Characterization of new fungal carbohydrate esterase family 1 proteins leads to the discovery of two novel dual feruloyl/acetyl xylan esterases

Background Feruloyl esterases (FAEs) and acetyl xylan esterases (AXEs) are important accessory enzymes in the deconstruction of plant biomass. Carbohydrate Esterase family 1 (CE1) of the Carbohydrate-Active enZymes database contains both fungal FAEs and AXEs, sharing a high amino acid sequence similarity, even though they target different structural molecules on plant cell wall polysaccharides. Results We recently classified fungal CE1 into five subfamilies (CE1_SF1-5). In this study, ten novel fungal CE1 enzymes from different subfamilies were heterologously produced in Aspergillus niger and characterized to gain insight on relationships among these esterases. The enzymes from CE1_SF1 possess AXE activity, as they hydrolyzed p NP-acetate and released acetic acid from wheat arabinoxylan, but were not active towards FAE substrates. CE1_SF5 showed FAE activity as they hydrolyzed methyl ferulate and other FAE related substrates, and release ferulic acid from wheat arabinoxylan. These FAEs preferred feruloylated arabinoxylan over pectin. Two CE1_SF2, sharing over 70% amino acid sequence identity, possessed the opposite activity. Interestingly, one enzyme from CE1_SF1 and one from CE1_SF5 possess dual feruloyl/acetyl xylan esterase (FXE) activity. These dual activity enzymes showed expansion of substrate specificity. Conclusions The new FXEs from CE1 can efficiently release both ferulic acid and acetic acid from feruloylated xylan, making them particularly interesting novel components of industrial enzyme cocktails for plant biomass degradation.