High-level expression, purification and characterization of recombinant Aspergillus oryzae alkaline protease in Pichia pastoris.

The alkaline protease gene from Aspergillus oryzae was cloned, and then it was successfully expressed in the heterologous Pichia pastoris GS115 with native signal peptide or alpha-factor secretion signal peptide. The yield of the recombinant alkaline protease with native signal peptide was about 1.5-fold higher than that with alpha-factor secretion signal peptide, and the maximum yield of the recombinant alkaline protease was 513 mg/L, which was higher than other researches. The recombinant alkaline protease was purified by ammonium sulfate precipitation, ion exchange chromatography and gel filtration chromatography. The purified recombinant alkaline protease showed on SDS-PAGE as a single band with an apparent molecular weight of 34 kDa. The recombinant alkaline protease was identical to native alkaline protease from A. oryzae with regard to molecular weight, optimum temperature for activity, optimum pH for activity, stability to pH, and similar sensitivity to various metal ions and protease inhibitors. The native enzyme retained 61.18% of its original activity after being incubated at 50 degrees C for 10 min, however, the recombinant enzyme retained 56.22% of its original activity with same disposal. The work demonstrates that alkaline protease gene from A. oryzae can be expressed largely in P. pastoris without affecting its enzyme properties and the recombinant alkaline protease could be widely used in various industrial applications.