Characterization and mode of action of two acetyl xylan esterases from Chrysosporium lucknowense CI active towards acetylated xylans

摘要

Two novel acetyl xylan esterases, Axe2 and Axe3, from Chrysosporium lucknowense (Cl), belonging to the carbohydrate esterase families 5 and 1, respectively, were purified and biochemically characterized. Axe2 and Axe3 are able to hydrolyze acetyl groups both from simple acetylated xylo-oligosaccharides and complex non-soluble acetylglucuronoxylan. Both enzymes performed optimally at pH 7.0 and 40 °C. Axe2 has a clear preference for acetylated xylo-oligosaccharides (AcXOS) with a high degree of substitution and Axe3 does not show such preference. Axe3 has a preference for large AcXOS (DP 9-12) when compared to smaller AcXOS (especially DP 4-7) while for Axe2 the size of the oligomer is irrelevant. Even though there is difference in substrate affinity towards acetylated xylooligosaccharides from Eucalyptus wood, the final hydrolysis products are the same for Axe2 and Axe3: xylo-oligosaccharides containing one acetyl group located at the non-reducing xylose residue remain as examined using MALDI-TOF MS, CE-LIF and the application of an endo-xylanase (GH 10).