The potential of hexatungstotellurate(VI) to induce a significant entropic gain during protein crystallization

• Main Authors: Christian Molitor, Aleksandar Bijelic, Annette Rompel
• Format: Article
• Language: English
• Published: International Union of Crystallography 2017-11-01
• Series: IUCrJ
• Subjects: polyoxotungstate; crystallization additives; crystal contacts; liquid–liquid phase separation; solvent entropy
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2052252517012349

The limiting factor in protein crystallography is still the production of high-quality crystals. In this regard, the authors have recently introduced hexatungstotellurate(VI) (TEW) as a new crystallization additive, which proved to be successful within the liquid–liquid phase separation (LLPS) zone. Presented here are comparative crystal structure analyses revealing that protein–TEW binding not only induces and stabilizes crystal contacts, but also exhibits a significant impact on the solvent-driven crystallization entropy, which is the driving force for the crystallization process. Upon the formation of TEW-mediated protein–protein contacts, the release of water molecules from the hydration shells of both molecules, i.e. TEW and the protein, causes a reduced solvent-accessible surface area, leading to a significant gain in solvent entropy. Based on the crystal structures of aurone synthase (in the presence and absence of TEW), insights have also been provided into the formation of a metastable LLPS, which is caused by the formation of protein clusters, representing an ideal starting point in protein crystallization. The results strongly encourage the classification of TEW as a valuable crystallization additive.