1W8W

CBM29-2 mutant Y46A: Probing the Mechanism of Ligand Recognition by Family 29 Carbohydrate Binding Modules

Summary for 1W8W

• Entry DOI: 10.2210/pdb1w8w/pdb
• Related: 1GWK 1GWL 1GWM 1OH3 1W8T 1W8U 1W8Z 1W90 1W9F
• Descriptor: NON-CATALYTIC PROTEIN 1 (2 entities in total)
• Functional Keywords: carbohydrate binding domain, carbohydrate binding module, glucomannan, cellohexaose, mannohexaose, cellulosome
• Biological source: PIROMYCES EQUI
• Total number of polymer chains: 2
• Total formula weight: 33148.50

Authors

Flint, J.,Bolam, D.N.,Nurizzo, D.,Taylor, E.J.,Williamson, M.P.,Walters, C.,Davies, G.J.,Gilbert, H.J. (deposition date: 2004-09-30, release date: 2005-03-22, Last modification date: 2023-12-13)

Primary citation

Flint, J.,Bolam, D.N.,Nurizzo, D.,Taylor, E.J.,Williamson, M.P.,Walters, C.,Davies, G.J.,Gilbert, H.J.
Probing the Mechanism of Ligand Recognition in Family 29 Carbohydrate-Binding Modules
J.Biol.Chem., 280:23718-, 2005

PubMed Abstract: The recycling of photosynthetically fixed carbon, by the action of microbial plant cell wall hydrolases, is integral to one of the major geochemical cycles and is of considerable industrial importance. Non-catalytic carbohydrate-binding modules (CBMs) play a key role in this degradative process by targeting hydrolytic enzymes to their cognate substrate within the complex milieu of polysaccharides that comprise the plant cell wall. Family 29 CBMs have, thus far, only been found in an extracellular multienzyme plant cell wall-degrading complex from the anaerobic fungus Piromyces equi, where they exist as a CBM29-1:CBM29-2 tandem. Here we present both the structure of the CBM29-1 partner, at 1.5 A resolution, and examine the importance of hydrophobic stacking interactions as well as direct and solvent-mediated hydrogen bonds in the binding of CBM29-2 to different polysaccharides. CBM29 domains display unusual binding properties, exhibiting specificity for both beta-manno- and beta-gluco-configured ligands such as mannan, cellulose, and glucomannan. Mutagenesis reveals that "stacking" of tryptophan residues in the n and n+2 subsites plays a critical role in ligand binding, whereas the loss of tyrosine-mediated stacking in the n+4 subsite reduces, but does not abrogate, polysaccharide recognition. Direct hydrogen bonds to ligand, such as those provided by Arg-112 and Glu-78, play a pivotal role in the interaction with both mannan and cellulose, whereas removal of water-mediated interactions has comparatively little effect on carbohydrate binding. The interactions of CBM29-2 with the O2 of glucose or mannose contribute little to binding affinity, explaining why this CBM displays dual gluco/manno specificity.

PubMed: 15784618
DOI: 10.1074/JBC.M501551200

Experimental method

X-RAY DIFFRACTION (2.1 Å)