Cloning, expression and characterization of metalloproteinase HypZn from Aspergillus niger

A predicted metalloproteinase gene, HypZn, was cloned from Aspergillus nigerCGMCC 3.7193 and expressed in Pichia pastoris GS115, and the physicochemical characteristics of recombinant HypZn were investigated after separation and purification. The results showed that the specific activity of the purified HypZn reached 1859.2 U/mg, and the optimum temperature and pH value of HypZn were 35 degrees C and 7.0, respectively. HypZn remained stable both at 40 degrees C and at pH values between 5.0 and 8.0. The preferred substrate of HypZn was soybean protein isolates, and the K-m and V-max values were 21.5 mu mol/mL and 4926.6 mu mol/(mL center dot min), respectively. HypZn was activated by Co2+ and Zn2+ and inhibited by Cu2+ and Fe2+. The degree of soybean protein isolate hydrolysis reached 14.7%, and the hydrolysates were of uniform molecular weight. HypZn could tolerate 5000 mM NaCI and completely lost its activity after 30 min at 50 degrees C. The enzymological characterizations indicated that HypZn has great application potential in the food industry, especially in fermented food processing.