Experimental and theoretical evidence of enhanced catalytic performance of lipase B from Candida antarctica acquired by the chemical modification with amino acid ionic liquids

Four types of amino acid ionic liquids (AAILs) with chiral structure were used to modify Candida antarctica lipase B (CALB). The results showed that the catalytic activity at different temperatures and pH, thermostability, and tolerance to organic solvents of all modified lipases were improved. The composition and configuration of modifiers have great influence on the catalytic performance of the modified lipases. AAILs composed of L-proline exhibited better modification effect than those containing D-proline. The use of [N-AC-L-Pro] [Cl] led to the highest modification degree (47.92 %) of the lipase, which exhibited the highest hydrolytic activity (430.67 U/g), as well as enhanced thermal stability and tolerance to organic solvents. The structure of CALB was characterized by circular dichroism (CD) and fluorescence spectroscopy. It was found that the introduction of a modifier changes the secondary structure of CALB to a certain extent, and the microenvironment around the fluorescent group changed slightly. The structural stability of CALB modified with [N-AC-L-Pro] [Cl] and the mechanism of reaction were studied by molecular dynamics simulations. The molecular dynamics simulations of the native and modified CALB were performed for 20 ns at 300 and 328 K. The simulation results showed that the root mean square deviation (RMSD) and total energy of modified CALB were less than those of native CALB, indicating a more stable structure for the modified CALB. The root mean square fluctuation (RMSF) calculations showed that the rigidity of the modified CALB and the flexibility of the active center region were both enhanced. The solvent accessibility area (SASA) calculations showed that both hydrophilicity and hydrophobicity of the modified enzyme-protein were improved. The increase in radial distribution function (RDF) of water molecules confirmed that the number of water molecules around the active sites was also increased. Thus, the modified CALB has enhanced structural stability and higher hydrolytic activity towards the triglyceride substrates.