Enzyme research speeds cellulosic ethanol development

By Bryan Sims
Two enzyme research efforts are getting closer to their goals of perfecting enzymes for cellulosic ethanol production.

In March, Royal Dutch Shell PLC expanded its collaborative partnership with Redwood City, Calif.-based biocatalyst developer Codexis Inc. to enhance the performance of enzymes and microbes used in cellulosic ethanol production.

Under the agreement, Codexis will work with Canadian cellulosic ethanol producer Iogen Corp. to improve the efficiency of biocatalysts used in Iogen's ethanol production process at its demonstration facility in Ottawa. Iogen's plant, which opened in 2004, uses an enzymatic hydrolysis pathway to produce ethanol from wheat straw.

According to Codexis, the company uses DNA shuffling, a research technique that manipulates the DNA blueprint of an enzyme and recombines the DNA, to create new hybrid genes. The resulting gene library is screened to find enzymes that meet or exceed desired targeted performance characteristics. Codexis has been working with Shell since
November 2006 to tailor its technology to the biofuels industry.

Iogen and Shell first formed their partnership in 2002, when Shell acquired an equity stake in Iogen. As part of their collaborative agreement, Shell made a significant investment in Iogen by increasing its shares in Iogen Energy Corp., a subsidiary that is focused on technology development, from 26.3 percent to 50 percent.

Meanwhile, researchers at the California Institute of Technology (Caltech), and DNA2.0 Inc. are seeing the fruits of their labor as they develop a cost-efficient process to extract sugars from cellulose.

Frances Arnold, the Dick and Barbara Dickinson professor of chemical engineering and biochemistry at Caltech, and researchers from gene-synthesis company DNA2.0 Inc. created 15 highly stable fungal enzyme catalysts that efficiently break down cellulose into sugars at high temperatures using a method called structure-guided recombination. Prior to this finding, fewer than 10 such fungal cellobiohydrolase II enzymes were known to exist.

Arnold, along with Caltech postdoctoral scholar Pete Heinzelman, used a computer program to design where specific genes recombine by mating the sequences of three known fungal cellulases that make more than 6,000 progeny sequences different from any of the parents while encoding proteins with the same structure and cellulose-degradation characteristics.

By analyzing the enzymes encoded by a small subset of the sequences, researchers at Caltech and DNA2.0 were able to predict which of the 6,000 possible new enzymes would be the most stable, particularly under high temperatures-a characteristic called thermostability.

According to Arnold, the next stage entails using the structure-guided recombination process to perfect each of the six cellulases that make up the mixture of enzymes required for the industrial degradation of cellulose.

"We've demonstrated the process on one of the components," Arnold said. "Now, we have to create families of all of the other components, and then look for the ideal mixtures for each individual application."