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Eukaryotic Cell, October 2003, p. 867-875, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.867-875.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

D-Xylose Metabolism in Hypocrea jecorina: Loss of the Xylitol Dehydrogenase Step Can Be Partially Compensated for by lad1-Encoded L-Arabinitol-4-Dehydrogenase

Bernhard Seiboth,* Lukas Hartl, Manuela Pail, and Christian P. Kubicek

Abteilung für Angewandte Biochemie und Gentechnologie, Institut für Verfahrenstechnik, Umwelttechnik, und Technische Biowissenschaften, A-1060 Wien, Austria

Received 24 March 2003/ Accepted 16 July 2003

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.

* Corresponding author. Mailing address: Abteilung für Angewandte Biochemie und Gentechnologie, Institut für Verfahrenstechnik, Umwelttechnik, und Technische Biowissenschaften, TU Wien, Getreidemarkt 9-1665, A-1060 Wien, Austria. Phone: 43-1-58801-17255. Fax: 43-1-58801-17299. E-mail: bseiboth{at}mail.zserv.tuwien.ac.at.

Eukaryotic Cell, October 2003, p. 867-875, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.867-875.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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