Brookhaven, Carnegie Scientists Report First "Morphing" Of Plant Enzyme Function

The achievement advances the prospects of "designer" plants forrenewable industrial raw materials, fuel and food. It also sheds newlight on how plant enzymes evolved to perform different functions.

The team of scientists from the U.S. Department of Energy’s BrookhavenNational Laboratory and the Carnegie Institution of Washington’sStanford, California, campus reports its accomplishment in today’s issueof Science.

"We have shown that it is possible to change an enzyme’s functiondramatically by tweaking its structure just slightly," said JohnShanklin, who co-led the research team. "Nature has been doing this foreons through mutation; our experiment shows how such changes might comeabout and what their end result is."

DOE’s Director of the Office of Science, Martha Krebs, commented, "Thisis not only a discovery of fundamental scientific significance, but itclearly demonstrates a pathway to develop an alternative,biologically-based source for many oils used in industry which currentlydepend upon petroleum for their production."

Shanklin and his colleagues worked with enzymes called desaturases andhydroxylases, taken from different species of related cruciferousplants.

Both enzymes perform important tasks. Desaturase converts plantmolecules called fatty acids from straight to bent, by turning singlechemical bonds into double ones. Hydroxylase adds hydroxy groups to thefatty acids’ structure.

These simple chemical changes can make huge differences in plant oilproperties. For example, a fatty acid molecule with two bends may besensitive to heat, while a fatty acid with an added hydroxy group isheat-resistant and performs wells as a high-temperature lubricant.

While there are hundreds of applications for existing plant oils, evenmore uses could arise from novel oils produced by plants that are givennew enzymes.

The Brookhaven-Carnegie experiments were not performed on crop plantswhose oils are harvested for industrial use, but if crop plants could besimilarly changed, farmers could produce a far more diverse set of oils.

Enzymes are made of chains of amino acids, strung together in a certainorder to create a specific architecture that determines its uniquechemical function.

By careful detective work, Shanklin and Brookhaven’s Ed Whittle, alongwith Carnegie colleagues Chris Somerville and Pierre Broun, were able toidentify which amino acids in the sequence are responsible for aparticular activity of the desaturase and hydroxylase enzymes. Bymodifying the genetic blueprint for the enzymes, they swapped severalamino acids from one enzyme for their equivalents in another enzyme.

Then, they examined the consequences by implanting the genes in a plantknown as Arabidopsis, plant scientists’ equivalent of animalgeneticists’ well-studied fruit fly. An analysis of the oil thataccumulated in the modified plant’s seeds showed that the "morphing" hadbeen successful — the desaturase had become a hydroxylase and viceversa.

The changes centered around the enzymes’ ‘active sites’ — areas thatgrab fatty acids and catalyze the chemical changes. "Picture an enzymeas an industrial punch press and its active site as the die," saidShanklin. "What we have essentially done is learned how to change thedie 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. "Notonly can this knowledge be put to work in the field of designer oils, italso has implications for the concept of patenting enzymes."

Shanklin and his colleagues have studied desaturase and other plantenzymes for several years. In 1997, a team from Brookhaven and Sweden’sKarolinska Institute were the first to alter a desaturase so that itmade fatty acids bend at a different point and created an oil withslightly different characteristics.

The research was funded by DOE’s Office of Science.

The U.S. Department of Energy’s Brookhaven National Laboratory createsand operates major facilities available to university, industrial andgovernment personnel for basic and applied research in the physical,biomedical and environmental sciences, and in selected energytechnologies. The Laboratory is operated by Brookhaven ScienceAssociates, a not-for -profit research management company, undercontract with the U.S. Department of Energy.