Carrard G, Linder M
VTT Biotechnology and Food Research, Finland.
Eur J Biochem. 1999 Jun;262(3):637-43. doi: 10.1046/j.1432-1327.1999.00455.x.
The filamentous fungus Trichoderma reesei produces two cellobiohydrolases (CBHI and CBHII). These, like most other cellulose-degrading enzymes, have a modular structure consisting of a catalytic domain linked to a cellulose-binding domain (CBD). The isolated catalytic domains bind poorly to cellulose and have a much lower activity towards cellulose than the intact enzymes. For the CBDs, no function other than binding to cellulose has been found. We have previously described the reversibility and exchange rate for the binding of the CBD of CBHI to cellulose. In this work, we studied the binding of the CBD of CBHII and showed that it differs markedly from the behaviour of that of CBHI. The apparent binding affinities were similar, but the CBD of CBHII could not be dissociated from cellulose by buffer dilution and did not show a measurable exchange rate. However, desorption could be triggered by shifting the temperature. The CBD of CBHII bound reversibly to chitin. Two variants of the CBHII CBD were made, in which point mutations increased its similarity to the CBD of CBHI. Both variants were found to bind reversibly to cellulose.
丝状真菌里氏木霉可产生两种纤维二糖水解酶（CBHI和CBHII）。与大多数其他纤维素降解酶一样，它们具有模块化结构，由连接到纤维素结合结构域（CBD）的催化结构域组成。分离出的催化结构域与纤维素的结合能力较差，对纤维素的活性也远低于完整酶。对于CBD，除了与纤维素结合外，尚未发现其他功能。我们之前描述了CBHI的CBD与纤维素结合的可逆性和交换速率。在这项工作中，我们研究了CBHII的CBD的结合情况，结果表明它与CBHI的CBD的行为有显著差异。表观结合亲和力相似，但CBHII的CBD不能通过缓冲液稀释从纤维素上解离，也没有可测量的交换速率。然而，温度变化可以引发解吸。CBHII的CBD与几丁质可逆结合。制备了CBHII CBD的两个变体，其中的点突变增加了它与CBHI的CBD的相似性。发现这两个变体都能与纤维素可逆结合。
