The construction of 15 new highly stable fungal enzyme catalysts that break down cellulose into sugars at high temperatures, to produce ethanol or butanol, has been revealed a team of researchers at Caltech. The findings of the research from Frances H. Arnold, the Dick and Barbara Dickinson Professor of Chemical Engineering and Biochemistry and her team at Caltech, were published this week in the Proceedings of the National Academy of Sciences.

According to the paper, previously, fewer than 10 such fungal cellobiohydrolase II enzymes were known, but perhaps more importantly, in addition to their remarkable stabilities, the new enzymes degrade cellulose over a wide range of conditions. The cost implications of the findings are potentially huge, says Arnold.

Arnold and Caltech postdoctoral scholar Pete Heinzelman created the 15 new enzymes using a process called structure-guided recombination. Using a computer program to design where the genes recombine, the Caltech researchers "mated" the sequences of three known fungal cellulases to make more than 6,000 progeny sequences that were different from any of the parents, yet encoded proteins with the same structure and cellulose-degradation ability.

"Enzymes that are highly thermostable also tend to last for a long time, even at lower temperatures," Arnold says. "And, longer-lasting enzymes break down more cellulose, leading to lower cost."

Next, the researchers plan to use the structure-guided recombination process to perfect each of the half-dozen or so cellulases that make up the soup of enzymes required for the industrial degradation of cellulose. "We've demonstrated the process on one of the components. Now we have to create families of all of the other components, and then look for the ideal mixtures for each individual application," Arnold says, with the ultimate goal of creating a cost-efficient recipe for cellulosic biofuel.

"If you think about it, energy is the biggest industry there is," Arnold says. "If we can replace foreign oil with renewable biofuels, that's an enormous contribution. And that replacement is slow right now because these enzymes are just too expensive."