The scientists who re-engineered the plastic-eating enzyme PETase have now created an enzyme ‘cocktail’ which can digest plastic up to six times faster.
A second enzyme, found in the same rubbish dwelling bacterium that
lives on a diet of plastic bottles, has been combined with PETase to
speed up the breakdown of plastic.
PETase breaks down polyethylene terephthalate (PET) back into its
building blocks, creating an opportunity to recycle plastic infinitely
and reduce plastic pollution and the greenhouse gases driving climate
change.
PET is the most common thermoplastic, used to make single-use drinks
bottles, clothing and carpets and it takes hundreds of years to break
down in the environment, but PETase can shorten this time to days.
The initial discovery set up the prospect of a revolution in plastic
recycling, creating a potential low-energy solution to tackle plastic
waste. The team engineered the natural PETase enzyme in the laboratory
to be around 20 percent faster at breaking down PET.
Now, the same trans-Atlantic team have combined PETase and its
‘partner’, a second enzyme called MHETase, to generate much bigger
improvements: simply mixing PETase with MHETase doubled the speed of PET
breakdown, and engineering a connection between the two enzymes to
create a ‘super-enzyme’, increased this activity by a further three
times.
The study is published in the journal Proceedings of the National Academy of Sciences of the United States of America.
It took a great deal of work on both sides of the Atlantic, but it was worth the effort – we were delighted to see that our new chimeric enzyme is up to three times faster than the naturally evolved separate enzymes, opening new avenues for further improvements.
Professor John McGeehan, Director of the Centre for Enzyme Innovation
The team was co-led by the scientists who engineered PETase, Professor John McGeehan, Director of the Centre for Enzyme Innovation (CEI) at the University of Portsmouth, and Dr Gregg Beckham, Senior Research Fellow at the National Renewable Energy Laboratory (NREL) in the US.
Professor McGeehan said: “Gregg and I were chatting about how PETase
attacks the surface of the plastics and MHETase chops things up further,
so it seemed natural to see if we could use them together, mimicking
what happens in nature.
“Our first experiments showed that they did indeed work better
together, so we decided to try to physically link them, like two Pac-men
joined by a piece of string.
“It took a great deal of work on both sides of the Atlantic, but it
was worth the effort – we were delighted to see that our new chimeric
enzyme is up to three times faster than the naturally evolved separate
enzymes, opening new avenues for further improvements.”
The original PETase enzyme discovery heralded the first hope that a
solution to the global plastic pollution problem might be within grasp,
though PETase alone is not yet fast enough to make the process
commercially viable to handle the tons of discarded PET bottles
littering the planet.
Combining it with a second enzyme, and finding together they work
even faster, means another leap forward has been taken towards finding a
solution to plastic waste.
PETase and the new combined MHETase-PETase both work by digesting PET
plastic, returning it to its original building blocks. This allows for
plastics to be made and reused endlessly, reducing our reliance on
fossil resources such as oil and gas.
Professor McGeehan used the Diamond Light Source,
in Oxfordshire, 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. This allowed the team to solve the 3D
structure of the MHETase enzyme, giving them the molecular blueprints to
begin engineering a faster enzyme system.
The new research combined structural, computational, biochemical and
bioinformatics approaches to reveal molecular insights into its
structure and how it functions. The study was a huge team effort
involving scientists at all levels of their careers.
One of the most junior authors, Rosie Graham, a joint Portsmouth
CEI-NREL PhD student said: “My favourite part of research is how the
ideas start, whether it’s over coffee, on a train commute or when
passing in the university corridors it can really be at any moment.
“It’s a really great opportunity to learn and grow as part of this
UK-USA collaboration and even more so to contribute another piece of the
story on using enzymes to tackle some of our most polluting plastics.”
The Centre for Enzyme Innovation takes enzymes from the natural environment and, using synthetic biology, adapts them to create new enzymes for industry.