The changes in molecular interaction and conformation of lysozyme mediated by ionic liquids

Using Ionic liquids（ILs）to regulate protein crystallization has attracted great attention, but the mechanism of ILs mediating crystallization is still unclear. Herein, we chose 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1,3-dimethylimidazolium iodide ([C1mim]I) as additives to mediate lysozyme crystallization, and use situ Raman to track the conformational changes of lysozyme in solution. Meanwhile, molecular simulation was used to explore the binding between ILs and lysozyme molecules. The results demonstrated that the addition of ILs produced new characteristic peaks in Raman spectra, suggesting some changes to occur in solution structure. The changes of peaks at 1340 cm−1 and 1359 cm−1, and the enhancement of peak at 1450 cm−1 indicated the unfolding of lysozyme molecules. The quantitative analysis of amide Ⅰ band showed that the addition of ILs increased the β-sheet content in secondary structures. Molecular docking showed that [C4mim]Cl and [C1mim]I could both bind to the active site of lysozyme molecules, and the binding energy were −3.1 kcal/mol and −4.5 kcal/mol, respectively. Molecular dynamics results showed that [C4mim]Cl could stably bind to lysozyme molecules, while [C1mim]I left the active site after several ns, which means that [C4mim]Cl brought about stronger impact on interaction of lysozyme molecules than [C1mim]I in solution.