Heterologous expression system of Aspergillus oryzae strain isolated from Korean traditional fermented foods
It is important to find an efficient way to amplify the expression of heterologous gene(s) of interest in a fungal expression system for giving the high potential of fungi as genetic resources. Also, mass production systems of foreign protein is important for bio-industry, including pharmaceutical engineering and functional foods production. In addition, for ensuring the safety of the products, it is highly suggested to use GRAS (Generally Recognized As Safe) strain as a host. Here, we constructed a heterologous gene expression system for producing foreign gene product including bacterial origin one such as bacterial β-glucosidase. The produced β-glucosidase is a hydrolytic enzyme and the expression of the gene was stimulated by placing it under the control of the constitutively activated gpdA gene promoter or threonine-inducing alcA gene promoter of Aspergillus nidulans. The pyrithiamine-resistant gene, ptrA, was used as the selection marker for Aspergillus transformation. The signal peptide of A. oryzae α-amylase AmyB was linked to the N-terminus of the bacterial β-glucosidase protein, and 3X FLAG was tagged at the C-terminus. The fungal transformants successfully overexpressed the β-glucosidase gene and expression level was monitored by western blot analysis with anti-FLAG antibody. The functional activity of the protein was detected by esculin converting test. The expression system of A. oryzae could be beneficial for industrial applications.