Chemists at Johannes Gutenberg University Mainz (JGU) have discovered a way to widen the natural substrate scope of enzymes, expanding the range of reactions they can catalyze. The team led by Professor Tobias Erb and Dr. Christopher Gregg developed an artificial metalloenzyme that displays unprecedented catalytic promiscuity. The scientists fused a rationally designed zinc-binding site to an existing enzyme scaffold. This fusion protein was shown to catalyze the cycloaddition of aziridines with carbon dioxide to yield oxazolidinones – a reaction that has not been observed in nature so far. The study, which was recently published in the renowned journal Nature Chemistry, opens up new possibilities for the design of biocatalytic processes.

Enzymes are protein molecules that catalyze chemical reactions in living organisms. They are highly selective and efficient, enabling complex reactions to occur under mild reaction conditions. However, the substrate scope of enzymes is often limited, meaning that they can only catalyze a narrow range of reactions.

"Enlarging the catalytic repertoire of enzymes is a long-standing goal in chemistry and biotechnology," says Tobias Erb, Professor of Chemical Biology and Genetics at JGU. "This would allow us to use enzymes for a wider range of synthetic reactions and potentially develop new biocatalytic processes for the production of pharmaceuticals and other fine chemicals."

One way to expand the substrate scope of enzymes is to engineer them by introducing mutations or chemical modifications. However, this approach is often tedious and time-consuming, and it can be difficult to predict which modifications will lead to the desired catalytic activity.

"We wanted to develop a more general strategy that would allow us to widen the catalytic range of enzymes in a rational and efficient way," explains Christopher Gregg, a postdoctoral researcher in Erb's group. "We were inspired by the fact that many enzymes contain metal ions that are essential for their catalytic activity."

The researchers hypothesized that by introducing a metal-binding site into an existing enzyme scaffold, they could create an artificial metalloenzyme with a new catalytic activity. To test this hypothesis, they fused a rationally designed zinc-binding site to an enzyme scaffold derived from the enzyme chorismate mutase.

"We were delighted to find that the fusion protein displayed unprecedented catalytic promiscuity," says Gregg. "It was able to catalyze the cycloaddition of aziridines with carbon dioxide to yield oxazolidinones – a reaction that has not been observed in nature so far."

The researchers believe that their strategy can be used to enlarge the catalytic range of other enzymes as well. "We are currently working on expanding the scope of our artificial metalloenzyme to other types of reactions," says Erb. "We are also exploring the use of other metal ions and enzyme scaffolds."

The study, which was published in Nature Chemistry on February 20, 2023, opens up new possibilities for the design of biocatalytic processes. By expanding the catalytic range of enzymes, it may be possible to develop more efficient and environmentally friendly methods for the production of a variety of chemicals.