title: D-xylose metabolism in Hypocrea jecorina: loss of the xylitol dehydrogenase step can be partially compensated for by lad1-encoded L-arabinitol-4-dehydrogenase.
abstract: With the goal of the genetic characterization of the D-xylose pathway in Hypocrea jecorina (anamorph: Trichoderma reesei), we cloned the xdh1 gene, encoding NAD-xylitol dehydrogenase, which catalyzes the second step of fungal D-xylose catabolism. This gene encodes a 363-amino-acid protein which has a mass of 38 kDa, belongs to the zinc-containing alcohol dehydrogenase family, exhibits high sequence identity to the published sequences of xylitol dehydrogenases from yeast origins, but contains a second, additional binding site for Zn2+. The enzyme catalyzed the NAD-dependent oxidation of xylitol and D-sorbitol and the NADH-dependent reduction of D-xylulose and D-fructose. No activity was observed with NADP, L-arabinose, or L-arabinitol. A single 1.4-kb transcript was formed during growth on xylan, D-xylose, L-arabinose, L-arabinitol and, at a lower abundance, xylitol, D-galactose, galactitol, and lactose but not on D-glucose and glycerol. xdh1 deletion mutants exhibited 50% reduced growth rates on D-xylose, whereas growth rates on xylitol remained unaltered. These mutants contained 30% of the xylitol dehydrogenase activity of the parent strain, indicating the presence of a second xylitol dehydrogenase. This activity was shown to be due to lad1-encoded L-arabinitol-4-dehydrogenase, because H. jecorina xdh1 lad1 double-deletion strains failed to grow on D-xylose or xylitol. In contrast, lad1 deletion strains of H. jecorina grew normally on these carbon sources. These results show that H. jecorina contains a single xylitol dehydrogenase which is encoded by xdh1 and is involved in the metabolism of D-xylose and that lad1-encoded L-arabinitol-4-dehydrogenase can compensate for it partially in mutants with a loss of xdh1 function.
authors.affiliation: Abteilung für Angewandte Biochemie und Gentechnologie, Institut für Verfahrenstechnik, Umwelttechnik, und Technische Biowissenschaften, A-1060 Wien, Austria. bseiboth@mail.zserv.tuwien.ac.at
authors.forename: Bernhard
authors.initials: B
authors.lastname: Seiboth
authors.forename: Lukas
authors.initials: L
authors.lastname: Hartl
authors.forename: Manuela
authors.initials: M
authors.lastname: Pail
authors.forename: Christian P
authors.initials: CP
authors.lastname: Kubicek
mesh_terms: D000595:Amino Acid Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D003001:Cloning, Molecular; D050542:D-Xylulose Reductase; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005990:Glycerol / Q000494:pharmacology; D006601:Hexoses / Q000494:pharmacology; D035901:Hypocrea / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D007700:Kinetics; D007064:L-Iditol 2-Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010429:Pentoses / Q000494:pharmacology; D010802:Phylogeny; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013012:Sorbitol / Q000378:metabolism / Q000494:pharmacology; D013379:Substrate Specificity; D013401:Sugar Alcohol Dehydrogenases / Q000235:genetics* / Q000378:metabolism; D014993:Xylitol / Q000378:metabolism / Q000494:pharmacology; D014994:Xylose / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D006601:Hexoses; D010429:Pentoses; D013012:Sorbitol; D014994:Xylose; D013401:Sugar Alcohol Dehydrogenases; C440029:L-arabinitol 4-dehydrogenase; D007064:L-Iditol 2-Dehydrogenase; D050542:D-Xylulose Reductase; D005990:Glycerol; D014993:Xylitol