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183 a.a.
_CA
Key reference
DOI no: 10.1016/j.jmb.2004.04.072 J Mol Biol 340:543-554 (2004) PubMed id: 15210353
High-resolution crystal structures of Caldicellulosiruptor strain Rt8B.4 carbohydrate-binding module CBM27-1 and its complex with mannohexaose. Y.Roske, A.Sunna, W.Pfeil, U.Heinemann. ABSTRACT
Carbohydrate-binding modules (CBMs) are the most common non-catalytic modules associated with enzymes active in plant cell-wall hydrolysis. Despite the large number of putative CBMs being identified by amino acid sequence alignments, only few representatives have been experimentally shown to have a carbohydrate-binding function. Caldicellulosiruptor strain Rt8B.4 Man26 is a thermostable modular glycoside hydrolase beta-mannanase which contains two non-catalytic modules in tandem at its N terminus. These modules were recently shown to function primarily as beta-mannan-binding modules and have accordingly been classified as members of a novel family of CBMs, family 27. The N-terminal CBM27 (CsCBM27-1) of Man26 from Caldicellulosiruptor Rt8B.4 displays high-binding affinity towards mannohexaose with a Ka of 1 x 10(7) M(-1). Accordingly, the high-resolution crystal structures of CsCBM27-1 native and its mannohexaose complex were solved at 1.55 angstroms and 1.06 angstoms resolution, respectively. In the crystal, CsCBM27-1 shows the typical beta-sandwich jellyroll fold observed in other CBMs with a single metal ion bound, which was identified as calcium. The crystal structures reveal that the overall fold of CsCBM27-1 remains virtually unchanged upon sugar binding and that binding is mediated by three solvent-exposed tryptophan residues and few direct hydrogen bonds. Based on binding affinity and thermal unfolding experiments this structural calcium is shown to play a role in the thermal stability of CsCBM27-1 at high temperatures. The higher binding affinity of CsCBM27-1 to mannooligosaccharides when compared to other members of CBM family 27 might be explained by the different orientation of the residues forming the "aromatic platform" and by differences in the length of loops. Finally, evidence is presented, on the basis of fold similarities and the retention of the position of conserved motifs and a calcium ion, for the consolidation of related CBM families into a superfamily of CBMs.
Selected figure(s)
Figure 3.
Figure 3. Stereo representation of the ligand-binding site of CsCBM27-1. The four b-strands lining the binding cleft are shown in blue. Tryptophan residues forming the aromatic platform that are involved in stacking interactions with the sugar rings of the mannohexaose are depicted in dark blue. The mannohexaose with its alternative conformation for the sixth mannose residue is shown in dark grey and red (oxygen).Figure 6.
Figure 6. Stereo superposition of the observed conformations of mannohexaose bound to CsCBM27-1 and TmCBM27. The tryptophan residues and mannohexaose are shown in dark blue and yellow in CsCBM27-1 and TmCBM27, respectively.The above figures are reprinted by permission from Elsevier: J Mol Biol (2004, 340, 543-554) copyright 2004. Figures were selected by an automated process.
Literature references that cite this PDB file's key reference
PubMed id Reference
19129644 M.Tanaka, Y.Umemoto, H.Okamura, D.Nakano, Y.Tamaru, and T.Araki (2009).
Cloning and characterization of a beta-1,4-mannanase 5C possessing a family 27 carbohydrate-binding module from a marine bacterium, Vibrio sp. strain MA-138.Biosci Biotechnol Biochem, 73, 109-116.
16990278 E.Ficko-Blean, and A.B.Boraston (2006).
The interaction of a carbohydrate-binding module from a Clostridium perfringens N-acetyl-beta-hexosaminidase with its carbohydrate receptor.J Biol Chem, 281, 37748-37757.
PDB codes: 2j1a 2j1e 2j1f 2j7m The most recent references are shown first. Citation data come partly from CiteXplore and partly from an automated harvesting procedure. Note that this is likely to be only a partial list as not all journals are covered by either method. However, we are continually building up the citation data so more and more references will be included with time. Where a reference describes a PDB structure, the PDB codes are shown on the right.
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