Effect of 1-methyl-3-octyleimmidazolium chloride on the stability and activity of lysozyme: a spectroscopic and molecular dynamics studies

Abstract

Herein, the binding of 1-methyl-3-octylimidazolium chloride [OMIM][Cl] ionic liquid with hen egg white lysozyme (HEWL) has been studied using fluorescence, time resolved fluorescence, UV–visible and circular dichroism (CD) spectroscopy, in combination with computational study. The fluorescence results revealed that [OMIM][Cl] quenches the fluorophore of HEWL through static quenching mechanism. The calculated thermodynamic parameters show that [OMIM][Cl] bind with HEWL through hydrophobic interactions. In addition, the negative value of Gibbs energy change (∆G) indicates that the binding process was spontaneous. Furthermore, UV–vis and CD results indicate that [OMIM][Cl] induce the conformational change in HEWL and increase its enzymatic activity. Additionally, molecular docking results showed that [OMIM][Cl] binds at the active site of HEWL where both the fluorophore residues (Trp108 and Trp62) and the catalytic residues (Glu35 and Asp52) reside. Molecular dynamic simulation results show the reduction of intra-molecular hydrogen bond of HEWL when it binds with [OMIM][Cl].

Keywords:

• ionic liquid
• lysozyme
• quenching
• activity
• molecular docking

Acknowledgments

Dr. Rajan Patel thanks Science and engineering research board, New Delhi for providing research grant with Sanction Order No. (SR/S1/PC-19/2011) and SB/EMEQ-097/2013. One of the authors (Meena Kumari) is also thankful to CSIR, New Delhi for SRF fellowship file No. 09/466(0142)/2012-EMR-I. Authors also thank DST for providing the FIST grant with Sanction Order No. (SR/FIST/LS-541/2012).