title: Xylanase XYN IV from Trichoderma reesei showing exo- and endo-xylanase activity.
abstract: A minor xylanase, named XYN IV, was purified from the cellulolytic system of the fungus Trichoderma reesei Rut C30. The enzyme was discovered on the basis of its ability to attack aldotetraohexenuronic acid (HexA-2Xyl-4Xyl-4Xyl, HexA(3)Xyl(3)), releasing the reducing-end xylose residue. XYN IV exhibited catalytic properties incompatible with previously described endo-β-1,4-xylanases of this fungus, XYN I, XYN II and XYN III, and the xylan-hydrolyzing endo-β-1,4-glucanase EG I. XYN IV was able to degrade several different β-1,4-xylans, but was inactive on β-1,4-mannans and β-1,4-glucans. It showed both exo-and endo-xylanase activity. Rhodymenan, a linear soluble β-1,3-β-1,4-xylan, was as the best substrate. Linear xylooligosaccharides were attacked exclusively at the first glycosidic linkage from the reducing end. The gene xyn4, encoding XYN IV, was also isolated. It showed clear homology with xylanases classified in glycoside hydrolase family 30, which also includes glucanases and mannanases. The xyn4 gene was expressed slightly when grown on xylose and xylitol, clearly on arabinose, arabitol, sophorose, xylobiose, xylan and cellulose, but not on glucose or sorbitol, resembling induction of other xylanolytic enzymes from T. reesei. A recombinant enzyme prepared in a Pichia pastoris expression system exhibited identical catalytic properties to the enzyme isolated from the T. reesei culture medium. The physiological role of this unique enzyme remains unknown, but it may involve liberation of xylose from the reducing end of branched oligosaccharides that are resistant toward β-xylosidase and other types of endoxylanases. In terms of its catalytic properties, XYN IV differs from bacterial GH family 30 glucuronoxylanases that recognize 4-O-methyl-D-glucuronic acid (MeGlcA) substituents as substrate specificity determinants.
authors.affiliation: VTT Technical Research Centre of Finland, Espoo, Finland.
authors.forename: Maija
authors.initials: M
authors.lastname: Tenkanen
authors.forename: Mária
authors.initials: M
authors.lastname: Vršanská
authors.forename: Matti
authors.initials: M
authors.lastname: Siika-aho
authors.forename: Dominic W
authors.initials: DW
authors.lastname: Wong
authors.forename: Vladimír
authors.initials: V
authors.lastname: Puchart
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
authors.forename: Markku
authors.initials: M
authors.lastname: Saloheimo
authors.forename: Peter
authors.initials: P
authors.lastname: Biely
mesh_terms: D000595:Amino Acid Sequence; D002236:Carbohydrate Conformation; D043364:Endo-1,4-beta Xylanases / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification; D005656:Fungal Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification; D015966:Gene Expression Regulation, Fungal; D005965:Glucuronates / Q000737:chemistry; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry; D025942:Oligosaccharides, Branched-Chain / Q000737:chemistry; D010843:Pichia; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014242:Trichoderma / Q000201:enzymology*; D014990:Xylans / Q000737:chemistry
chemical_list: D005656:Fungal Proteins; D005965:Glucuronates; D009844:Oligosaccharides; D025942:Oligosaccharides, Branched-Chain; D014990:Xylans; C570991:xylooligosaccharide; D043364:Endo-1,4-beta Xylanases