High Protein-Loading Silica Template for Heterogeneous Protein Crystallization

As a purification technology, crystallization is advantageous over chromatography and precipitation in terms of purity, cost, and scalability. In general, proteins have slow crystallization kinetics due to their complex configurations, but this problem can be overcome with heterogeneous nucleants. High protein-loading mesoporous silica is a promising nucleant due to its favorable interaction with protein. The current study employs such a template in the batch crystallization of lysozyme and thaumatin at 1 mL scale. Using lysozyme as the main model protein, the results show that the template had high protein loading (220–300 mg lysozyme/g silica) and induced significantly faster crystallization as compared to the unseeded samples over a wide range of initial protein concentration (10.0–47.5 mg/mL) at 25 °C with 0.5 M potassium sodium tartrate tetrahydrate (precipitant) concentration. It was found that the template had to be saturated with the target protein before the experiments to achieve faster kinetics, or else it could delay the crystallization process. These findings were reaffirmed by the crystallization experiments of thaumatin. The current study demonstrates the effectiveness of high protein-loading silica as a nucleant in protein crystallization and the importance of its pretreatment with the target protein.