Single-atom technique could tackle 350 million tons of global PET plastic waste

To break down a plastic bottle, science doesn’t need a hammer, but a microscopic scalpel.

Researchers at The Australian National University (ANU) found that swapping out a single atom inside a plastic-munching enzyme can boost its power.

The tweak lets the enzyme devour polyethylene terephthalate (PET) at nearly twice its normal speed, without melting under heat. So it is a tiny modification, which could play a huge role for a planet drowning in trash.

The study showed that adding synthetic, non-canonical amino acids called azatryptophans to plastic-degrading enzymes (PETases) can break the trade-off between catalytic activity and thermal stability.

“Enzymes can be engineered over and over again to improve their performance, but eventually you reach a point where making them more active can also make them less stable, and vice versa,” said Dr. Elwy Abdelkader, lead author of the study. “What we have shown is that you can go beyond this limit by making an incredibly precise change – down to a single atom – while largely preserving the structure and stability of the enzyme.”

Single-atom solution

Bioengineers attempting to combat plastic pollution have long faced an issue when optimizing PETase enzymes. Enhancing an enzyme’s plastic-degrading speed typically required extensive genetic modifications that compromised its structural integrity. Using only the 20 natural amino acids, making an enzyme break down plastic faster almost always caused it to unravel at high temperatures.

Highly active variants quickly degraded under thermal stress, and stable variants operated far too slowly to be commercially viable.

The ANU team overcame this issue by shrinking their focus down to the absolute limit: “one atom”.

In particular, the standard amino acid tryptophan was swapped for a synthetic counterpart called azatryptophan. Visually and chemically, the two are almost identical — except the synthetic version replaces a single carbon-hydrogen pair with a nitrogen atom.

That atomic nudge made all the difference. The upgraded enzyme shredded PET plastic in half the time while retaining its heat resistance.

“Building on the team’s experience with the site-specific introduction of noncanonical amino acids into proteins, we can introduce tiny chemical changes that allow us to tune proteins with a level of precision that was previously difficult to achieve,” co-author Professor Thomas Huber said.

Global plastic crisis

To figure out if their atomic surgery worked, the team also had to reinvent how they test it.

Standard assays for measuring plastic breakdown are exceptionally slow because solid PET plastic resists dissolution, stretching testing timelines across several days. To eliminate this obstacle, the ANU research team designed a fluorescent assay named PETra. The tool relies on a soluble liquid substitute that glows during the reaction, reducing measurement times to minutes and enabling rapid evaluation of large libraries of enzyme variants.

Every year, more than 350 million tons of PET plastic waste are generated globally. However, conventional disposal tactics like landfills and incineration trigger severe environmental pollution while squandering valuable resources. This new technique could help curb it.

The future uses could go far beyond the recycling bin. Nature limits life to just 20 standard amino acids.

But scientists can now tune proteins with surgical accuracy by expanding that toolkit with custom, synthetic building blocks.

The same single-atom strategy could soon be used to design hyper-efficient enzymes for green manufacturing, advanced biofuels, and targeted medical therapies.

The study was published in the journal Angewandte Chemie International Edition.