Evaluating the role of ionic liquids (ILs) in the crystallization of lysozyme

Abstract

This investigation focuses on revealing the role of ionic liquids (ILs) on protein crystallization. Three different ILs, 1-Ethyl-3-methylimidazolium bromide ([Emim]Br), 1-Ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), and 1-Butyl-3-methylimidazolium bromide ([Bmim]Br), and the model protein lysozyme were chosen for investigation. Studies were carried out both thermodynamically and kinetically. With the presence of ILs, a slight increase in the solubility and an obvious decrease in induction time were discovered. Results showed that ILs can affect lysozyme nucleation by arranging molecules in nuclei to linear like. The intermolecular interactions between ILs and lysozyme molecules were further revealed using Circular Dichroism Spectroscopy. The addition of ILs interacted with lysozyme molecules through changes in secondary structure. An increase in α-helix content of lysozyme was achieved with the addition of a small amount of ILs, leading to more stable lysozyme molecules favorable for crystallization.