Temperature-Dependent Interactions Explain Normal and Inverted Solubility in a γD-Crystallin Mutant

• Published in: Biophysical journal 2019-09, Vol.117 (5), p.930-937
• Main Authors: Khan, Amir R., James, Susan, Quinn, Michelle K., Altan, Irem, Charbonneau, Patrick, McManus, Jennifer J.
• Format: Article
• Language: English
• Subjects: gamma-Crystallins - chemistry; Humans; Models, Molecular; Mutant Proteins - chemistry; Solubility; Temperature
• ISSN: 0006-3495; 1542-0086; 1542-0086
• DOI: 10.1016/j.bpj.2019.07.019

Protein crystal production is a major bottleneck in the structural characterization of proteins. To advance beyond large-scale screening, rational strategies for protein crystallization are crucial. Understanding how chemical anisotropy (or patchiness) of the protein surface, due to the variety of amino-acid side chains in contact with solvent, contributes to protein-protein contact formation in the crystal lattice is a major obstacle to predicting and optimizing crystallization. The relative scarcity of sophisticated theoretical models that include sufficient detail to link collective behavior, captured in protein phase diagrams, and molecular-level details, determined from high-resolution structural information, is a further barrier. Here, we present two crystal structures for the P23T + R36S mutant of γD-crystallin, each with opposite solubility behavior: one melts when heated, the other when cooled. When combined with the protein phase diagram and a tailored patchy particle model, we show that a single temperature-dependent interaction is sufficient to stabilize the inverted solubility crystal. This contact, at the P23T substitution site, relates to a genetic cataract and reveals at a molecular level the origin of the lowered and retrograde solubility of the protein. Our results show that the approach employed here may present a productive strategy for the rationalization of protein crystallization.