Mode of action of acetylxylan esterases on acetyl glucuronoxylan and acetylated oligosaccharides generated by a GH10 endoxylanase

Background Substitutions on the xylanmain chain are widely accepted to limit plant cell wall degradability andacetylations are considered as one of the most important obstacles. Hence,understanding the modes of action of a range of acetylxylan esterases (AcXEs)is of ample importance not only to increase the understanding of the enzymologyof plant decay/bioremediation but also to enable efficient bioconversion ofplant biomass. Methods In this study, the modes of action of acetylxylanesterases (AcXEs) belonging to carbohydrate esterase (CE) families 1, 4, 5 and6 on xylooligosaccharides generated from hardwood acetyl glucuronoxylan werecompared using MALDI ToF MS.

Supporting data were obtained by followingenzymatic deacetylation by ¹H NMR spectroscopy. Conclusions None ofthe used enzymes were capable of complete deacetylation, except from linearxylooligosaccharides which were completely deacetylated by some of theesterases in the presence of endoxylanase. A clear difference was observedbetween the performance of the serine-type esterases of CE families 1, 5 and 6,and the aspartate-metalloesterases of family CE4. The difference is mainly dueto the inability of CE4 AcXEs to catalyze deacetylation of 2,3-di-O-acetylatedxylopyranosyl residues. Complete deacetylation of a hardwood acetylglucuronoxylan requires additional deacetylating enzyme(s). Generalsignificance The results contribute to the understanding of microbialdegradation of plant biomass and outline the way to achieve complete saccharificationof plant hemicelluloses which did not undergo alkaline pretreatment.