Structure and Ligand Binding of Carbohydrate-Binding Module Cscbm6-3 Reveals Similarities with Fucose-Specific Lectins and Galactose-Binding DomainsBoraston, A.B., Notenboom, V., Warren, R.A.J., Kilburn, D.G., Rose, D.R., Davies, G.J.
(2003) J.Mol.Biol. 327: 659
- PubMed: 12634060
- Primary Citation of Related Structures:  1NAE, 1O8P, 1OD3
- PubMed Abstract:
Carbohydrate-binding polypeptides, including carbohydrate-binding modules (CBMs) from polysaccharidases, and lectins, are widespread in nature. Whilst CBMs are classically considered distinct from lectins, in that they are found appended to polysacch ...
Carbohydrate-binding polypeptides, including carbohydrate-binding modules (CBMs) from polysaccharidases, and lectins, are widespread in nature. Whilst CBMs are classically considered distinct from lectins, in that they are found appended to polysaccharide-degrading enzymes, this distinction is blurring. The crystal structure of CsCBM6-3, a "sequence-family 6" CBM in a xylanase from Clostridium stercorarium, at 2.3 A reveals a similar, all beta-sheet fold to that from MvX56, a module found in a family 33 glycoside hydrolase sialidase from Micromonospora viridifaciens, and the lectin AAA from Anguilla anguilla. Sequence analysis leads to the classification of MvX56 and AAA into a family distinct from that containing CsCBM6-3. Whilst these polypeptides are similar in structure they have quite different carbohydrate-binding specificities. AAA is known to bind fucose; CsCBM6-3 binds cellulose, xylan and other beta-glucans. Here we demonstrate that MvX56 binds galactose, lactose and sialic acid. Crystal structures of CsCBM6-3 in complex with xylotriose, cellobiose, and laminaribiose, 2.0 A, 1.35 A, and 1.0 A resolution, respectively, reveal that the binding site of CsCBM6-3 resides on the same polypeptide face as for MvX56 and AAA. Subtle differences in the ligand-binding surface give rise to the different specificities and biological activities, further blurring the distinction between classical lectins and CBMs.
Department of Chemistry, The University of York, Heslington, York, YO10 5YW, UK.