Cellulase C. bescii CelA, a highly active and stable enzyme, exhibits a new cellulose digestion paradigm promoting inter-cellulase synergy.
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C. bescii CelA, a hydrolytic enzyme with multiple functional domains, may have several advantages over other fungal and bacterial cellulases for use in biofuels production: very high specific activity, stability at elevated temperatures, and a novel digestion mechanism. Read the research of Michael Resch about Combination of Enzyme Systems Could Lower Biofuel Costs.
A research team from the U.S. Department of Energy’s Bio Energy Science Center, which comprised scientists from the National Renewable Energy Laboratory (NREL) and the University of Georgia, isolated the thermophilic cellulase CelA from C. bescii. A comparison was conducted of its cellulolytic activity with that of a binary mixture containing both T. reesei Cel7A exoglucanase and A. cellulolyticus Cel5A endoglucanase on several substrates. The researchers also compared the cellulose digestion mechanisms of these two enzyme systems using electron microscopy and modeling.
CelA was shown to retain high activity at all temperatures tested, converting 60% of glucan at 85°C compared to 28% glucan conversion for the common exo/endo cellulase standard mixture, Cel7A/Cel5A, at its optimal temperature of 50°C. This difference in activity translates to a seven-fold increase in activity for CelA at the molecular level.
Transmission electron microscopy studies of cellulose following incubation with CelA sug- gest that CelA is capable of not only the common surface ablative mechanism driven by general cellulase processivity, but also of excavating extensive cavities into the surface of the substrate. Additionally, during the digestion experiments, CelA achieved 60% conversion of xylan in native switchgrass, showing its potential for industrial processes using mild or no pretreatment.
Key Research Results
The research team isolated CelA, a highly active cellulase with a novel cellulose digestion mechanism. The X-ray structures of the primary protein components of CelA were also determined, advancing the understanding of the mode of action of this cellulase.
CelA was shown to retain high activity at all temperatures tested, converting 60% of glucan compared to 28% glucan conversion for the more common exo/endo cellulase standard mixture, Cel7A/Cel5A, at its optimal temperature of 50°C.
CelA and similar multi-functional cellulases represent a new and distinct paradigm for cellulose digestion. This mechanism is fundamentally different from conventional cellulases and could help increase inter-cellulase synergy in consolidated bioprocessing microorganisms, as well as in commercial cellulase formulations used for biofuels production.
Technical Contact: Yannick Bomble, firstname.lastname@example.org
Reference: Brunecky, R.; Alahuhta, P.; Xu, Q.; Donohoe, B.; Crowley, M.; Kataeva, I, Yang, SJ, Adams, M; Lunin, V.; Himmel, M.; Bomble, Y. (2013). “Revealing Nature’s Cellulase Diversity: The Digestion Mechanism of Caldicellulosiruptor bescii CelA.” Science (342:6165); pp. 1513–1516. DOI: 10.1126/science.1244273.
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