Comparison of catalytic properties of acetyl xylan esterases from three carbohydrate esterase families

Most natural hemicelluloses are acetylated. Some xylans carryalso esterified phenolic acid side groups. Carbohydrate-actingesterases (CE) have been recently classified according tostructural similarities into several CE families. However, thisclassification does not necessarily predict the substrate specificity of these enzymes. In this work eight different hemicellulose-acting esterases from three different esterase families were studied. The substrate specificities and the modes of action of esterases from different families varied significantly. Some esterases acted on a wide range of substrates, i.e. on acetyl and on feruloyl groups in xylan and on acetyl groups in glucomannan, while others were strictly specific for one substrate. The CE family 1 and 5 esterases deacetylated first at the position 3 and 2, respectively, whereas the CE family 4 esterase performed a fast double deacetylation at both positions in methyl per-O-acetyl-β-D-xylopyranoside.