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Open Access Research

Paradigmatic status of an endo- and exoglucanase and its effect on crystalline cellulose degradation

Sarah Moraïs12, Yoav Barak13, Raphael Lamed4, David B Wilson5, Qi Xu6, Michael E Himmel6 and Edward A Bayer1*

Author Affiliations

1 Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel

2 Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel

3 Chemical Research Support, The Weizmann Institute of Science, Rehovot, 76100, Israel

4 Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, 69978, Israel

5 Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA

6 Biosciences Center, National Renewable Energy Laboratory (NREL) and BioEnergy Science Center (BESC), Golden, CO, USA

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Biotechnology for Biofuels 2012, 5:78  doi:10.1186/1754-6834-5-78

Published: 24 October 2012

Abstract

Background

Microorganisms employ a multiplicity of enzymes to efficiently degrade the composite structure of plant cell wall cellulosic polysaccharides. These remarkable enzyme systems include glycoside hydrolases (cellulases, hemicellulases), polysaccharide lyases, and the carbohydrate esterases. To accomplish this challenging task, several strategies are commonly observed either separately or in combination. These include free enzyme systems, multifunctional enzymes, and multi-enzyme self-assembled designer cellulosome complexes.

Results

In order to compare these different paradigms, we employed a synthetic biology approach to convert two different cellulases from the free enzymatic system of the well-studied bacterium, Thermobifida fusca, into bifunctional enzymes with different modular architectures. We then examined their performance compared to those of the combined parental free-enzyme and equivalent designer-cellulosome systems. The results showed that the cellulolytic activity displayed by the different architectures of the bifunctional enzymes was somewhat inferior to that of the wild-type free enzyme system.

Conclusions

The activity exhibited by the designer cellulosome system was equal or superior to that of the free system, presumably reflecting the combined proximity of the enzymes and high flexibility of the designer cellulosome components, thus enabling efficient enzymatic activity of the catalytic modules.

Keywords:
Bifunctional cellulase; Thermobifida fusca; Enzyme paradigm