title: Functions of family-22 carbohydrate-binding module in Clostridium thermocellum Xyn10C.
abstract: Clostridium thermocellum xylanase Xyn10C (formerly XynC) is a modular enzyme, comprising a family-22 carbohydrate-binding module (CBM), a family-10 catalytic module of the glycoside hydrolases, and a dockerin module responsible for cellulosome assembly consecutively from the N-terminus. To study the functions of the CBM, truncated derivatives of Xyn10C were constructed: a recombinant catalytic module polypeptide (rCM), a family-22 CBM polypeptide (rCBM), and a polypeptide composed of the family-22 CBM and CM (rCBM-CM). The recombinant proteins were characterized by enzyme and binding assays. Although the catalytic activity of rCBM-CM toward insoluble xylan was four times higher than that of rCM toward the same substrate, removal of the CBM did not severely affect catalytic activity toward soluble xylan or beta-1,3-1,4-glucan. rCBM showed an affinity for amorphous celluloses and insoluble and soluble xylan in qualitative binding assays. The optimum temperature of rCBM-CM was 80 degrees C and that of rCM was 60 degrees C. These results indicate that the family-22 CBM of C. thermocellum Xyn10C not only was responsible for the binding of the enzyme to the substrates, but also contributes to the stability of the CM in the presence of the substrate at high temperatures.
authors.affiliation: Faculty of Bioresources, Mie University, Tsu, Japan.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Ali
authors.forename: Guangshan
authors.initials: G
authors.lastname: Zhao
authors.forename: Makiko
authors.initials: M
authors.lastname: Sakka
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kimura
authors.forename: Kunio
authors.initials: K
authors.lastname: Ohmiya
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sakka
mesh_terms: D001483:Base Sequence; D048013:Acetivibrio thermocellus / Q000201:enzymology*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D030781:Organisms, Genetically Modified; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding; D013379:Substrate Specificity; D013696:Temperature; D014995:Xylosidases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D011134:Polysaccharides; D014995:Xylosidases