The research activity of the laboratory of physics of living matter is mainly devoted to the study of DNA topology, cellular machines, protein mechanics and high-resolution low temperature Atomic Force Microscopy (AFM). Through internal and external collaborations, a certain number of other research activities are carried out in particular on knots hydrodynamics, DNA gel electrophoresis, cell elasticity, cell motility, etc.
The DNA topology activity is mainly centered on the statistical physics of linear and knotted DNA and the scaling exponents for linear DNA were recently determined by AFM.
Concerning the protein mechanics we have developed a new method to determine the spring constant of a single protein by AFM. Cellular machines, like chaperonin, are studied at the single molecule level with the aim of understanding their detailed function.
High resolution AFM at low temperature (liquid nitrogen temperature) is under development in our laboratory. This technique relies on the fact that polymers (such as proteins or DNA) becomes stiff as the temperature is lowered, thus we expect an increase in resolution for the AFM.

SEMINARS - WORKSHOPS

Vous êtes conviés au séminaire qui se tiendra à L’auditoire BSP I, le jeudi 15 octobre à 10h00 heures

Neutron scattering and statistical thermodynamic studies of eye lens protein solutions

Prof. George Thurston
Rochester Institute of Technology, USA

Mixtures of the eye lens proteins gamma-B and alpha crystallin show phase separation that is not a simple combination of individual protein properties[1].
Combined small-angle neutron scattering, thermodynamic perturbation theory and molecular dynamics simulation has indicated that gamma-alpha phase separation depends non-monotonically and sensitively on gamma-alpha interaction strength[2,3]. We review and extend these findings as follows. First, we investigate the Barboy-Tenne mixture extension of the Baxter sticky-sphere model[4] for its capability of providing additional free energy and liquid structure models for this system. With use of gamma-B stickiness parameters that reproduce light and neutron scattering data on pure gamma-B solutions, we find that the Barboy-Tenne sticky-sphere mixture model indeed shows non-monotonic dependence of spinodal temperature on the strength of gamma-alpha attraction, and is also capable of reproducing salient features of light scattering data on gamma-alpha mixtures[1].
Second, we provide a geometric construction that can aid in studying the extent to which non-monotonic dependence of stability on interaction strengths could be generic, for a given liquid mixture free energy model. Third, we describe ongoing neutron scattering and theoretical studies of electrostatically-mediated gamma-B interactions. Each of these steps is oriented towards understanding the phase behavior and other properties of these concentrated protein mixtures that are of potential importance for understanding cataract disease.
[1] Thurston GM, J. Chem. Phys., 124, 134909 (2006)
[2] Stradner, Foffi, Dorsaz, Thurston, Schurtenberger, PRL 99:198103 (2007)
[3] Dorsaz, Thurston, Stradner, Schurtenberger and Foffi, J. Phys. Chem. B
113:1693-1709 (2009)
[4] Barboy B and Tenne R, Chem. Phys. 38(3):369-387 (1979)

TROISIÈME CYCLE DE LA PHYSIQUE EN SUISSE ROMANDE
COURS DU SEMESTRE D'AUTOMNE 2009

Les jeudis 1, 8, 15, et 22 octobre 2009, de 14h15 à 18h00 − EPFL, Lausanne, salle ELG 116
Conformational transitions in polymers : analytical and Monte Carlo methods ■ Enzo Orlandini, Universita di Padova, Italie

First Lesson: Introduction and phenomenology of conformational transitions for polymers in dilute solutions: adsorption, collapse and DNA denaturation transition.
Second Lesson: Scaling theory and modelling: DeGennes blob theory, lattice models and some rigorous results.
Third Lesson: Monte Carlo methods for conformational transitions: ergodicity and efficiency. Importance sampling techniques. Multiple Markov chains and parallel tempering techniques.
Fourth lesson: Somerecent applications and still open problems: mechanical desorption and DNA unzipping transition, knot localization in adsorbed polygons. Filling the gap between experiments and theory.

Lecture_I.pdf