Thermal methods for crystallizing biological macromolecules

Abstract

While thermal methods are generally preferred for controlling crystal growth processes because of their simplicity and controllability, they surprisingly have not been widely used for protein crystal growth. Proteins which exhibit a temperature dependent solubility can in principle be grown using these techniques. Two thermal gradient methods have been successfully applied to protein crystallization. The first method was developed as a means to control and localize nucleation in protein solutions. The viability of this "thermonucleation" technique was demonstrated using the well-known protein lysozyme, whose solubility increases with increasing temperature. This technique has now been extended to include the nucleation of proteins exhibiting retrograde solubility and cases where solubility-temperature relationships are unknown. The second method, a thermal gradient transport technique, was successfully used for the first time to grow a lysozyme crystal. Supersaturation gradients were calculated from the temperature gradients and calculated growth rates were compared with the actual growth rates. The possibility of combining these two techniques to grow protein crystals is discussed.