The enzyme which eats plastic can probably be the solution to our plastic cataclysm.
In the dirt at a Japanese plastics recycling plant, researchers found a microbe which had evolved to eat the plastic bottles dominating its environment.
The discovery occurred in 2016, and scientists have now gone further. While examining how the “Japanese bug” breaks down plastic, they have accidentally created a mutant enzyme which outperforms the natural one. Could it offer a vital solution to the enormous plastic problem of the society?
The structural biologist John McGeehan from the University of Portsmouth in the UK says:
“Serendipity usually plays an important role in fundamental scientific research and our discovery here is no exception. This unanticipated discovery also suggests that there is space for further improvement of these enzymes, leading us closer to some recycling solutions for the ever-growing mountain of discarded plastics.”
The team of McGeehan, which includes researchers at the Us Department of Energy’s National Renewable Energy Laboratory (NREL), stumbled onto their mutant tweak while they were investing the crystal structure of PETase. PETase is the enzyme which helps the Japanese microbe, named Ideonella sakaiensis, to break down PET plastics (aka polyethylene terephthalate).
PET was registered back in the 1940s. While that appears like a long time ago, in evolutionary terms, it is pretty recent. The point being, while the I. sakaiensis can indeed eat plastic, it is only lately that it had the opportunity to learn this trick, which means it does not mean munch real quick.
The vast scale of plastic pollution on Earth is a serious problem. A billion of tonnes of dumped waste is piling up in landfills and spilling into the oceans.
Not that PETase is a slouch – as PET by itself takes a lot of time to break down (maybe centuries) naturally, and the enzyme enables the bacteria to shorten that to just a matter of days.
NREL structural biologist Bryon Donohoe says:
“After just 96 hours, you can actually see clearly via electron microscopy which the PETase is degrading PET. And this test is actually using real examples of what is found in the oceans and landfills.”
The team used X-rays to generate an ultra-high-resolution 3D model of the enzyme to examine the efficiency of PET at a molecular level. The model revealed an unprecedented glimpse of PETase’s active site. The scientist could now grip and break down its pet target and try to improve its mechanism.
“Having the ability to see the inner working of this biological catalyst provided us with the blueprints to engineer a faster, as well as more efficient enzyme.”
The hypothesis is that the PETase enzyme must have evolved in the presence of PET. It somehow figured out how to degrade the plastic. So, the researchers have mutated PETase’s active site, to see if they could bring closer to some other enzyme, which is called cutinase.
While they didn’t expect it, this adjustment has ended up showing further ways to optimize the enzyme.
Nic Rorrer, the NREL materials scientist, says:
“Surprisingly, we have found that the PETase mutant outperforms the wild-type PETase in degrading PET. Also, understanding how PET binds to the PETase catalytic site by using computational tools also helped in illuminating the reasons for this improved performance. Given these results, it is completely clear that important potential remains for improving its activity further on.”
So far, the mutant PETase is only about 20% more efficient at breaking down plastic, than the naturally happening enzyme. However, the team says the significant thing is that they now know how to optimize these enzymes.
Some future engineered versions should work even better at munching through plastic. Maybe they will also help us recycle some other types of materials as well. For example, the tweaked PETase can break down PET substitutes.
It will take time before these discoveries succeed to break down the billions of tones of plastic. However, now that we have got a proof of concept, we can genuinely use science to help mother nature. A genuine help in breaking down an unnatural material that just won’t go away fast enough otherwise.
The biotechnologist Gregg Beckham from NREL explains:
“What we have learned is that PETase is still not fully optimized to degrade PET. And now that we have shown this, it is the real time to apply the tools of protein engineering, as well as evolution, continues to improve it.”
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Image Credit: Shutterstock (licensed by IBMN)/By Rich Carey