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Proposal for a Master 2 internship (starting March 2022) at Institut Laue Langevin (Grenoble).
Intrinsically disordered proteins from a polymer physics perspective


The discovery of intrinsically unfolded or disordered proteins (IDPs) approximately 20 years ago has caused a paradigm shift away from the original picture that it is mainly protein structure which determines
protein function. Rather, IDPs constitute a crucial fraction of the proteins in a living organism and are defined by their lack of a stable, ordered three-dimensional structure.


The proposed internship is part of a collaborative project that aims at:
(1) characterizing the conformations sampled by model IDPs under different well-controlled conditions,
(2) studying how these conformations depend on the chemical properties of the IDPs, and
(3) understanding how and why small differences in chemical properties and conformations lead to large differences in self-assembly pathways of IDPs.


The project will combine state-of-the-art neutron and X-ray techniques and coarse grained simulations. The proposed internship focuses on modeling IDPs in aqueous solutions, a challenging task due to a
large number of distinct conformational states explored by them. Recently, several coarse-grained (CG) models have been developed to accurately reproduce structural properties of IDPs. We will employ molecular dynamics simulations to explore CG models with two approaches, namely implicit and explicit solvent simulations, to treat solvent molecules (i.e. water). Structural and dynamical properties of the proteins will be investigated as a function of protein concentration. The computational study will be complemented by an experimental work, where the rheological properties of the protein solution will be investigated. During this project, the candidate will get a unique opportunity to explore theoretical modeling and experimental approaches in research.


The thesis will be carried out in collaboration between the Laboratoire Interdisciplinaire de Physique (LIPhy) and the Institut Laue-Langevin (ILL) in Grenoble. The experimental part (rheology) will take place
in the laboratories of the Partnership for Soft Condensed Matter (ILL-ESRF).


A PhD project at the ILL funded by ANR can follow the master 2 project.


Contacts: Tilo Seydel (seydel@remove-this.ill.eu), Tatiana Morozova (morozova@remove-this.ill.eu), Olga Matsarskaia
(matsarskaia@remove-this.ill.eu), Jean-Louis Barrat ( jean-louis.barrat@remove-this.univ-grenoble-alpes.fr)

Description

For the last 20 years exotic states of matter, such as high temperature superconductivity, quantum critical points, spins liquids etc...,  have been discoverred in strongly correlated systems. It is also in these compounds that can be found coupled  properties highly desirable for applications, as for instance magneto-electric or magneto-optic couplings.  

The origin and variety of  the properties found in strongly correlated compounds originates in the preservation in these systems of numerous degrees of freedom (spin, charge, network, orbital, etc...) that are hindered in more conventional systems. In Grenoble we have the chance to host several large scale facilities, such as neutrons diffraction, able to provide experimental insights in these systems. 

In order to build a complete and coherent picture one however needs some theoretical support. On this point, the need to treat on an equel footing many degrees of freedom increases the difficulty for the theoreticians. 

The objective of this internship is to participate to the theoretical development of numerical methods able to describe strongly correleted systems. The methods that will be used are named ab initio as they aim is to solve the Schrödinger equation as exactly as possible while taking into account the whole complexity of its chemical composition and crystallographic structure.  

The student will thus be initiated to:

  • the analytical development of controled approximations for solving the Schrödinger equation
  • the design and implementation of  the associated algorithm
  • the application of the methods to real examples

Activities of the trainee

After a first initiation to the Configuration Interaction methods (allowing to solve in an approximate however contoled and accurate manner the Schrödinger equation for ground and excited states), the student will participate to the work in progress  in the group around the development of a software aiming at computing the ground and excited (in particular magnetic) states of strongly correlated compounds and able to efficiently use hundreds or even thounsands of precessors.

In this framework the student will have access to regional and national computer centers.  

Adviser

M.B. Lepetit (lepetit@remove-this.ill.fr)

Description:

On désigne par transition dynamique l’écart au comportement linéaire de la variation des déplacements carrés moyens des atomes en fonction de la température. Plusieurs expériences ont mis en évidence l’existence de la transition dynamique dans les systèmes protéiques hydratés autour de 180 – 200 K.

Cette transition traduit un changement activé des états conformationnels de la protéine en fonction de la température. L’image simple qu’on a de la transition dynamique est celle deux états conformationnels au moins correspondant à des puits de potentiel séparés par une barrière de potentiel. A basse température, les mouvements (harmoniques) des atomes de la protéine étant localisés autour du minimum des états conformationnels de plus basses énergies, les déplacements carrés moyens augmentent linéairement avec la température.

A haute température, l’amplitude des mouvements (anharmoniques) devient plus grande de sorte à effectuer un franchissement de barrière des états conformationnels de basses énergies vers ceux de hautes énergies. Il en résulte une augmentation non-linéaire des déplacements carrés moyens. La transition dynamique peut donc être résumée comme la transition de mouvements harmoniques vers des mouvements anharmoniques due au franchissement de barrière de potentiel.

En pratique, pour étudier la transition dynamique dans les expériences diffusion incohérente des neutrons, par exemple, on utilise classiquement les déplacements carrés moyens des atomes (d’hydrogènes) obtenus à partir de la pente à l’origine en fonction de Q2 du facteur ou fonction de structure dynamique de la diffusion quasi-élastique (ω = 0) incohérente des neutrons. Les déplacements carrés moyens ainsi obtenus ne dépendent pas ni de Q ou du temps et considèrent donc le système protéine comme un ensemble à l’équilibre moyenné sur toutes les échelles spatiales.

L’objectif de ce travail est d’étudier la manifestation de la transition dynamique en fonction de Q et du temps pour mieux comprendre comment se propage de la transition dynamique au sein d’une protéine. Pour ce faire nous comptons investiguer la faisabilité d’utiliser des méthodes statistiques multi-variées d’Analyse par Composantes Principales (ACP) pour analyser la fonction de structure dynamique (ou les déplacements carrés moyens) selon les deux échelles Q et temps à la fois.

Encore nouvelles dans ce domaine mais certainement prometteuses, de telles approches ont été récemment utilisées par une collaboration groupe Suédois – ILL pour étudier la dynamique d’une enzyme avec et sans inhibiteur.  

Activités du stagiaire : 

  1. Utiliser le modèle de Bicout – Zaccai de la transition dynamique pour développer l’approche par ACP ;
  2. Appliquer cette approche pour analyser des données expérimentales de diffusion des neutrons sur des protéines obtenues par J. Peters (ILL).

Mots clés : diffusion des neutrons incohérentes, transition dynamique, ACP

Directeur:

D. Bicout (bicout @ ill.fr)

Post-doc

A post doc position wil be opened in the ILL Theory group starting any time from October 1st 2019. 

Titre :  Many-body ab-initio calculations for magnetic and multiferroic materials

Contract : fixed-term 18 months contract possibly renewed once. 

Job description : The position is to work under the supervision of MB Lepetit on ab initio electronic structure and spectroscopic calculations in strongly correlated systems, with a focus on magnetic excitations and multiferroic compounds. The objective will be to decipher the key degrees of fredom reponsible for the amplitude of the magneto-electric coupling in some of the most intersting multiferroic materials. To reach this goal the group has recently set up a method for the ab-initio calculation of the magneto-electric coupling tensor and is presently developping an ab-initio code for this purpose. The candidate will thus be able to use the fist version of the code to study the magneto-electric coupling in some of the most interresting multiferric compounds as well as participate to the further developments of the code. 

Candidate : the candidate should have a PhD in Theoretical Condensed Matter Physics, Theoretical Molecular Physics or Quantum Chemistry. A good background in Quantum Physics will be required as well as knowledge of basic ab-initio electronic structure calculation methods. Knowledge in modern parallelisation and programming methods (open MP, MPI, …) will be appreciated as well as group theory and crystallography.

Applications are to be sent prior to  November 24th 2019 (24h00) to lepetit@ill.fr and include
    • an application letter
    • a CV
    • recommendation letters are welcome

The candidates retained in the short list will be interviewed either in Grenoble of by visioconference during the two first weeks after the candidacy deadline.