Bacterial Enzymes’ Effect on PET’s Degradation in Visual Representation

The hardness, transparency, and toughness of PET (polyethylene terephthalate) make it one of the most valuable plastics for manufacturing plastic bottles, packaging, and other single-use products. However, these properties make it very persistent in the environment, to the point where a plastic PET bottle can take several hundred years to decompose in the ocean.

At the molecular level, PET and all plastics have a polymeric structure made up of tens of thousands of repeats of tiny subunits called monomers. In the past decades, the degradation of PET by a type of bacterial enzyme called polyester hydrolases (or PETases) has been viewed as a potential environmentally friendly way to recycle plastic waste and recover the original monomers, thus enabling an efficient circular economic loop.

Now, a new study led by the Institute for Science at Del Mar (ICM-CSIC) and the University of Leipzig (Germany) has revealed details, at the molecular level, of the process of degradation of PET by these enzymes.

“The results of our work could be very useful to industry, as it is the first time we can ‘see’ a moving picture of the process. It also paves the way for the design of new enzymes capable of breaking down plastics into the original soluble components with high efficiency,” explains Francesco Colizzi, Lead author of the study.

For her part, Ania Di Pede-Mattatelli, one of the co-authors of the work, adds that “these enzymes can also be used to process PET microplastics from washing microtextiles that end up in wastewater treatment plants, thus contributing to the preservation of the marine environment.” .

3D experiments and simulations

To unravel the mechanism underlying the biodegradation of PET at the atomic level, the authors of the work, which was recently published in the journal ACS catalyst, a glass matrix that stabilizes the enzymatic reaction intermediates and allows for their real-time detection by specific MRI spectroscopy experiments. Then, using molecular calculations on a supercomputer, they were able to interpret the spectral data and create a detailed 3D molecular model of the enzymatic process of PET degradation.

To date, how PET binds to and interacts with these enzymes has been the subject of intense research, and controversial hypotheses have been put forward. For example, simultaneous binding of a large fraction of PET with the enzyme was thought to be necessary for the enzyme to break down the plastic polymer into its original components.

Instead, this work shows that the reaction of only two subunits of PET is sufficient for the enzyme to cut the polymer. Finally, the study revealed that the enzyme can “walk,” or slide, on the PET chain to move from one piece to the next.

Colizzi concludes, “Understanding how PET interacts with an enzyme is important to guide the design of new improved recycling systems. Ultimately, nature itself provides us with the starting material for reducing plastic pollution, but we must use it appropriately.”