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Title :

Tapping Nature’s Strategies for Biomass Degradation: Free-Enzyme Systems

Description :

Nature has devised two types of enzyme-based strategies for breaking down plant cell walls. One strategy observed in oxygen-rich environments involves fungi and bacteria that secrete individual enzymes with complementary functions for degrading cell walls. These free enzymes work as a team to deconstruct plant cell-wall carbohydrates into simple sugars (see figure, Free-Enzyme Systems). Some of the most-studied free enzymes are cellulases secreted by Trichoderma reesei, a canvas-eating fungus isolated during World War II from tents and uniforms damaged by jungle rot. The DOE Bioenergy Research Centers are exploring natural environments to identify and produce new mixes of biomass-degrading enzymes that can substantially increase the efficiency of cellulosic biofuel production. A second strategy, occurring in oxygen-free environments, is exhibited by bacteria that produce cellulosomes— large multiprotein complexes that degrade the cell wall by assembling several different enzymes into a single structure. Cellulosomes protrude from bacterial surfaces, latch onto plant cell walls, and tear carbohydrates into simple sugars. Clostridium thermocellum, a model bacterium for studying cellulosomes, can produce more than 25 different cell wall–degrading enzymes that it can “plug and play” into its large protein scaffold (see figure, The Cellulosome). By sensing the surrounding environment, C. thermocellum can modify the functionality of its cellulosomes on demand by assembling different combinations of enzymes to attack various compounds in the plant cell wall. The LEGO-like arrangement of enzymes in cellulosomes offers a unique opportunity to engineer “designer” multienzyme complexes targeted to specific biomass types or different stages of biomass deconstruction.

Citation :

Bioenergy Research Centers: An Overview of the Science, U.S. Department of Energy, July 2009. DOE/SC-0116. Document

Credit or Source :

Genome Management Information System, Oak Ridge National Laboratory

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