Engineering a plastic-eating enzyme

Global blight: Plastic bottles take centuries to biodegrade, but new enzyme discovery brings hope CREDIT: DAVID JONES

Scientists have engineered an enzyme which can digest some of our most commonly polluting plastics, providing a potential solution to one of the world’s biggest environmental problems.

The discovery could result in a recycling solution for millions of tonnes of plastic bottles, made of polyethylene terephthalate, or PET, which currently persists for hundreds of years in the environment.

The research was led by teams at the University of Portsmouth and the US Department of Energy’s National Renewable Energy Laboratory (NREL) and is published in Proceedings of the National Academy of Sciences (PNAS).

 Professor John McGeehan at the University of Portsmouth and Dr Gregg Beckham at NREL solved the crystal structure of PETase—a recently discovered enzyme that digests PET— and used this 3D information to understand how it works. During this study, they inadvertently engineered an enzyme that is even better at degrading the plastic than the one that evolved in nature.

Serendipity: Professor John McGeehan and colleagues inadvertently engineered an enzyme better at degrading plastic than the enzyme which evolved in nature  CREDIT Stefan Venter, UPIX Photography – www.upixphotography.com

The researchers are now working on improving the enzyme further to allow it to be used industrially to break down plastics in a fraction of the time.

Professor McGeehan, Director of the Institute of Biological and Biomedical Sciences in the School of Biological Sciences at Portsmouth, said: “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.

“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.”

Close-up: Electron microscope image of enzyme degrading PET plastic CREDIT: Dennis Schroeder / NREL

The researchers made the breakthrough when they were examining the structure of a natural enzyme which is thought to have evolved in a waste recycling centre in Japan, allowing a bacterium to degrade plastic as a food source.

PET, patented as a plastic in the 1940s, has not existed in nature for very long, so the team set out to determine how the enzyme evolved and if it might be possible to improve it.

The goal was to determine its structure, but they ended up going a step further and accidentally engineered an enzyme which was even better at breaking down PET plastics.

“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.

Benjamin Luethi inspecting the I23 beamline detector at the Diamond Light Source which played a major role in the discovery CREDIT: Diamond Light Source

The University of Portsmouth and NREL collaborated with scientists at the Diamond Light Source in the United Kingdom, a synchrotron that uses intense beams of X-rays 10 billion times brighter than the sun to act as a microscope powerful enough to see individual atoms.

Using their latest laboratory, beamline I23, an ultra-high-resolution 3D model of the PETase enzyme was generated in exquisite detail.

Professor McGeehan said: “The Diamond Light Source recently created one of the most advanced X-ray beamlines in the world and having access to this facility allowed us to see the 3D atomic structure of PETase in incredible detail. Being able to see the inner workings of this biological catalyst provided us with the blueprints to engineer a faster and more efficient enzyme.”

Chief Executive of the Diamond Light Source, Professor Andrew Harrison, said: “With input from five institutions in three different countries, this research is a fine example of how international collaboration can help make significant scientific breakthroughs.

“The detail that the team were able to draw out from the results achieved on the I23 beamline at Diamond will be invaluable in looking to tailor the enzyme for use in large-scale industrial recycling processes. The impact of such an innovative solution to plastic waste would be global. It is fantastic that UK scientists and facilities are helping to lead the way.”

With help from the computational modeling scientists at the University of South Florida and the University of Campinas in Brazil, the team discovered that PETase looks very similar to a cutinase, but it has some unusual features including a more open active site, able to accommodate man-made rather than natural polymers. These differences indicated that PETase may have evolved in a PET-containing environment to enable the enzyme to degrade PET. To test that hypothesis, the researchers mutated the PETase active site to make it more like a cutinase.

And that was when the unexpected happened – the researchers found that the PETase mutant was better than the natural PETase in degrading PET.

Discovery means it’s now “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” – Professor McGeehan CREDIT: DAVID JONES

Significantly, the enzyme can also degrade polyethylene furandicarboxylate, or PEF, a bio-based substitute for PET plastics that is being hailed as a replacement for glass beer bottles.

Professor McGeehan said: “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 was funded by the University of Portsmouth, NREL and the Biotechnology and Biological Sciences Research Council (BBSRC).

Dr Colin Miles, Head of Strategy for Industrial Biotechnology at BBSRC, said: “This is a highly novel piece of science based on a detailed molecular-level understanding of an enzyme able to depolymerise a common type of plastic, whose persistence in the environment has become a global issue.  It will be interesting to see whether, based on this study, the performance of the enzyme can be improved and made suitable for industrial-scale application in the recycling and the future circular economy of plastic.”

The paper’s lead author is postgraduate student jointly funded by the University of Portsmouth and NREL, Harry Austin.

He said: “This research is just the beginning and there is much more to be done in this area. I am delighted to be part of an international team that is tackling one of the biggest problems facing our planet.”

Aerial view of Diamond CREDIT: Diamond Light Source

Principal beamline scientist on I23 at Diamond, Dr Armin Wagner, said: “The long-wavelength macromolecular crystallography beamline I23 at Diamond is an incredibly advanced and unique facility that enables us to solve structures that are usually difficult to characterise. In the case of PETase, the protein crystals diffracted really well and we were able to achieve very high resolution. While most of the known protein structures have been determined to resolutions between 1.5 and 3.0 Å (0.15 – 0.3 nanometres), and we could achieve from for one of the investigated structures 0.92 Å. It basically makes what we are looking at much clearer and therefore easier to understand.

“The high resolution 3D structure allowed us to get a clear picture of where the enzyme grips its target which then informed the next step of computational modelling to investigate the mechanism of PET degradation further. The large, curved area detector in combination with the vacuum environment on the I23 beamline is ideal for this work as it allows high resolution structure determinations at low X-ray doses limiting detrimental radiation damage effects to the crystals.”

 

21 total comments on this postSubmit yours
  1. Oops! EUREKA!! Science!

  2. What is the by product of the enzyme? What type of reaction is it? What happens at the state of equilibrium?

    This all sounds wonderful but with so little shouted about the other side of the chemical reaction, one wonders what is being hidden….

    • The PETase (PET-digesting enzyme) converts PET to mono(2-hydroxyethyl) terephthalic acid (MHET), with trace amounts of terephthalic acid (TPA) and bis(2-hydroxyethyl)-TPA (BHET) as secondary products. The bacteria produces a second enzyme, MHETase (MHET-digesting enzyme), which further converts MHET into the two monomers, TPA and ethylene glycol (EG). See this picture http://www.pnas.org/content/pnas/early/2018/04/16/1718804115/F1.large.jpg

  3. Wonderful news. Let’s hope that this gets through to the decision-makers. 13 hours since you posted this information and yet zero-waste Scotland has nothing on their web-site. Moreover I understand that a scheme to recycle mattresses 1 million a year in Scotland fell foul of a PPI contract that zero-waste Scotland said it would make it too expensive to adopt the scheme (2016). This is a different field but the same attitude applies. I want to know that you have direct contact with Michael Gove, who like Ruth Davidson in Scotland, is a politician who is prepared to reform systems and take on vested interests. I would also like to see a mention of the 21 countries taking part therefore the technology being available to all (no rushing for patents like the USA team did with the human genome project whilst the UK team led by (then) John Sulston immediately put any identification on the web to allow the science to be used by everyone. Plus the Professor’s mention of the need for industrialist to get involved (quickly and significantly). There is an on-line project to recruit 250.000 volunteers* to tag all the plastic waste on our shores – also the processing plants could bring work to areas of the UK not adapting quickly (or at all ) to creating alternative jobs when heavy industry declined substantially.As well as not supporting research significantly and over the long term and other countries taking this on successfully and benefitting in usage and job creation. A scenario well known in the scientific communities as well in other spheres. *The British Library has successfully launched such a scheme several years ago and have been appointed as a consultant e.g. in the USA. All best wishes. Elizabeth Richardson

  4. Could this enzyme help prevent cancer ?

  5. Or could some other enzyme help mobilize cancer

  6. Dear sir

    i have gone through your article for the treatment of plastic waste, in our country Pakistan we suffering from this problem, The wastewater drains are choked due through away culture .The plastic bags rapers for sweets and PET bottles are thrown on the roads and these thrown away thing go into open drains for wastewater and sewerage system , if you and your department will support us a third world country like Pakistan. i and my colleagues will try to solve this problem at lab scale level then on pilot scale. your support in the this field will be highly appreciated

    Regards

    Dr. Muhammad Tahir Butt
    Principal Scientific Officer
    CEPS,PCSIR Labs Lahore
    Pakistan
    Cell:0092-3224330908
    E.Mail: pcsir322@gmail.com

  7. I’ve said this before but why have a press release without a link to the paper?

    • Hi John, We can post the link – http://www.pnas.org/content/early/2018/04/16/1718804115 – but it requires a subscription to read, hence not of as much value to those outside academia. We always link when a journal is open access.

      • Without having read the answer from the press office, I googled the article and found it in the above mentioned link. The full article can be read online and can also be downloaded (including the figures in Powerpoint) without subscription. The article is authored by 21 scientists, which is amazing. We all love plastics and polymers, but ignore or forget the huge environmental problem they pose. Dr. Tahir from Pakistan refers to the same problem we have here in Peru: huge amounts of plastic waste are generated in developing countries and end up in sewers, rivers, lakes, ocean and in the environment. I really hope these scientists succeed in finding a solution to this problem.

        Best regards

        Dr.-Ing. Gerge Power
        Universidad de Lima, Peru

  8. The first question that comes to my mind is “What are the by-products of the bacteria consuming plastic as a food source?” The next question: “Do these plastic eating bacteria consume other food sources? What else do they eat?”

  9. This is FANTASTIC! Congratulations to everyone who made this possible.

  10. Thank you for doing this exceptional iniciative! Let’s start working together to create an International Committee of Recycling! – I think it’s right time to unite ourselves! Let’s start to talk widely about the problem of omnipresent TRASH (waste, garbage, debris, dumps…)! Let’s involve much people to cause some real changes / Get up, Humans! Share your idea on a forum: http://www.AGHARTY.COM (I already published your video there also) / I trully believe that we are not just a colleagues in this subject; actually, WE ARE ONE! / Please, let’s stay in touch! // Sincerely, I wish you, Strength, Luck, Stability and unbreakable Will that should lead us to victory in our common good deed! Good Luck in all beginnings!

  11. When the unexpected happened!!!!!
    This is both exciting and real scary stuff.
    A word of caution to our brilliant scientists.
    Pleases test beyond the obvious and ensure we don’t create a travesty out of a great find.
    Too often exhilaration forging ahead and with no caution to what monster we may be creating as an off shoot. Please be careful.

  12. We have been working with biodegradable polymer additives for some time and would be interested in understanding more about your work.

  13. What happens when a marine animal ingests water where the enzyme is breaking down the plastic?
    ;-). roxie

  14. Well done! The amount of plastic in the world is scary and depressing. Can’t wait for this to be introduced to fight with plastic overload in the world. Good luck with further research. 🙂

  15. Really, an excellent article with full details of the research on plastic devouring enzyme. Very useful for science communicatots to bring the story before the lay public Keep it up.

  16. I am so interested in cleaning the oceans and the thought of an enzyme eating plastic is so hopeful and needed. Do you need funders or investors? Please let me know!

  17. Dear Sir,
    I am working on the same theme on the Degradation of electronic waste and I wanted to know the enzyme involved in it with the help of the 123 beamline diamond. Will be helpful.
    Thank you

  18. What else is this manipulated enzyme going to eat?
    I have become very wary of scientific hurray stories,too often I have seen that they are only part of the reality (as is the official information about vaccines, chemotherapy, brain death organ donation…).

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