Site-directed lysine modification of xylanase for oriented immobilization onto silicon dioxide nanoparticles.

Enhanced covalent immobilization of xylanase from Chaetomium globosum (XylCg) onto SiO2 nanoparticles was achieved by the modification of surface residues. The mutation of surface residues to lysine by site-directed mutagenesis increased the immobilization efficiency (IE) and immobilization yield (IY). The immobilized mutant XylCg (N172K-H173K-S176K-K133A-K148A) exhibited an IY of 99.5% and IE of 135%, which were 1.8- and 4.3-fold higher than immobilized wildtype (WT). Regarding the catalytic properties, the kcat and kcat/Km values were 1850 s-1 and 2030 mL mg-1 s-1 for the immobilized mutant, and 331 s-1 and 404 mL mg-1 s-1 for the immobilized WT, respectively. Additionally, the immobilized mutant exhibited four times higher thermal stability than the immobilized WT at 60 °C. These results suggest that surface-mutated lysine residues confer good stability and orientation on the support matrix, thus improving the overall performance of xylanase.