Protein Crystallization Irradiated by Audible Sound: The Effect of Varying Sound Frequency

Protein crystallization is a process that is very sensitive to the physical environment. Audible sound is an environmental characteristic that can significantly affect the crystallization process. Previously, it was found that the crystallization result is frequency dependent, that is, the crystallization of protein under different sound frequencies yields different results. Here, we further investigate the effect of varying frequency (or a frequency program) on protein crystallization. Twelve different frequency programs and six proteins were used to test the effect of varying sound frequency on protein crystallization. The results showed that varying the audible sound frequency from high to low exhibited the most significant improvement in protein crystallization. Varying frequency linearly from 15 000 to 100 Hz in 12 h best promoted crystallization, with the average number of crystallization hits 36.5% higher than in the control. Crystal quality was improved with sound irradiation using STW2 program. Our study showed that varying the sound frequency has positive effects on facilitating protein crystallization and purposely optimizing sound frequency programs may be helpful for obtaining protein crystals.