Crystallization in protein solutions. what can we learn from light scattering?

摘要

Simultaneous static and dynamic light scattering was used to study the state of hen-egg while lysozyme in aqueous solutions. The Rayleigh ratios and diffusivities of the protein were determined as function of both protein and salt concentration for two different salts. Neither static nor dynamic results showed signs of prenucleation aggregation. Further-more, prior to nucleation, there were no changes in the light scattering data to indicate the crossover from under- to supersaturated solutions. At low salt concentrations the scattering intensity fell below the value expected for monomeric solutions, and the diffusivity increased with protein concentration. With increasing salt concentration, this trend was eventually reversed. These findings indicate a change in protein interactions from net repulsion to net attraction. The effectiveness of the salt to screen the electrostatic repulsion correlated with its effectiveness to crystallize the protein from solution. Combining static and dynamic data, we extracted the dependence of the hydrodynamic friction factor on protein concentration, salt conentration and salt type. The pronounced salt-dependence found further proves the presence of interaction effects rather than aggregate formation.