title: Cloning and expression of a xylitol-4-dehydrogenase gene from Pantoea ananatis.
abstract: The Pantoea ananatis ATCC 43072 mutant strain is capable of growing with xylitol as the sole carbon source. The xylitol-4-dehydrogenase (XDH) catalyzing the oxidation of xylitol to L-xylulose was isolated from the cell extract of this strain. The N-terminal amino acid sequence of the purified protein was determined, and an oligonucleotide deduced from this peptide sequence was used to isolate the xylitol-4-dehydrogenase gene (xdh) from a P. ananatis gene library. Nucleotide sequence analysis revealed an open reading frame of 795 bp, encoding the xylitol-4-dehydrogenase, followed by a 5' region of another open reading frame encoding an unknown protein. Results from a Northern analysis of total RNA isolated from P. ananatis ATCC 43072 suggested that xdh is transcribed as part of a polycistronic mRNA. Reverse transcription-PCR analysis of the transcript confirmed the operon structure and suggested that xdh was the first gene of the operon. Homology searches revealed that the predicted amino acid sequence of the P. ananatis XDH shared significant identity (38 to 51%) with members of the short-chain dehydrogenase/reductase family. The P. ananatis xdh gene was successfully overexpressed in Escherichia coli, XDH was purified to homogeneity, and some of its enzymatic properties were determined. The enzyme had a preference for NAD+ as the cosubstrate, and in contrast to previous reports, the enzyme also showed a side activity for the D-form of xylulose. Xylitol was converted to L-xylulose with a high yield (>80%) by the resting recombinant cells, and the L-xylulose was secreted into the medium. No evidence of D-xylulose being synthesized by the recombinant cells was found.
authors.affiliation: Division of Microbiology and Epidemiology, Department of Basic Veterinary Sciences, Faculty of Veterinary Medicine, University of Helsinki, Finland. johannnes.aarnikunnas@helsinki.fi
authors.forename: J S
authors.initials: JS
authors.lastname: Aarnikunnas
authors.forename: A
authors.initials: A
authors.lastname: Pihlajaniemi
authors.forename: A
authors.initials: A
authors.lastname: Palva
authors.forename: M
authors.initials: M
authors.lastname: Leisola
authors.forename: A
authors.initials: A
authors.lastname: Nyyssölä
mesh_terms: D000595:Amino Acid Sequence; D001709:Biotechnology / Q000379:methods; D003001:Cloning, Molecular; D050542:D-Xylulose Reductase / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D020636:Pantoea / Q000201:enzymology* / Q000235:genetics; D017422:Sequence Analysis, DNA; D014993:Xylitol / Q000378:metabolism; D014996:Xylulose / Q000378:metabolism
chemical_list: D014996:Xylulose; D050542:D-Xylulose Reductase; D014993:Xylitol