Protein crystallization screening through scattering techniques

We have employed dynamic light scattering and X-ray small-angle scattering for monitoring the cluster formation of hen-egg white lysozyme solutions under crystallization conditions. From time-resolved dynamic light scattering experiments we can obtain a set of observables that exhibit clear extrema, when simultaneously plotted as functions of protein and electrolyte molarity. Close to these extrema, lysozyme crystals appear rapidly and with high probability. Both dynamic light scattering and small-angle X-ray scattering retrieve, under optimal crystallization conditions, particles 12 to 15 times larger than monomeric lysozyme; they could correspond to stable critical nuclei. Scattering amplitude analysis provides also useful information that correlates well with the size observables. A combination of both techniques can thus be successfully employed for screening supersaturated protein solutions.