PhD: New experimental and theoretical approaches to quasi-elastic neutron scattering on proteins - Agathe Nidriche

Proteins undergo dynamics that span several orders of magnitude in time, englobing the femtosecond to microsecond timescale which are investigated with neutron scattering techniques. It is a valuable tool to study the dynamics of hydrogen nuclei in proteins. However, neutron scattering is not just a probe for self-diffusion, but also encodes collective dynamics through its division into an incoherent (self) and coherent (self and collective) contributions. It is always stated that coherent scattering is negligible in hydrogen-rich systems like proteins. In order to challenge this assumption, the advent of neutron polarisation set-ups for the Time-Of-Flight technique permits us to investigate separately both contributions in powder-state Green Fluorescent Protein (pGFP) and its per-deuterated counterpart (dGFP) hydrated in.

First and foremost, polarized neutron diffraction drives us to understand the extent of D/H exchange between the atmosphere and the hydration shell of the protein. This is then pushed forward with a pico-second dynamical study with polarised quasi-elastic neutron scattering, where we prove that coherent scattering is non-negligible due to D-bond collective relaxation in the hydration water of both proteins. The features of this collective relaxation share similarity with recent studies on liquids and polymers. In a more general manner, we have brought the use of a theoretical framework for complex systems with self-similar dynamics, as well as new experimental techniques, to enhance studies of biomolecules with QENS and question usual assumptions.

Jury :

• ARBE Arantxa (Rapporteur)
• STADLER Andreas (Rapporteur)
• GEISELMANN Hans (Examinateur)
• NILSEN Goran (Examinateur)
• SMITH Jeremy C (Examinateur)
• PETERS Judith (Directrice de thèse)