Two noncellulosomal cellulases of Clostridium thermocellum, Cel9I and Cel48Y, hydrolyse crystalline cellulose synergistically.
The genome of Clostridium thermocellum contains a number of genes for polysaccharide degradation-associated proteins that are not cellulosome bound. The list includes beta-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 beta-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.
Berger
Emanuel
E
Dept of Microbiology Technische Universitaet Muenchen, Am Hochanger, Freising-Weihenstephan, Germany.
Zhang
Dong
D
Zverlov
Vladimir V
VV
Schwarz
Wolfgang H
WH
D044602:Cellulases / Q000235:genetics*; D002482:Cellulose / Q000378:metabolism; D003001:Cloning, Molecular; D048013:Acetivibrio thermocellus / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial; D006868:Hydrolysis; D008969:Molecular Sequence Data; D012995:Solubility; D013379:Substrate Specificity
D002482:Cellulose; D044602:Cellulases