CAL TECH CLOSER TO BIOFUEL ENZYME REFINING

Caltech scientists create new enzymes for biofuel production; Enzymes are important step toward cheaper biofuels
Kathy Svitil, 23 March 2009 (Cal Tech via EurekAlert)

"Researchers at the California Institute of Technology (Caltech) and world-leading gene-synthesis company DNA2.0 have taken an important step toward the development of a cost-efficient process to extract sugars from cellulose--the world's most abundant organic material and cheapest form of solar-energy storage. Plant sugars are easily converted into a variety of renewable fuels such as ethanol or butanol.

"…Frances H. Arnold, the Dick and Barbara Dickinson Professor of Chemical Engineering and Biochemistry at Caltech, and her colleagues report the construction of 15 new highly stable fungal enzyme catalysts that efficiently break down cellulose into sugars at high temperatures…[and] over a wide range of conditions."

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"…Most biofuels used today are made from the fermentation of starch from corn kernels. That process, although simple, is costly because of the high price of the corn kernels themselves…Agricultural waste, such as corn stover (the leaves, stalks, and stripped cobs of corn plants, left over after harvest), is cheap. These materials are largely composed of cellulose, the chief component of plant-cell walls. Cellulose is far tougher to break down…[and] requires a whole suite of enzymes, or cellulases, working in concert.

"The [10] cellulases currently used industrially, all of which were isolated from various species of plant-decaying filamentous fungi, are both slow and unstable, and, as a result, the process remains prohibitively expensive…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" …more than 6,000 progeny sequences that were different…yet encoded proteins with the same structure and cellulose-degradation ability."

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"…the Caltech and DNA2.0 researchers were able to predict which of the more than 6,000 possible new enzymes would [have thermostability]…a requirement of efficient cellulases, because at higher temperatures--say, 70 or even 80 degrees Celsius--chemical reactions are more rapid. In addition, cellulose swells at higher temperatures, which makes it easier to break down…cellulases from nature typically won't function at temperatures higher than about 50 degrees Celsius…[C]oauthor Jeremy Minshull and colleagues from DNA2.0…synthesized [a yeast that produced] 15 new cellulases…[Each] was more stable, worked at significantly higher temperatures (70 to 75 degrees Celsius), and degraded more cellulose than the parent enzymes…

"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…"