Oriented Coimmobilization of Oxidase and Catalase on Tailor-Made Ordered Mesoporous Silica

Abstract

Mesoporous silica materials are promising carriers for enzyme immobilization in heterogeneous biocatalysis applications. By tailoring their pore structural framework, these materials are designable for appropriate enzyme binding capacity and internal diffusivity. To supply O2 efficiently to solid-supported immobilized enzymes represents a core problem of heterogeneously catalyzed oxidative biotransformations. In this study, therefore, we synthesized and compared three internally well-ordered and two amorphous silica materials as enzyme carriers, each of those with pore sizes of ≥10 nm, to enable the coimmobilization of d-amino-acid oxidase (79 kDa) and catalase (217 kDa). Both enzymes were fused to the silica-binding module Zbasic2 to facilitate their selective and oriented immobilization directly from crude protein mixtures on native silica materials. Analyzing the effects of varied pore architecture and internal surface area on the performance of the immobilized bienzymatic system, we showed that a uniform pore structural framework was beneficial for enzyme loading (≥70 mg protein/g carrier), immobilization yield (≥90%), surface and pore volume filling without hindered adsorption, and catalytic effectiveness (≥60%) of the coimmobilizate. Using the best carrier LP-SBA-15, we obtained a solid oxidase-catalase preparation with an activity of 2000 μmol/(min g_material) that was recyclable and stable during oxidation of d-methionine. These results affirm a strategy of optimizing immobilized O2-dependent enzymes via tunable internal structuring of the silica material used as carrier. They thus make a significant advance toward the molecular design of heterogeneous oxidation biocatalysts on mesoporous silica supports.