Improvement on the crystallization of lysozyme in the presence of hydrophilic ionic liquid.

The crystallization of lysozyme with hydrophilic ionic liquid 1,3-butylimidazolium chloride (BBimCl) as an additive was investigated with hanging-drop vapor diffusion crystallization protocol. The elevated threshold to super-saturation caused by the increased solubility of lysozyme in the presence of BBimCl and the slower super-saturation process of lysozyme induced by the negligible vapor pressure of BBimCl contributed to a lower super-saturation degree, offering a promoted ambient circumstance for nucleation and providing a controlled velocity for the growth of lysozyme crystal. These eventually offer a prominent promotion to the crystallization of lysozyme, i.e., less crystal polymorphism and precipitation while larger crystals and significantly improved the tolerance to the concomitant impurities or sample matrices for the crystallization of lysozyme. Therefore, the presence of BBimCl enables the direct crystallization of lysozyme from a real complex sample matrix, i.e., egg-white, which opens a promising avenue for the development of protein crystallization methodology with ionic liquids as an additive and offers vast potentials for the practical separation/purification of proteins of interest from complex real sample matrices.