Ionic liquid interface modification of magnetic carboxymethyl cellulose-immobilized lipase: Improvement of lid and tunnel structures to enhance stability and catalytic performance

Ionic liquids (ILs) interface modification strategies have been widely utilized as designable novel modifiers in the field of immobilized enzymes to enhance enzyme stability. However, the mechanism underlying the modification of the spatial structure of enzyme molecules and enhancement of enzyme catalytic performance by carrier materials and ILs interface remains unclear. In this study, Candida rugosa lipase (CRL) was adsorbed onto magnetic carboxymethyl cellulose with interface modification by ILs, resulting in an immobilized enzyme that exhibited excellent thermal stability, solvent tolerance, and denaturant tolerance. Furthermore, the immobilized enzyme retained 73.1 % activity after seven cycles and maintained 83.0 % activity after being stored at 4 ℃ for 20 days. The immobilized enzyme successfully synthesized phytosterol esters in a solvent-free system, achieving a remarkable yield of 93.5 %, and 71.5 % yield was maintained after 6 cycles. The molecular dynamics simulation results showed that the modification of ILs was beneficial in enhancing the rigidity of CRL to maintain the stable spiral structure in its lid. The pocket structure and substrate interaction analysis revealed that the introduction of ILs favored the maintenance of the CRL pocket structure and enhanced pocket structure hydrophobicity, which was conducive to maintaining the enzyme activity enhancement and stability. The immobilized enzyme possesses a larger bottleneck radius and narrower length, which improves both the transport rate and catalytic efficiency of the tunnel. This study provides a new idea for the design of novel carriers to obtain immobilized enzymes with better performance and provides a theoretical basis for the design of modifications.