Plant Enzymes Learned to Tell Mirror-Image Molecules Apart

Many natural molecules, from menthol to limonene, come in two mirror-image forms called enantiomers. They look almost identical, like a left hand and a right hand, yet they can smell, taste or act on the body in completely different ways. Enzymes — the protein catalysts that drive chemistry inside living things — can often tell the two forms apart with remarkable precision, which is exactly why they are so prized by the chemical and pharmaceutical industries. How that precision evolved in the first place, however, has remained largely unknown until now, according to Phys.org. A new study shows exactly how Plant Enzymes Learned to Tell Mirror-Image Molecules Apart.

That mystery just got a detailed answer: Plant Enzymes Learned to Tell Mirror-Image Molecules Apart, one mutation at a time. A team led by Dr. Bernhard Loll of Freie Universität Berlin, working with researchers from Graz University of Technology and the Georgia Institute of Technology, traced how one family of plant enzymes gained its mirror-image precision over the course of evolution. Their study, published in Nature Communications, reconstructed enzymes that have not existed for ages and compared how each ancient protein behaved in the laboratory.

Rebuilding enzymes from the deep past

The researchers focused on plant borneol dehydrogenases, a group of enzymes that convert the alcohol borneol into camphor. Using a technique called ancestral sequence reconstruction, they computationally inferred the sequences of ancient enzymes from the borneol dehydrogenase family tree of 97 plant sequences, then synthesized those ancient proteins in the laboratory and compared how each behaved.

Two resurrected ancestors told the story. The oldest, known as N30, barely distinguished between the two borneol forms. A younger ancestor, N32, was highly selective. Between them sat 19 amino-acid mutations — the individual building blocks of proteins — and just a single one of those changes was located in the enzyme's active site, the pocket where the chemical reaction actually takes place.

The lone active-site switch doubled precision

When the team introduced that lone catalytic-site mutation into the unselective ancient enzyme, its selectivity for the two borneol forms doubled. Reversing the change in the younger, selective ancestor made that enzyme lose its preference. A well-placed swap, it seemed, carried real weight — but it could not explain the whole picture on its own.

Only when the researchers combined that catalytic-site mutation with three additional changes far from the active site did the ancient N30 become highly selective for one of the two borneol forms. The distant mutations did not touch the reaction pocket at all, yet they completed the transformation. It was direct proof that peripheral regions of an enzyme can fine-tune what happens at the catalytic site — a result with sharp implications for how scientists design enzymes today.

Dynamics, not just shape, held the key

At first glance the resurrected enzymes showed no obvious structural differences that could explain why one was picky and the other was not. Computational simulations revealed the difference instead: both borneol forms behaved differently inside the enzyme-substrate complex. The form that reacted better stayed locked in a catalytically productive position for longer, while the less favored form was held more loosely and exposed to the surrounding water, according to the team's computational simulations.

In other words, selectivity was not simply a matter of a lock matching one key and rejecting the other. It emerged from the interplay of many small changes that influenced the dynamics of the enzyme and the bound molecule — how the parts move, shift and settle over time. As Loll explained, that interplay mattered far more than any major structural overhaul of the enzyme.

What this means for greener drugmaking

The finding lands in a practical arena. Borneol and its mirror-image counterpart isoborneol can be obtained as a mixture from alpha-pinene, an inexpensive bio-based raw material. Enzymes with stronger selectivity for one of the two forms could therefore help produce individual molecule forms for use in pharmaceuticals, cosmetics and fragrances, or separate them from mixtures, the researchers report.

The deeper lesson is for enzyme engineering itself. Conventional design strategies tend to focus mutations on the active site, but this work suggests those strategies may miss some of the most useful tuning knobs. "This provides us with important indications of how enzymes could be specifically engineered for biotechnological applications in the future," said Loll of Freie Universität Berlin, one of the study's authors.

A fair caveat: the ancient enzymes are computationally inferred rather than directly observed, so the reconstruction rests on statistical models of protein evolution — and the principle has so far been demonstrated in detail for this one enzyme family. Still, the researchers argue the message generalizes: Plant Enzymes Learned to Tell Mirror-Image Molecules Apart not through one dramatic redesign but through a long accumulation of small changes, including some far from the reaction itself. When building tomorrow's biocatalysts, do not ignore the regions far from the action. Sometimes the mutations that matter most are the ones you would never think to look at.

For more plant science, read about how trees carry a chemical memory of past droughts in their leaves and how duckweed shrank into the world's tiniest flowering plant.

The study, "Deciphering the evolutionary origin of the enantioselectivity of short-chain dehydrogenases from plants toward 1-borneol," was published in Nature Communications on October 9, 2026 (DOI: 10.1038/s41467-026-76435-1). Read the original coverage on Phys.org, with a summary of the findings on BrightSurf.