Using Schematic Models to Understand the Microscopic Basis for Inverted Solubility in ?D-Crystallin

Irem Altan, Amir R. Khan, Susan James, Michelle K. Quinn, Jennifer J. McManus, Patrick Charbonneau*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

Abstract

Inverted solubility-melting a crystal by cooling-is observed in a handful of proteins, such as carbomonoxy hemoglobin C and ?D-crystallin. In human ?D-crystallin, the phenomenon is associated with the mutation of the 23rd residue, a proline, to a threonine, serine, or valine. One proposed microscopic mechanism entails an increase in surface hydrophobicity upon mutagenesis. Recent crystal structures of a double mutant that includes the P23T mutation allow for a more careful investigation of this proposal. Here, we first measure the surface hydrophobicity of various mutant structures of ?D-crystallin and discern no notable increase in hydrophobicity upon mutating the 23rd residue. We then investigate the solubility inversion regime with a schematic patchy particle model that includes one of three variants of temperature-dependent patch energies: Two of the hydrophobic effect, and one of a more generic nature. We conclude that, while solubility inversion due to the hydrophobic effect may be possible, microscopic evidence to support it in ?D-crystallin is weak. More generally, we find that solubility inversion requires a fine balance between patch strengths and their temperature-dependent component, which may explain why inverted solubility is not commonly observed in proteins. We also find that the temperature-dependent interaction has only a negligible impact on liquid-liquid phase boundaries of ?D-crystallin, in line with previous experimental observations.

Original languageEnglish
Pages (from-to)10061-10072
Number of pages12
JournalJournal of Physical Chemistry B
Volume123
Issue number47
DOIs
Publication statusPublished - 27 Nov 2019

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