Berlin Alex, Gilkes Neil, Kurabi Arwa, Bura Renata, Tu Maobing, Kilburn Douglas, Saddler John
Forest Products Biotechnology, Department of Wood Science, University of British Columbia, 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
Appl Biochem Biotechnol. 2005 Spring;121-124:163-70. doi: 10.1385/abab:121:1-3:0163.
Economic barriers preventing commercialization of lignocellulose-to-ethanol bioconversion processes include the high cost of hydrolytic enzymes. One strategy for cost reduction is to improve the specific activities of cellulases by genetic engineering. However, screening for improved activity typically uses "ideal" cellulosic substrates, and results are not necessarily applicable to more realistic substrates such as pretreated hardwoods and softwoods. For lignocellulosic substrates, nonproductive binding and inactivation of enzymes by the lignin component appear to be important factors limiting catalytic efficiency. A better understanding of these factors could allow engineering of cellulases with improved activity based on reduced enzyme-lignin interaction ("weak lignin-binding cellulases"). To prove this concept, we have shown that naturally occurring cellulases with similar catalytic activity on a model cellulosic substrate can differ significantly in their affinities for lignin. Moreover, although cellulose-binding domains (CBDs) are hydrophobic and probably participate in lignin binding, we show that cellulases lacking CBDs also have a high affinity for lignin, indicating the presence of lignin-binding sites on the catalytic domain.
阻碍木质纤维素转化为乙醇生物转化过程商业化的经济障碍包括水解酶的高成本。降低成本的一种策略是通过基因工程提高纤维素酶的比活性。然而，筛选提高活性通常使用“理想”的纤维素底物，其结果不一定适用于更实际的底物，如预处理的硬木和软木。对于木质纤维素底物，木质素成分对酶的非生产性结合和失活似乎是限制催化效率的重要因素。更好地理解这些因素可以设计出基于减少酶与木质素相互作用（“弱木质素结合纤维素酶”）而具有更高活性的纤维素酶。为了证明这一概念，我们已经表明，在模型纤维素底物上具有相似催化活性的天然存在的纤维素酶对木质素的亲和力可能有显著差异。此外尽管纤维素结合结构域（CBD）具有疏水性且可能参与木质素结合，但我们表明缺乏CBD的纤维素酶对木质素也有高亲和力这表明催化结构域上存在木质素结合位点。
