Issued 6/4/97
Featured in Science News, May 31, 1997




UPTON, NY - Plant biochemists from the U.S. Department of Energy's Brookhaven National Laboratory and Sweden's Karolinska Institute have successfully used genetic techniques to manipulate the way plants transform saturated fat molecules into monounsaturated fat molecules.

The work may lead to "designer" plant oils for the $100 billion oil crop industry.

In a paper published in a recent issue of the Proceedings of the National Academy of Sciences, BNL biochemist John Shanklin and his colleagues describe their efforts to deliberately alter an important plant enzyme called desaturase.

"Desaturase changes fat molecules called fatty acids from straight and saturated to bent and monounsaturated," Shanklin explained. "The chemical change that desaturase causes - turning a single chemical bond in the fatty acid into a double bond - is small but significant, because it can turn a solid, 'bad-for-you' saturated fat into a liquid, monounsaturated one that's not so bad. What we've done is deliberately change a desaturase just slightly, so that it transforms fatty acids slightly differently and the plant makes a slightly different oil."

The team's achievement lays the groundwork for future advances in "designing" vegetable oils - and therefore everything from low-calorie margarine to nylon - by altering desaturases at the molecular level in order to change the resulting plant oil's properties, whether melting point or digestibility.

"This will likely lead to the development of crops that can make fatty acids with particular properties and applications," Shanklin said. "Such plants could become an alternate source of materials for which we now use non-renewable petroleum products. So, if we needed more of a given industrial material, we could just plant more of a certain designer oil crop."

A Tiny Change Makes a Big Difference

As part of their study, Shanklin and his colleagues first identified a variety of desaturase enzymes from different plants that are related genetically, but whose desaturases function differently. They then used a genetic approach to identify which region of the desaturase molecule was responsible for each property of the resulting oil.

Then, the researchers combined this genetic information with information from their studies of desaturase's three-dimensional atomic structure - studies they had performed using intense X-rays at BNL's National Synchrotron Light Source facility. The 3-D structure revealed a cleft on the desaturase molecule that fits around a saturated fatty acid like a glove on a hand. The researchers then identified which parts of the desaturase molecule near the cleft are most crucial to desaturase's action.

The next step in creating a "designer" desaturase was to change just a few crucial sites in the long chain of 360 amino acids that make up each desaturase molecule. "In desaturase, or any enzyme, the smallest changes can make the biggest difference - if they're the right changes," said Shanklin. By changing only five amino acids in one plant's desaturase to the equivalent amino acids from the other plant's desaturase, the properties of the first desaturase were changed to that of the other.

The final goal, though, was even more ambitious: to create an entirely new desaturase. Armed with the validated 3-D desaturase structure, they redesigned a desaturase with certain properties in mind - a process known as "rational design." They have applied for patents for this new enzyme, and for the methods they used to switch the properties of two desaturases.

"We are no longer constrained by the variation of desaturases found in nature," Shanklin explained. "If we can't find an existing enzyme with properties that we want, we will design one for ourselves."

The next step, he continued, will be to test their new desaturase by introducing it into a plant. "We still need to confirm that the changes we see in the test tube will translate into changes in the composition of fatty acids in oil crop plants," he said.

The research was funded by DOE's Office of Basic Energy Sciences and the Swedish Natural Science Research Council.

Brookhaven National Laboratory carries out basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. BNL is operated by Associated Universities, Inc., a nonprofit research management organization, under contract with the U.S. Department of Energy.

- 30 -