Recognition of the helical structure of beta-1,4-galactan by a new family of carbohydrate-binding modules.
The microbial enzymes that depolymerize plant cell wall polysaccharides, ultimately promoting energy liberation and carbon recycling, are typically complex in their modularity and often contain carbohydrate-binding modules (CBMs). Here, through analysis of an unknown module from a Thermotoga maritima endo-β-1,4-galactanase, we identify a new family of CBMs that are most frequently found appended to proteins with β-1,4-galactanase activity. Polysaccharide microarray screening, immunofluorescence microscopy, and biochemical analysis of the isolated module demonstrate the specificity of the module, here called TmCBM61, for β-1,4-linked galactose-containing ligands, making it the founding member of family CBM61. The ultra-high resolution X-ray crystal structures of TmCBM61 (0.95 and 1.4 Å resolution) in complex with β-1,4-galactotriose reveal the molecular basis of the specificity of the CBM for β-1,4-galactan. Analysis of these structures provides insight into the recognition of an unexpected helical galactan conformation through a mode of binding that resembles the recognition of starch.
Cid
Melissa
M
Department Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8W 3P6, Canada.
Pedersen
Henriette Lodberg
HL
Kaneko
Satoshi
S
Coutinho
Pedro M
PM
Henrissat
Bernard
B
Willats
William G T
WG
Boraston
Alisdair B
AB
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002241:Carbohydrates / Q000737:chemistry; D018360:Crystallography, X-Ray; D005685:Galactans / Q000737:chemistry / Q000378:metabolism*; D005690:Galactose / Q000737:chemistry / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D046228:Microarray Analysis; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020124:Thermotoga maritima / Q000201:enzymology
D001426:Bacterial Proteins; D002241:Carbohydrates; D005685:Galactans; D009844:Oligosaccharides; D011134:Polysaccharides; D006026:Glycoside Hydrolases; C094192:arabinogalactan endo-1,4-beta-galactosidase; D005690:Galactose
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