Enzyme Immobilization in Mesoporous Silica for Enhancement of Thermostability

Direct enzyme immobilization by encapsulation in the pores of mesoporous silica particles enhances protein thermal and chemical stability. In this study, we investigated the effect of pore size on the thermostability and catalytic activity of Escherichia coli glutaminase YbaS encapsulated under high temperature conditions in two SBA-type mesoporous silicas: SBA5.4 and SBA10.6 with pore diameters of 5.4 and 10.6 nm, respectively. The changes in enzyme conformation under high temperature conditions were assessed using PSA, a benzophenoxazine-based fluorescent dye that is sensitive to denatured aggregated proteins. The results showed that YbaS adsorption to SBA10.6 was higher than that to SBA5.4 and that SBA10.6-encapsulated YbaS was more resistant to heat treatment and maintained higher conformational stability than SBA5.4-encapsulated or free enzyme. Moreover, the heat-treated YbaS-SBA10.6 composite demonstrated high catalytic activity in glutamine hydrolysis. Thus, enzyme encapsulation in suitable silica mesopores can prevent heat-induced denaturation and subsequent aggregation of the enzyme.