Plastic Eating Enzymes

Whether it’s stopping the use of plastic straws or only using reusable water bottles, people everywhere are looking to find easy and efficient ways to stop the growth of plastic in our oceans and landfills. 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, took on the challenge of finding a new way to slow down the production of plastic waste, and made an important scientific discovery. When discussing the effects of PETase and MEHTase enzymes on the decomposition of plastic separately, Professor McGeehan said it just made sense to put them together to mimic what would happen in nature, and their results were very exciting.

PETase is the enzyme that breaks down polyethylene terephthalate (PET) into its original building blocks and allows it to be recycled infinitely, this process reduces plastic pollution and the greenhouse gases that ultimately contribute to climate change. Plastic is made of complex polymers that are extremely long. PETase works by breaking down the bonds in PET and leaving smaller molecules for the bacteria to absorb and use as food. The natural PETase enzyme is about 20 times faster at breaking down the plastic than the natural environment. PETase’s partner, MEHTase, also plays an important role in this discovery. MEHTase is considerably bigger than PETase and it completes the decomposition of plastic that was started by PETase.

PETase 5XH3 with HEMT-cartoon
Crystal Structure of a PETase
Image from Wikimedia Commons

Professor McGeehan and Dr Beckham first used the two enzymes in the same environment and saw that they do work better together at breaking down PET. They then tried to physically link the two enzymes to maximize results in this environment.

“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 McGeehan said.

This discovery is huge for the productiveness of recycling and preventing more plastic from entering the ocean and landfills. The MHETase-PETase enzyme can break down plastic up to three times faster than just PETase, and allow it to be reproduced without waste. This enzyme can also continue to break down PET plastic while in the presence of other dyes and plastics, basically disregarding them while turning PET into its original form. This creates the job of recycling easier and more efficient. Before, only about 30% of recycled plastic was turned into new plastic, and it was typically lower quality. Now these enzymes can convert 90% of the plastic back into its starting materials.

Companies are already building demonstration plants that are expected to recycle and break down hundreds of tons of PET per year. Although these enzymes can not break down all types of plastic and it is not a complete solution, it is a great first step in ending the plastic crisis of the world.

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