The structural basis of alpha-glucan recognition by a family 41 carbohydrate-binding module from Thermotoga maritima |
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Authors: | van Bueren Alicia Lammerts Boraston Alisdair B |
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Institution: | Biochemistry and Microbiology, University of Victoria, PO Box 3055 STN CSC, Victoria, BC, Canada V8W 3P6. |
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Abstract: | 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. |
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Keywords: | CBM carbohydrate-binding module FOM figure of merit |
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