Glucuronoxylans in angiosperms are O-acetylated in their native form and carry O-2 and/or O-3 acetylation on the backbone xylopyranosyl (Xylp) residues. Xylp substituted with 4-O-methyl glucopyranosyl uronic acid (MeGlcA) on O-2 are also invariably acetylated on O-3 in many xylans. Acetyl groups restrict the action of microbial xylan-degrading enzymes and thus efficient saccharification. Two types of esterases are known to take part in xylan deacetylation: acetyl esterases (AE), which act on short xyloologosaccharides (XOS), and acetyl xylan esterases (AXE) which are able to deacetylate polymeric xylans. AXEs described thus far belong to carbohydrate esterase (CE) families 1-7 and 12. The AEs belong to the lately established family CE16. We have compared the roles of two AEs and three AXEs in deacetylation of neutral and MeGlcA-substituted XOS by applying mass spectrometric analysis. AEs were found to remove primary only one acetyl group from the non-reducing end of XOS. In contrast, AXEs completely deacetylated longer neutral XOS but had difficulties with the shorter ones. Complete deacetylation was obtained after the combined action of AEs and AXEs. MeGlcA substituents restricted the action of AXEs and the remaining acidic XOS were mainly substituted with one MeGlcA and one acetyl group. These resisting structures were degraded only after combined action of AE, AXE and a-glucuronidase. When used together with xylan backbone degrading endoxylanase and �-xylosidase, both AE and AXE enhanced the hydrolysis of complex XOS almost equally.

Role of family CE16 acetyl esterases in xylan deacetylation and saccharification

247th National Meeting (2014)

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