title: The role of carbohydrate-binding module (CBM) repeat of a multimodular xylanase (XynX) from Clostridium thermocellum in cellulose and xylan binding.
abstract: A non-cellulosomal xylanase from Clostridium thermocellum, XynX, consists of a family-22 carbohydratebinding module (CBM22), a family-10 glycoside hydrolase (GH10) catalytic module, two family-9 carbohydrate-binding modules (CBM9-I and CBM9-II), and an S-layer homology (SLH) module. E. coli BL21(DE3) (pKM29), a transformant carrying xynX', produced several truncated forms of the enzyme. Among them, three major active species were purified by SDS-PAGE, activity staining, gel-slicing, and diffusion from the gel. The truncated xylanases were different from each other only in their C-terminal regions. In addition to the CBM22 and GH10 catalytic modules, XynX(1) had the CBM9-I and most of the CBM9-II, XynX(2) had the CBM9-I and about 40% of the CBM9-II, and XynX(3) had about 75% of the CBM9-I. The truncated xylanases showed higher binding capacities toward Avicel than those toward insoluble xylan. XynX(1) showed a higher affinity toward Avicel (70.5%) than XynX(2) (46.0%) and XynX(3) (42.1%); however, there were no significant differences in the affinities toward insoluble xylan. It is suggested that the CBM9 repeat, especially CBM9-II, of XynX plays a role in xylan degradation in nature by strengthening cellulose binding rather than by enhancing xylan binding.
authors.affiliation: Department of Agricultural Chemistry, Sunchon National University, Suncheon, 540-742, Republic of Korea.
authors.forename: Thangaswamy
authors.initials: T
authors.lastname: Selvaraj
authors.forename: Sung Kyum
authors.initials: SK
authors.lastname: Kim
authors.forename: Yong Ho
authors.initials: YH
authors.lastname: Kim
authors.forename: Yu Seok
authors.initials: YS
authors.lastname: Jeong
authors.forename: Yu-Jeong
authors.initials: YJ
authors.lastname: Kim
authors.forename: Nguyen Dinh
authors.initials: ND
authors.lastname: Phuong
authors.forename: Kyung Hwa
authors.initials: KH
authors.lastname: Jung
authors.forename: Jungho
authors.initials: J
authors.lastname: Kim
authors.forename: Han Dae
authors.initials: HD
authors.lastname: Yun
authors.forename: Hoon
authors.initials: H
authors.lastname: Kim
mesh_terms: D001665:Binding Sites; D002482:Cellulose / Q000378:metabolism*; D003001:Cloning, Molecular; D048013:Acetivibrio thermocellus / Q000201:enzymology* / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017384:Sequence Deletion; D014990:Xylans / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D014990:Xylans; D002482:Cellulose; D006026:Glycoside Hydrolases