laboratoire de physique statistique
laboratoire de physique statistique


Can We Trust Hydrodynamic Models to Determine the Bilayer Viscosity Experienced by Transmembrane Proteins? - Adrien, Vladimir and Astafyeva, Ksenia and Kuimova, Marina and Urbach, Wladimir and Taulier, Nicolas
Effect of a Cosolvent in Binding Events of Hydrophobic Molecules. An Experimental and Numerical Study - Senac, Caroline and Fuchs, Patrick and Urbach, Wladimir and Taulier, Nicolas
AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity - Sarrazin, Baptiste and Tsapis, Nicolas and Mousnier, Ludivine and Taulier, Nicolas and Urbach, Wladimir and Guenoun, Patrick
LANGMUIR 324610-4618 (2016) 

Abstract : Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer.
FRAP to Characterize Molecular Diffusion and Interaction in Various Membrane Environments - Pincet, Frederic and Adrien, Vladimir and Yang, Rong and Delacotte, Jerome and Rothman, James E. and Urbach, Wladimir and Tareste, David
PLOS ONE 11 (2016) 

Abstract : Fluorescence recovery after photobleaching (FRAP) is a standard method used to study the dynamics of lipids and proteins in artificial and cellular membrane systems. The advent of confocal microscopy two decades ago has made quantitative FRAP easily available to most laboratories. Usually, a single bleaching pattern/area is used and the corresponding recovery time is assumed to directly provide a diffusion coefficient, although this is only true in the case of unrestricted Brownian motion. Here, we propose some general guidelines to perform FRAP experiments under a confocal microscope with different bleaching patterns and area, allowing the experimentalist to establish whether the molecules undergo Brownian motion (free diffusion) or whether they have restricted or directed movements. Using in silico simulations of FRAP measurements, we further indicate the data acquisition criteria that have to be verified in order to obtain accurate values for the diffusion coefficient and to be able to distinguish between different diffusive species. Using this approach, we compare the behavior of lipids in three different membrane platforms (supported lipid bilayers, giant liposomes and sponge phases), and we demonstrate that FRAP measurements are consistent with results obtained using other techniques such as Fluorescence Correlation Spectroscopy (FCS) or Single Particle Tracking (SPT). Finally, we apply this method to show that the presence of the synaptic protein Munc 18-1 inhibits the interaction between the synaptic vesicle SNARE protein, VAMP2, and its partner from the plasma membrane, Syn1A.
Characterization of a Biomimetic Mesophase Composed of Nonionic Surfactants and an Aqueous Solvent - Adrien, V. and Rayan, G. and Reffay, M. and Porcar, L. and Maldonado, A. and Ducruix, A. and Urbach, W. and Taulier, N.
LANGMUIR 3210268-10275 (2016) 

Abstract : We have investigated the physical and biomimetic properties of a sponge (L3) phase composed of pentaethylene glycol monododecyl ether (C12E5), a nonionic surfactant, an aqueous solvent, and a cosurfactant. The following cosurfactants, commonly used for solubilizing membrane proteins, were incorporated: n-octyl-beta-d-glucopyranoside (beta-OG), n-dodecyl-beta-d-maltopyranoside (DDM), 4-cyclohexyl-1-butyl-beta-d-maltoside (CYMAL-4), and 5-cyclohexyl-1-pentyl-beta-d-maltoside (CYMAL-5). Partial phase diagrams of these systems were created. The L3 phase was characterized using crossed polarizers, diffusion of a fluorescent probe by fluorescence recovery after pattern photobleaching (FRAPP), and freeze fracture electron microscopy (FFEM). By varying the hydration of the phase, we were able to tune the distance between adjacent bilayers. The characteristic distance (db) of the phase was obtained from small angle scattering (SAXS/SANS) as well as from FFEM, which yielded complementary db values. These db values were neither affected by the nature of the cosurfactant nor by the addition of membrane proteins. These findings illustrate that a biomimetic surfactant sponge phase can be created in the presence of several common membrane protein-solubilizing detergents, thus making it a versatile medium for membrane protein studies.
Perfluorocarbon nanodroplets stabilized by fluorinated surfactants: characterization and potentiality as theranostic agents - Astafyeva, K. and Somaglino, L. and Desgranges, S. and Berti, R. and Patinote, C. and Langevin, D. and Lazeyras, F. and Salomir, R. and Polidori, A. and Contino-Pepin, C. and Urbach, W. and Taulier, N.

Abstract : We aim to produce emulsions that can act as contrast agents and drug carriers for cancer imaging and therapy. To increase tumor detection and decrease drug side effects, it is desirable to take advantage of the enhanced permeability and retention effect that allows nanoparticles to accumulate in tumor tissues. To do so, the emulsion droplets need to be small enough and stable over time in addition to enhancing image contrast and carrying a drug payload. In the present study, we have investigated the properties and potentiality as theranostic agents of perfluorocarbon emulsions stabilized by a biocompatible fluorinated surfactant called FTAC. To obtain better control of our system, the synthesis of those surfactants was studied and their physico- chemical properties were explored in different configurations such as micelles, in the perfluorocarbon droplet shell and at water/air and water/perfluorocarbon interfaces. The originality of this work lies in the determination of numerous characteristics of emulsions and fluorinated surfactants including surface tension, interfacial tension, critical micelle concentration, adiabatic compressibility, density, size distribution (aging studies), and ultrasonic echogenicity. These characterization studies were conducted using different types of FTAC and several perfluorocarbons (perfluoropentane, perfluorohexane, and perfluorooctyl bromide). We have also shown that a hydrophobic drug could be encapsulated in the FTAC-stabilized perfluorocarbon droplets thanks to triacetin addition. Finally, the perfluorocarbon emulsions were detectable in vitro by a clinical 3 T MRI scanner, equipped with a double frequency F-19/H-1 transmit-receive coil.
Stability of C12Ej Bilayers Probed with Adhesive Droplets - Astafyeva, Ksenia and Urbach, Wladimir and Garroum, Nabil and Taulier, Nicolas and Thiam, Abdou R.
LANGMUIR 316791-6796 (2015) 

Abstract : The stability of model surfactant bilayers from the poly(ethylene glycol) mono-n-dodecyl ether (C12Ej) family was probed. The surfactant bilayers were formed by the adhesion of emulsion droplets. We generated C12Ej bilayers by forming water-in-oil (w/o) emulsions with saline water droplets, covered by the surfactant, in a silicone and octane oil mixture. Using microfluidics, we studied the stability of those bilayers. C12E1 allowed only short-lived bilayers whereas C12E2 bilayers were stable over a wide range of oil mixtures. At high C12E2 concentration, a two-phase region was displayed in the phase diagram: bilayers formed by the adhesion of two water droplets and Janus-like particles consisting of adhering aqueous and amphiphilic droplets. C12E8 and C12E25 did not mediate bilayer formation and caused phase inversion leading to o/w emulsion. With intermediate C12E4 and C12E5 surfactants, both w/o and o/w emulsions were unstable. We provided the titration of the C12E2 bilayer with C12E4 and C12E5 to study and predict their stability behavior.
Correlated Lateral Diffusion of Lipids - Adrien, Vladimir and Rayan, Gamal and Taulier, Nicolas and Urbach, Wladimir
Surfactant Bilayers Maintain Transmembrane Protein Activity - Rayan, Gamal and Adrien, Vladimir and Reffay, Myriam and Picard, Martin and Ducruix, Arnaud and Schmutz, Marc and Urbach, Wladimir and Taulier, Nicolas
BIOPHYSICAL JOURNAL 1071129-1135 (2014) 

Abstract : In vitro studies of membrane proteins are of interest only if their structure and function are significantly preserved. One approach is to insert them into the lipid bilayers of highly viscous cubic phases rendering the insertion and manipulation of proteins difficult. Less viscous lipid sponge phases are sometimes used, but their relatively narrow domain of existence can be easily disrupted by protein insertion. We present here a sponge phase consisting of nonionic surfactant bilayers. Its extended domain of existence and its low viscosity allow easy insertion and manipulation of membrane proteins. We show for the first time, to our knowledge, that transmennbrane proteins, such as bacteriorhodopsin, sarcoplasmic reticulum Ca(2+)ATPase (SERCA1a), and its associated enzymes, are fully active in a surfactant phase.
A New Biomimetic Phase of Surfactant Bilayers Maintains Membrane Protein Activity - Adrien, Vladimir and Rayan, Gamal and Reffay, Myriam and Picard, Martin and Ducruix, Arnaud and Maldonado, Amir and Porcar, Lionel and Taulier, Nicolas and Urbach, Wladimir
Lateral Diffusion and Association of Transmembrane Proteins Inside a Biomimetic Bilayer Mesophase - Rayan, Gamal and Reffay, Myriam and Picard, Martin and Taulier, Nicolas and Ducruix, Arnaud and Urbach, Wladimir
A model for ultrasound absorption and dispersion in dilute suspensions of nanometric contrast agents - Coulouvrat, Francois and Thomas, Jean-Louis and Astafyeva, Ksenia and Taulier, Nicolas and Conoir, Jean-Marc and Urbach, Wladimir

Abstract : Ultrasound dispersion and absorption are examined in dilute suspensions of contrast agents of nanometric size, with a typical radius around 100 nm. These kinds of contrast agents are designed for targeted delivery of drugs for cancer treatment. Compared to standard contrast agents used for imaging, particles are of smaller size to pass through the endothelial barrier, their shell, made up of biocompatible polymer, is stiffer to undergo a longer lifetime, and they have a liquid core instead of a gaseous one. Ultrasound propagation in dilute suspension is modeled by combining two modes for particle oscillations. The first one is a dilatational mode assuming an incompressible shell with a rheological behavior of Kelvin-Voigt or Maxwell type. The second one is a translational mode induced by visco-inertial interaction with the ambient fluid. The relative importance of these two modes of interaction on both dispersion and absorption is quantified and analyzed for a model system and for two radii (75 and 150 nm) and the two rheological models. The influence of shell parameters (Young modulus, viscosity, and relative thickness) is finally discussed. (C) 2012 Acoustical Society of America. []
A versatile Bilayer Phase for the Studies of Transmembrane Proteins' Association - Rayan, Gamal and Reffay, Myriam and Picard, Martin and Taulier, Nicolas and Ducruix, Arnaud and Urbach, Wladimir
Two-dimensional simulation of linear wave propagation in a suspension of polymeric microcapsules used as ultrasound contrast agents - Haiat, Guillaume and Berti, Romain and Galaz, Belfor and Taulier, Nicolas and Amman, Jean-Jacques and Urbach, Wladimir

Abstract : A generation of tissue-specific stable ultrasound contrast agent (UCA) composed of a polymeric capsule with a perfluorocarbone liquid core has become available. Despite promising uses in clinical practice, the acoustical behavior of such UCA suspensions remains unclear. A simulation code (2-D finite-difference time domain, FDTD) already validated for homogeneous particles [Galaz Haiat, Berti, Taulier, Amman and Urbach, (2010). J. Acoust. Soc. Am. 127, 148-154] is used to model the ultrasound propagation in such UCA suspensions at 50 MHz to investigate the sensitivity of the ultrasonic parameters to physical parameters of UCA. The FDTD simulation code is validated by comparison with results obtained using a shell scatterer model. The attenuation coefficient (respectively, the sound velocity) increases (respectively, decreases) from 4.1 to 58.4 dB/cm (respectively, 1495 to 1428 m/s) when the concentration varies between 1.37 and 79.4 mg/ml, while the backscattered intensity increases non-linearly, showing that a concentration of around 30 mg/ml is sufficient to obtain optimal backscattering intensity. The acoustical parameters vary significantly as a function of the membrane thickness, longitudinal and transverse velocity, indicating that mode conversions in the membrane play an important role in the ultrasonic propagation. The results may be used to help manufacturers to conceive optimal liquid-filled UCA suspensions. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3543966]
Experimental validation of a time domain simulation of high frequency ultrasonic propagation in a suspension of rigid particles - Galaz, Belfor and Haiat, Guillaume and Berti, Romain and Taulier, Nicolas and Amman, Jean-Jacques and Urbach, Wladimir

Abstract : Ultrasonic propagation in suspensions of particles is a difficult problem due to the random spatial distribution of the particles. Two-dimensional finite-difference time domain simulations of ultrasonic propagation in suspensions of polystyrene 5.3 mu m diameter microdisks are performed at about 50 MHz. The numerical results are compared with the Faran model, considering an isolated microdisk, leading to a maximum difference of 15\% between the scattering cross-section values obtained analytically and numerically. Experiments are performed with suspensions in through transmission and backscattering modes. The attenuation coefficient at 50 MHz (alpha), the ultrasonic velocity (V), and the relative backscattered intensity (I(B)) are measured for concentrations from 2 to 25 mg/ml, obtained by modifying the number of particles. Each experimental ultrasonic parameter is compared to numerical results obtained by averaging the results derived from 15 spatial distributions of microdisks. alpha increases with the concentration from 1 to 17 dB/cm. IB increases with concentration from 2 to 16 dB. The variation of V versus concentration is compared with the numerical results, as well as with an effective medium model. A good agreement is found between experimental and numerical results (the larger discrepancy is found for alpha with a difference lower than 2.1 dB/cm ). (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3270399]
Modulation of the Lateral Mobility of Transmembrane Peptides with Hydrophobic Mismatch - Gambin, Yann and Reffay, Myriam and Sierecki, Emma and Homble, Francois and Genest, Marc and Hodges, Robert S. and Gov, Nir and Taulier, Nicolas and Urbach, Wladimir
Surfactant Sponge Phase Is a Versatile, Tunable and Biologically Relevant Medium To Study Membrane Protein Interactions - Picard, Martin and Rayan, Gamal and Taulier, Nicolas and Broutin, Isabelle and Ducruix, Arnaud and Urbach, Wladimir
Transmembrane Protein Association in a Biomimetic Medium - Rayan, Gamal and Reffay, Myriam and Picard, Martin and Taulier, Nicolas and Ducruix, Arnaud and Urbach, Wladimir
Variation of the Lateral Mobility of Transmembrane Peptides with Hydrophobic Mismatch - Gambin, Yann and Reffay, Myriam and Sierecki, Emma and Homble, Fabrice and Hodges, Robert S. and Gov, Nir S. and Taulier, Nicolas and Urbach, Wladimir

Abstract : A hydrophobic mismatch between protein length and membrane thickness call lead to a modification of protein conformation, function, and oligomerization. To study the role of hydrophobic mismatch, we have measured the change in mobility of transmembrane peptides possessing a hydrophobic helix of various length d(pi), ill lipid membranes of giant vesicles. We also used a model system where the hydrophobic thickness of the bilayers, h, call be tuned at Will. We precisely Measured the diffusion coefficient of the embedded peptides and gained access to the apparent size of diffusing, objects. For bilayers thinner than d(pi) diffusion coefficient decreases, and the derived characteristic sizes are larger than the peptide radii. Previous studies Suggest that peptides accommodate by tilting. This scenario was confirmed by ATR-FTIR spectroscopy. As the membrane thickness increases, the value of the diffusion coefficient increases to reach a maximum at h approximate to d(pi). We show that this variation ill diffusion Coefficient is consistent with a decrease in peptide tilt. To do so, we have derived a relation between the diffusion coefficient and the tilt angle, and We used this relation to derive the peptide tilt from our diffusion measurements. As the membrane thickness increases, the peptides raise (i.e., their tilt is reduced) and reach all upright position and a maximal mobility for h approximate to d(pi). Using accessibility measurements, we show that when the membrane becomes too thick, the peptide polar heads sink into the interfacial region. Surprisingly, this ``pinching'' behavior does not hinder the lateral diffusion of the transmembrane peptides. Ultimately, a break in the peptide transmembrane anchorage is observed and is revealed by a ``jump'' in the D values.
Recent Applications of Fluorescence Recovery after Photobleaching (FRAP) to Membrane Bio-Macromolecules - Rayan, Gamal and Guet, Jean-Erik and Taulier, Nicolas and Pincet, Frederic and Urbach, Wladimir
SENSORS 105927-5948 (2010) 

Abstract : This review examines some recent applications of fluorescence recovery after photobleaching (FRAP) to biopolymers, while mainly focusing on membrane protein studies. Initially, we discuss the lateral diffusion of membrane proteins, as measured by FRAP. Then, we talk about the use of FRAP to probe interactions between membrane proteins by obtaining fundamental information such as geometry and stoichiometry of the interacting complex. Afterwards, we discuss some applications of FRAP at the cellular level as well as the level of organisms. We conclude by comparing diffusion coefficients obtained by FRAP and several other alternative methods.