Influence of rapid cooling on crystal nucleation in lysozyme crystallization solutions of low supersaturation

Crystallization of lysozyme is investigated upon rapid cooling to 4 degrees C of undersaturated solutions equilibrated at temperatures in the range 30 degrees C-44 degrees C, and for incubation times varying from 12 to 36 min. The results indicate a tendency for the crystallization systems to respond in such a way that a solution of lower supersaturation may produce crystal populations of higher density. Analysis of the average crystal size shows that higher supersaturations might still be responsible for earlier nucleation, and the effects of solution incubation temperature (and its rapid decrease) are most likely on the dynamics of pre-crystallization protein-protein interactions, e.g. on the processes of formation of clusters/aggregates that could serve as active centers for nucleation, or as structures depleting the effective supersaturation for nucleation. The study demonstrates that lysozyme crystal nucleation could be strongly influenced by sharp temperature variation as long as crystallization systems of relatively low final supersaturation are investigated.