title: Co-operative binding of triplicate carbohydrate-binding modules from a thermophilic xylanase.
abstract: Family 6 carbohydrate-binding modules were amplified by polymerase chain reaction (PCR) from Clostridium stercorarium strain NCIB11754 genomic DNA as a triplet. Individually, these modules bound to xylooligosaccharides and cellooligosaccharides with affinities varying from approximately 3 x 10(3) M(-1) to approximately 1 x 10(5) M(-1). Tandem and triplet combinations of these modules bound co-operatively to soluble xylan and insoluble cellulose to give approximately 20- to approximately 40-fold increases in affinity relative to the individual modules. This co-operativity was an avidity effect resulting from the modules within the tandems and triplet interacting simultaneously with proximal binding sites on the polysaccharides. This occurred by both intrachain and interchain interactions. The duplication or triplication of modules appears to be linked to the growth temperature of the organism; co-operativity in these multiplets may compensate for the loss of affinity at higher temperatures.
authors.affiliation: The Protein Engineering Network of Centres of Excellence, PENCE Inc., National Business Centre, 750 Heritage Medical Research Centre, Edmonton, Alberta, T6G 2S2, Canada.
authors.forename: Alisdair B
authors.initials: AB
authors.lastname: Boraston
authors.forename: Bradley W
authors.initials: BW
authors.lastname: McLean
authors.forename: Grace
authors.initials: G
authors.lastname: Chen
authors.forename: Anson
authors.initials: A
authors.lastname: Li
authors.forename: R Antony J
authors.initials: RA
authors.lastname: Warren
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Kilburn
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D020134:Catalytic Domain; D002482:Cellulose / Q000378:metabolism; D003013:Clostridium / Q000201:enzymology* / Q000235:genetics; D004269:DNA, Bacterial; D006867:Hydrolases / Q000378:metabolism; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D012995:Solubility; D043325:Xylan Endo-1,3-beta-Xylosidase; D014990:Xylans / Q000378:metabolism; D014995:Xylosidases / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D009844:Oligosaccharides; D014990:Xylans; D002482:Cellulose; D006867:Hydrolases; D014995:Xylosidases; D043325:Xylan Endo-1,3-beta-Xylosidase