The U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and the United Kingdom’s University of Portsmouth have announced a major breakthrough in enzyme research. The new research has developed an improved enzyme that can break down plastic bottles made out of polyethylene (PET).

Plastic is a huge source of waste on Earth.Plastic is a huge source of waste on Earth.

This discovery was not made on purpose. The researchers were working to solve the crystal structure of PETase — an enzyme that digests PET — and they accidentally created an enzyme that is even better at degrading PET than PETase. The discovery suggests that there is even more room to develop and improve the enzymes. This is a huge step toward solving the growing discarded-plastic problem. Experts estimate that by 2050 there will be as much plastic in the ocean as there are fish. This is a risk to all of the life on Earth.

PET-digesting bacteria were first discovered in 2017 in Japan. While this was a major development, the bacteria do not work fast enough to make a dent in the plastic waste at an industrial scale.

The research team’s experiments set out to find have effective PETase digests PETs. Researchers tested PETase using samples of PET from soda bottles.

"After just 96 hours you can see clearly via electron microscopy that the PETase is degrading PET," said Bryon Donohoe, senior scientist and researcher of the study. "And this test is using real examples of what is found in the oceans and landfills."

"We originally set out to determine how this enzyme evolved from breaking down cutin — the waxy substance on the surface of plants — with cutinase, to degrading synthetic PET with PETase," said Gregg Beckham, from NREL and lead author of the paper. "We hoped to determine its structure to aid in protein engineering, but we ended up going a step further and accidentally engineered an enzyme with improved performance at breaking down these plastics. What we've learned is that PETase is not yet fully optimized to degrade PET — and now that we've shown this, it's time to apply the tools of protein engineering and evolution to continue to improve it."

NREL and the University of Portsmouth worked with a multidisciplinary research team at the Diamond Light Source in the U.K. The Diamond Light Source is a large synchrotron that acts like a giant microscope powerful enough to see individual atoms by using intense beams of x-rays. The researchers used this to create an ultra-high-resolution 3D model of PETase. Researchers discovered that PETase looks similar to cutinase, but it has an open active site and strange surface futures. Based on these findings, the researchers believe that PETase evolved in a PET-containing environment. The team tested this by mutating the PETase active site to make it like cutinase.

"Surprisingly, we found that the PETase mutant outperforms the wild-type PETase in degrading PET," said Nic Rorrer, postdoctoral researcher, "Understanding how PET binds in the PETase catalytic site using computational tools helped illuminate the reasons for this improved performance. Given these results, it's clear that significant potential remains for improving its activity further."

This discovery means that PETase can degrade polyethylene furandicarboxylate (PEF), a bio-based substitute for PET plastics.

"We were thrilled to learn that PETase works even better on PEF than on PET," said Beckham. "It is literally drilling holes through the PEF sample. This shows that by using PETase, PEF is even more biodegradable than PET."

The team wants to use their findings to improve how the new enzymes break down man-made plastics in a short amount of time.

The paper on this research was published in Proceedings of the National Academy of Sciences (PNAS).