Molecular Cloning and Heterologous Expression of an Acid-Stable Endoxylanase Gene from Penicillium oxalicum in Trichoderma reesei

An endoxylanase gene (PoxynA) that belongs to the glycoside hydrolase (GH) family 11 was cloned from a xylanolytic strain, Penicillium oxalicum B3-11(2). PoxynA was overexpressed in Trichoderma reesei QM9414 by using a constitutive strong promoter of the encoding pyruvate decarboxylase (pdc). The high extracellular xylanase activities in the fermentation liquid of the transformants were maintained 29~35-fold higher compared with the wild strain. The recombinant POXYNA was purified to homogeneity, and its characters were analyzed. Its optimal temperature and pH value were 50 degrees C and 5.0, respectively. The enzyme was stable at a pH range of 2.0 to 7.0. Using beechwood as the substrate, POXYNA had a high specific activity of 1,856 +/- 53.5 IU/mg. In the presence of metal ions, such as Cu2+, and Mg2+, the activity of the enzyme increased. However, strong inhibition of the enzyme activity was observed in the presence of Mn2+ and Fe2+. The recombinant POXYNA hydrolyzed birchwood xylan, beechwood xylan, and oat spelt xylan to produce short-chain xylooligosaccharides, xylopentaose, xylotriose, and xylobiose as the main products. This is the first report on the expression properties of a recombinant endoxylanase gene from Penicillium oxalicum. The properties of this endoxylanase make it promising for applications in the food and feed industries.