Implications of Carbohydrate Binding Modules of Cellulases Summarized from Visualization

Cellulase is an important enzyme in biotechnology, and has signal domain, catalytic domain, carbohydrate binding module (CBM) and linker. CBM helps the association of soluble cellulases with insoluble cellulose in cellulosic hydrolysis. We review the visualizations of CBM from three aspects: CBM adsorption to cellulose, CBM occupying space in cellulose and cellulose surface accessibility to CBM. Our review reveals: the most effective crystal faces are 220 and 22̅0 for cellulose; cellulase is more efficient to catalyze the cellulose with at least 50 cellobioses; and a bunch of celluloses can be stratified into not only traditional amorphous and crystalline regions, but also disordered/dislocated region, and each region is subject to a specific type of CBM. Our review implies: cellulases usually approach cellulose through 100, 11̅0 and 010 crystal faces although β-1,4-glycosidic bond is located near to crystal faces 220 and 22̅0; and it requires the small sized cellulases to access to fragment of cellulose because cellulases appear much larger for cellulose smaller than 50 cellobioses.