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Combining two different types of enzyme systems could speed breakdown of biomass for lower cost biofuels

Enzymes could break down cell walls faster—leading to less expensive biofuels for transportation—if two different types of enzyme systems are brought together in an industrial setting, new research by the Energy Department’s National Renewable Energy Laboratory (NREL) suggests. A paper on the work appears in the RSC journal Energy and Environmental Science.

NREL researchers found that two enzyme paradigms—free and complexed—use significantly different mechanisms to degrade biomass at the nanometer scale.

Many microorganisms secrete synergistic cocktails of individual enzymes, with one or several catalytic domains per enzyme (“free”). Conversely, some bacteria synthesize large multi-enzyme complexes, called cellulosomes, which contain multiple catalytic units per complex (“complexed”). While both systems use similar catalytic chemistries, the ways they degrade polysaccharides has been unclear.

NREL researchers found that the free enzymes are more active on pretreated biomass, while the cellulosomes are more active on purified cellulose. Using electron microscopes they found that free enzymes attack the plant cell wall surface by chipping and eroding, helped along by sharpening the thread-like cellulose fibers.

By contrast, the cellulosomes physically separate individual cellulose microfibrils from larger particles to enhance access to the cellulose surfaces. They assemble protein scaffolding to help get the job done.

The NREL researchers found that mixing the two systems enhances catalytic performance. When the two enzyme systems are combined, the substrate changes in unexpected ways and that result suggests the two systems work with each other to deconstruct the cell walls more efficiently. The findings suggest that there may be an optimal strategy between the two mechanisms.

Resources

  • Resch, Michael G.; Donohoe, Bryon S.; Baker, John O.; Decker, Stephen R.; Bayer, Edward A.; Beckham, Gregg T.; and Himmel, Michael E. (2013) Fungal cellulases and complexed cellulosomal enzymes exhibit synergistic mechanisms in cellulose deconstruction. Energy Environ. Sci. doi: 10.1039/C3EE00019B

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