Overproduction, purification, crystallization and preliminary X-ray characterization of the C-terminal family 65 carbohydrate-binding module (CBM65B) of endoglucanase Cel5A from Eubacterium cellulosolvens.

The rumen anaerobic cellulolytic bacterium Eubacterium cellulosolvens produces a large range of cellulases and hemicellulases responsible for the efficient hydrolysis of plant cell wall polysaccharides. One of these enzymes, endoglucanase Cel5A, comprises a tandemly repeated carbohydrate-binding module (CBM65) fused to a glycoside hydrolase family 5 (Cel5A) catalytic domain, joined by flexible linker sequences. The second carbohydrate-binding module located at the C-terminus side of the endoglucanase (CBM65B) has been co-crystallized with either cellohexaose or xyloglucan heptasaccharide. The crystals belong to the hexagonal space group P6(5) and tetragonal space group P4(3)2(1)2, containing a single molecule in the asymmetric unit. The structures of CBM65B have been solved by molecular replacement.