Comparison of domains function between cellobiohydrolase I and endoglucanase I from Trichoderma pseudokoningii S-38 by limited proteolysis

Abstract

Two homogeneous catalytic domains (CD) and cellulose-binding domains (CBD) of cellobiohydrolase I (CBHI) and endoglucanase I (EGI) from Trichoderma pseudokoningii S-38 are obtained from the products of limited proteolysis by papain and purified followed a series of gel filtration. A comparison of the catalytic activities and binding capacities between these two intact cellulases and their CD and CBD were made. Binding and de-sorption experiments indicate intact CBHI has stronger binding capacity on cotton fibers than others, and cannot be released from cotton fibers upon simple dilution by 20 mM NaAc, pH 4.8 buffer, while both CBDs can be completely eluted by the same buffer. Non-hydrolytic disruption of cotton fibers after adsorption of CBHI-CBD was clearly observed by scanning tunneling microscope. FT-IR spectroscopy studies demonstrate that those disruptions were driven by weakening and splitting of hydrogen bonds in cellulose. The binding capacities, as a measure of the maximum amounts of binding enzymes, and hydrolysis rates of both intact enzymes are all higher than those of the combination of their two corresponding domains in equal mole. Similarly, the effect of synergism between CBHI and EGI in hydrolysis rate of cotton fibers are also higher than those of the combination of their four domains. These results clearly suggest that the binding and catalytic functions of a cellulase molecule is mainly dependent on the coupling work of its two domains and any one domain alone is not sufficient for its full function as in an intact enzyme.