Carbohydrate Binding Module Family 44

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• Author: Marie-Katherin Zühlke
• Responsible Curator: Elizabeth Ficko-Blean

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CAZy DB link

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

Ligand specificities

CBM44 targets ß-1,4-polymers such as xyloglucan and cellulose (hydroxyethylcellulose and Avicel), mixed linkage ß-1,3/ß1,4- glucans (lichenan and barley) or glucomannan (konjac) [1]. Affinity for xylan was very low and binding to laminarin, curdlan, pullulan, pustulan, galactomannan or galactan was negative. Isothermal titration calorimetry (ITC) revealed highest affinity for xyloglucan as a polysaccharide, which was comparable to the affinity for cellohexaose as an oligosaccharide. For other cello-oligosaccharides, this affinity decreased with decreasing chain length, while no binding was detected for cellotriose.

Structural Features

Like many CBMs, CBM44 exhibits a typical ß-sandwich fold: two antiparallel ß-sheets form a concave and a convex surface. The concave surface forms a deep hydrophobic ligand-binding cleft that is estimated to accommodate up to five glucose residues (~24 Å) [1]. Here, three tryptophans (W189, W194 and W198) act as key residues to mediate ligand binding, as confirmed by affinity gel electrophoresis (AGE) and ITC analyses of specific mutants. The orientation of the tryptophans corresponds to the slightly twisted conformation of cello-oligosaccharides in solution.

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

1. Najmudin S, Guerreiro CI, Carvalho AL, Prates JA, Correia MA, Alves VD, Ferreira LM, Romão MJ, Gilbert HJ, Bolam DN, and Fontes CM. (2006). Xyloglucan is recognized by carbohydrate-binding modules that interact with beta-glucan chains. J Biol Chem. 2006;281(13):8815-28. DOI:10.1074/jbc.M510559200 |