title: Ab initio structure determination and functional characterization of CBM36; a new family of calcium-dependent carbohydrate binding modules.
abstract: The enzymatic degradation of polysaccharides harnesses multimodular enzymes whose carbohydrate binding modules (CBM) target the catalytic domain onto the recalcitrant substrate. Here we report the ab initio structure determination and subsequent refinement, at 0.8 A resolution, of the CBM36 domain of the Paenibacillus polymyxa xylanase 43A. Affinity electrophoresis, isothermal titration calorimetry, and UV difference spectroscopy demonstrate that CBM36 is a novel Ca(2+)-dependent xylan binding domain. The 3D structure of CBM36 in complex with xylotriose and Ca(2+), at 1.5 A resolution, displays significant conformational changes compared to the native structure and reveals the molecular basis for its unique Ca(2+)-dependent binding of xylooligosaccharides through coordination of the O2 and O3 hydroxyls. CBM36 is one of an emerging spectrum of carbohydrate binding modules that increasingly find applications in industry and display great potential for mapping the "glyco-architecture" of plant cells.
authors.affiliation: Structural Biology Laboratory, Department of Chemistry, The University of York, Heslington, York YO10 5YW, United Kingdom.
authors.forename: Sheelan
authors.initials: S
authors.lastname: Jamal-Talabani
authors.forename: Alisdair B
authors.initials: AB
authors.lastname: Boraston
authors.forename: Johan P
authors.initials: JP
authors.lastname: Turkenburg
authors.forename: Nicolas
authors.initials: N
authors.lastname: Tarbouriech
authors.forename: Valérie M-A
authors.initials: VM
authors.lastname: Ducros
authors.forename: Gideon J
authors.initials: GJ
authors.lastname: Davies
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000737:chemistry*; D001665:Binding Sites; D002151:Calorimetry; D002236:Carbohydrate Conformation; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D013379:Substrate Specificity; D014990:Xylans / Q000737:chemistry / Q000378:metabolism; D014995:Xylosidases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008024:Ligands; D014990:Xylans; D014995:Xylosidases