A novel carbohydrate : acceptor oxidoreductase from Microdochium nivale

A Microdochium nivale carbohydrate:acceptor oxidoreductase was purified, cl oned, heterologously expressed, and characterized. The gene encoding the pr otein showed one intron, and the ORF showed a sequence with low homology (l ess than or equal to 25% identity or 65% similarity) to other known flavin- containing carbohydrate oxidases. The maturation of the protein required th e cleavage of a tetrameric propeptide in addition to an 18 amino-acid signa l peptide. The enzyme was found to have a relative molecular mass of 55 000 Da, an isoelectric point of 9, and one FAD per protein. It could oxidize m ono-, oligo-, or polymeric saccharides, and transfer their electrons to O-2 or other accepters. When D-glucose served as electron-donating substrate, an activity of 2 s(-1) was observed at pH 5.5 and 23 degreesC. Among variou s oligosaccharides, the enzyme preferred tetrameric dextrins, indicating a favorable interaction of four linked glucose units with the substrate pocke t. The unique structure and ability of oxidizing oligo/polymeric saccharide s suggest a promising prospect of this enzyme for various industrial/medici nal applications.