Characterization of fungal cellulases

Cellulose is the most abundant polysaccharide on earth, found in nature almost exclusively in plant cell walls. Cellulose is a chemically simple molecule composed of linear homopolymers of D-glucose units linked by beta-1,4-glycosidic linkages and having a degree of polymerisation ranging from 100 up to 15,000. The smallest structural repeating unit in native cellulose is cellobiose, a disaccharide. This arrangement of glucose units leads to extended conformation of the cellulose chains which can pack together via inter- and intramolecular hydrogen bonds forming highly ordered crystalline fibers. Cellulases are a group of enzymes, secreted by micro-organisms living in plant litter and soil, and effectively degrading crystalline cellulose into soluble sugars in a concerted manner. Cellulases are also important industrial enzymes, which can be used e.g. in pulp and paper, textile, and detergent industry, as well as in conversion of cellulosic biomass to ethanol, a transport fuel. Thermostable enzymes are needed for many of these applications. Thermophilic organisms offer a potential source of thermostable enzymes for industrial applications, or alternatively thermostability of an enzyme can also be improved by structure-based rational mutagenesis or by directed evolution. Cellobiohydrolases are a class of cellulases especially active on crystalline cellulose hydrolysis. They degrade cellulose from the chain ends, producing mainly cellobiose (disaccharide) in a processive manner. Cellobiohydrolases are often modular enzymes consisting of a minimum of one catalytic module and one carbohydrate-binding module (CBM). The CBM is responsible for bringing the catalytic module near the substrate and improving the action on polymeric substrates while not affecting the activity on small soluble substrates. Results from the characterisation of enzymatic properties of three novel thermostable cellobiohydrolases belonging to the glycosyl hydrolase (GH) family 7 (http://afmb.cnrs-mrs.fr/CAZY/citing.html) will be presented. Acknowledgements: This study was part of an EU-project ¡§Technological improvement for ethanol production from lignocellulose (EU-TIME)¡¨.