Weak lignin-binding enzymes |
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Authors: | Alex Berlin Neil Gilkes Arwa Kurabi Renata Bura Maobing Tu Douglas Kilburn John Saddler |
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Institution: | (1) Forest Products Biotechnology, Department of Wood Science, University of British Columbia, 2424 Main Mall, V6T 1Z4 Vancouver, BC, Canada |
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Abstract: | 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. |
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Keywords: | Cellulase lignin unproductive binding softwood hydrolysis |
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