Carbohydrate Binding Module Family 8

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

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CAZy DB link

https://www.cazy.org/CBM08.html

Ligand specificities

Prior to being found in the CBM8 family, these CBMs were called CBDVIII (family 8 cellulose-binding domains). DdCBM8, from the slime mold Dictyostelium discoideum CelA enzyme (270-6) binds insoluble forms of cellulose and glucomannan, there is no evidence for binding to oligosaccharides [1]. It appears to be broadly specific with both type A and type B CBM characteristics.

Structural Features

DdCBM8 is found C-terminal to the GH9 endo-(1,4)-beta-D-glucanase (cellulase) catalytic module of the CelA enzyme (270–6) and connected via a Thr-Glu-Thr-Pro type repeat linker [2].

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

CelA and CelB from Dictyostelium discoideum are predicted to be important for amoebae release from spores as transcriptomic experiments show that their mRNA levels are low in dormant spores, they rise during germination and then rapidly disappear after germination [2]. Cellulase activities from differently sized cellulases are also shown to increase during spore germination [3]

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

It is unclear where the first identification of binding to cellulose for the CBM8 family was determined from the literature. A mention of the possibility was found in [3], another mention was found in [4] which itself cited [5] (which this author was unable to access).

First Structural Characterization

The first crystal structures are from DdCBM8, from the slime mold Dictyostelium discoideum [1], see 7T7Y and 7T7Z.

References

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5. P. Tomme, R.A.J. Warren, R.C. Miller Jr., D.G. Kilburn, N.R. Gilkes, in: J.N. Saddler, M.H. Penner (Eds.), Enzymatic Degradation of Insoluble Carbohydrates, American Chemical Society Symposium Series, 1995, p. 142.