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Carbohydrate Binding Module Family 75
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CBM75 is a small bacterial family containing only 3 members comprising around 290 amino acids and found exclusively in Ruminococci. The only family member characterized is CBM75RfGH43 from Ruminococcus flavefaciens that specifically binds to xyloglucan . By isothermal titration calorimetry, the affinity to xyloglucan repeating unit XXXG (X comprises glucose decorated at O6 with xylose and G corresponds to undecorated glucose) is similar to the polysaccharide, suggesting that CBM75RfGH43 has four binding sites that recognize the backbone glucose units. However, the specific binding to xyloglucan and not to other β-glucan polysaccharides indicates that at least some of the xylose side chains also have a major contribution to ligand recognition .
No three-dimensional structure has been solved for this CBM family.
Ruminococcus flavefaciens CBM75RfGH43, is a biding module of a protein containing a glycoside hydrolase family 43 (GH43) and a C-terminal dockerin module . The GH43 catalytic domain, is a member of subfamily 16 (GH43_16) that is populated only with arabinofuranosidases . Indeed, the catalytic module RfGH43 is active against 4-nitrophenyl-α-L-arabinofuranose but does not cleave arabinoxylans and arabinans, suggesting that this enzyme may target arabinofuranose residues that decorate other polysaccharides . The CBMs specificity is consistent with the activity of the appended enzyme. Since CBM75RfGH43 binds specifically to xyloglucan it was suggested that the enzyme GH43_16 may target arabinofuranose decorations present on xyloglucan from tomato .
- First Identified
- CBM75RfGH43 from Ruminococcus flavefaciens .
- First Structural Characterization
- No three-dimensional structure has been solved for this family.
- Venditto I, Luis AS, Rydahl M, Schückel J, Fernandes VO, Vidal-Melgosa S, Bule P, Goyal A, Pires VM, Dourado CG, Ferreira LM, Coutinho PM, Henrissat B, Knox JP, Baslé A, Najmudin S, Gilbert HJ, Willats WG, and Fontes CM. (2016) Complexity of the Ruminococcus flavefaciens cellulosome reflects an expansion in glycan recognition. Proc Natl Acad Sci U S A. 113, 7136-41. DOI:10.1073/pnas.1601558113 |
- Mewis K, Lenfant N, Lombard V, and Henrissat B. (2016) Dividing the Large Glycoside Hydrolase Family 43 into Subfamilies: a Motivation for Detailed Enzyme Characterization. Appl Environ Microbiol. 82, 1686-1692. DOI:10.1128/AEM.03453-15 |