Cloning and Expression of an Aspartic Protease Gene from Trichoderma asperellum and Its Application to the Hydrolysis of Soy Protein Isolate

Abstract

In order to explore the application potential of aspartic protease (Asp) of Trichoderma sp., the protease gene (asp) was cloned from Trichoderma asperellum by real-time polymerase chain reaction, and was successfully expressed in Pichia Pastoris GS115. The recombinant protease (rAsp) was isolated and purified, and its biochemical properties and its effectiveness in hydrolyzing soy protein isolate (SPI) were studied. The results showed that the protease encoded by the asp gene belonged to the aspartic protease family, and its sequence identity with other members of this family was up to 47.74%. The protease activity of rAsp in the fermentation broth obtained by induced expression in a conical flask was 25.8 U/mL. The optimal reaction pH and temperature of rAsp were 2.5 and 45 ℃, respectively, and rAsp had strong stability in the pH range of 2.0–6.0 and below 45 ℃. The activity of rAsp was promoted by Cu2+ and Mn2+ but inhibited by Fe3+, sodium dodecylsulfate (SDS) and pepstantin. The hydrolysis efficiency of SPI with rAsp was 7.7% higher than that with commercial pepsin. Moreover, the ability of rAsp to reduce the allergenicity of β-conglycinin and glycinin was 1.4 and 1.8 times greater than that of the pepsin, respectively. Therefore, rAsp has potential application in soy protein processing.

Keywords

• trichoderma asperellum; recombinant aspartic protease; biochemical properties; soy protein isolate; allergenicity