Characterization of a novel thermostable glucose-tolerant GH1 β-glucosidase from the hyperthermophile Ignisphaera aggregans and its application in the efficient production of baohuoside I from icariin and total epimedium flavonoids

Abstract

The minor flavonoid baohuoside I from Herba epimedii has better bioactivities than its precursor compounds icariin and other major epimedium flavonoids. In this study, a novel β-glucosidase gene (Igag_0940) was cloned and expressed to improve the conversion efficiency in the process of baohuoside I production. For the first time, the recombinant IagBgl1 was purified and then identified uniquely as a trimer in GH 1 family protein from Archaea. The maximum activity of recombinant IagBgl1 was exhibited at 95 °C, pH 6.5, and it retained more than 70% after incubation at 90 °C for 4 h. IagBgl1 had a high catalytic activity towards icariin with a K_cat/K_m ratio of 488.19 mM^-1·s^-1. Under optimized conditions (65 °C, pH 6.5, 0.8 U/mL enzyme, and 90 min), 10 g/L icariin was transformed into 7.564 g/L baohuoside I with a molar conversion of 99.48%. Meanwhile, 2.434 g/L baohuoside I was obtained from 10 g/L total epimedium flavonoids by a two-step conversion system built with IagBgl1 and two other thermostable enzymes. This is the first report of enzymatic conversion for producing baohuoside I by thermostable enzymes.

Keywords: Baohuoside I; Ignisphaera aggregans; The total epimedium flavonoids; Thermostability; β-glucosidase.