Gene hunting and semi-rational design of β-xylosidase from Aspergillus aculeatus for highly efficient hydrolysis of astragaloside.

Abstract

Cycloastragenol (CA), the triterpenoid aglycone of astragaloside (ASI), is a telomerase activator and potential anti-aging drug with broad application prospects. Due to the rapid increase of its market demand in recent years, efficient production of CA has attracted increasing attention. In this study, the novel β-xylosidase XylO2 from Aspergillus aculeatus was identified through genome mining. It is capable of hydrolyzing ASI into cycloastragenol-6-O-β-D-glucoside (CMG), a significant precursor in the preparation of CA. Subsequently, structure-guided semi-rational design and virtual screening were used to obtain the highly active variant C23T, which exhibited more than 1.94 and 2.10-fold improvement of catalytic activity with ASI and p-nitrophenyl-β-D-xylopyranoside, respectively. According to structural modelling and molecule docking, the reduced volume of the binding pocket as well as the decreased distance between the substrate and active site residues positively influenced the catalytic activity. Moreover, the conversion yield of 1 g/L ASI increased to 99.10 %, suggesting the potential application of this variant in CA production. This study not only provides a novel enzyme for glycoside hydrolysis, but also offers theoretical insights for understanding and modifying these enzymes.