title: Fungal α-arabinofuranosidases of glycosyl hydrolase families 51 and 54 show a dual arabinofuranosyl- and galactofuranosyl-hydrolyzing activity.
abstract: Aspergillus niger possesses a galactofuranosidase activity, however, the corresponding enzyme or gene encoding this enzyme has never been identified. As evidence is mounting that enzymes exist with affinity for both arabinofuranose and galactofuranose, we investigated the possibility that α-L-arabinofuranosidases, encoded by the abfA and abfB genes, are responsible for the galactofuranosidase activity of A. niger. Characterization of the recombinant AbfA and AbfB proteins revealed that both enzymes do not only hydrolyze p-nitrophenyl-α-L-arabinofuranoside (pNp-α-Araf) but are also capable of hydrolyzing p-nitrophenyl-β-D-galactofuranoside (pNp-β-Galf). Molecular modeling of the AbfB protein with pNp-β-Galf confirmed the possibility for AbfB to interact with this substrate, similarly as with pNp-α-Araf. We also show that galactomannan, a cell wall compound of A. niger, containing β-linked terminal and internal galactofuranosyl moieties, can be degraded by an enzyme activity that is present in the supernatant of inulin-grown A. niger. Interestingly, purified AbfA and AbfB did not show this hydrolyzing activity toward A. nigergalactomannan. In summary, our studies demonstrate that AbfA and AbfB, α-L-arabinofuranosidases from different families, both contain a galactofuranose (Galf)-hydrolyzing activity. In addition, our data support the presence of a Galf-hydrolase activity expressed by A. niger that is capable of degrading fungal galactomannan.
authors.affiliation: Department of Molecular Cell Biology and Immunology, VU University Medical Center, van den Boechorststraat 7, NL-1081 BT Amsterdam, The Netherlands. b.tefsen@vumc.nl
authors.forename: Boris
authors.initials: B
authors.lastname: Tefsen
authors.forename: Ellen L
authors.initials: EL
authors.lastname: Lagendijk
authors.forename: Joohae
authors.initials: J
authors.lastname: Park
authors.forename: Michiel
authors.initials: M
authors.lastname: Akeroyd
authors.forename: Doreen
authors.initials: D
authors.lastname: Schachtschabel
authors.forename: Robert
authors.initials: R
authors.lastname: Winkler
authors.forename: Irma
authors.initials: I
authors.lastname: van Die
authors.forename: Arthur F J
authors.initials: AF
authors.lastname: Ram
mesh_terms: D001089:Arabinose / Q000031:analogs & derivatives / Q000378:metabolism; D001234:Aspergillus niger / Q000201:enzymology* / Q000378:metabolism; D005690:Galactose / Q000031:analogs & derivatives; D005696:Galactosidases / Q000378:metabolism*; D005697:Galactosides / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D007444:Inulin / Q000378:metabolism; D008351:Mannans / Q000378:metabolism; D008958:Models, Molecular; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D005697:Galactosides; D008351:Mannans; D011994:Recombinant Proteins; C431714:arabinofuranose; C012990:galactomannan; D007444:Inulin; D001089:Arabinose; D005696:Galactosidases; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase; D005947:Glucose; D005690:Galactose