Rolling and ageing in T-ramp soft adhesion

Immediately before adsorption to a horizontal substrate, sinking polymer-coated colloids can undergo a complex sequence of landing, jumping, crawling and rolling events. Using video tracking we studied the soft adhesion to a horizontal flat plate of micron-size colloids coated by a controlled molar fraction $f$ of the polymer PLL-g-PNIPAM which is temperature sensitive. We ramp the temperature from below to above $T_c=32\pm 1^{\circ}$C, at which the PNIPAM polymer undergoes a transition triggering attractive interaction between microparticles and surface. The adsorption rate, the effective in-plane ($x-y$) diffusion constant and the average residence time distribution over $z$ were extracted from the Brownian motion records during last seconds before immobilisation. Experimental data are understood within a rate-equations based model that includes ageing effects and includes three populations: the untethered, the rolling and the arrested colloids. We show that pre-adsorption dynamics casts analyze a characteristic scaling function $\alpha (f)$ proportional to the number of available PNIPAM patches met by soft contact during Brownian rolling. In particular, the increase of in-plane diffusivity with increasing $f$ is understood: the stickiest particles have the shortest rolling regime prior to arrest, so that their motion is dominated by untethered phase

Importance of the dynamics of adsorption and of a transient interfacial stress on the formation of aggregates of IgG antibodies

International audienceIt is common knowledge that aggregation of proteins may occur in aqueous solutions under mechanical stress (shaking or high shear), even in solutions that are stable at rest. Addition of surfactants is a practical generic means to prevent this stress-induced aggregation (e.g. in formulations of therapeutic proteins), which suggests that interfaces contribute to destabilization. We studied here the role of interfacial stress by applying brief mechanical impacts on the air-water interface, in the presence or absence of surfactants, in solutions of immunoglobulin G (IgG), a class of proteins of high importance to the developments of new therapeutics. A variety of surfactants was tested including the neutral ones Tween80, C10-C14 fos-cholines, alkylaminoxide, surfactin, and two ionic ones, TTAB and lauroylsarcosine sodium salt. We determined the presence of aggregates in solution by light scattering. Irrespective of the type of antibody, either human polyclonal or a monoclonal one, we show that the amount of aggregated IgG increases in proportion to the number of impacts on the interface. In the absence of stress, we recorded images of oblate aggregates of IgG (ca. 12 nm height and 200-1200 nm diameter) present at the air-water interface (fluorescence microscopy using anti-Fab or anti-Fc markers, and AFM scans after transfer on freshly cleaved mica). Our results evidence that aggregates are formed at the air-water interface, and are brought in solution by transient stresses applied on the water surface. Rupture of interfacial films is an important source of aggregates in solution. Finally, the role of surface dynamics in the protection brought by surfactants is discussed based on the comparison of protective efficiencies with dynamic surface tension properties (measured by the maximum bubble pressure method). Our work indicates that better protection is conferred by surfactants showing the faster interfacial dynamics, which corresponds also to conditions of faster lowering of the interfacial energy at a short time scale

Tannin-controlled micelles and fibrils of κ\kappa-casein

Effects of green tea tannin epigallocatechin-gallate (EGCG) on thermal-stress-induced amyloid fibril formation of reduced carboxymethylated bovine milk protein $\kappa$-casein (RCMK) were studied by dynamical light scattering (DLS) and small angle x-rays scattering (SAXS). Two populations of aggregates, micelles and fibrils, dominated the time evolution of light scattering intensity and of effective hydrodynamic diameter. SAXS experiments allowed to resolve micelles and fibrils so that the time dependence of scattering profile revealed structural evolution of the two populations. The low-Q scattering intensity prior to an expected increase with time due to fibril growth, shows an intriguing rapid decrease which is interpreted as the release of monomers from micelles. This phenomenon, observed both in the absence and in the presence of EGCG, indicates that under thermal stress free native monomers are converted to amyloid-prone monomers that do not form micelles. The consumption of free native monomers results in a release of native monomers from micelles, because only native protein participate in micelle-monomer (quasi-)equilibrium. This release is reversible, indicating also that native-to-amyloid-prone monomers conversion is reversible as well. We show that EGCG does not bind to protein in fibrils, neither does it affect/prevent the pro-amyloid conversion of monomers. EGCG hinders the addition of monomers to growing fibrils. These facts allowed us to propose kinetics model for EGCG-controlled amyloid aggregation of micellar proteins. Therein, we introduced the growth-rate inhibition function which quantitatively accounts for the effect of EGCG on the fibril growth at any degree of thermal stress

Bacteria‐Based Production of Thiol‐Clickable, Genetically Encoded Lipid Nanovesicles

International audienceDespite growing research efforts on the preparation of (bio)functional liposomes, synthetic capsules cannot reach the densities of protein loading and the control over peptide display that is achieved by natural vesicles. Here we present a microbial platform for high yield production of lipidic nanovesicles, with clickable thiol moieties in their outer corona. These nanovesicles show low size dispersity, are decorated with a dense, perfectly oriented and customizable corona of transmembrane polypeptides. In addition, this approach enables encapsulation of soluble proteins into the nanovesicles. Due to the mild preparation and loading conditions (absence of organic solvents, pH gradients or detergents) and their straightforward surface functionalization taking advantage of the diversity of commercially-available maleimide derivatives, engineering bacterial-based proteoliposomes are an attractive eco-friendly alternative that can outperform current liposome preparation methods

Refolding of Aggregation-Prone ScFv Antibody Fragments Assisted by Hydrophobically Modified Poly(sodium acrylate) Derivatives

ScFv antibody fragments are a promising alternative to full-length antibodies for both therapeutic and diagnosis applications. They can be overexpressed in bacteria, which enables easy large scale production. Since scFv are artificial constructs, they are poorly soluble and prone to aggregation, which makes them difficult to manipulate and to refold. Here, stabilization and refolding of scFv fragments from urea-unfolded solutions are reported based on the use of micromolar amounts of polymers playing the role of artificial chaperons. Using fluorescence correlation spectroscopy, the size and aggregation number of complexes of scFv with unmodified or hydrophobically modified poly(sodium acrylate) are determined. The evolution of the secondary structure along the refolding procedure, in the presence or absence of 0.4 m L-arginine at scFv:polymerPeer reviewe

Cascade d'effets induits par la lumière aux interfaces liquides (du photo-surfactant à la mousse)

PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Photo-renaturation de protéines par des macromolécules chaperonnes

Nous avons cherché à concevoir des macromolécules ayant un comportement de chaperonne vis à vis de diverses protéines et notamment en fondant leur activité sur des propriétés stimulables par la lumière. Les interactions hydrophobes constituent un paramètre clé de l'effet chaperonne qui a été mis en évidence dans les chaperonnes biologiques aussi bien que dans les chaperonnes artificielles. Nous avons synthétisé des polymères à amphiphilie photo-stimulable portant des chaînes pendantes azobenzènes. Ces polymères sont capables d'association/dissociation photo-stimulables avec des particules colloïdales à coeur hydrophobe. Différents paramètres peuvent moduler ces associations comme la force ionique, le taux de modification hydrophobe, la nature du greffon... Ces polymères ont montré plusieurs propriétés caractéristiques de chaperonnes artificielles : ils déstabilisent une protéine modèle, le cytochrome C, protègent de l'agrégation et augmentent l'efficacité des procédés de renaturation de l'anhydrase carbonique et d'un fragment d'anticorps surexprimé en bactérie. L'évolution du repliement a été caractérisée par suivi des structures secondaires en dichroïsme circulaire et par suivi de la compacité des protéines en fluorescence. L'association polymère/protéine a été étudiée par électrophorèse capillaire et par diffusion de la lumièrePARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Lattice model for polymer propagation in confined media

info:eu-repo/semantics/publishe

Photoresponsive viscosity and host-guest association in aqueous mixtures of poly-cyclodextrin with azobenzene-modified poly(acrylic acid)

International audienc

Well-Defined Critical Association Concentration and Rapid Adsorption at the Air/Water Interface of a Short Amphiphilic Polymer, Amphipol A8-35: A Study by Förster Resonance Energy Transfer and Dynamic Surface Tension Measurements

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