Scientists accidentally create mutant enzyme that eats plastic waste

We may have a new weapon in our fight against the rising tide of plastic pollution – and it was discovered by accident. 

By studying the structure of an existing enzyme previously found to be useful at digesting plastic, researchers at the University of Portsmouth and the US Department of Energy’s National Renewable Energy Laboratory (NREL) created a mutant version that works even more effectively. 

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The mutated version digests some of the most commonly polluting plastics, including those made of polyethylene terephthalate, or PET, faster than the original enzyme. But, more significantly, it can also degrade polyethylene furandicarboxylate (PEF) – a bio-based substitute for PET plastics being hailed as a replacement for glass bottles.

PET currently lasts for hundreds of years in the environment and this accidental discovery could provide a viable recycling solution for millions of tonnes of bottles and packaging. The researchers are now working on improving the enzyme so it can be used to break down plastics in an industrial setting. 

 “Few could have predicted that since plastics became popular in the 1960s huge plastic waste patches would be found floating in oceans, or washed up on once pristine beaches all over the world,” said Professor John McGeehan at the University of Portsmouth. “We can all play a significant part in dealing with the plastic problem, but the scientific community who ultimately created these ‘wonder-materials’, must now use all the technology at their disposal to develop real solutions.”

PET, patented as a plastic in the 1940s, has not existed in nature for long, so the team set out to determine how an enzyme called PETase evolved and if it might be possible to improve it by determining its structure. This natural enzyme is thought to have evolved in a waste recycling centre in Japan to allow a bacterium degrade plastic as a food source. 

In collaboration with scientists at the Diamond Light Source in the UK, Professor McGeehan and Dr Gregg Beckham at NREL used a synchrotron that uses intense beams of X-rays, 10 billion times brighter than the sun, as a microscope powerful enough to see individual atoms. Using this technology, the team created an ultra-high-resolution 3D model of the PETase enzyme in “exquisite detail.”

This image shows an electron microscope image of the enzyme interacting with plastic

Then, with help of computational modelling and scientists at the University of South Florida and the University of Campinas in Brazil, the team discovered PETase may have evolved in a PET-heavy environment to enable the enzyme to degrade PET. To test this theory, the researchers mutated the PETase and that was when the unexpected happened.

As the researchers were using the 3D information of this stucture to understand how it works, they inadvertently engineered an enzyme that is even better at degrading the plastic than the one that evolved in nature. 

“Serendipity often plays a significant role in fundamental scientific research and our discovery here is no exception,” Professor McGeehan said. “Although the improvement is modest, this unanticipated discovery suggests that there is room to further improve these enzymes, moving us closer to a recycling solution for the ever-growing mountain of discarded plastics.”

The research team can now apply the tools of protein engineering and evolution to continue to improve it.

Professor McGeehan added: “The engineering process is much the same as for enzymes currently being used in bio-washing detergents and in the manufacture of biofuels – the technology exists and it’s well within the possibility that in the coming years we will see an industrially viable process to turn PET and potentially other substrates like PEF, PLA, and PBS, back into their original building blocks so that they can be sustainably recycled.”

The research is published in Proceedings of the National Academy of Sciences (PNAS).

Images: Shutterstock/NREL

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