Over the past five years, we’ve seen major breakthroughs showing how enzymes can be used to break down common plastics, such as PET which is used for everything from drink bottles to shampoo containers. In the quest for a circular economy for plastic waste, scientists have now discovered a new enzyme that further breaks down one of the main building blocks of plastic left behind by this process, leaving behind simple molecules that can be reused in new new products.
In 2016, Japanese scientists discovered bacteria with a natural appetite for PET plastics, using enzymes to break them down within weeks. Researchers at the University of Portsmouth managed to engineer a more efficient version of this enzyme, called PETase, and in 2020 they combined it with another called MHETase to form a superenzyme that digests PET plastics six times faster .
What remains after the process are the two chemical constituents of PET, ethylene glycol (EF) and TPA, and one is more problematic than the other.
Although EG is a chemical with many uses, it’s part of the antifreeze you put in your car, for example, TPA doesn’t have many uses outside of PET, and that’s not also not something most bacteria can even digest. Our group then showed that this enzyme, called TPADO, breaks down TPA, and practically only TPA, with astonishing efficiency.
Jen DuBois, author of the study.
The team’s previous discoveries were made by studying these enzymes at the UK’s Diamond Light Source Facility, which blasts them with beams of powerful X-rays. The result is a very high-resolution model of the enzyme that reveals the individual atoms of its structure. .inside, showing how the TPADO performs its TPA consumption functions. As in his previous work, this incredible detail offers a blueprint for scientists to design even more efficient versions of the enzyme.
In recent years, incredible progress has been made in the design of enzymes that break down PET plastic into its component parts. This work goes further and investigates the first enzyme in a cascade capable of breaking down these components into simpler molecules. These can be used by bacteria to generate chemicals and durable materials, which is essential for making valuable products from plastic waste.
John McGeehan, author of the study.
More information: www.pnas.org (English text).