Characterization of a recombinant zein-degrading protease from Zea mays by Pichia pastoris and its effects on enzymatic hydrolysis of corn starch

A zein-degrading protease (ZDP) from Zea mays was heterologously expressed using Pichia pastoris and its characteristics and effects on enzymatic hydrolysis of corn starch were investigated in the current study. The optimal temperature and pH for ZDP activity was 40 °C and pH 5.0, respectively. The ZDP exhibited a degree of thermal stability and was repressed by some metal ions (5 mM) including Zn²⁺, Mg²⁺, Cu²⁺, Mn²⁺, Ni²⁺, K⁺, and Ca²⁺, especially Mn²⁺ and Cu²⁺, which caused near complete inhibition. Dithiothreitol and β-mercaptoethanol (5 mM) could tremendously increase the ZDP activity by 102.1% and 60.7%, respectively. The ZDP could not tolerate organic solvents such as ethanol, acetone, and dimethyl sulphoxide. The ZDP could efficiently degrade the pure commercial zein and the native zein in the corn, increase the leaching of corn soluble sugars, destroy the cross-linked starch-zein structure, and release the starch granules, consequently increasing the α-amylase hydrolysis of corn starch. The recombinant ZDP might be useful to improve the utilization of corn.

Keywords: Corn starch; Hydrolysis; Recombinant zein-degrading protease; Zein.