Palonen Hetti, Tjerneld Folke, Zacchi Guido, Tenkanen Maija
VTT Biotechnology, P.O. Box 1500, FIN-02044 VTT, Espoo, Finland.
J Biotechnol. 2004 Jan 8;107(1):65-72. doi: 10.1016/j.jbiotec.2003.09.011.
The presence of lignin has shown to play an important role in the enzymatic degradation of softwood. The adsorption of enzymes, and their constituent functional domains on the lignocellulosic material is of key importance to fundamental knowledge of enzymatic hydrolysis. In this study, we compared the adsorption of two purified cellulases from Trichoderma reesei, CBH I (Cel7A) and EG II (Cel5A) and their catalytic domains on steam pretreated softwood (SPS) and lignin using tritium labeled enzymes. Both CBH I and its catalytic domain exhibited a higher affinity to SPS than EG II or its catalytic domain. Removal of cellulose binding domain decreased markedly the binding efficiency. Significant amounts of CBH I and EG II also bound to isolated lignin. Surprisingly, the catalytic domains of the two enzymes of T. reesei differed essentially in the adsorption to isolated lignin. The catalytic domain of EG II was able to adsorb to alkaline isolated lignin with a high affinity, whereas the catalytic domain of CBH I did not adsorb to any of the lignins tested. The results indicate that the cellulose binding domain has a significant role in the unspecific binding of cellulases to lignin.
木质素的存在已表明在软木的酶促降解中起重要作用。酶及其组成功能域在木质纤维素材料上的吸附对于酶促水解的基础知识至关重要。在本研究中，我们使用氚标记的酶比较了里氏木霉的两种纯化纤维素酶CBH I（Cel7A）和EG II（Cel5A）及其催化域在蒸汽预处理软木（SPS）和木质素上的吸附情况。CBH I及其催化域对SPS的亲和力均高于EG II或其催化域。去除纤维素结合域显著降低了结合效率。大量的CBH I和EG II也与分离出的木质素结合。令人惊讶的是，里氏木霉这两种酶的催化域在对分离出的木质素的吸附上存在本质差异。EG II的催化域能够以高亲和力吸附到碱分离木质素上，而CBH I的催化域对所测试的任何木质素都不吸附。结果表明，纤维素结合域在纤维素酶与木质素的非特异性结合中起重要作用。
