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Two noncellulosomal cellulases of Clostridium thermocellum, Cel9I and Cel48Y, hydrolyse crystalline cellulose synergistically

Berger, Emanuel, Zhang, Dong, Zverlov, Vladimir V., Schwarz, Wolfgang H.
FEMS microbiology letters 2007 v.268 no.2 pp. 194-201
Clostridium thermocellum, barley, xylanases, cellulosome, chitinase, carboxymethylcellulose, genes, hydrolysis, amylases, synergism, endo-1,4-beta-glucanase, beta-glucans, Escherichia coli
The genome of Clostridium thermocellum contains a number of genes for polysaccharide degradation-associated proteins that are not cellulosome bound. The list includes β-glucanases, glycosidases, chitinases, amylases and a xylanase. One of these 'soluble'-enzyme genes codes for a second glycosyl hydrolase (GH)48 cellulase, Cel48Y, which was expressed in Escherichia coli and biochemically characterized. It is a cellobiohydrolyse with activity on native cellulose such as microcrystalline and bacterial cellulose, and low activity on carboxymethylcellulose. It is about 100 times as active on amorphic cellulose and mixed-linkage barley β-glucan compared with cellulase Cel9I. The enzyme Cel48Y shows a distinct synergism of 2.1 times with the noncellulosomal processive endoglucanase Cel9I on highly crystalline bacterial cellulose at a 17-fold excess of Cel48Y over Cel9I. These data show that C. thermocellum has, besides the cellulosome, the genes for a second cellulase system for the hydrolysis of crystalline cellulose that is not particle bound.