Characterization of Acetylxylan Esterase from White-Rot Fungus Irpex lacteus

The carbohydrate esterase family 1 (CE1) in CAZy contains acetylxylan esterases (AXEs) and feruloyl esterases (FAEs). Here we cloned a gene coding for an AXE belonging to CE1 from Irpex lacteus (IlAXE1). IlAXE1 was heterologously expressed in Pichia pastoris, and the recombinant enzyme was purified and characterized. IlAXE1 hydrolyzed p-nitrophenyl acetate, alpha-naphthyl acetate and 4-methylumbelliferyl acetate, however, it did not show any activity on ethyl ferulate and methyl p-coumarate. We also examined the activity on partially acetylated and feruloylated xylan extracted from corncob by hydrothermal reaction. Similarly, ferulic and p-coumaric acids were not liberated, and acetic acid was only detected in the reaction mixture. The results indicated that IlAXE1 is an acetylxylan esterase actually reacted to acetyl xylan. However, since IlAXE1 was unable to completely release acetic acid esterifying xylopyranosyl residues, it is assumed that acetyl groups exhibiting resistance to deacetylation by IlAXE1 are present in corn cob xylan.