Characterization of the Highly Efficient Acid-Stable Xylanase and β-Xylosidase System from the Fungus ATHUM 8891 ( ATHUM 8891).

Two novel xylanolytic enzymes, a xylanase and a β-xylosidase, were simultaneously isolated and characterized from the extracellular medium of ATHUM 8891 (anamorph ATHUM 8891), grown on Brewer's Spent Grain as a sole carbon source. They represent the first pair of characterized xylanolytic enzymes of the genus and the first extensively characterized xylanolytic enzymes of the family . In contrast to other xylanolytic enzymes isolated from the same family, both enzymes are characterized by exceptional thermostability and stability at low pH values, in addition to activity optima at temperatures around 65 °C and acidic pH values. Applying nano-LC-ESI-MS/MS analysis of the purified SDS-PAGE bands, we sequenced fragments of both proteins. Based on sequence-comparison methods, both proteins appeared conserved within the genus . Xylanase was classified within Glycoside Hydrolase family 11 (GH 11), while β-xylosidase in Glycoside Hydrolase family 3 (GH 3). The two enzymes showed a synergistic action against xylan by rapidly transforming almost 40% of birchwood xylan to xylose. The biochemical profile of both enzymes renders them an efficient set of biocatalysts for the hydrolysis of xylan in demanding biorefinery applications.