The dual function of impurity in protein crystallization

It is widely believed that high-purity protein is critical to crystallization. Impurities can induce lattice strain, internal stress, and rotation disorder, thus decreasing protein crystallization success rate and crystal quality. However, some studies showed that protein could be crystallized from impure solutions; thus, the effect of impurities on protein crystallization remains unclear. Here, we systemically studied the effect of impurity type and concentration on protein crystallization. Results showed that protein crystallization was different when using different impurities. Protein crystallization could be promoted with a low concentration of impurities and inhibited with a high concentration of impurities, and this inhibition can be weakened by an audible sound. The effect of impurities on protein crystallization can be explained by the phase separation theory. In summary, we suggest that proper impurities might be beneficial to enhance protein crystallization.