A novel xylanase was purified from xylan-spent culture fluid of the fungus Trichoderma reesei RUT-30. The novel xylanase, named XYL IV, exhibited catalytic properties incompatible with previously described endo--xylanases of Trichoderma reesei, XYL I and XYL II [1,2], XYL III  and xylan-hydrolyzing EG I . The enzyme was discovered on the basis of its ability to attack aldotetrahexenuronic acid (HexA-2Xyl-4Xyl-4Xyl) releasing xylopyranosyl residue from the reducing end. XYL IV showed lower affinity toward glucuronoxylan than to acetylated beechwood glucuronoxylan and rhodymenan. Valuble information on the substrate-binding site of XYL IV was obtained by following the bond cleavage frequencies and kinetic parameters k0 /Km of [1-3H]-reducing end labeled xylooligosaccharides. Xyl2 was hydrolyzed by three orders of magnitude slower than longer xylooligosaccharides. Xyl3 and Xyl4 were found to be better enzyme substrates than Xyl5. Regardless, the substrate concentration, all three [1-3H]-xylooligosaccharides were exclusively cleaved at the first glycosidic linkage from the reducing end, to liberate [1-3H]-xylose as the only radioactive product. All experimental evidence suggests that the substrate-binding site of the Xyl IV is composed of three subsites, -II, -I and +I, with a serious steric barrier at the position +II. Degradation of methyl xylotrioside by XYL IV showed, that the hydrolysis leads exclusively to the liberation of the -anomer of Xyl2, which is slowly mutarotated to the -anomer. The time course of signals intensities of the -anomer and -anomer of Xyl2 confirmed that XYL IV is a retaining glycosyl hydrolase sign a double displacement reaction mechanism of hydrolysis of glycosidic linkage.  M. Tenkanen et al. Enzyme Microb. Technol. 14 (1992) 566-574.  P. Biely et al. In: Trichoderma reesei cellulases and other hydrolases (P. Souminen and T. Reinikainen, eds.). Foundation for Biotechnical and Industrial Fermentation Research, Helsinki, Vol. 8, (1993) 125-135.  J.Xu et al. Appl. Microbiol. Biotechnol. 49 (1998) 718-724.  P. Biely et al. Eur. J. Biochem. 200 (1991) 157-163.
|Number of pages||1|
|Publication status||Published - 2003|
|MoE publication type||Not Eligible|
|Event||Molecular, Biochemical, Structural and Genetic Aspects of Carbohydrate-Modifying Enzymes - Galway, Ireland|
Duration: 14 Apr 2003 → 15 Apr 2003
|Conference||Molecular, Biochemical, Structural and Genetic Aspects of Carbohydrate-Modifying Enzymes|
|Period||14/04/03 → 15/04/03|