Engineering a plastic-eating enzyme
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.
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.”
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.
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.
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 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.”
The research was funded by the University of Portsmouth, NREL and the Biotechnology and Biological Sciences Research Council (BBSRC).
About University of Portsmouth
The University of Portsmouth is a progressive and dynamic university with an outstanding reputation for innovative teaching and globally significant research and innovation.
It was rated 'Gold' in the UK government's Teaching Excellence Framework (TEF) and was ranked in the top 150 under 50 in the world according to the Times Higher Education rankings. The university is also in the top 40 in the Guardian’s 2017 league table and is ranked number one in the UK for boosting graduate salaries according to The Economist.
The university's research and innovation culture is impacting lives today and in the future and addressing local, national and global challenges across science, technology, humanities, business and creative industries.
The National Renewable Energy Laboratory is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.
About Diamond Light Source
Diamond Light Source is the UK’s synchrotron science facility. Shaped like a huge ring, it works like a giant microscope, harnessing the power of electrons to produce bright light that scientists can use to study anything from fossils to jet engines to viruses and vaccines. Diamond accelerates electrons to near light speeds, producing a light 10 billion times brighter than the Sun, which is then channelled into 31 laboratories known as ‘beamlines’.
Thousands of scientists use the UK’s synchrotron each year, with 57% visiting and 43% accessing the facility remotely. Diamond’s state-of-the-art facilities and world class people act as agents of change, addressing 21st century challenges such as disease, clean energy and food security. Diamond research supports new medicines, technologies and advances of all kinds.
In 2017, Diamond celebrated a double anniversary: 15 years since the company was formed, and 10 years of research operations. More than 6,500 papers have been published because of research conducted at the facility.
Funded by the UK government through the Science and Technology Facilities Council (STFC), and by the Wellcome Trust, Diamond is one of the most advanced scientific facilities in the world, and its pioneering capabilities are helping to keep the UK at the forefront of scientific research.
The Biotechnology and Biological Sciences Research Council (BBSRC) is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
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