Fungal PQQ-dependent dehydrogenases and their potential in biocatalysis

•The first eukaryotic PQQ-dependent dehydrogenase was discovered in a plant saprophytic fungus.•This multi-domain enzyme, CcPDH, defines a new family of PQQ-dependent eukaryotic enzymes.•CcPDH oxidizes 2-keto-d-glucose, l-fucose, and rare pyranoses, such as d-arabinose and l-galactose.•The dehydrogenase domain of CcPDH is the founding member of family AA12 in CAZy.•CcPDH can activate on LPMOs. In 2014, the first fungal pyrroloquinoline-quinone (PQQ)-dependent enzyme was discovered as a pyranose dehydrogenase from the basidiomycete Coprinopsis cinerea (CcPDH). This discovery laid the foundation for a new Auxiliary Activities (AA) family, AA12, in the Carbohydrate-Active enZymes (CAZy) database and revealed a novel enzymatic activity potentially involved in biomass conversion. This review summarizes recent progress made in research on this fungal oxidoreductase and related enzymes. CcPDH consists of the catalytic PQQ-binding AA12 domain, an N-terminal cytochrome b AA8 domain, and a C-terminal family 1 carbohydrate-binding module (CBM1). CcPDH oxidizes 2-keto-d-glucose (d-glucosone), l-fucose, and rare sugars such as d-arabinose and l-galactose, and can activate lytic polysaccharide monooxygenases (LPMOs). Bioinformatic studies suggest a widespread occurrence of quinoproteins in eukaryotes as well as prokaryotes.