The structural basis of alpha-glucan recognition by a family 41 carbohydrate-binding module from Thermotoga maritima.
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.
van Bueren
Alicia Lammerts
AL
Biochemistry and Microbiology, University of Victoria, PO Box 3055 STN CSC, Victoria, BC, Canada V8W 3P6.
Boraston
Alisdair B
AB
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D020124:Thermotoga maritima / Q000378:metabolism*
D001426:Bacterial Proteins; D005936:Glucans; D009844:Oligosaccharides; D011956:Receptors, Cell Surface; C055213:saccharide-binding proteins