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

Zhang, Chunyu, Liu, Yang, Sun, Yan
Biochemical engineering journal 2019 v.146 pp. 124-131
Candida rugosa, anhydrides, carboxylic ester hydrolases, catalytic activity, enzyme activity, enzyme stability, enzyme substrates, hydrophilicity, hydrophobicity, nanoparticles, polymers, silica, single nucleotide polymorphism, thermal stability, zwitterions
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.