Glucuronoxylan 3-O-acetylated on uronic acid-substituted xylopyranosyl residues and its hydrolysis by GH10, GH11 and GH30 endoxylanases

[Display omitted] •CE6 acetylxylan esterase almost completely deacetylated aspen acetylglucuronoxylan.•Only the 3-O-acetyl group on MeGlcA-substituted xylosyl residues was enzyme resistant.•The 3-O-acetylation did not alter the action of GH10, GH11 and GH30 xylanases.•All three types of xylanases generated unique 3-O-acetylated aldouronic acids.•The compounds represent one of the most enzyme-resistant xylan structural motifs. Glucuronoxylan selectively 3-O-acetylated on uronic acid-substituted xylopyranosyl residues was prepared by deacetylation of steam explosion-extracted aspenwood acetylglucuronoxylan by the CE6 acetylxylan esterase from Orpinomyces sp. The 3-O-acetylation of MeGlcA-substituted xylopyranosyl residues did not influence the mode of action of GH10, 11 and 30 xylanases, resulting in similar aldouronic acids as are found in alkali-extracted glucuronoxylan hydrolysates. In all three hydrolysates of the selectively acetylated glucuronoxylan, however, 3-O-acetylated aldouronic acids predominated over non-acetylated ones, suggesting that in native aspenwood xylan almost all MeGlcA-substituted Xylp residues are 3-O-acetylated. The results contribute to current knowledge of the mode of action of xylanases and also point to a possibility to produce novel types of xylooligosaccharides. The 3-O-acetylated aldouronic acids, along with the specifically 3-O-acetylated glucuronoxylan, may serve as model substrates for searching for a novel type of esterase able to liberate this MeGlcA-shielded acetyl group. Such esterases are important to improve significantly saccharification yields.