Applied and Environmental Microbiology, October 2001, p. 4426-4431, Vol. 67, No. 10
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.10.4426-4431.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, United Kingdom
Received 7 May 2001/Accepted 16 July 2001
The mechanisms by which cellulolytic enzymes and enzyme complexes in Ruminococcus spp. bind to cellulose are not fully understood. The product of the newly isolated cellulase gene endB from Ruminococcus flavefaciens 17 was purified as a His-tagged product after expression in Escherichia coli and found to be able to bind directly to crystalline cellulose. The ability to bind cellulose is shown to be associated with a novel cellulose-binding module (CBM) located within a region of 200 amino acids that is unrelated to known protein sequences. EndB (808 amino acids) also contains a catalytic domain belonging to glycoside hydrolase family 44 and a C-terminal dockerin-like domain. Purified EndB is also shown to bind specifically via its dockerin domain to a polypeptide of ca. 130 kDa present among supernatant proteins from Avicel-grown R. flavefaciens that attach to cellulose. The protein to which EndB attaches is a strong candidate for the scaffolding component of a cellulosome-like multienzyme complex recently identified in this species (S.-Y. Ding et al., J. Bacteriol. 183:1945-1953, 2001). It is concluded that binding of EndB to cellulose may occur both through its own CBM and potentially also through its involvement in a cellulosome complex.
Present address: Ohio State University, Columbus, Ohio.
Present address: Department Plant and Microbial Biology,
University of California, Berkeley, California.
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