Efficient bioconversion of epimedin C to icariin by a glycosidase from Aspergillus nidulans

Herba Epimedii is a traditional Chinese herbal medicine that contains a mixture of bioactive flavonoid glycosides. Among them, icariin has the most outstanding bioactive functions, while epimedin C exhibits substantial toxicity. A recombinant alpha-L-rhamnosidase ((syn)AnRhaE) from Aspergillus nidulans was expressed in Escherichia coli to promote the efficient bioconversion of epimedin C to icariin. A hydrolase activity of 574.5 U L-1 was acquired via optimized fed-batch fermentation in a 5-L bioreactor. The enzyme proved to be stable in an acidulous pH range below 55 degrees C with an optimal pH of 4.5 and optimal temperature of 55 degrees C. Epimedin C (1 g L-1) was 100% converted to icariin within 90 min using recombinant cells. The resting cells proved to be selective for epimedin C and 2 ''-O-rhamnosylicariside II in crude extracts of the epimedium plant. This work provides an original and efficient biocatalyst system that can be applied in industrialized production of icariin.