Carbohydrate Binding Module Family 2

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• Author: ^^^Elizabeth Ficko-Blean^^^
• Responsible Curator: ^^^Elizabeth Ficko-Blean^^^

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CAZy DB link

http://www.cazy.org/CBM2.html

Ligand specificities

The vast majority of family 2 CBMs (CBM2s), ~95%, are bacterial in origin. These protein modules have been shown to bind to crystalline cellulose [1], insoluble chitin [2] or xylan [3]. The xylan-specific CBM2s bind only to the hemicellulose, while some cellulose binding modules also recognize chitin. The CBM2s from some chitinases show a strong preference for crystalline chitin [2]. Cellulose-specific CBM2s were also shown to bind to xyloglucan, albeit with affinities ~1000 lower than for crystalline cellulose [4]. Extremely weak binding to cellulooligosaccharides was detected in cellulose binding CBM2s using NMR [5]. In contrast affinities of xylan binding CBM2s for their polysaccharide or oligosaccharide ligands with a degree of polymerization of six were similar [6]. Some enzymes contain multiple CBM2s that, with respect to xylan, show enhanced affinity through avidity effects [5]. Isothermal titration calorimetry showed that the binding of cellulose and xylan binding of CBM2s to their target ligands was mediated by entropic [7] and enthalpic [5] forces, respectively. These differences in thermodynamic forces driving ligand recognition was proposed to reflect the conformational freedom of cellulose and xylan in free solution and when bound to CBMs. Family 2 is thus highly unusual, containing both type A and type B CBMs. Labelling of type A crystalline cellulose specific CBMs, including CBM2s, which all present three aromatic planar surface residues, showed differences in specificity for pure forms of crystalline cellulose and plant cell walls [8, 9].

Structural Features

Content in this section should include, in paragraph form, a description of:

• Fold: Structural fold (beta trefoil, beta sandwich, etc.)
• Type: Include here Type A, B, or C and properties
• Features of ligand binding: Describe CBM binding pocket location (Side or apex) important residues for binding (W, Y, F, subsites), interact with reducing end, non-reducing end, planar surface or within polysaccharide chains. Include examples pdb codes. Metal ion dependent. Etc.

Functionalities

Content in this section should include, in paragraph form, a description of:

• Functional role of CBM: Describe common functional roles such as targeting, disruptive, anchoring, proximity/position on substrate.
• Most Common Associated Modules: 1. Glycoside Hydrolase Activity; 2. Additional Associated Modules (other CBM, FNIII, cohesin, dockerins, expansins, etc.)
• Novel Applications: Include here if CBM has been used to modify another enzyme, or if a CBM was used to label plant/mammalian tissues? Etc.

Family Firsts

First Identified

Insert archetype here, possibly including very brief synopsis.

First Structural Characterization

Insert archetype here, possibly including very brief synopsis.

References

10. Cantarel BL, Coutinho PM, Rancurel C, Bernard T, Lombard V, and Henrissat B. (2009). The Carbohydrate-Active EnZymes database (CAZy): an expert resource for Glycogenomics. Nucleic Acids Res. 2009;37(Database issue):D233-8. DOI:10.1093/nar/gkn663 |

11. Davies, G.J. and Sinnott, M.L. (2008) Sorting the diverse: the sequence-based classifications of carbohydrate-active enzymes. The Biochemist, vol. 30, no. 4., pp. 26-32. Download PDF version.

12. Boraston AB, Bolam DN, Gilbert HJ, and Davies GJ. (2004). Carbohydrate-binding modules: fine-tuning polysaccharide recognition. Biochem J. 2004;382(Pt 3):769-81. DOI:10.1042/BJ20040892 |
13. Hashimoto H (2006). Recent structural studies of carbohydrate-binding modules. Cell Mol Life Sci. 2006;63(24):2954-67. DOI:10.1007/s00018-006-6195-3 |
14. Shoseyov O, Shani Z, and Levy I. (2006). Carbohydrate binding modules: biochemical properties and novel applications. Microbiol Mol Biol Rev. 2006;70(2):283-95. DOI:10.1128/MMBR.00028-05 |
15. Guillén D, Sánchez S, and Rodríguez-Sanoja R. (2010). Carbohydrate-binding domains: multiplicity of biological roles. Appl Microbiol Biotechnol. 2010;85(5):1241-9. DOI:10.1007/s00253-009-2331-y |