title: Comparison of fungal carbohydrate esterases of family CE16 on artificial and natural substrates.
abstract: The enzymatic conversion of acetylated hardwood glucuronoxylan to functional food oligomers, biochemicals or fermentable monomers requires besides glycoside hydrolases enzymes liberating acetic acid esterifying position 2 and/or 3 in xylopyranosyl (Xylp) residues. The 3-O-acetyl group at internal Xylp residues substituted by MeGlcA is the only acetyl group of hardwood acetylglucuronoxylan and its fragments not attacked by acetylxylan esterases of carbohydrate esterase (CE) families 1, 4, 5 and 6 and by hemicellulolytic acetyl esterases classified in CE family 16. Monoacetylated aldotetraouronic acid 3″-Ac(3)MeGlcA(3)Xyl3, generated from the polysaccharide by GH10 endoxylanases, appears to be one of the most resistant fragments. The presence of the two substituents on the non-reducing-end Xylp residue prevents liberation of MeGlcA by α-glucuronidase of family GH67 and blocks the action of acetylxylan esterases. The Ac(3)MeGlcA(3)Xyl3 was isolated from an enzymatic hydrolysate of birchwood acetylglucuronoxylan and characterized by (1)H NMR spectroscopy as a mixture of two positional isomers, 3″-Ac(3)MeGlcA(3)Xyl3 and 4″-Ac(3)MeGlcA(3)Xyl3, the latter being the result of acetyl group migration. The mixture was used as a substrate for three members of CE16 family of fungal origin. Trichoderma reesei CE16 esterase, inactive on polymeric substrate, deacetylated both isomers. Podospora anserina and Aspergillus niger esterases, active on acetylglucuronoxylan, deesterified effectively only the 4″-isomer. The results indicate catalytic diversity among CE16 enzymes, but also their common and unifying catalytic ability to exo-deacetylate positions 3 and 4 on non-reducing-end Xylp residues, which is an important step in plant hemicellulose saccharification.
authors.affiliation: Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovak Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Puchart
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway.
authors.forename: Jane W
authors.initials: JW
authors.lastname: Agger
authors.affiliation: INRA, Aix Marseille Univ., BBF, UMR1163, 13288 Marseille, France.
authors.forename: Jean-Guy
authors.initials: JG
authors.lastname: Berrin
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway.
authors.forename: Anikó
authors.initials: A
authors.lastname: Várnai
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Aas, Norway.
authors.forename: Bjørge
authors.initials: B
authors.lastname: Westereng
authors.affiliation: Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovak Republic. Electronic address: peter.biely@savba.sk.
authors.forename: Peter
authors.initials: P
authors.lastname: Biely
mesh_terms: D000107:Acetylation; D000115:Acetylesterase / Q000378:metabolism*; D001234:Aspergillus niger / Q000201:enzymology*; D005656:Fungal Proteins / Q000378:metabolism*; D009844:Oligosaccharides; D013237:Stereoisomerism; D014934:Wood / Q000378:metabolism*; D014990:Xylans / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D009844:Oligosaccharides; D014990:Xylans; D000115:Acetylesterase; C081851:acetylxylan esterase
keywords: Acetylxylan esterase; Aldouronic acid; Aspergillus niger; CE16 family; Hardwood xylan deacetylation; Regiospecificity