1Arabinoxylan structures vary based on the degree and pattern of substitution of the 2 β-(1→4)-linked D-xylopyranose backbone with α-L-arabinofuranose units, acetyl groups, 3 uronic acids, and feruloylated side chains. Substitution differences affect arabinoxylans' 4 physicochemical and physiological characteristics. Wheat bran arabinoxylans were 5 hydrolyzed with GH10 and GH11 endo-1,4-β-xylanases, and feruloylated oligosaccharides 6 were isolated and purified (Amberlite XAD-2, Sephadex LH-20, and preparative RP-HPLC). 7 The pure, isolated compounds were structurally characterized via LC-ESI-MS and 1D-and 8 2D-NMR analyses. In addition to the well-known products of endo-xylanase hydrolysis 9 (xylotriose and xylobiose O-3-substituted with a 5-O-trans-feruloyl-α-arabinofuranosyl unit 10 on the middle and non-reducing xylose residue, respectively), novel structural features, 11 including O-2-monosubstitution of xylose adjacent to a xylose carrying feruloylated 12 arabinose, were observed. Additionally, a simultaneously acetylated and feruloylated 13 oligosaccharide has been isolated and tentatively characterized. Oligosaccharides esterified 14with caffeic acid were also isolated, but these were proven to result, at least in part, as 15 artefacts of the enzymatic hydrolysis.
Arabinofuranosidases act synergistically with other enzymes to depolymerize arabinoxylans by cleaving arabinofuranose substituents from the β‐(1→4)‐linked d‐xylopyranose backbone. Because arabinose feruloylation is a barrier to some, but not all, arabinofuranosidases, we investigated the actions of three α‐l‐arabinofuranosidases from the glycoside hydrolase (GH) family 51 on feruloylated arabinoxylan‐oligosaccharide standard compounds with and without feruloyl esterase. GH51 α‐l‐arabinofuranosidases from Clostridium thermocellum and Cellvibrio japonicus both partially released feruloylated arabinose (up to 59% for C. thermocellum). Simultaneous incubation with arabinofuranosidases and feruloyl esterase quantitatively released arabinose from feruloylated standard compounds. Therefore, although feruloylation does not completely obstruct GH51 arabinofuranosidases, synergistic approaches utilizing multiple enzymes remain the most effective tactic for enzymatic breakdown of feruloylated compounds.
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