Bacterial enzymes ‘cut down’ to make complex molecules that are normally made by plants

Chemists at Scripps Research have efficiently created three families of complex, oxygen-containing molecules that are normally obtained only from plants.

These molecules, called terpenes, are potential starting points for new drugs and other high-value products – marking an important development for multiple industries. In addition, the new approach could allow chemists to build many other classes of compounds.

The chemistry feat is detailed in the August 13 edition of the magazine Science.

The key to this new method of making molecules is to utilize, or cut down, natural enzymes – from bacteria, in this case – to aid in complex chemical transformations that have been impractical or impossible using only synthetic chemistry techniques, he says. lead researcher Hans Renata, Ph.D., an assistant professor in the Department of Chemistry at Scripps Research.

Natural enzymes that help build molecules in cells normally perform only one or two very specific tasks. But the Scripps Research team showed that natural enzymes, even without modification, can be made to perform a wider range of tasks.

“We think that in general enzymes are a most unused source for solving problems in chemical synthesis,” says Renata. “Enzymes have the most promising activity, in terms of their ability to stimulate chemical reactions above their primary function, and we were able to take advantage of this.”

Apply to hidden talents of enzymes

Enzymes help build molecules in all plant, animal and microbial species. Inspired by their efficiency in attaching highly complex molecules, chemists have been using enzymes in the lab for more than half a century to build valuable compounds, including drug compounds – but usually these compounds are the same molecules that help the enzymes build in nature.

Deploying natural enzymes in a broader way, according to their basic biochemical activity, is a new strategy with great potential.

“Our view now is that when we want to synthesize a complex molecule, the solution probably already exists among the enzymes of nature – we just need to know how to find the enzymes that will work,” says senior author Ben Shen, Ph.D., chair of the Florida Campus Department of Chemistry and director of Scripps Research’s Natural Products Discovery Center.

The team managed to create nine terpenes that were known to be produced in Isodon, a family of flowering plants related to mint. The complex compounds belong to three terpene families with related chemical structures: ent-kauranes, ent-atisanes, and ent-trachylobanes. Members of these terpene families have a wide range of biological activities including the suppression of inflammation and tumor growth.

A recipe for success of synthesis

The synthesis of each compound, in less than 10 steps each, was a hybrid process that combined current methods of organic synthesis with enzyme-mediated synthesis, starting with an inexpensive compound called stevioside, the main component of the artificial sweetener Stevia.

The main obstacle was the direct replacement of hydrogen atoms with oxygen atoms in a complex pattern on the carbon atom skeleton of the starting mass. Current methods of organic synthesis have a limited arsenal for such transformations. However, nature has produced many enzymes that can enable these transformations – each able to perform its function with a degree of control that is not matched by man-made methods.

As an interdisciplinary research team, we were fully aware of the limitations of current methods of organic synthesis, but also of the many unique ways that enzymes can overcome these limitations – and we had the insight to combine traditional synthetic chemistry. with enzymatic methods in a synergistic fashion, “says Renata.

The three enzymes used, which were identified and characterized only last year by Shen, Renata and colleagues, are naturally produced by a bacterium – one of the 200,000-plus species in the Microbial Strain Collection at Scripps Research’s Natural Products Discovery Center.

“We could use these enzymes not only to modify the starting molecules, as scaffolds as we call them, but also to transform one scaffold into another so that we could transform a mound from one family into a mound from another family,” says second author Emma King-Smith, a Ph.D. student in the Renata lab.

The chemists now intend to use their new approach to create useful amounts of the nine compounds, such as chemical variants of the compounds, and, with collaborative laboratories, to explore their properties as potential medicines as other products.

“With our strategy, we can make these highly oxidized diter pens much easier and in larger quantities than would be possible by isolating them from the plants where they are naturally found,” says first author Xiao Zhang, Ph.D. ., a postdoctoral fellow in the Renata lab.

Just as importantly, the researchers say, they are working to identify reactions and enzymes that will allow them to extend their approach to other classes of molecules.

Central to all of these efforts is the ongoing development of methods to sift through the DNA of microbes and other organisms to identify the enzymes they encode – and to predict the activities of these enzymes. Billions of distinct enzymes exist in plants, animals, and bacteria on Earth and only a small fraction of them have been cataloged to date.

“We are excited about the potential to discover new and useful enzymes from our strain library here at Scripps Research,” says Renata. “We think we can solve many other problems with chemical synthesis.”