Acetylxylan esterase involved in the degradation of xylan, a major structural heterogeneous polysaccharide found in plant biomass representing the second most abundant polysaccharide in the biosphere, after cellulose. Cleaves acetyl side groups from the xylose backbone units of the hemicellulolytic polymer xylan and xylo-oligosaccharides. Hydrolyzes about 20%-30% of the available acetyl groups on fully acetylated birch wood xylan. Completely deacetylates xylobiose peracetate (fully acetylated), and is active on both the alpha- and beta-forms of the sugar. Also hydrolyzes fully acetylated methyl-beta-D-xylopyranoside and methyl-beta-D-glucopyranoside, and the synthetic substrates 2-naphthyl acetate, 4-nitrophenyl acetate, 4-methylumbelliferyl acetate, and phenyl acetate. Deacetylation of xylans and xylo-oligosaccharides. kcat is 77 sec(-1) with phenyl acetate as substrate. kcat is 190 sec(-1) with 2-naphtyl acetate as substrate. kcat is 123 sec(-1) with 4-methylumbelliferyl acetate as substrate. kcat is 31 sec(-1) with 4-nitrophenyl acetate as substrate (at pH 6.0 and 30 degrees Celsius). Optimum pH is 7.1-9.2. Optimum temperature is 50-60 degrees Celsius. Is stable at 60 degrees Celsius and loses most of its activity at 70 degrees Celsius. Glycan degradation; xylan degradation. Homooctamer, presenting a unique donut-shaped quaternary structure built of two staggered tetrameric rings. The eight active sites are organized in four closely situated pairs, which face the relatively wide internal cavity. Up-regulated by xylose. Belongs to the 'GDSL' lipolytic enzyme family.