Fast X-ray Photon Correlation Spectroscopy measurements from the diffusion of concentrated Alpha Crystallin suspensions

Alpha Crystallin constitute up to half of the total protein found in the mammalian eye lens. It has chaperone like behavior and may play a key role in maintaining lens transparency by preventing condensation of other lens proteins. We report here Fast X-ray Photon Correlation Spectroscopy (XPCS) measurements of protein diffusion within concentrated suspensions of Alpha Crystallin. Bovine calf eye lens cortices were homogenized, centrifuged and ultra-filtered to obtain concentrated Alpha Crystallin suspensions. Diffusion of proteins within these suspensions was measured as a function of temperature. The overall observed diffusion rates imply that the proteins exist in a glassy or gel phase, even at concentrations where equivalent hard sphere system would still be liquid. We interpret these results within the context of strongly interacting proteins, with protein-protein interactions possibly mediated by subunit exchange among Alpha Crystallin oligormers.