Characterization and structural analysis of a novel glucurono-xylanase from Chaetomium fimeti and its potential...

A novel glucurono-xylanase gene (CfXyn11A) was successfully expressed in Pichia pastoris, which was isolated from Chaetomium fimeti. After 120 h of high-density fermentation in a 5 L bioreactor, xylanase activity reached 635.84 U/mL (with a protein concentration of 7.95 mg/mL). At pH 7.0 and 55 °C, the purified glucurono-xylanase CfXyn11A showed optimal activity, with an enzyme specific activity of 320 U/mg (purified) against glucuronoxylan. Structural analysis indicated that CfXyn11A could recognize ferulic acid-1,5-arabinofuranose-α1,3-xylotriose (FAX3) and 4-O-methylglucuronic acid (MeGA). Arg135 specifically interacted with the arabinose side chain, and Gln138 specifically interacted with the ferulic acid side chain of FAX3 via hydrogen bonding, while Gln149, Tyr86, and Asn84 target the glucuronic acid side chain through hydrogen bonds. CfXyn11A was applied in pear juice clarification (3 U/mL, 55 °C, 40 min), the clarification degree of pear juice increased by 34 %. Then, it was found that the addition of 0.2 % ascorbic acid (AA) could maintain better color, resulting in a browning inhibition rate of 30.61 %. Besides, the total flavonoid content (TFC) and total phenolic compounds (TPC) concentrations were 78.44 μg/mL and 3.15 μg/mL, respectively, following ultra-high-pressure (UHP) treatment. This study introduces CfXyn11A as a novel glucurono-xylanase that selectively recognizes FAX3 and MeGA, demonstrating significant potential for improving pear juice clarification and offering a new strategy for enzyme-based juice processing.