1E5C

Internal xylan binding domain from C. fimi Xyn10A, R262G mutant

Summary for 1E5C

• Entry DOI: 10.2210/pdb1e5c/pdb
• Related: 1E5B 1XBD 2XBD
• NMR Information: BMRB: 4623
• Descriptor: XYLANASE D (1 entity in total)
• Functional Keywords: hydrolase, xylan binding domain, xylanase, beta-sheet
• Biological source: CELLULOMONAS FIMI
• Total number of polymer chains: 1
• Total formula weight: 8687.27

Authors

Simpson, P.J.,Hefang, X.,Bolam, D.N.,Gilbert, H.J.,Williamson, M.P. (deposition date: 2000-07-24, release date: 2001-05-25, Last modification date: 2024-11-13)

Primary citation

Simpson, P.J.,Hefang, X.,Bolam, D.N.,Gilbert, H.J.,Williamson, M.P.
The Structural Basis for the Ligand Specificity of Family 2 Carbohydrate Binding Nodules
J.Biol.Chem., 275:41137-, 2000

PubMed Abstract: The interactions of proteins with polysaccharides play a key role in the microbial hydrolysis of cellulose and xylan, the most abundant organic molecules in the biosphere, and are thus pivotal to the recycling of photosynthetically fixed carbon. Enzymes that attack these recalcitrant polymers have a modular structure comprising catalytic modules and non-catalytic carbohydrate-binding modules (CBMs). The largest prokaryotic CBM family, CBM2, contains members that bind cellulose (CBM2a) and xylan (CBM2b), respectively. A possible explanation for the different ligand specificity of CBM2b is that one of the surface tryptophans involved in the protein-carbohydrate interaction is rotated by 90 degrees compared with its position in CBM2a (thus matching the structure of the binding site to the helical secondary structure of xylan), which may be promoted by a single amino acid difference between the two families. Here we show that by mutation of this single residue (Arg-262-->Gly), a CBM2b xylan-binding module completely loses its affinity for xylan and becomes a cellulose-binding module. The structural effect of the mutation has been revealed using NMR spectroscopy, which confirms that Trp-259 rotates 90 degrees to lie flat against the protein surface. Except for this one residue, the mutation only results in minor changes to the structure. The mutated protein interacts with cellulose using the same residues that the wild-type CBM2b uses to interact with xylan, suggesting that the recognition is of the secondary structure of the polysaccharide rather than any specific recognition of the absence or presence of functional groups.

PubMed: 10973978
DOI: 10.1074/JBC.M006948200

Experimental method

SOLUTION NMR