Characterization of EngF from Clostridium cellulovorans and identification of a novel cellulose binding domain

The physical and enzymatic properties of noncellulosomal endoglucanase F (EngF) from Clostridium cellulovorans were studied. Binding studies revealed that the Kd and the maximum amount of protein bound for acid-swollen cellulose were 1.8 microM and 7.1 mumol/g of cellulose, respectively. The presence of cellobiose but not glucose or maltose could dissociate EngF from cellulose. N- and C-terminally truncated enzymes showed that binding activity was located at some site between amino acid residues 356 and 557 and that enzyme activity was still present when 20 amino acids but not 45 amino acids were removed from the N terminus and when 32 amino acids were removed from the C terminus; when 57 amino acids were removed from the C terminus, all activity was lost. EngF showed low endoglucanase activity and could hydrolyze cellotetraose and cellopentaose but not cellotriose. Activity studies suggested that EngF plays a role as an endoglucanase during cellulose degradation. Comparative sequence analyses indicated strongly that the cellulose binding domain (CBD) is different from previously reported CBDs.