Characterization of a xylitol dehydrogenase from Aspergillus flavus and its application in l-xylulose production

An NAD(+)-dependent xylitol dehydrogenase from A. flavus (AfXDH) was cloned and successfully expressed in Escherichia coli. AfXDH gene sequence revealed an open reading frame of 1,110 bp, encoding a polypeptide of 369 amino acids with a calculated molecular mass of 38,893 Da. Among various polyols, sorbitol and xylitol were preferred substrates of AfXDH with K-m values of 16.2 and 16.9 mM, respectively. AfXDH showed the highest activity in Tris-glycine-NaOH buffer (pH 9.5) at 50 & DEG;C; it required Zn2+ or Mn2+ for enzyme activity. The half-life at 40? and half denaturation temperature (T-1/2) was 200 min and 45?, respectively. Bioinformatic analyses along with biochemical properties confirmed that AfXDH belonged to the medium-chain dehydrogenase/reductase family. AfXDH exhibits higher thermostability and k ( cat ) values than those of other XDHs. The feasibility of using AfXDH in l-xylulose production was demonstrated. AfXDH, when coupled with Streptococcus pyogenes NADH oxidase, efficiently converted xylitol to l-xylulose with 97% yield, suggesting its usefulness for the industrial l-xylulose production from xylitol.