Identification and magnetic immobilization of a pyrophilous aspartic protease from Antarctic psychrophilic fungus

Aspartic protease is a versatile protease used in the food processing industry. A novel aspartic protease gene (P10) was cloned from an Antarctic psychrophilic fungus Geomyces pannorum and successfully expressed in Aspergillus oryzae when cultured at 20 degrees C. However, purified P10 exhibited optimal activity at 60 degrees C and retained approximately 80% activity at 50-70 degrees C. The Km and Vmax values for this protease toward BSA were 1.01 mg/ml and 4.4 x 10-2 mg/(ml min), respectively, with a specific activity of 585 U/mg. P10 showed broad substrate specificity, with an increased affinity for hydrolyzing kappa-casein than for alpha-casein and beta-casein, indicating a potential value for cheese-making. P10 also presented wide peptide bond specificity toward the oxidized insulin B chain with high affinity for the C-terminus. Furthermore, P10 was immobilized on iron oxide nanoparticles, wherein it displayed improved thermo-stability and pH tolerance. These results provide novel insights into psychrophilic fungal enzymes, suggesting P10 as a potential biocatalyst.