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Applied and Environmental Microbiology, November 2009, p. 6655-6661, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01260-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Processivity, Synergism, and Substrate Specificity of Thermobifida fusca Cel6B {triangledown}

Thu V. Vuong and David B. Wilson*

Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853

Received 1 June 2009/ Accepted 25 August 2009

A relationship between processivity and synergism has not been reported for cellulases, although both characteristics are very important for hydrolysis of insoluble substrates. Mutation of two residues located in the active site tunnel of Thermobifida fusca exocellulase Cel6B increased processivity on filter paper. Surprisingly, mixtures of the Cel6B mutant enzymes and T. fusca endocellulase Cel5A did not show increased synergism or processivity, and the mutant enzyme which had the highest processivity gave the poorest synergism. This study suggests that improving exocellulase processivity might be not an effective strategy for producing improved cellulase mixtures for biomass conversion. The inverse relationship between the activities of many of the mutant enzymes with bacterial microcrystalline cellulose and their activities with carboxymethyl cellulose indicated that there are differences in the mechanisms of hydrolysis for these substrates, supporting the possibility of engineering Cel6B to target selected substrates.

* Corresponding author. Mailing address: 458 Biotechnology Building, Cornell University, Ithaca, NY 14850. Phone: (607) 255-5706. Fax: (607) 255-2428. E-mail: dbw3{at}cornell.edu

{triangledown} Published ahead of print on 4 September 2009.

Applied and Environmental Microbiology, November 2009, p. 6655-6661, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01260-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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