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A new discovery from researchers at Northeastern University has uncovered previously unknown aspects of plant evolution, with major implications for creating new lifesaving drugs.

The researchers' breakthrough traced, for the first time, the genetic and molecular path a particular plant, Canadian moonseed, took to be able to perform a chemical reaction that was previously thought impossible for a plant to do naturally: adding a chlorine atom to a molecule.

The findings, recently in Science Advances, point to opportunities for creating new, more efficient methods of developing pharmaceuticals.

The work provides closure on "a molecular detective story millions of years in the making," says Jing-Ke Weng, a professor of chemistry, chemical biology and chemical engineering at Northeastern whose Weng Lab led this project.

"To understand what has happened in the past that leads to the current state of things in terms of cultures, countries and many other things, we rely on archaeology," Weng says. "The work we took here is essentially molecular archaeology."

At the heart of the researchers' work is an enzyme called dechloroacutumine halogenase, or DAH, which helps moonseed produce acutumine, a compound that allows the plant to ward off predators and disease.

"The compound has been found to [have] some really interesting medicinal properties," Weng says. "It has selective cancer-killing activity towards leukemia cells, and some other studies indicate it may have applications in neuroscience regulating GABA receptors for memory loss."

As its name implies, DAH includes a halogen atom, in this case chlorine, which is far from normal for a plant. The ability for a plant to add chlorine to an organic molecule is exceptionally rare and valuable: Chlorine is often used to boost the potency and stability of drugs and agrochemicals.

For Weng and his team, they had their central mystery: How exactly does a plant evolve the ability to do the seemingly impossible and produce a halogenated compound like this in the first place? The answer to that question could help scientists use evolution as a model for creating their own designer enzymes, Weng says.

To crack this evolutionary mystery, the researchers became the first to sequence the entire moonseed genome. This gave them a genetic map that they could use to trace the ancestry of moonseed step by step.

"That resolution of the genomic information gives us the first glimpse of how this DAH gene could emerge because we can identify where exactly this gene is in the genome," Weng says.

They tracked DAH back to a gene found in other plants, flavonol synthase (FLS), giving them their first indication that DAH started as a much more common enzyme. They were then able to see how, over the course of hundreds of millions of years, moonseed underwent a gradual series of gene duplications, losses and mutations to reach the point where a once-regular enzyme could swap oxygen for chlorine.

Weng says it's a glimpse at evolution in action that also sheds light on a previously unknown path for plant evolution. In between FLS and DAH on the evolutionary chain are several other non-functional mutated genes, "evolutionary relics," Weng explains.

"It's not one stop from a flavonoid gene to a halogenase gene—it took multiple steps," he says. "Although we didn't know exactly what these intermediates were used for between the last hundreds of millions of years, at least it led to this process."

Once they had traced the evolutionary path of this enzyme and pinpointed specific mutations that let this enzyme rewrite its own chemistry, Weng's team set about trying to recreate this process in their lab.

"We managed to recover around 1% to 2% of the halogenase activity by starting from the ancestral state," Weng says. "That means evolution really has taken a really narrow path to come to this newly optimized activity. There's a lot of serendipity in the path and it took many turns, but it eventually found a way to achieve this reactivity in this newly evolved enzyme."

In following in the footsteps of evolution, Weng says his team's discovery could help accelerate the move toward "designer enzymes" that are occurring in several industries. Enzymes are vital for catalyzing the chemical processes that assist in the creation of new drugs and therapeutics.

However, a lot of pharmaceutical companies struggle to find the right enzyme for the right drug. The molecular archaeology Weng's lab has done here could provide answers from hundreds of millions of years ago to questions we have today.

"One approach is to evolve such enzymes based on our understanding of enzymology and how things evolved," Weng says. "Knowledge learned from this particular case can really enlighten ways for us to design novel catalysts for making new molecules."