Role of cellulose-binding domain of exocellulase I from white rot basidiomycete Irpex lacteus

The core fragment (designated P-42), devoid of the cellulose-binding domain (CBD) in the C-terminus and prepared from Irpex lacteus exocellulase I(Ex- l), was isolated by limited proteolysis using papain. Both the hydrolytic a ctivity and binding ability of the isolated P-42 toward insoluble cellulose were lower than those of the native Ex-1, whereas Ex-1 and P-42 showed sim ilar hydrolytic activities toward soluble substrates. These results indicat e that the CBD of I. lacteus Ex-1 is the important domain which could enhan ce hydrolytic activity and binding ability of the enzyme toward insoluble c ellulose. In addition, the isolated P-42 was different from the native Ex-1 in terms of enzymatic properties such as pH and temperature stabilities. T hese differences in stability, with regard to pH and temperature, between P -42 and the native Ex-1 are probably due to the O-linked sugar chains exist ing in the linker region.