2018 |
Bacellar, I. O. L., Baptista, M. S., Junqueira, H. C., Wainwright, M., Thalmann, F., Marques, C. M., et al. (2018). Permeability of DOPC bilayers under photoinduced oxidation: Sensitivity to photosensitizer. Biochim Biophys Acta, .
Abstract: The modification of lipid bilayer permeability is one of the most striking yet poorly understood physical transformations that follow photoinduced lipid oxidation. We have recently proposed that the increase of permeability of photooxidized 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers is controlled by the time required by the oxidized lipid species to diffuse and aggregate into pores. Here we further probe this mechanism by studying photosensitization of DOPC membranes by methylene blue (MB) and DO15, a more hydrophobic phenothiazinium photosensitizer, under different irradiation powers. Our results not only reveal the interplay between the production rate and the diffusion of the oxidized lipids, but highlight also the importance of photosensitizer localization in the kinetics of oxidized membrane permeability.
Keywords: Lipid photooxidation; Membrane permeabilization; Model membrane; Phenothiazinium photosensitizers; Pore formation
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de Oliveira, T. E., Marques, C. M., & Netz, P. A. (2018). Molecular dynamics study of the LCST transition in aqueous poly(N-n-propylacrylamide). Phys Chem Chem Phys, 20(15), 10100–10107.
Abstract: The breadth of technological applications of smart polymers relies on the possibility of tuning their molecular structure to respond to external stimuli. In this context, N-substituted acrylamide-based polymers are widely studied thermoresponsive polymers. Poly(N-n-propylacrylamide) (PNnPAm), which is a structural isomer of the poly(N-isopropylacrylamide) (PNIPAm) exhibits however, a lower phase transition in aqueous solution. In this work, we use all-atom molecular dynamics simulations of PNnPAm in aqueous solutions to study, from a microscopic point-of-view, the influence of chain size and concentration on the LCST of PNnPAm. Our analysis shows that the collapse of a single oligomer of PNnPAm upon heating is dependent on the chain length and corresponds to a complex interplay between hydration and intermolecular interactions. Analysis of systems with multiple chains shows an aggregation of PNnPAm chains above the LCST.
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Kluzek, M., Schmutz, M., Marques, C. M., & Thalmann, F. (2018). Kinetic evolution of DOPC lipid bilayers exposed to alpha-cyclodextrins. Soft Matter, 14(28), 5800–5810.
Abstract: Cyclodextrins are cyclic oligosaccharides capable of forming inclusion complexes with a variety of molecules, and as such have been recognized as a pharmaceutical and biotechnological asset. Cyclodextrins are known to interact with the components of cell membranes, and this correlates with a significant degree of cytotoxicity. In this work, we report on the mechanism of degradation of a model dioleoyl-phosphatidylcholine (DOPC) bilayer exposed to a solution with increasing concentrations of alpha-cyclodextrins. By combining optical fluorescence microscopy and quartz-crystal microbalance experiments, we study the evolution of supported lipid bilayers (SLBs) and giant unilamellar vesicles (GUVs). The rate of lipid removal is found to display a strong nonlinear dependence on the cyclodextrin concentration. A mechanism involving lipid aggregates is proposed.
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Morandi, M. I., Sommer, M., Kluzek, M., Thalmann, F., Schroder, A. P., & Marques, C. M. (2018). DPPC Bilayers in Solutions of High Sucrose Content. Biophys J, 114(9), 2165–2173.
Abstract: The properties of lipid bilayers in sucrose solutions have been intensely scrutinized over recent decades because of the importance of sugars in the field of biopreservation. However, a consensus has not yet been formed on the mechanisms of sugar-lipid interaction. Here, we present a study on the effect of sucrose on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayers that combines calorimetry, spectral fluorimetry, and optical microscopy. Intriguingly, our results show a significant decrease in the transition enthalpy but only a minor shift in the transition temperature. Our observations can be quantitatively accounted for by a thermodynamic model that assumes partial delayed melting induced by sucrose adsorption at the membrane interface.
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Mukherji, D., Marques, C. M., & Kremer, K. (2018). Collapse in two good solvents, swelling in two poor solvents: defying the laws of polymer solubility? Journal Of Physics-Condensed Matter, 30(2).
Abstract: In this work we discuss two mirror but distinct phenomena of polymer paradoxical properties in mixed solvents: co-non-solvency and co-solvency. When a polymer collapses in a mixture of two miscible good solvents the phenomenon is known as co-non-solvency, while co-solvency is a phenomenon that is associated with the swelling of a polymer in poor solvent mixtures. A typical example of co-non-solvency is provided by poly(N-isopropylacrylamide) in aqueous alcohol, while poly(methyl methacrylate) in aqueous alcohol shows co-solvency. We discuss these two phenomena to compare their microscopic origins and show that both can be understood within generic universal concepts. A broad range of polymers is therefore expected to exhibit these phenomena where specific chemical details play a lesser role than the appropriate combination of interactions between the trio of molecular components.
Keywords: coil-globule transition; mixed solvents; smart responsive polymers
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2017 |
Blachon, F., Harb, F., Munteanu, B., Piednoir, A., Fulcrand, R., Charitat, T., et al. (2017). Nanoroughness Strongly Impacts Lipid Mobility in Supported Membranes. Langmuir, 33(9), 2444–2453.
Abstract: In vivo lipid membranes interact with rough supramolecular structures such as protein clusters and fibrils. How these features whose size ranges from a few nanometers to a few tens of nanometers impact lipid and protein mobility is still being investigated. Here, we study supported phospholipid bilayers, a unique biomimetic model, deposited on etched surfaces bearing nanometric corrugations. The surface roughness and mean curvature are carefully characterized by AFM imaging using ultrasharp tips. Neutron specular reflectivity supplements this surface characterization and indicates that the bilayers follow the large-scale corrugations of the substrate. We measure the lateral mobility of lipids in both the fluid and gel phases by fluorescence recovery after patterned photobleaching. Although the mobility is independent of the roughness in the gel phase, it exhibits a 5-fold decrease in the fluid phase when the roughness increases from 0.2 to 10 nm. These results are interpreted with a two-phase model allowing for a strong decrease in the lipid mobility in highly curved or defect-induced gel-like nanoscale regions. This suggests a strong link between membrane curvature and fluidity, which is a key property for various cell functions such as signaling and adhesion.
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Weinberger, A., Walter, V., MacEwan, S. R., Schmatko, T., Muller, P., Schroder, A. P., et al. (2017). Cargo self-assembly rescues affinity of cell-penetrating peptides to lipid membranes. Sci Rep, 7, 43963.
Abstract: Although cationic cell-penetrating peptides (CPPs) are able to bind to cell membranes, thus promoting cell internalization by active pathways, attachment of cargo molecules to CPPs invariably reduces their cellular uptake. We show here that CPP binding to lipid bilayers, a simple model of the cell membrane, can be recovered by designing cargo molecules that self-assemble into spherical micelles and increase the local interfacial density of CPP on the surface of the cargo. Experiments performed on model giant unilamellar vesicles under a confocal laser scanning microscope show that a family of thermally responsive elastin-like polypeptides that exhibit temperature-triggered micellization can promote temperature triggered attachment of the micelles to membranes, thus rescuing by self-assembly the cargo-induced loss of the CPP affinity to bio-membranes.
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2016 |
Guo, Y., Baulin, V. A., & Thalmann, F. (2016). Peroxidised phospholipid bilayers: insight from coarse-grained molecular dynamics simulations. Soft Matter, 12(1), 263–271.
Abstract: An original coarse-grained model for peroxidised phospholipids is presented, based on the MARTINI lipid force field. This model results from a combination of thermodynamic modelling and structural information on the area per lipid, which have been made available recently. The resulting coarse-grained lipid molecules form stable bilayers, and a set of elastic coefficients (compressibility and bending moduli) is obtained. We compare the compressibility coefficient to the experimental values [Weber et al., Soft Matter, 2014, 10, 4241]. Predictions for the mechanical properties, membrane thickness and lateral distribution of hydroperoxide groups in the phospholipid bilayer are presented.
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Hemmerle, A., Fragneto, G., Daillant, J., & Charitat, T. (2016). Reduction in Tension and Stiffening of Lipid Membranes in an Electric Field Revealed by X-Ray Scattering. Phys Rev Lett, 116(22), 228101.
Abstract: The effect of ac electric fields on the elasticity of supported lipid bilayers is investigated at the microscopic level using grazing incidence synchrotron x-ray scattering. A strong decrease in the membrane tension up to 1 mN/m and a dramatic increase of its effective rigidity up to 300 k_{B}T are observed for local electric potentials seen by the membrane less, similar1 V. The experimental results are analyzed using detailed electrokinetic modeling and nonlinear Poisson-Boltzmann theory. Based on a modeling of the electromagnetic stress, which provides an accurate description of the bilayer separation versus pressure curves, we show that the decrease in tension results from the amplification of charge fluctuations on the membrane surface whereas the increase in bending rigidity results from the direct interaction between charges in the electric double layer. These effects eventually lead to a destabilization of the bilayer and vesicle formation. Similar effects are expected at the tens of nanometers length scale in cell membranes with lower tension, and could explain a number of electrically driven processes.
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Micheletto, Y. M. S., Marques, C. M., Silveira, N. P. da, & Schroder, A. P. (2016). Electroformation of Giant Unilamellar Vesicles: Investigating Vesicle Fusion versus Bulge Merging. Langmuir, 32(32), 8123–8130.
Abstract: Partially ordered stacks of phospholipid bilayers on a flat substrate can be obtained by the evaporation of a spread droplet of phospholipid-in-chloroform solution. When exposed to an aqueous buffer, numerous micrometric buds populate the bilayers, grow in size over minutes, and eventually detach, forming the so-called liposomes or vesicles. While observation of vesicle growth from a hydrated lipid film under an optical microscope suggests numerous events of vesicle fusion, there is little experimental evidence for discriminating between merging of connected buds, i.e., a shape transformation that does not imply bilayer fusion and real membrane fusion. Here, we use electroformation to grow giant unilamellar vesicles (GUVs) from a stack of lipids in a buffer containing either (i) nanometric liposomes or (ii) previously prepared GUVs. By combining different fluorescent labels of the lipids in the substrate and in the solution, and by performing a fluorescence analysis of the resulting GUVs, we clearly demonstrate that merging of bulges is the essential pathway for vesicle growth in electroformation.
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Micheletto, Y. M. S., Moro, C. F., Lopes, F. C., Ligabue-Braun, R., Martinelli, A. H. S., Marques, C. M., et al. (2016). Interaction of jack bean (Canavalia ensiformis) urease and a derived peptide with lipid vesicles. Colloids Surf B Biointerfaces, 145, 576–585.
Abstract: Ureases are metalloenzymes that catalyze the hydrolysis of urea to ammonia and carbon dioxide. Jack bean (Canavalia ensiformis) produces three isoforms of urease (Canatoxin, JBU and JBURE-II). Canatoxin and JBU display several biological properties independent of their ureolytic activity, such as neurotoxicity, exocytosis-inducing and pro-inflammatory effects, blood platelets activation, insecticidal and antifungal activities. The Canatoxin entomotoxic activity is mostly due to an internal peptide, named pepcanatox, released upon the hydrolysis of the protein by insect cathepsin-like digestive enzymes. Based on pepcanatox sequence, Jaburetox-2Ec was produced in Escherichia coli. JBU and its peptides were shown to permeabilize membranes through an ion channel-based mechanism. Here we studied the JBU and Jaburetox-2Ec interaction with platelet-like multilamellar liposomes (PML) using Dynamic Light Scattering and Small Angle X-ray Scattering techniques. We also analyzed the interaction of JBU with giant unilamellar vesicles (GUVs) using Fluorescence Microscopy. The interaction of vesicles with JBU led to a slight reduction of hydrodynamic radius, and caused an increase in the lamellar repeat distance of PML, suggesting a membrane disordering effect. In contrast, Jaburetox-2Ec decreased the lamellar repeat distance of PML membranes, while also diminishing their hydrodynamic radius. Fluorescence microscopy showed that the interaction of GUVs with JBU caused membrane perturbation with formation of tethers. In conclusion, JBU can interact with PML, probably by inserting its Jaburetox “domain” into the PML external membrane. Additionally, the interaction of Jaburetox-2Ec affects the vesicle's internal bilayers and hence causes more drastic changes in the PML membrane organization in comparison with JBU.
Keywords: Jaburetox-2Ec; Jack bean urease; Light scattering; Liposomes; Saxs
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2015 |
Aoki, P. H. B., Schroder, A. P., Constantino, C. J. L., & Marques, C. M. (2015). Bioadhesive giant vesicles for monitoring hydroperoxidation in lipid membranes. Soft Matter, 11(30), 5995–5998.
Abstract: Osmotic stresses, protein insertion or lipid oxidation lead to area increase of self-assembled lipid membranes. However, methods to measure membrane expansion are scarce. Challenged by recent progress on the control of phospholipid hydroperoxidation, we introduce a method to quantitatively evaluate membrane area increase based on the bio-adhesion of Giant Unilamellar Vesicles.
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Bauer, M., Kekicheff, P., Iss, J., Fajolles, C., Charitat, T., Daillant, J., et al. (2015). Sliding tethered ligands add topological interactions to the toolbox of ligand-receptor design. Nature Communications, 6.
Abstract: Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand-receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand-receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering.
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Gromer, A., Nassar, M., Thalmann, F., Hebraud, P., & Holl, Y. (2015). Simulation of Latex Film Formation Using a Cell Model in Real Space: Vertical Drying. Langmuir, 31(40), 10983–10994.
Abstract: This paper presents a simulation tool applied to latex film formation by drying, a hybrid between a classical numerical resolution method using finite differences and cellular automata, and making use of object-oriented programming. It consists of dividing real space into cells and applying local physical laws to simulate the exchange of matter between neighboring cells. In a first step, the simulation was applied to the simple case of vertical drying of a latex containing only one population of monodisperse particles and water. Our results show how the distribution of latex particles evolves through the different drying stages due to a combination of diffusion, convection, and particle deformation. While repulsive interactions between the particles tend to favor homogeneous distributions in the first drying stage, concentration gradients that develop in opposite ways can be observed depending on the drying regime. The distributions, calculated in various cases, reproduce and extend several theoretical results and are in qualitative agreement with some experimental findings.
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Hemmerle, A., Froehlicher, G., Bergeron, V., Charitat, T., & Farago, J. (2015). Worm-like instability of a vibrated sessile drop. Epl, 111(2).
Abstract: We study the effects of vertical sinusoidal vibrations on a liquid droplet with a low surface tension (ethanol) deposited on a solid substrate. In a precise range of amplitudes and frequencies, the drop exhibits a dramatic worm-like shape instability with a strong symmetry breaking, comparable to the one observed by Pucci et al. (Phys. Rev. Lett., 106 (2011) 024503) on a vibrated floating lens. However, the geometry of our system is much simpler since it does not involve the oscillation and deformation of a liquid-liquid-air contact line. We show that the Faraday waves appearing on the surface of the droplet control its shape and we draw a systematic phase diagram of the instability. A simple theoretical model allows us to derive a relation between the elongation of the droplet and the amplitude of the Faraday wave, in good agreement with measurements of both quantities. Copyright (C) EPLA, 2015
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