Molecular Simulation Study Of Candida Rugose Lipase Adsorption On ZIF-8 Surfaces

Zeolitic imidazolate frameworks（ZIFs）are porous materials with intramolecular pores formed by periodic arrangements of metal ions and organic ligands,which are widely used in biomedical and gas separation and storage fields because of their high porosity and excellent biocompatibility.Enzyme immobilization is commonly used in industrial enzyme catalysis production as an effective method to confine enzymes within a particular space.In this thesis,the adsorption behavior of Candida rugose lipase（CRL）on the surface of ZIF-8 material was investigated using molecular simulation.The mechanism and phenomenon of lipase adsorption were elucidated from the microscopic point of view.The immobilized enzyme performance of ZIF-8 material was predicted.The main contents and points are as follows.1.The orientation and conformation of Candida rugose lipase adsorbed on a neutral ZIF-8 surface were studied using all-atom molecular dynamics simulation.Two main adsorption orientations were found for CRL on the neutral ZIF-8 surface,with the majority being effective adsorption orientations with the protein active center facing the solution,and a minority being ineffective adsorption orientations with the active center facing the surface.The adsorption process is driven by the synergistic action of electrostatic and van der Waals（vd W）interactions,with vd W interactions dominating in most systems and both vd W and electrostatic interactions dominating in a few systems.Additionally,the existence of ZIF-8 surface pore structure plays a critical role in breaking the surface’s dense hydration layer,providing an anchor for CRL to bind to the surface and allowing CRL to adsorb stably on the ZIF-8 surface.On the other hand,the highly hydrated structure of ZIF-8 also provides a good environment for the conformation of CRL..2.The orientation and conformation of CRL adsorbed on the oppositely charged ZIF-8（i.e.,ZIF-8-COOH,ZIF-8-NH₂）surfaces were investigated by combining parallel tempering Monte Carlo algorithm（PTMC）and all-atom molecular dynamics simulations.The results showed that CRL could be stably adsorbed on the charged ZIF-8 surface,and an ordered adsorption orientation of CRL can be obtained.ZIF-8-NH₂ is a good candidate for lipase immobilization,and the ZIF-8-NH₂ surface can maximize the catalytic activity of CRL.Similarly,the presence of the pore structure on the ZIF-8 surface disrupts the dense water layer on the surface,providing an anchor point for CRL binding and the conformational integrity of CRL through the presence of water molecules.3.Based on the above work combined with parallel tempering Monte Carlo algorithm and all-atom molecular dynamics simulations,the orientation and conformation of CRLs adsorbed on different degrees of surface defects（i.e.,S-ZIF-8,M-ZIF-8,and L-ZIF-8）and other modified surfaces（i.e.,ZIF-8-OH and ZIF-8-NH₂）were investigated.The results show that the adsorption process is dominated by electrostatic and van der Waals interactions.The neutral ZIF-8 surface defect structure can induce the orientation reversal of CRL adsorption and the aminated ZIF-8 surface effectively enhanced the immobilized enzyme’s stability and catalytic activity.In addition,the presence of surface defects increased the contact surface and adsorption sites during the adsorption of CRL on the material surface,allowing CRL to show more robust adsorption stability during adsorption.Likewise,the higher water molecule content of defective ZIF-8 allows for good retention of the CRL conformation.As a material for immobilized enzymes,the three-dimensional porous structure and the tunability of surface properties of ZIF-8 significantly improve the various properties of immobilized enzymes.This work provides theoretical support for applying porous materials for enzyme immobilization.