Lipase immobilized to a short alkyl chain-containing zwitterionic polymer grafted on silica nanoparticles: Moderate activation and significant increase of thermal stability

Abstract

We recently reported that Candida rugosa lipase (CRL) bonded on zwitterionic polymer-grafted silica nanoparticles (SNPs-pOD-CRL) showed remarkably enhanced catalytic activity and substrate affinity. The polymer, pOD, with long cetane side chains, was a polymer derivative of poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylethylenediamine. Here, a new zwitterionic polymer with shorter alkyl side chains was synthesized by reaction between poly(isobutylene-alt-maleic anhydride) and N,N-dimethylethylenediamine, denoted as pID, and grafted onto SNPs to develop a new zwitterionic support, SNPs-pID. CRL was coupled onto SNPs-pID, and SNPs-pID-CRL was extensively characterized and compared with SNPs-pOD-CRL. It was found that SNPs-pID-CRL presented higher enzyme-substrate affinity and catalytic activity than free lipase because of lipase activation by the hydrophobic alkyl chains of the polymer. Comparison with SNPs-pOD-CRL demonstrated that decreased hydrophobicity of the side chains was unfavorable for lipase activation, resulting in lower activity of lipase coupled on pID than on pOD. However, SNPs-pID-CRL exhibited significant increased thermal stability than SNPs-pOD-CRL because higher hydrophilicity of pID favored protein stabilization. These results indicate that a zwitterionic polymer with long alkyl side chains favor lipase activation rather than enzyme stability, while that with short alkyl side chains are beneficial to thermostability. Together, pID-functionalized support is promising for immobilized lipase of long-term applications. The work has thus provided new insights into the fabrication of thermostable immobilized lipase.