Real-Time Observation of Protein Dense Liquid Cluster Evolution during Nucleation in Protein Crystallization

Controlled navigation in the phase diagram of protein crystallization and probing by advanced Dynamic Light Scattering (DLS) technology provided new information and more insight on the early processes during the nucleation process. The observed hydrodynamic radius distribution pattern clearly reveals a two-step mechanism of nucleation and the occurrence of liquid dense protein clusters, which were verified by transmission electron microscopy. The growth kinetics of these protein clusters, forming distinct radii fractions, is analyzed in real time. Further, the data confirmed that critical nuclei show a distinctly different radius distribution than the liquid dense clusters. The data and results provide experimental evidence that during nucleation, a formation of distinct liquid clusters with high protein concentration occur prior to a transition to crystal nuclei by increasing the internal structural order of these clusters, subsequently.