Cysteine-modified poly(glycidyl methacrylate) grafted onto silica nanoparticles: New supports for significantly enhanced performance of immobilized lipase

Abstract

Our recent work proved that Candida rugosa lipase (CRL) covalently bonded on poly(glycidyl methacrylate) grafted silica nanoparticles (S-pGMA) showed hyperactivation while on a zwitterionic polymer grafted silica exhibited higher stability. Inspired by the research, we have herein proposed to modify S-pGMA with cysteine (Cys) to introduce zwitterionic moieties on the polymer backbones. This design was to simultaneously achieve high activation and stability of immobilized CRL on the new supports. S-pGMA modified with low and high (complete) Cys modifications (S-pGMA-Cys-L/H) were synthesized and CRL was coupled via reactions with epoxy groups (CRL-1 on S-pGMA and CRL-2 on S-pGMA-Cys-L) and carboxyl groups (CRL-3 on S-pGMA-Cys-L and CRL-4 on S-pGMA-Cys-H). The results revealed the hyperactivation of the four enzyme preparations. Kinetic study proved that the immobilization resulted in significantly higher enzymatic reaction efficiency and enzyme-substrate affinity than the free enzyme. More importantly, CRL-2, -3, -4, especially CRL-4 on S-pGMA-Cys-H, presented superior thermal stability and pH tolerance than those of CRL-1. Enzyme coupling reaction also significantly affected the enzyme activation and stability. Taken together, the results indicate that zwitterionization of pGMA by modification with Cys is promising to provide supports for immobilized lipase of high activity and stability, and complete modification of Cys was favorable. The research has thus provided new insights into the development of new materials and methods for enzyme immobilization.