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J. Bacteriol., 08 1995, 4356-4363, Vol 177, No. 15
P Tomme, DP Driver, EA Amandoron, RC Miller Jr, R Antony, J Warren and DG Kilburn
A family II cellulose-binding domain (CBD) of an exoglucanase/xylanase
(Cex) from the bacterium Cellulomonas fimi was replaced with the family I
CBD of cellobiohydrolase I (CbhI) from the fungus Trichoderma reesei.
Expression of the hybrid gene in Escherichia coli yielded up to 50 mg of
the hybrid protein, CexCBDCbhI, per liter of culture supernatant. The
hybrid was purified to homogeneity by affinity chromatography on cellulose.
The relative association constants (Kr) for the binding of Cex, CexCBDCbhI,
the catalytic domain of Cex (p33), and CbhI to bacterial microcrystalline
cellulose (BMCC) were 14.9, 7.8, 0.8, and 10.6 liters g-1, respectively.
Cex and CexCBDCbhI had similar substrate specificities and similar
activities on crystalline and amorphous cellulose. Both released
predominantly cellobiose and cellotriose from amorphous cellulose.
CexCBDCbhI was two to three times less active than Cex on BMCC, but
significantly more active than Cex on soluble cellulose and on xylan.
Unlike Cex, the hybrid protein neither bound to alpha-chitin nor released
small particles from dewaxed cotton fibers.
Copyright © 1995, American Society for Microbiology
Comparison of a fungal (family I) and bacterial (family II) cellulose- binding domain
Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
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