Carbohydrate Binding Module Family 6

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• Author: ^^^Mirjam Czjzek^^^
• Responsible Curator: ^^^Mirjam Czjzek^^^

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CAZy DB link

https://www.cazy.org/CBM6.html

Ligand specificities

The ligand specificity of the first characterized CBM6, originating from a multimodular xylanase from Clostridium thermocellum, was determined to be xylan [1], although the results showed that this CBM6 was also able to bind to Avicel and acid-swollen cellulose. This was also the first CBM6 for which a 3D structure was determined [2], and multiple sequence alignments, analyzed in the light of the first 3D structure, already gave clear indications that large diversity in specificity was to be expected among CBM6 modules [2]. CBM6 modules are in general attached to bacterial or archeal polysaccharide degrading enzymes and can be found attached to xylanases, cellulases, agarases, laminarinases, etc [3]. Interestingly, modules assigned to the CBM6 family have also been found associated to fungal enzymes and to the α-subunit of the coagulation factor G in horseshoe crabs eukarotic CBM6 occurence. In the latter case, the β-1,3-glucan binding of the C-terminal tandem CBM6s has been demonstrated [4]. Those CBM6s having characterized binding activities cover : both linear and branched/decorated xylan, β-1,4-glucan (or cellulose), mixed-linked β-1,3-1,4-glucan (or lichenan), agarose, β-1,3-glucan (or laminarin) and chitin. Remarkably, the characterization and 3D structure of a CBM6 from Cellvibrio mixtus revealed two distinct binding sites that displayed differential binding specificities [5, 6].

Note: Here is an example of how to insert references in the text, together with the "biblio" section below: Please see these references for an essential introduction to the CAZy classification system: [7, 8]. CBMs, in particular, have been extensively reviewed [9, 10, 11, 12].

Structural Features

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

• Fold: Likewise many other CBMs, the overall fold corresponds to a β-sandwich, but the first identified ligand binding site was not, as usual, located at a shallow cleft on the concave surface of the β-sheets (cleft B in CBM6). Alternatively, a binding site was found located within the connecting loops of the two β-sheets (cleft A in CBM6). Interestingly, some CBM6s display binding affinities for both binding sites,
• 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

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First Structural Characterization

Insert archetype here, possibly including very brief synopsis.

References

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