Properties of Native and Site-Mutagenized Cellobiohydrolase II

The cellulase system of Trichoderma reesei (also T. longibrachiatum ) comprises endoglucanases, cellobiohydrolases and β-D-glucosidases which act synergistically to convert cellulose to glucose. Although cellobiohydrolase I (CBH I) is the most abundant component, cellobiohydrolase II (CBH II) is required for optimum rates ofconversion of crystalline cellulose. The three dimensional structure of the catalytic core of CBH II recendy reported by Swedish and Finnish investigators ( 1 ) has made it possible to interpret more precisely the results of experiments regarding structure-function relationships. Changes in activity and specificity due to site specific mutagenesis have been used to study the putative active site of CBH II to confirm the essentiality of specific amino acid residues and the effect on the substrate specificity and kinetics of reaction using model substrates. In this study, CBH II genes were expressed in Aspergillus awamori and the properties of the resulting enzymes were examined. The results indicate a multi-site enzyme with activity on polymeric and soluble substrates dependent on specific amino acid residues.