Crystal structure and functional characterization of an oligosaccharide dehydrogenase from Pycnoporus cinnabarinus provides insights into fungal breakdown of lignocellulose

Abstract Background Fungal glucose dehydrogenases (GDHs) are FAD-dependent enzymes belonging to the glucose-methanol-choline oxidoreductase superfamily. These classified in “Auxiliary Activity” family 3 (AA3) of Carbohydrate-Active enZymes database, and more specifically subfamily AA3_2, that also includes closely related flavoenzymes aryl-alcohol oxidase 1-oxidase. Based on sequence similarity known fungal GDHs, an AA3_2 enzyme active was identified genome Pycnoporus cinnabarinus , a model Basidiomycete able completely degrade lignin. Results In our work, substrate screening functional characterization showed unexpected preferential activity this toward oligosaccharides containing ?(1?3) glycosidic bond, with highest efficiency observed for disaccharide laminaribiose. Despite its we defined novel enzymatic activity, namely oligosaccharide dehydrogenase (ODH), enzyme. The crystallographic structures ODH sugar-free form complex laminaribiose unveiled peculiar saccharide recognition mechanism which is not shared previously characterized AA3 oxidoreductases accounts oligosaccharides. sugar molecules site mainly stabilized through CH-? interactions aromatic residues rather than hydrogen bonds highly conserved residues, as instead oxidases date. Finally, three sugar-binding sites were external surface, might be importance physiological scenario. Conclusions Structure–function analysis consistent role auxiliary lignocellulose degradation unveils yet another function within database. Our findings allow deciphering molecular determinants binding provide insight into ODH, opening new perspectives exploit biodiversity transformation fuels chemicals.