title: Differential oligosaccharide recognition by evolutionarily-related beta-1,4 and beta-1,3 glucan-binding modules.
abstract: Enzymes active on complex carbohydrate polymers frequently have modular structures in which a catalytic domain is appended to one or more carbohydrate-binding modules (CBMs). Although CBMs have been classified into a number of families based upon sequence, many closely related CBMs are specific for different polysaccharides. In order to provide a structural rationale for the recognition of different polysaccharides by CBMs displaying a conserved fold, we have studied the thermodynamics of binding and three-dimensional structures of the related family 4 CBMs from Cellulomonas fimi Cel9B and Thermotoga maritima Lam16A in complex with their ligands, beta-1,4 and beta-1,3 linked gluco-oligosaccharides, respectively. These two CBMs use a structurally conserved constellation of aromatic and polar amino acid side-chains that interact with sugars in two of the five binding subsites. Differences in the length and conformation of loops in non-conserved regions create binding-site topographies that complement the known solution conformations of their respective ligands. Thermodynamics interpreted in the light of structural information highlights the differential role of water in the interaction of these CBMs with their respective oligosaccharide ligands.
authors.affiliation: Protein Engineering Network of Centres of Excellence, Edmonton, Alberta, Canada T6G 2S2.
authors.forename: Alisdair B
authors.initials: AB
authors.lastname: Boraston
authors.forename: Didier
authors.initials: D
authors.lastname: Nurizzo
authors.forename: Valerie
authors.initials: V
authors.lastname: Notenboom
authors.forename: Valérie
authors.initials: V
authors.lastname: Ducros
authors.forename: David R
authors.initials: DR
authors.lastname: Rose
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Kilburn
authors.forename: Gideon J
authors.initials: GJ
authors.lastname: Davies
mesh_terms: D000192:Actinomycetales / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002480:Cellulase / Q000737:chemistry* / Q000378:metabolism*; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D013816:Thermodynamics; D020124:Thermotoga maritima / Q000737:chemistry*
chemical_list: D005936:Glucans; D008024:Ligands; D009844:Oligosaccharides; C092781:laminariheptaose; C019193:maltopentaose; D002480:Cellulase