Refined study of the interaction between HIV-1 p6 late domain and ALIX

The interaction between the HIV-1 p6 late budding domain and ALIX, a class E vacuolar protein sorting factor, was explored by using the yeast two-hybrid approach. We refined the ALIX binding site of p6 as being the leucine triplet repeat sequence (Lxx)4 (LYPLTSLRSLFG). Intriguingly, the deletion of the C-terminal proline-rich region of ALIX prevented detectable binding to p6. In contrast, a four-amino acid deletion in the central hinge region of p6 increased its association with ALIX as shown by its ability to bind to ALIX lacking the proline rich domain. Finally, by using a random screening approach, the minimal ALIX391–510 fragment was found to specifically interact with this p6 deletion mutant. A parallel analysis of ALIX binding to the late domain p9 from EIAV revealed that p6 and p9, which exhibit distinct ALIX binding motives, likely bind differently to ALIX. Altogether, our data support a model where the C-terminal proline-rich domain of ALIX allows the access of its binding site to p6 by alleviating a conformational constraint resulting from the presence of the central p6 hinge

Analyse fiabiliste du taux de restitution d'énergie en milieux viscoélastiques orthotropes

Un modèle mécano-fiabiliste est développé pour l'analyse de la fissuration dans un milieu viscoélastique orthotrope en mode mixte de chargement. La formulation analytique est introduite par l'intégrale M généralisée au comportement viscoélastique et résolue par une approche incrémentale issue du théorème des travaux virtuels. Les incertitudes sur les propriétés du matériau sont prises en compte par des variables aléatoires afin de calculer la probabilité de propagation de fissure. L'application numérique est effectuée sur un modèle éléments finis d'une plaque fissurée en matériau composite

Coronin-1A Links Cytoskeleton Dynamics to TCRαβ-Induced Cell Signaling

Actin polymerization plays a critical role in activated T lymphocytes both in regulating T cell receptor (TCR)-induced immunological synapse (IS) formation and signaling. Using gene targeting, we demonstrate that the hematopoietic specific, actin- and Arp2/3 complex-binding protein coronin-1A contributes to both processes. Coronin-1A-deficient mice specifically showed alterations in terminal development and the survival of αβT cells, together with defects in cell activation and cytokine production following TCR triggering. The mutant T cells further displayed excessive accumulation yet reduced dynamics of F-actin and the WASP-Arp2/3 machinery at the IS, correlating with extended cell-cell contact. Cell signaling was also affected with the basal activation of the stress kinases sAPK/JNK1/2; and deficits in TCR-induced Ca2+ influx and phosphorylation and degradation of the inhibitor of NF-κB (IκB). Coronin-1A therefore links cytoskeleton plasticity with the functioning of discrete TCR signaling components. This function may be required to adjust TCR responses to selecting ligands accounting in part for the homeostasis defect that impacts αβT cells in coronin-1A deficient mice, with the exclusion of other lympho/hematopoietic lineages

A NEW INCREMENTAL FORMULATION FOR LINEAR VISCOELASTIC ANALYSIS: CREEP DIFFERENTIAL APPROACH

International audienceThis paper presents a new incremental formulation in the time domain for linear, non-aging viscoelastic materials undergoing mechanical deformation. The formulation is derived from linear differential equations based on a discrete spectrum representation for the creep tensor. The incremental constitutive equations are then obtained by finite difference integration. Thus the difficulty of retaining the stress history in computer solutions is avoided. A complete general formulation of linear viscoelastic stress analysis is developed in terms of increments of strains and stresses. Numerical results of good accuracy are achieved. The analytical and numerical solutions are compared using the energy release rate in pure mode I and pure mode II

THEORETICAL AND NUMERICAL STUDIES OF RELAXATION DIFFERENTIAL APPROACH IN VISCOELASTIC MATERIALS USING GENERALIZED VARIABLES

International audienceThe phenomenon of incrementalization in the time domain, for linear non-ageing viscoelastic materials undergoing mechanical deformation, is investigated. Analytical methods of solution are developed for linear vi-scoelastic behavior in two dimensions utilizing generalized variables and realistic material properties. This is accomplished by the use of time-dependent material property characterization through a Dirchilet series representation, thus the transformation of the viscoelastic continuum problem from the integral to a differential form is achieved. The behavior equations are derived from linear differential equations based on the discrete relaxation spectrum. This leads to incremental constitutive formulations using the finite difference integration, thus the difficulty of retaining the strain history in computer solutions is avoided. A complete general formulation of linear viscoelastic strain analysis is developed in terms of increments of generalized stresses and strains

Incremental constitutive formulation for time dependent materials: creep integral approach

International audienceThis paper deals with the development of a mathematical approach for the solution of linear, non-ageing viscoelastic materials undergoing mechanical deformation. The formulation is derived from integral approach based on a discrete spectrum representation for the creep tensor. Finite difference integration is used to discretize the integral operators. The resulting constitutive model contains an internal state variable which represents the influence of the whole past history of stress and strain. Thus the difficulty of retaining the strain history in computer solutions is avoided. A complete general formulation of linear viscoelastic stress-strain analysis is developed in terms of increments of stresses and strains. Numerical simulations are included in order to validate the incremental constitutive equations

INTEGRAL APPROACH FOR TIME DEPENDENT MATERIALS USING FINITE ELEMENT METHOD

International audienceIn this work, we present the development of a mathematical approach for the solution of linear, non-ageing viscoelastic materials undergoing mechanical deformation. We use an integral approach based on a discrete spectrum representation for the creep tensor in order to derive the incremental viscoelastic formulation. Integral operators are discretized using finite difference techniques. The incremental viscoelastic consti-tutive model contains an internal state variable which represents the influence of the whole past history of stress and strain, thus the difficulty of retaining the stress-strain history in numerical solutions is avoided. A complete general formulation of linear viscoelastic stress-strain analysis is developed in terms of increments of stresses and strains. Numerical simulations are included in order to validate the incremental constitutive equations

Incremental viscoelastic formulation using generalized variables for thin structures: relaxation differential approach

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Modelling of ageing viscoelastic materials in three dimensional finite element approach

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