1 Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke Street West, Montreal, QC, H4B 1R6, Canada.
2 Department of Food and Nutrition, Faculty of Agriculture and Forestry, University of Helsinki, Agnes Sjöbergin katu 2, 00014, Helsinki, Finland.
3 Fungal Physiology, Westerdijk Fungal Biodiversity Institute & Fungal Molecular Physiology, Utrecht University, Uppsalalaan 8, 3584CT Utrecht, The Netherlands.
4 Department of Microbiology, Faculty of Agriculture and Forestry, University of Helsinki, Viikinkaari 9, 00014, Helsinki, Finland.
5 SPR-MS Facility, Department of Pharmacology & Therapeutics, McGill University, 3655 Prom. Sir William Osler, Montreal, QC, H3G 1Y6, Canada.
6 Department of Food and Nutrition, Faculty of Agriculture and Forestry, University of Helsinki, Agnes Sjöbergin katu 2, 00014, Helsinki, Finland. Electronic address: maija.tenkanen@helsinki.fi

Acetyl esterases are an important component of the enzymatic machinery fungi use to degrade plant biomass and are classified in several Carbohydrate Esterase families of the CAZy classification system. Carbohydrate Esterase family 16 (CE16) is one of the more recently discovered CAZy families, but only a small number of its enzyme members have been characterized so far, revealing activity on xylan-derived oligosaccharides, as well as activity related to galactoglucomannan. The number of CE16 genes differs significantly in the genomes of filamentous fungi. In this study, four CE16 members were identified in the genome of Aspergillus niger NRRL3 and it was shown that they belong to three of the four phylogenetic Clades of CE16. Significant differences in expression profiles of the genes and substrate specificity of the enzymes were revealed, demonstrating the diversity within this family of enzymes. Detailed characterization of one of these four A. niger enzymes (HaeA) demonstrated activity on oligosaccharides obtained from acetylated glucuronoxylan, galactoglucomannan and xyloglucan, thus establishing this enzyme as a general hemicellulose acetyl esterase. Their broad substrate specificity makes these enzymes highly interesting for biotechnological applications in which deacetylation of polysaccharides is required.