Stability and Fibrillation of Lysozyme in the Mixtures of Ionic Liquids with Varying Hydrophobicity

Abstract

Combinatorial effects of small molecules provide newer avenues to improve protein stability. The combined effect of two different classes of ILs on the stability and fibrillation of lysozyme was investigated. Imidazolium‐ILs (aromatic‐moiety) with varying alkyl chains, methyl (MIC), butyl (BMIC) and hexyl (HMIC), and pyrrolidinium‐IL (alicylic‐moiety) with butyl substitution (BPyroBr) were chosen. The fibrillation was delayed by all the ILs. In mixtures, the presence of HMIC with MIC or BMIC at 2:1 ratio delayed the fibrillation synergistically by increasing lag‐time and reducing elongation rate. Lysozymes’s stability was reduced at these conditions compared to lower molar ratios of HMIC with MIC or BMIC. Computational studies indicated that water molecules were reduced around lysozyme upon adding Im‐ILs, whereas BPyroBr slightly increased water. Preferential interaction studies suggest that the binding of HMIC with the protein was the most favored and it synergistically facilitated the binding of MIC. BMIC was preferentially binding to lysozyme but disfavoured the interaction of MIC whereas BMIC and BPyroBr had a competitive binding. The mixture of ILs containing the longer alkyl chain destabilizes the protein more, but delays the fibrillation. Further, the effect of aromatic ILs could be greater than alicyclic ILs having the same alkyl chain length.