The Solubility and Characterization of Thaumatin

Arieh Greenbaum, Department of Physics and Department of Biology, Yeshiva University, New York, N Neer Asherie, Department of Physics and Department of Biology, Yeshiva University, New York, N Charles Ginsberg, Department of Physics and Department of Biology, Yeshiva University, New York, N Samuel Blass, Department of Physics and Department of Biology, Yeshiva University, New York, N S. Knafo, Department of Physics and Department of Biology, Yeshiva University, New York, N

Abstract Thaumatin is a globular protein which crystallizes rapidly in the presence of tartrate ions. Therefore, thaumatin-tartrate mixtures are frequently used as model systems to study protein crystallization. Previous solubility studies on such mixtures, however, yield inconsistent results. In some studies thaumatin displayed direct solubility (the solubility increased with temperature), while in other studies the solubility was shown to be retrograde (the solubility decreased with temperature). Our results show that the solubility of thaumatin is significantly affected by the three dimensional configuration of the tartrate precipitant. The crystal solubility increases with temperature in L-tartrate, while it decreases with temperature in D-tartrate. Also, by using protein from two different commercial sources, we illustrate the importance of protein purity and homogeneity in the process of protein crystallization. We have purified thaumatin from Natex UK, Ltd and compared it with the more commonly used thaumatin from Sigma-Aldrich. Both proteins were characterized by quasielastic light scattering, size-exclusion HPLC, ion-exchange HPLC and electrospray ionization mass spectrometry. We find that the purer Natex protein yields consistent solubility results unlike the heterogeneous protein from Sigma-Aldrich. Our research suggests that the chirality of additives can be a useful tool to alter protein phase behavior. Moreover, our solubility results are the first part of a complete phase diagram for thaumatin and thus another step towards establishing the universal features of the phase behavior of globular proteins.

Full Text: PDF