title: Characterization of a unique Caulobacter crescentus aldose-aldose oxidoreductase having dual activities.
abstract: We describe here the characterization of a novel enzyme called aldose-aldose oxidoreductase (Cc AAOR; EC 1.1.99) from Caulobacter crescentus. The Cc AAOR exists in solution as a dimer, belongs to the Gfo/Idh/MocA family and shows homology with the glucose-fructose oxidoreductase from Zymomonas mobilis. However, unlike other known members of this protein family, Cc AAOR is specific for aldose sugars and can be in the same catalytic cycle both oxidise and reduce a panel of monosaccharides at the C1 position, producing in each case the corresponding aldonolactone and alditol, respectively. Cc AAOR contains a tightly-bound nicotinamide cofactor, which is regenerated in this oxidation-reduction cycle. The highest oxidation activity was detected on D-glucose but significant activity was also observed on D-xylose, L-arabinose and D-galactose, revealing that both hexose and pentose sugars are accepted as substrates by Cc AAOR. The configuration at the C2 and C3 positions of the saccharides was shown to be especially important for the substrate binding. Interestingly, besides monosaccharides, Cc AAOR can also oxidise a range of 1,4-linked oligosaccharides having aldose unit at the reducing end, such as lactose, malto- and cello-oligosaccharides as well as xylotetraose. (1)H NMR used to monitor the oxidation and reduction reaction simultaneously, demonstrated that although D-glucose has the highest affinity and is also oxidised most efficiently by Cc AAOR, the reduction of D-glucose is clearly not as efficient. For the overall reaction catalysed by Cc AAOR, the L-arabinose, D-xylose and D-galactose were the most potent substrates.
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland. martina.andberg@vtt.fi.
authors.forename: Martina
authors.initials: M
authors.lastname: Andberg
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Maaheimo
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Esa-Pekka
authors.initials: EP
authors.lastname: Kumpula
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Harry
authors.initials: H
authors.lastname: Boer
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Mervi
authors.initials: M
authors.lastname: Toivari
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
authors.affiliation: VTT, Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Anu
authors.initials: A
authors.lastname: Koivula
mesh_terms: D000449:Aldehyde Reductase / Q000378:metabolism*; D055162:Biocatalysis; D016935:Caulobacter crescentus / Q000201:enzymology* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D009005:Monosaccharides / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010088:Oxidoreductases / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014994:Xylose / Q000378:metabolism; D017355:Zymomonas / Q000201:enzymology / Q000378:metabolism
chemical_list: D009005:Monosaccharides; D014994:Xylose; D010088:Oxidoreductases; D000449:Aldehyde Reductase; C074291:glucose-fructose oxidoreductase; D005947:Glucose
keywords: Carbohydrate; Enzyme catalysis; Glucose-fructose oxidoreductase; Nuclear magnetic resonance; Tightly-bound cofactor