Studying the Formation Process of Clusters in Solution at the Initial Stage of Protein Crystallization

Abstract

The monomers or aggregates of protein molecules in protein crystallization solution at the initial stage of crystallization process are the basis of subsequent nucleation process. Tanaka et al (Tanaka S., et al, J. Cryst. Growth, 1996) concluded that there are units and clusters of lysozyme molecules in solution at the beginning of lysozyme crystallization process, and the decrease of clusters' amount showed the nucleation process comes up. Therefore, cluster of protein molecules in solution is one of important parameters, by which we can judge the crystallization process, in particular, nucleation process. However, the formation process of lysozyme clusters was not reported up to now. In this paper, we studied the aggregates of lysozyme molecules in solution 1 hr and 12 hrs after the mixture of lysozyme and NaCl (precipitant) solution, by atomic force microscopy (AFM) and dynamic light scattering (DLS). Moreover, we studied the effect of solution temperature on the aggregates in solution. Our results showed that, 1 hr after the mixture of lysozyme and NaCl solution, the mean size of aggregates in solution first increased and then decreased. Our results also showed that the aggregates of lysozyme molecules in solution gradually disassembled and clusters of lysozyme molecules appeared within 12 hrs after the mixture of lysozyme and NaCl solution. The decrease of solution temperature decreased the period for appearance of clusters of lysozyme molecules in solution.