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We are surrounded by plastic in our daily life. From water bottles to our clothes. Around 400 million metric tons of plastic are produced worldwide every year. A large proportion of which later ends up in the natural environment, for example in our oceans. According to Environmental Action Germany around 10 million tons per year. It takes decades to centuries before this waste decomposes naturally. A plastic bag, for example, rots after about ten to twenty years. Whereas a PET bottle is thought to take about 450 years. Although, due to a lack of actual proof, this value is just an estimate.

Several years ago, scientists at the University of Portsmouth (UK) and the National Renewable Energy Laboratory in Colorado (NREL, US) developed the enzyme PETase. This enzyme can break down PET twenty times faster than regular enzymes. It breaks down polyethylene terephthalate (PET) back into its original building blocks. The same researchers have now further developed this enzyme into an enzyme ‘cocktail’ which is capable of breaking down plastic up to six times faster.

Just like two Pac Men

The team made up of Professor John McGeehan, director of the Center for Enzyme Innovation (CEI) at the University of Portsmouth, and Dr. Gregg Beckham, a senior research fellow at the National Renewable Energy Laboratory, combined PETase and an enzyme called MHETase. The result was that PET was broken down twice as fast. By combining the two enzymes to form a ‘super enzyme,’ the researchers were able to increase the speed by as much as six times.

“Gregg and I talked about how PETase attacks plastic surfaces and MHETase breaks things down further,” says Professor John McGeehan. “So, it seemed obvious to see if we could use the two together to mimic what happens in nature. Our first experiments showed that they actually work better when used together. So we decided to connect them physically, like two Pac Men tied together by a piece of string.”

Endless recycling of plastics

Both PETase and the new combined MHETase/PETase are able to break down PET plastic. As well as return it to its original building blocks. As a result, plastic can be recycled an infinite number of times, thereby reducing plastic pollution. In addition, this recycling of plastics reduces greenhouse gases that contribute to global warming. That is because less plastic has to be produced from scratch. Moreover, the researchers are also pleased to report that fewer raw materials from fossil fuels, such as oil and gas, would be needed.

In Oxfordshire, UK, Professor McGeehan used a Diamond Light Source which is a microscope that is powerful enough to identify individual atoms. This is a type of particle accelerator that uses intense X-rays 10 billion times brighter than the sun. The scientists succeeded in dissolving the 3D structure of the MHETase enzyme. Plus, they were able to obtain molecular blueprints for developing a faster enzyme system.

Structural, computational, biochemical and bioinformatics approaches have been combined in this research “so as to gain molecular insights into the structure and function of the enzyme,” the scientists point out. “The study was a tremendous team effort involving scientists at all stages of their careers.”

The study was published on the academic website of the Proceedings of the National Academy of Sciences of the United States of America (PNAS).