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Current Topics in Cereal Chemistry   Volumes    Volume 1 
Xylanolytic enzymes of Trichoderma reesei: properties and regulation of expression
Susanne Zeilinger, Robert Mach
Pages: 27 - 35
Number of pages: 9
Current Topics in Cereal Chemistry
Volume 1 

Copyright © 1998 Research Trends. All rights reserved

In nature, cycling of carbon is of great importance to living systems. It is estimated that the photosynthetic process produces 1.5x1011 tons of dry plant material every year, of which xylan is the most abundant hemicellulose mainly found in grasses, cereals and hardwoods. Xylans are heteropolysaccharides with a backbone composed of 150 - 200 ß-1,4-linked xylopyranose units; the degree of substitution of xylan with residues such as arabinose, galactose, 4-O-Me-D-glucuronic acid and acetic acid, varies depending on its botanical origin. During the last years, the interest in xylanases and other hemicellulases has increased heavily because of their applications e.g. in biobleaching and the feed and food industry such as those concerned with baking and the production of starch, sweetening agents and juices [1, 2]. The filamentous fungus Trichoderma reesei is an industrially important organism for the production of cellulolytic and hemicellulolytic enzymes. Significant progress has been made on the biochemistry and molecular biology of the xylanases of T. reesei. Enzymes such as the two endo-xylanases, XYN I and XYN II, the ß-xylosidase, and side-chain cleaving enzymes have been purified [3, 4, 5] and their corresponding genes cloned [3, 6, 7, 8, 9]. The three- dimensional structure of the two major xylanases, XYNI and XYNII (which are responsible for approximately 90% of the xylanolytic activity) has been analysed [10, 11]. The regulation on the molecular level of XYN I and XYN II formation was recently investigated in our laboratory and by Margolles-Clark and co-workers [12]. We found that both genes (xynl and xyn2) are under transcriptional control which is mediated by different induccrs derived from xylan and cellulose. In the induction of both genes DNA-binding proteins binding to a CCAAT-consensus are involved [13]. Furthermore, we could show that the xynl gene expression is directly under control of carbon catabolite repression [14] mediated by the carbon catabolite repressing protein Crel [15, 16, 17]. Recent findings in our laboratory also point to the involvement of a xlnR-like [18] xylanase-specific inducer for xynl expression.
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