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Starch recognition by carbohydrate-binding modules (CBMs) is important for the activity of starch-degrading enzymes. The N-terminal family 41 CBM, TmCBM41 (from pullulanase PulA secreted by Thermotoga maritima) was shown to have alpha-glucan binding activity with specificity for alpha-1,4-glucans but was able to tolerate the alpha-1,6-linkages found roughly every three or four glucose units in pullulan. Using X-ray crystallography, the structures were solved for TmCBM41 in an uncomplexed form and in complex with maltotetraose and 6(3)-alpha-D-glucosyl-maltotriose (GM3). Ligand binding was facilitated by stacking interactions between the alpha-faces of the glucose residues and two tryptophan side-chains in the two main subsites of the carbohydrate-binding site. Overall, this mode of starch binding is quite well conserved by other starch-binding modules. The structure in complex with GM3 revealed a third binding subsite with the flexibility to accommodate an alpha-1,4- or an alpha-1,6-linked glucose.

The structural basis of alpha-glucan recognition by a family 41 carbohydrate-binding module from Thermotoga maritima., van Bueren AL, Boraston AB, J Mol Biol. 2007 Jan 19;365(3):555-60. Epub 2006 Oct 11. PMID:17095014

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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Categories: Pullulanase | Thermotoga maritima | Boraston, A B. | Bueren, A Lammerts Van. | Alpha-glucan binding | Beta-sandwich fold | Carbohydrate-binding module | Glucosyl-maltotriose | Glycosidase | Hydrolase