The effect of different percentages of triethanolammonium butyrate ionic liquid on the structure and activity of urate oxidase: Molecular docking, molecular dynamics simulation, and experimental study

Ionic liquids (ILs) are a class of salts with low melting points that can change the structure, function, and stability of proteins. Numerous researches have been focused on finding the ionic liquids that increase protein stability. In this work, efforts are made to study the effect of triethanolammonium butyrate (TEAB) ionic liquid on the structure and function of urate oxidase (UOX) using the combination of experimental and theoretical approaches. We treated urate oxidase enzyme in different TEAB concentrations. The volume percentages of ionic liquid in the solvent phase are about 1%, 5%, and 10%. TEAB ionic liquid shows a concentration-dependent effect on the activity of UOX and its activity decreased at high concentrations of TEAB. The use of 1% ionic liquid increased the enzymatic activity in comparison to naked UOX. This increase in the enzymatic activity may be attributed to the changes in the UOX conformation induced by TEAB. Also, an attempt was made to investigate the effect of TEAB ionic liquid on the conformation of UOX in the atomistic level using molecular dynamics (MD) simulations. We performed MD simulations of UOX enzyme in the presence of 1% ionic liquid. The MD results showed that the intramolecular hydrogen bond of UOX enzyme in the UOX/TEAB system increased. Also, theoretical results represent that the enzyme random coil converted to beta-sheet and alpha-helix in the presence of TEAB may preserve the enzyme active site integrity and may be responsible for increasing its activity. The results of molecular docking indicate that the cationic and anionic parts of IL were surrounded by some polar and hydrophobic residues which represent that the binding phenomenon was mainly influenced by electrostatic and hydrophobic interactions. The lower C alpha-RMSD and RMSF values indicate the more stabilization of UOX structure in the presence of 1% TEAB. (C) 2019 Elsevier B.V. All rights reserved.