Overexpression, purification and crystallization of the two C-terminal domains of the bifunctional cellulase ctCel9D-Cel44A from Clostridium thermocellum

Clostridium thermocellum produces a highly organized multi‐enzyme complex of cellulases and hemicellulases for the hydrolysis of plant cell‐wall polysaccharides, which is termed the cellulosome. The bifunctional multi‐modular cellulase ctCel9D‐Cel44A is one of the largest components of the C. thermocellum cellulosome. The enzyme contains two internal catalytic domains belonging to glycoside hydrolase families 9 and 44. The C‐terminus of this cellulase, comprising a polycystic kidney‐disease module (PKD) and a carbohydrate‐binding module (CBM44), has been crystallized. The crystals belong to the tetragonal space group P43212, containing a single molecule in the asymmetric unit. Native and seleno‐l‐methionine‐derivative crystals diffracted to 2.1 and 2.8 Å, respectively.