Researchers describe 'implausible' chemistry that produces herbicida...( CHAMPAIGN Ill. A soil microbe that ...)

CHAMPAIGN, Ill. A soil microbe that uses chemical warfare to fight off competitors employs an unusual chemical pathway in the manufacture of its arsenal, researchers report, making use of an enzyme that can do what no other enzyme is known to do: break a non-activated carbon-carbon bond in a single step.

Their study, appearing this week in the journal Nature, provides the first three-dimensional structure of the enzyme, hydroxyethylphosphonate dioxygenase (HEPD) and proposes a mechanism by which it performs its task.

University of Illinois researchers first reported the enzyme in Nature Chemical Biology in 2007, said Wilfred van der Donk, an author on both papers with microbiologist William Metcalf.

"Our team discovered this very implausible chemical reaction," van der Donk said. "And the more we learned about it the more unusual it became. The enzyme is unusual because it breaks a carbon-carbon bond without needing anything except oxygen."

The study is important because HEPD catalyzes a critical step in the chemical pathway that produces phosphinothricin (PT), a bacterial compound that is widely used as an agricultural herbicide. This compound, which is a component of two top-selling weed killers (Liberty and Basta), is effective when used with transgenic crops that have a PT-resistance gene inserted into their DNA. The resistance gene also comes from the bacteria that produce PT. It allows the bacteria (which belong to the genus Streptomyces) to emit the antibiotic to kill off their competitors without killing themselves. Similarly, corn and other crops that contain the resistance gene are able to withstand PT-based herbicides that kill the weeds around them.

The new findings are part of an ongoing exploration at Illinois of naturally produced molecules that contain carbon-phosphorus (C-P) bonds. Although little understood, these phosphonates (which contain C-P bonds) and phosphinates (with C
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