The bacteria forms scaffolds for its enzymes, which work together to break apart the plant. The fungal enzymes, on the other hand, are not tethered to a large complex, but act independently.
It isn't clear how the enzyme scaffolds form, so the researchers created a computational model of the active molecules and set them into motion in a virtual environment. Contrary to expectations, the larger, slower-moving enzymes lingered near the scaffold longer, allowing them to bind to the frame more frequently; the smaller ones moved faster and more freely through the solution, but bound less often.
The results of the study, led by NREL researchers Yannick Bomble and Mike Crowley, were reported in the Journal of Biological Chemistry in February 2011. The insights are being used in the creation of designer enzymes to make biomass conversion faster, more efficient and less expensive.
Unexplored enzyme function
The scientists also studied parts of the enzyme called the carbohydrate binding molecule--a sticky "foot" that helps the enzymes find and guide the cellulose into their active site and the linker region, which joins the foot to the main body of the enzyme. The carbohydrate binding molecule and linker region were long thought to play a minor role in enzyme function; yet without them, the enzyme can't convert cellulose to glucose effectively. The researchers wondered why that is.
Using the Ranger supercomputer, the researchers made several important discoveries. First, they found that the cellulose surface has energy wells that are set 1 nanometer apart, a perfect fit for the binding module. They also found that the linker region, previously believed to contain both stiff and flexible regions, behaves more like a highly flexible tether. Those insights would have been difficult to determine experimentally, but, now hypothesized and backed up with advanced computing simulations, they can be tested in the laboratory.
"It's a very messy problem for the experimentalists," said Crowley, a principal scientist at the Energy Laboratory and Beckham's colleague. "We're using rational design to understand how the enzyme works, and then to predict the best place to change something and test it."
The research addresses the enzymatic activity bottlenecks that prevent renewable energy from cellulose containing biomass from being competitive with fossil fuels. "If we can help industry understand and improve these processes for renewable fuel production, we'll be able to offset a significant fraction of fossil fuel use in the long term," Beckham said.