No abstract

Isoflavone occurs abundantly in leguminous seeds in the form of glycoside and aglycone. However, isoflavone glycoside has anti-nutritional effect and only the free type is beneficial to human health. In the present study we identified a β-glucosidase from thermophilic Neosartorya fischeri P1, termed NfBGL1, capable of efficiently converting isoflavone glycosides into free isoflavones. The gene, belonging to glycoside hydrolase family 3, was successfully overexpressed in Pichia pastoris at high cell density in a 3.7-l fermentor. Purified recombinant NfBGL1 had higher specific activity (2189±1.7 U/mg) and temperature optimum (80°C) than other fungal counterparts when using p-nitrophenyl β-d-glucopyranoside as the substrate. It retained stable at temperatures up to 70°C and over a broad pH range of 3.0−10.0. NfBGL1 had broad substrate specificity including glucosidase, cellobiase, xylanase and glucanase activities, and displayed preference for hydrolysis of β-1,2 glycosidic bond rather than β-1,3, β-1,4, β-1,6 bonds. The enzyme showed high bioconversion ability for major soybean isoflavone glycosides (daidin, gensitin and glycitin) into free forms. These properties make NfBGL1 potential for the wide use in the food, feed, pharmacy and biofuel industries.

A new α-arabinofuranosidase gene (Hiabf43) was cloned from Humicola insolens Y1 and successfully expressed in Pichia pastoris GS115. Deduced HiAbf43 contained a putative signal peptide and a catalytic domain of glycoside hydrolase (GH) family 43. Purified recombinant HiAbf43 showed optimal activity at pH 5.0 and 50 °C, and was active over a broad pH range. The enzyme was specific for the cleavage of α-1,3-linkage and showed high activity against 4-nitrophenyl α-L-arabinofuranoside, debranched arabinan, and sugar beet arabinan. Sequential addition of HiAbf43 followed by Xyn11A increased the degradation efficiency of birchwood and beechwood xylans but not wheat arabinoxylan. The synergy degree was high up to 1.21-fold.