title: Novel sugar-binding specificity of the type XIII xylan-binding domain of a family F/10 xylanase from Streptomyces olivaceoviridis E-86.
abstract: The type XIII xylan-binding domain (XBD) of a family F/10 xylanase (FXYN) from Streptomyces olivaceoviridis E-86 was found to be structurally similar to the ricin B chain which recognizes the non-reducing end of galactose and specifically binds to galactose containing sugars. The crystal structure of XBD [Fujimoto, Z. et al. (2000) J. Mol. Biol. 300, 575-585] indicated that the whole structure of XBD is very similar to the ricin B chain and the amino acids which form the galactose-binding sites are highly conserved between the XBD and the ricin B chain. However, our investigation of the binding abilities of wt FXYN and its truncated mutants towards xylan demonstrated that the XBD bound xylose-based polysaccharides. Moreover, it was found that the sugar-binding unit of the XBD was a trimer, which was demonstrated in a releasing assay using sugar ranging in size from xylose to xyloheptaose. These results indicated that the binding specificity of the XBD was different from those of the same family lectins such as the ricin B chain. Somewhat surprisingly, it was found that lactose could release the XBD from insoluble xylan to a level half of that observed for xylobiose, indicating that the XBD also possessed the same galactose recognition site as the ricin B chain. It appears that the sugar-binding pocket of the XBD has evolved from the ancient ricin super family lectins to bind additional sugar targets, resulting in the differences observed in the sugar-binding specificities between the lectin group (containing the ricin B chain) and the enzyme group.
authors.affiliation: Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, Yamagata, Japan. kuno@sci.kj.yamagata-u.ac.jp
authors.forename: A
authors.initials: A
authors.lastname: Kuno
authors.forename: S
authors.initials: S
authors.lastname: Kaneko
authors.forename: H
authors.initials: H
authors.lastname: Ohtsuki
authors.forename: S
authors.initials: S
authors.lastname: Ito
authors.forename: Z
authors.initials: Z
authors.lastname: Fujimoto
authors.forename: H
authors.initials: H
authors.lastname: Mizuno
authors.forename: T
authors.initials: T
authors.lastname: Hasegawa
authors.forename: K
authors.initials: K
authors.lastname: Taira
authors.forename: I
authors.initials: I
authors.lastname: Kusakabe
authors.forename: K
authors.initials: K
authors.lastname: Hayashi
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D050260:Carbohydrate Metabolism; D006868:Hydrolysis; D018716:Molecular Mimicry; D008970:Molecular Weight; D011487:Protein Conformation; D013302:Streptomyces / Q000201:enzymology* / Q000378:metabolism; D043325:Xylan Endo-1,3-beta-Xylosidase; D014990:Xylans / Q000378:metabolism; D014995:Xylosidases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D014990:Xylans; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase