UPTON, NY -- In a transformation worthy of Hollywood special effects, biochemists have for the first time "morphed" a plant enzyme, turning it into another enzyme with a different function, through genetic manipulation.
The achievement advances the prospects of "designer" plants for renewable industrial raw materials, fuel and food. It also sheds new light on how plant enzymes evolved to perform different functions.
The team of scientists from the U.S. Department of Energy's Brookhaven National Laboratory and the Carnegie Institution of Washington's Stanford, California, campus reports its accomplishment in today's issue of Science.
"We have shown that it is possible to change an enzyme's function dramatically by tweaking its structure just slightly," said John Shanklin, who co-led the research team. "Nature has been doing this for eons through mutation; our experiment shows how such changes might come about and what their end result is."
DOE's Director of the Office of Science, Martha Krebs, commented, "This is not only a discovery of fundamental scientific significance, but it clearly demonstrates a pathway to develop an alternative, biologically-based source for many oils used in industry which currently depend upon petroleum for their production."
Shanklin and his colleagues worked with enzymes called desaturases and hydroxylases, taken from different species of related cruciferous plants.
Both enzymes perform important tasks. Desaturase converts plant molecules called fatty acids from straight to bent, by turning single chemical bonds into double ones. Hydroxylase adds hydroxy groups to the fatty acids' structure.
These simple chemical changes can make huge differences in plant oil properties. For example, a fatty acid molecule with two bends may be sensitive to heat, while a fatty acid with an added hydroxy group is heat-resistant and performs wells as a high-temperature lubricant.
While there are hundreds of applications for existing plant oils, even more uses could arise from novel oils produced by plants that are given new enzymes.
The Brookhaven-Carnegie experiments were not performed on crop plants whose oils are harvested for industrial use, but if crop plants could be similarly changed, farmers could produce a far more diverse set of oils.
Enzymes are made of chains of amino acids, strung together in a certain order to create a specific architecture that determines its unique chemical function.
By careful detective work, Shanklin and Brookhaven's Ed Whittle, along with Carnegie colleagues Chris Somerville and Pierre Broun, were able to identify which amino acids in the sequence are responsible for a particular activity of the desaturase and hydroxylase enzymes. By modifying the genetic blueprint for the enzymes, they swapped several amino acids from one enzyme for their equivalents in another enzyme.
Then, they examined the consequences by implanting the genes in a plant known as Arabidopsis, plant scientists' equivalent of animal geneticists' well-studied fruit fly. An analysis of the oil that accumulated in the modified plant's seeds showed that the "morphing" had been successful -- the desaturase had become a hydroxylase and vice versa.
The changes centered around the enzymes' "active sites" -- areas that grab fatty acids and catalyze the chemical changes. "Picture an enzyme as an industrial punch press and its active site as the die," said Shanklin. "What we have essentially done is learned how to change the die to make the punch press produce a different product."
This achievement, Shanklin continued, means that enzymes are more "plastic," or able to be changed, than scientists had recognized. "Not only can this knowledge be put to work in the field of designer oils, it also has implications for the concept of patenting enzymes."
Shanklin and his colleagues have studied desaturase and other plant enzymes for several years. In 1997, a team from Brookhaven and Sweden's Karolinska Institute were the first to alter a desaturase so that it made fatty acids bend at a different point and created an oil with slightly different characteristics.
The research was funded by DOE's Office of Science.
The U.S. Department of Energy's Brookhaven National Laboratory creates and operates major facilities available to university, industrial and government personnel for basic and applied research in the physical, biomedical and environmental sciences, and in selected energy technologies. The Laboratory is operated by Brookhaven Science Associates, a not-for -profit research management company, under contract with the U.S. Department of Energy.
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Science