Alkaline protease from alkaliphilic Bacillus sp. NPST-AK15 was immobilized onto functionalized and non-functionalized rattle-type magnetic core@mesoporous shell silica (RT-MCMSS) nanoparticles by physical adsorption and covalent attachment. However, the covalent attachment approach was superior for NPST-AK15 protease immobilization onto the activated RT-MCMSS-NH₂nanoparticles and was used for further studies. In comparison to free protease, the immobilized enzyme exhibited a shift in the optimal temperature and pH from 60 to 65 °C and pH 10.5-11.0, respectively. While free protease was completely inactivated after treatment for 1 h at 60 °C, the immobilized enzyme maintained 66.5% of its initial activity at similar conditions. The immobilized protease showed higher k cat and K m , than the soluble enzyme by about 1.3-, and 1.2-fold, respectively. In addition, the results revealed significant improvement of NPST-AK15 protease stability in variety of organic solvents, surfactants, and commercial laundry detergents, upon immobilization onto activated RT-MCMSS-NH₂nanoparticles. Importantly, the immobilized protease maintained significant catalytic efficiency for ten consecutive reaction cycles, and was separated easily from the reaction mixture using an external magnetic field. To the best of our knowledge this is the first report about protease immobilization onto rattle-type magnetic core@mesoporous shell silica nanoparticles that also defied activity-stability tradeoff. The results clearly suggest that the developed immobilized enzyme system is a promising nanobiocatalyst for various bioprocess applications requiring a protease.
Keywords: Alkaliphiles; Enzyme immobilization; Nanobiotechnology; Proteases; Rattle-type magnetic core@mesoporous shell silica nanoparticles.