisation of material in the monolayer). Fluorescence confocal microscopy on unsaturated phosphatidylcholine vesicles shows that the toxin initially aggregates at discrete sites followed by the formation of localised "droplets" accumulating the hydrolysis products. This process is accompanied by local increases in the membrane dipole potential by about 50 (±42) mV. In contrast, red blood cells incubated with the toxin suffered a decrease of the membrane dipole potential by 50 (±40) mV in areas of high toxin activity (equivalent to a change in electric field strength of 10(7) V m(-1)) which is sufficient to affect the functioning of the cell membrane. Changes in erythrocyte morphology caused by the toxin are presented, and the early stages of interaction between toxin and membrane are characterised using thermal shape fluctuation analysis of red cells which revealed two distinct regimes of membrane-toxin interaction.
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Affiliation(s)
- S A Jewell
- School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
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Bagatolli LA, Needham D. Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles. Chem Phys Lipids 2014; 181:99-120. [PMID: 24632023 DOI: 10.1016/j.chemphyslip.2014.02.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 02/25/2014] [Accepted: 02/26/2014] [Indexed: 12/01/2022]
Abstract
This manuscript discusses basic methodological aspects of optical microscopy and micromanipulation methods to study membranes and reviews methods to generate giant unilamellar vesicles (GUVs). In particular, we focus on the use of fluorescence microscopy and micropipet manipulation techniques to study composition-structure-property materials relationships of free-standing lipid bilayer membranes. Because their size (∼5-100 μm diameter) that is well above the resolution limit of regular light microscopes, GUVs are suitable membrane models for optical microscopy and micromanipulation experimentation. For instance, using different fluorescent reporters, fluorescence microscopy allows strategies to study membrane lateral structure/dynamics at the level of single vesicles of diverse compositions. The micropipet manipulation technique on the other hand, uses Hoffman modulation contrast microscopy and allows studies on the mechanical, thermal, molecular exchange and adhesive-interactive properties of compositionally different membranes under controlled environmental conditions. The goal of this review is to (i) provide a historical perspective for both techniques; (ii) present and discuss some of their most important contributions to our understanding of lipid bilayer membranes; and (iii) outline studies that would utilize both techniques simultaneously on the same vesicle thus bringing the ability to characterize structure and strain responses together with the direct application of well-defined stresses to a single membrane or observe the effects of adhesive spreading. Knowledge gained by these studies has informed several applications of lipid membranes including their use as lung surfactants and drug delivery systems for cancer.
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Affiliation(s)
- Luis A Bagatolli
- Membrane Biophysics and Biophotonics Group/MEMPHYS - Center for Biomembrane Physics, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark.
| | - David Needham
- DNRF Niels Bohr Professorship, Center for Single Particle Science and Engineering, Institute for Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark; Department of Mechanical Engineering and Material Science, Duke University, Durham, NC, USA
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Lin CY, Chao L. Tunable nucleation time of functional sphingomyelinase--lipid features studied by membrane array statistic tool. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:13008-17. [PMID: 24059643 DOI: 10.1021/la401826b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Aggregation or assembly of lipids and proteins could significantly change the proteins' function. A peripheral membrane enzyme, sphingomyelinase (SMase), has been reported to be able to assemble to a functional feature with its lipid substrate, sphingomyelin (SM), and its lipid product, ceramide (Cer). SMase seems to processes its substrate more effectively in this feature. Here, we report that the functional feature has a tunable formation time. The peculiar behavior is that the feature formation has a time lag depending on the membrane composition. We hypothesized that the time lag is due to the significant nucleation energy barrier when the feature phase forms in its metastable parent phase in the 2-D lipid membrane. To study the stochastic nucleation of the feature, we built a corralled lipid membrane platform with numerous isolated membrane systems in parallel to capture the nucleation statistics. Using the high-throughput approach and the appropriate experimental design to circumvent the interplay of the complicated phase segregation in membranes induced by SMase, we found that the nucleation rate of the feature can be tuned by the supersaturation of the enzyme, the lipid substrate, and the lipid product, in the fluid phase of the membrane. The correlation between the supersaturation and the nucleation rate can be well described by the classical nucleation theory equation, suggesting that the feature formation follows the nucleation process with a certain component ratio specified in the equation. The certain relative component ratio suggests that the feature may have certain organization instead of being random aggregation. In addition, our finding suggests that nucleation could serve as a time lag control mechanism in this enzymatic system, and ways to reduce nucleation energy barrier could be used to shorten the aggregation time lag and vice versa.
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Affiliation(s)
- Charng-Yu Lin
- Department of Chemical Engineering, National Taiwan University , Taipei 106, Taiwan
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Ibarguren M, López DJ, Encinar JA, González-Ros JM, Busquets X, Escribá PV. Partitioning of liquid-ordered/liquid-disordered membrane microdomains induced by the fluidifying effect of 2-hydroxylated fatty acid derivatives. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2553-63. [PMID: 23792066 DOI: 10.1016/j.bbamem.2013.06.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Revised: 05/19/2013] [Accepted: 06/10/2013] [Indexed: 01/15/2023]
Abstract
Cellular functions are usually associated with the activity of proteins and nucleic acids. Recent studies have shown that lipids modulate the localization and activity of key membrane-associated signal transduction proteins, thus regulating the cell's physiology. Membrane Lipid Therapy aims to reverse cell dysfunctions (i.e., diseases) by modulating the activity of membrane signaling proteins through regulation of the lipid bilayer structure. The present work shows the ability of a series of 2-hydroxyfatty acid (2OHFA) derivatives, varying in the acyl chain length and degree of unsaturation, to regulate the membrane lipid structure. These molecules have shown greater therapeutic potential than their natural non-hydroxylated counterparts. We demonstrated that both 2OHFA and natural FAs induced reorganization of lipid domains in model membranes of POPC:SM:PE:Cho, modulating the liquid-ordered/liquid-disordered structures ratio and the microdomain lipid composition. Fluorescence spectroscopy, confocal microscopy, Fourier transform infrared spectroscopy and differential detergent solubilization experiments showed a destabilization of the membranes upon addition of the 2OHFAs and FAs which correlated with the observed disordering effect. The changes produced by these synthetic fatty acids on the lipid structure may constitute part of their mechanism of action, leading to changes in the localization/activity of membrane proteins involved in signaling cascades, and therefore modulating cell responses.
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Affiliation(s)
- Maitane Ibarguren
- Laboratory of Molecular Cell Biomedicine, University of the Balearic Islands-Lipopharma Therapeutics, S.L., Palma, Spain
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Ibarguren M, Sot J, Montes LR, Vasil AI, Vasil ML, Goñi FM, Alonso A. Recruitment of a phospholipase C/sphingomyelinase into non-lamellar lipid droplets during hydrolysis of lipid bilayers. Chem Phys Lipids 2012; 166:12-7. [PMID: 23253877 DOI: 10.1016/j.chemphyslip.2012.12.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 11/30/2012] [Accepted: 12/01/2012] [Indexed: 01/05/2023]
Abstract
When giant unilamellar vesicles (GUVs) composed of sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, and cholesterol are treated with PlcHR(2), a phospholipase C/sphingomyelinase from Pseudomonas aeruginosa, the initial stages of lipid hydrolysis do not cause large changes in vesicle morphology (Ibarguren et al., 2011). However, when hydrolysis progresses confocal fluorescence microscopy reveals the formation of lipid aggregates, whose morphology is not compatible with that of bilayers. Smaller vesicles or droplets can also be seen inside the GUV. Our studies indicate that these aggregates or droplets are enriched in the non-lamellar lipid ceramide, an end-product of PlcHR(2) reaction. Moreover, the aggregates/droplets appear enriched in the hydrolytic enzyme PlcHR(2). At a final stage GUVs containing the enzyme-enriched droplets disintegrate and vanish from the microscope field. The observed non-lamellar enzyme-rich structures may be related to intermediates in the process of aggregation and fusion although the experimental design prevents vesicle free diffusion in the aqueous medium, thus actual aggregation or fusion cannot be observed.
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Affiliation(s)
- Maitane Ibarguren
- Unidad de Biofísica (Centro Mixto CSIS-UPV/EHU), Departamento de Bioquímica, Universidad del País Vasco, Barrio Sarriena s/n, 48940 Bilbao, Spain
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10
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Goñi FM, Montes LR, Alonso A. Phospholipases C and sphingomyelinases: Lipids as substrates and modulators of enzyme activity. Prog Lipid Res 2012; 51:238-66. [DOI: 10.1016/j.plipres.2012.03.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/23/2012] [Accepted: 03/26/2012] [Indexed: 11/30/2022]
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Campelo F, Cruz A, Pérez-Gil J, Vázquez L, Hernández-Machado A. Phase-field model for the morphology of monolayer lipid domains. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2012; 35:49. [PMID: 22714836 DOI: 10.1140/epje/i2012-12049-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Revised: 11/08/2011] [Accepted: 06/01/2012] [Indexed: 06/01/2023]
Abstract
Phase-separated domains exist in multicomponent lipid monolayers and bilayers. We present here a phase-field model that takes into account the competition between lipid dipole-dipole interactions and line tension to define the domain morphology. A dynamic equation for the phase-field is solved numerically showing stationary non-circular shapes like starfish shapes. This phase-field model could be applied to study the dynamic properties of complex problems like phase segregation in pulmonary surfactant membranes and films.
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Affiliation(s)
- F Campelo
- Department of Cell and Developmental Biology, Center for Genomic Regulation (CRG) and UPF, Barcelona, Spain.
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12
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Robinson P, Etheridge S, Song L, Shah R, Fitzgerald EM, Jones OT. Targeting of voltage-gated calcium channel α2δ-1 subunit to lipid rafts is independent from a GPI-anchoring motif. PLoS One 2011; 6:e19802. [PMID: 21695204 PMCID: PMC3112168 DOI: 10.1371/journal.pone.0019802] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Accepted: 04/14/2011] [Indexed: 12/12/2022] Open
Abstract
Voltage-gated calcium channels (Cav) exist as heteromultimers comprising a pore-forming α1 with accessory β and α2δ subunits which modify channel trafficking and function. We previously showed that α2δ-1 (and likely the other mammalian α2δ isoforms - α2δ-2, 3 and 4) is required for targeting Cavs to lipid rafts, although the mechanism remains unclear. Whilst originally understood to have a classical type I transmembrane (TM) topology, recent evidence suggests the α2δ subunit contains a glycosylphosphatidylinositol (GPI)-anchor that mediates its association with lipid rafts. To test this notion, we have used a strategy based on the expression of chimera, where the reported GPI-anchoring sequences in the gabapentinoid-sensitive α2δ-1 subunit have been substituted with those of a functionally inert Type I TM-spanning protein – PIN-G. Using imaging, electrophysiology and biochemistry, we find that lipid raft association of PIN-α2δ is unaffected by substitution of the GPI motif with the TM domain of PIN-G. Moreover, the presence of the GPI motif alone is not sufficient for raft localisation, suggesting that upstream residues are required. GPI-anchoring is susceptible to phosphatidylinositol-phospholipase C (PI-PLC) cleavage. However, whilst raft localisation of PIN-α2δ is disrupted by PI-PLC treatment, this is assay-dependent and non-specific effects of PI-PLC are observed on the distribution of the endogenous raft marker, caveolin, but not flotillin. Taken together, these data are most consistent with a model where α2δ-1 retains its type I transmembrane topology and its targeting to lipid rafts is governed by sequences upstream of the putative GPI anchor, that promote protein-protein, rather than lipid-lipid interactions.
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Affiliation(s)
- Philip Robinson
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
| | - Sarah Etheridge
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
| | - Lele Song
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
| | - Riddhi Shah
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
| | - Elizabeth M. Fitzgerald
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
- * E-mail: (OTJ); (EMF)
| | - Owen T. Jones
- Faculty of Life Sciences,University of Manchester,Core Technology Facility, Manchester, United Kingdom
- * E-mail: (OTJ); (EMF)
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