Termites and fungi already know how to digest cellulose, but the human process of producing ethanol from cellulose remains slow and expensive. The central bottleneck is the sluggish rate at which the cellulose enzyme complex breaks down tightly bound cellulose into sugars, which are then fermented into ethanol.
To help unlock the cellulose bottleneck, a team of scientists has conducted molecular simulations at the San Diego Supercomputer Center (SDSC), based at UC San Diego. By using "virtual molecules," they have discovered key steps in the intricate dance in which the enzyme acts as a molecular machine -- attaching to bundles of cellulose, pulling up a single strand of sugar, and putting it onto a molecular conveyor belt where it is chopped into smaller sugar pieces.
"By learning how the cellulase enzyme complex breaks down cellulose we can develop protein engineering strategies to speed up this key reaction," said Mike Cleary, who is coordinating SDSC's role in the project. "This is important in making ethanol from plant biomass a realistic 'carbon neutral' alternative to the fossil petroleum used today for transportation fuels."
The results were reported in the April 12 online edition of the Protein Engineering, Design and Selection journal, which also featured visualizations of the results on the cover.
A convergence of factors from looming global warming to unstable international oil supplies is driving a surge in renewable biofuels such as ethanol, with worldwide ethanol production more than doubling between 2000 and 2005. To date, corn has been the favorite ethanol source. While good news for farmers, corn prices have doubled in the past two years, and consumers worldwide are feeling the pinch as food prices climb.
A far better source is to produce ethanol from cellulose, easing pressure on foo d supplies and yielding greater greenhouse gas benefits. The fibrous part that makes up the bulk of plants, cel
Contact: Paul Tooby
University of California - San Diego