Cracking Cellulose

Converting cellulosic sugars to advanced biofuel just got more efficient
By Bryan Sims | September 20, 2011

For years, scientists around the world have tried to figure out how to efficiently break down plant-based material to better access fermentable cellulosic sugars for conversion to advanced biofuels. Two researchers at the University of York in the U.K. have discovered a novel method for overcoming the chemical intractability of cellulose that allows for efficient conversion to ethanol.

Working with scientists in Novozymes laboratories at Davis, Calif., and Bagsvaerd, Denmark, as well as researchers at the University of Copenhagen and the University of Cambridge, professors Paul Walton and Gideon Davies at York University’s department of chemistry identified the molecular mechanism behind an enzyme secreted by brown rot fungus—called TaGH61—that’s capable of degrading the cellulose chains of plant cell walls to release short-chained sugars. Their work is published in the Proceedings of the National Academy of Sciences.

“This now unlocks the potential of enzyme degradation of cellulose for cellulosic ethanol production,” Walton tells Biorefining Magazine. “Once cellulose becomes available and once you can convert it efficiently enough through to more soluble sugars into ethanol, then you’re in business because the availability of cellulosic biomass is just vast.”

According to Walton, Novozymes discovered the TaGH61 enzyme a few years ago, but the Danish enzyme developer was unable to fully unlock its true potential for degrading cellulose. Walton and Davies managed to determine the full structure of the TaGH61 enzyme and figure out how it works. More importantly, the researchers found a way to initiate oxidative degeneration of cellulose by using copper on the enzyme in order to overcome the chemical inertness of the material.

“Imagine ironing your clothes,” Walton explains. “The enzyme is shaped like the iron and sits down on the cellulosic surface, which are comprised of long chains of polyglucose that are difficult to break down. What happens is that the enzyme essentially forms a very reactive copper oxygen species that cleaves the cellulose, we think, at random points.”

When polyglucose chains are cleaved by copper, according to Walton, soluble sugars peel away from the surface of the cellulosic surface that ultimately end up in solution where traditional cellulases can then be utilized for fermentation into biofuels and other biochemicals. Walton says that the majority of cellulose obtained and used for the research was derived from pretreated corn stover that was used as a substrate in tests. The enzyme, he adds, isn’t capable of deconstructing lignin.

Novozymes’ copper-dependent TaGH61 enzyme is a breakthrough in cellulose degradation and is a key feature of its Cellic CTec products. In July 2010, the company launched its new Cellic CTec2 enzymes that can break down cellulosic biomass such as corn cobs, wheat straw, sugarcane bagasse or wood chips for conversion to cellulosic ethanol.

“Fully understanding the mechanism behind GH61 is important in the context of commercial production of biofuel from plant waste and a true scientific paradigm shift,” says Claus Crone Fuglsang, managing director for Novozymes’ research labs in Davis. “This discovery will continue to drive advances in production of other biobased chemicals and materials in the future.” 

—Bryan Sims