Solubility of thaumatin

Thaumatin, an intensely sweet protein, crystallizes rapidly in the presence of tartrate ions. The ease with which crystals form has led to the use of thaumatin over the past decade as a model system for the study of protein crystallization. The available data on the solubility of this protein, however, are inconsistent. We have purified thaumatin and determined its solubility with the L and D enantiomers of the tartrate ion. We find that the crystal habit and Solubility are significantly different for the two precipitants: the solubility increases with temperature in L-tartrate, while it decreases with temperature in D-tartrate. Our results suggest that the chirality of precipitants is an important factor that should be controlled when determining the solubility of proteins.