On the Extension Behavior of Helicogenic Polypeptides

The force laws governing the extension behavior of homopolypeptides are obtained from a phenomenological free energy capable of describing the helix-coil transition. Just above the melting temperature of the free chains, T*, the plot of force, f, vs. end-to-end distance, R, exhibits two plateaus associated with coexistence of helical and coil domains. The lower plateau is due to tension induced onset of helix-coil transition. The higher plateau corresponds to the melting of the helices by overextension. Just below T* the f-R plot exhibits only the upper plateau. The f-R plots, the helical fraction, the number of domains and their polydispersity are calculated for two models: In one the helical domains are viewed as rigid rods while in the second they are treated as worm like chains.Comment: 18 pages, 10 figures, to be published in Macromolecule

Neutron reflectivity of supported membranes incorporating terminally anchored polymers: Protrusions vs. blisters

The effect of terminally anchored chains on the structure of lipid bilayers adsorbed at the solid/water interface was characterized by neutron reflectivity. In the studied system, the inner leaflet, closer to the substrate, consisted of head-deuterated 1,2-distearoyl-sn-glycero-3-phosphorylcholine (DSPC) and the outer leaflet comprised a mixture of DSPC and polyethylene glycol (PEG) functionalized 1,2-distearoyl-sn-glycero-3-phosphoethanolamine. The DSPC headgroups were deuterated to enhance sensitivity and demarcate the bilayer/water interface. The effect on the inner and outer headgroup layers was characterized by w 1/2, the width at half-height of the scattering length density profile. The inner headgroup layer was essentially unperturbed while w 1/2 of the outer layer increased significantly. This suggests that the anchored PEG chains give rise to headgroup protrusions rather than to blister-like membrane deformations. © 2013 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Sélection d'anticorps recombinants dirigés contre des matériaux inorganiques pour des applications en nanosciences

Les matériaux inorganiques ont des propriétés uniques à l'échelle nanométrique. Ces propriétés ont généré beaucoup d'intérêt pour fabriquer des nouveaux matériaux utilisant des nano-objets comme unité de construction. Nous avons suivi une approche biomimétique pour la fabrication de dispositifs à base de nanoparticules afin d'améliorer les méthodes actuelles de fabrication top-down et bottom-up. Certaines protéines naturelles se lient en effet spécifiquement à des matériaux inorganiques, et déclenchent notamment la croissance de cristaux inorganiques. Une première étape dans cette approche biomimétique est de comprendre comment des protéines se lient spécifiquement à des nanomatériaux inorganiques. Nous avons exploré ce mécanisme de reconnaissance en sélectionnant des anticorps (les protéines de notre système immunitaire spécialisées dans les interactions avec de nombreuses cibles) contre des matériaux inorganiques par la méthode combinatoire biotechnologique appelée "phage display". Cette technique permet d'obtenir la séquence génétique codante des anticorps sélectionnés se liant à leur cible à partir d'une banque aléatoire d'anticorps. L'analyse statistique des séquences des anticorps sélectionnés fournit de nouvelles informations sur les interactions protéines/matériaux inorganiques. Notre principale conclusion est l'identification de l'acide aminé arginine en tant que contributeur majeur dans les interactions protéine/or. L'ingénierie génétique des anticorps permet de fonctionnaliser ces nouvelles sondes de matériaux inorganiques en vue de leur utilisation pour des applications dans le domaine des nanomatériaux. Les anticorps recombinants sélectionnés et leurs dérivés fonctionnalisés peuvent être exprimés par sécrétion à l'aide d'un hôte eucaryote (Dictyostelium discoideum) mis au point au cours de cette thèse.Inorganic materials have unique properties at the nanometer scale. These properties have generated a lot of interest among researchers to fabricate novel materials using nano objects as building units. In this PhD thesis, we have attempted to mimick nature in the fabrication of nanoparticle based devices in order to improve upon current top-down and bottom-up nanomaterial fabrication methods. Proteins can specifically bind inorganic materials and trigger crystal growth and thus are considered as the main building units for a biomimetic approach of fabrication. The first step towards mimicking nature is to explore how proteins bind specifically to nanomaterials. We have explored this recognition mechanism by selecting antibodies (the protein binders of our immune system) against inorganic nanomaterials using the combinatorial biotechnology method of phage display. This technique provides us with the genetic sequence of selected antibodies from a random antibody library exposed against a target. Statistical analysis of selected antibody sequences provides new information on proteins/inorganics interactions. Our main finding in this regard is the identification of the amino acid arginine as a major contributor to protein/gold interactions. Additional functionality to these new binders of inorganic materials is obtained by antibody engineering, allowing for their value added use in nanomaterial science applications. Selected recombinant antibodies and their engineered derivatives along with other recombinant protein can be expressed and secreted using a eukaryotic expression platform (Dictyostelium discoideum) developed during this thesis.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Early Stages of Homopolymer Collapse

Interest in the protein folding problem has motivated a wide range of theoretical and experimental studies of the kinetics of the collapse of flexible homopolymers. In this Paper a phenomenological model is proposed for the kinetics of the early stages of homopolymer collapse following a quench from temperatures above to below the theta temperature. In the first stage, nascent droplets of the dense phase are formed, with little effect on the configurations of the bridges that join them. The droplets then grow by accreting monomers from the bridges, thus causing the bridges to stretch. During these two stages the overall dimensions of the chain decrease only weakly. Further growth of the droplets is accomplished by the shortening of the bridges, which causes the shrinking of the overall dimensions of the chain. The characteristic times of the three stages respectively scale as the zeroth, 1/5 and 6/5 power of the the degree of polymerization of the chain.Comment: 11 pages, 3 figure

Theoretical considerations on mechanisms of harvesting cells cultured on thermoresponsive polymer brushes.

International audiencePoly (N-isopropylacrylamide) (PNIPAM) brushes and hydrogels serve as temperature-responsive cell culture substrates. The cells adhere at 37 °C and are detached by cooling to below the lower critical solution temperature T(LCST) ≈ 32 °C, an effect hitherto attributed to change in PNIPAM hydration. The article proposes a mechanism coupling the change of hydration to integrin mediated environmental sensing for cell culture on brushes and hydrogels in serum containing medium. Hydration is associated with swelling and higher osmotic pressure leading to two effects: (i) The lower osmotic pressure in the collapsed brush/hydrogel favors the adsorption of serum borne extracellular matrix (ECM) proteins enabling cell adhesion; (ii) Brush/hydrogel swelling at T < T(LCST) gives rise to a disjoining force f(cell) due to confinement by the ventral membrane of a cell adhering via integrin-ECM bonds. f(cell) places the integrin-ECM bonds under tension thus accelerating their dissociation and promoting desorption of ECM proteins. Self consistent field theory of PNIPAM brushes quantifies the effect of the polymerization degree N, the area per chain Σ, and the temperature, T on ECM adsorption, f(cell) and the dissociation rate of integrin-ECM bonds. It suggests guidelines for tuning Σ and N to optimize adhesion at 37 °C and detachment at T < T(LCST). The mechanism rationalizes existing experimental results on the influence of the dry thickness and the RGD fraction on adhesion and detachment

Thermoresponsive cell culture substrates based on PNIPAM brushes functionalized with adhesion peptides: theoretical considerations of mechanism and design.

International audienceThermoresponsive tissue culture substrates based on PNIPAM brushes are used to harvest confluent cell sheets for tissue engineering. The prospect of clinical use imposes the utilization of culture medium free of bovine serum, thus suggesting conjugation with adhesion peptides containing the RGD minimal recognition sequence. The optimum position of the RGD along the chain should ensure both cell adhesion at 37 °C and cell detachment at T(L) below the lower critical solution temperature of PNIPAM. Design guidelines are formulated from considerations of brush confinement by the cells: (i) Cell adhesion at 37 °C is controlled by the RGDs accessible without brush compression. (ii) Cell detachment at T(L) is driven by a disjoining force due to confinement of the swollen brush by cells retaining integrin-RGD bonds formed at 37 °C. These suggest placing the RGDs at the grafting surface or its vicinity. Randomly placed RGDs do not enable efficient detachment because a large fraction of the integrin-RGD bonds are not sufficiently tensioned at T(L), in line with experimental observations (Ebara, M.; Yamato, M.; Aoyagi, T.; Kikuchi, A.; Sakai, K.; Okano, T. Immobilization of celladhesive peptides to temperature-responsive surfaces facilitates both serum-free cell adhesion and noninvasive cell harvest. Tissue Eng. 2004, 10, 1125-1135). The theory framework enables analysis of culture media based on polymer brushes conjugated with adhesion peptides in general

Stretching of Homopolymeric RNA Reveals Single-Stranded Helices and Base-Stacking

International audienc