A scattering study of concentrated lens protein solutions and mixtures - Towards understanding the molecular origin of presbyopia

Healthy eye lenses are transparent and flexible, able to adapt shape in order to focus on far away and close-by objects. With age, however, this flexibility is lost, leading to a condition known as presbyopia. This vision disorder where close-by objects appear blurred commonly starts around the age of 40. The aim of this thesis is to elucidate the molecular origin of the gradual hardening of the core of the eye lens, made of fibre cells filled with concentrated mixtures of proteins, the so-called crystallins, which leads to the formation of presbyopia. To this end, various scattering techniques, static and dynamic light scattering (SLS & DLS), small-angle X-ray scattering (SAXS) and neutron spin echo (NSE), are used to study solutions of crystallins at concentrations up to those present in the lens. The first part of this work deals with solutions of the individual proteins. We show that different techniques allow us to access solution dynamics on different length scales. While DLS probes the collective dynamics, NSE accesses length scales corresponding to the average distance between nearest neighbors in the solution. We find that the dynamic behavior of protein solutions depends on the nature of the protein interactions, as well as on their patchiness. For the largest of the lens proteins, α-crystallin, well described by a model of polydisperse (20%) colloidal hard spheres, we find a slowing down of the local dynamics over a large range of volume fraction