Highly-Expressed Aspartic Protease from Aspergillus Fumigatus-Mediated Enzymolysis of Silkworm (Bombyx Mori) Pupae Protein

Abstract

Aspartic protease emerges as an optimistic hydrolytic agent to obtain several protein hydrolysates. An aspartic protease gene from Aspergillus fumigatus Af293 was successfully expressed in Pichia pastoris (GS115) and its hydrolytic potentials on silkworm (Bombyx mori) pupae protein were determined. It was optimum at pH 4.0 and 50 °C and stable over pH range 4.0-5.0 and temperatures 45-55 °C with a specific activity of 8408.9 ± 305.6 U/mg. SDS-PAGE analysis revealed the molecular weight of the recombinant protease to be 45 kDa. The half-life (t1/2) of the recombinant protease at 40, 50, 60, and 70 °C was 30, 25, 35, and 20 min, respectively. The protease showed enhanced activity in the presence of Cu2+, Pb2+ and SDS. Its substrate specificity studies were revealed in the order of cleaving ability to Bovine Serum Albumin (BSA) > Silkworm pupae powder (SPP) > Casein > Casein sodium salt (CSS). Upon hydrolysis of silkworm pupae protein, it showed enhanced and plausible hydrolytic potentials, increasing the degree of hydrolysis to 50 ± 6.1% at 6 h, increased solubility by 80%, and improved functional properties. The stable characteristics and hydrolytic performance of the recombinant aspartic protease qualify it for industrial application, especially within the food and related industries.