2YFZ: Cbm62 From Clostridium Thermocellum Xyl5a

Citation:
Abstract
The enzymic degradation of plant cell walls plays a central role in the carbon cycle and is of increasing environmental and industrial significance. The catalytic modules of enzymes that catalyze this process are generally appended to noncatalytic carbohydrate-binding modules (CBMs). CBMs potentiate the rate of catalysis by bringing their cognate enzymes into intimate contact with the target substrate. A powerful plant cell wall-degrading system is the Clostridium thermocellum multienzyme complex, termed the "cellulosome." Here, we identify a novel CBM (CtCBM62) within the large C. thermocellum cellulosomal protein Cthe_2193 (defined as CtXyl5A), which establishes a new CBM family. Phylogenetic analysis of CBM62 members indicates that a circular permutation occurred within the family. CtCBM62 binds to d-galactose and l-arabinopyranose in either anomeric configuration. The crystal structures of CtCBM62, in complex with oligosaccharides containing alpha- and beta-galactose residues, show that the ligand-binding site in the beta-sandwich protein is located in the loops that connect the two beta-sheets. Specificity is conferred through numerous interactions with the axial O4 of the target sugars, a feature that distinguishes galactose and arabinose from the other major sugars located in plant cell walls. CtCBM62 displays tighter affinity for multivalent ligands compared with molecules containing single galactose residues, which is associated with precipitation of these complex carbohydrates. These avidity effects, which confer the targeting of polysaccharides, are mediated by calcium-dependent oligomerization of the CBM.
PDB ID: 2YFZDownload
MMDB ID: 90570
PDB Deposition Date: 2011/4/11
Updated in MMDB: 2012/05
Experimental Method:
x-ray diffraction
Resolution: 1.8  Å
Source Organism:
Similar Structures:
Biological Unit for 2YFZ: monomeric; determined by author and by software (PISA)
Molecular Components in 2YFZ
Label Count Molecule
Protein (1 molecule)
1
Carbohydrate Binding Family 6
Molecule annotation
Chemicals (7 molecules)
1
1
2
1
3
3
4
1
5
1
* Click molecule labels to explore molecular sequence information.

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