PET (Polyethylene Terephthalate) is an invaluable plastic due to its rigidity, transparency, and hardness, which make it ideal for manufacturing plastic bottles, packaging, and other disposable products. However, these qualities also make it highly persistent in the environment, with PET bottles taking several hundred years to degrade in the ocean.
At the molecular level, PET and other plastics consist of repeating subunits called monomers, forming a polymeric structure. Over the past few decades, there has been optimism regarding the degradation of PET by certain bacterial enzymes known as polyester hydrolases or PETases. This process holds promise as an eco-friendly method for recycling plastic waste and recovering the original monomers, thus enabling an efficient circular-material economy loop.
A recent study led by the Institut de Ciències del Mar (ICM-CSIC) and the University of Leipzig (Germany) has shed light on the molecular-level details of PET degradation by these enzymes.
“Our findings have significant implications for the industry since we can now observe the process in action. Furthermore, they open the door to designing new enzymes with high efficiency to break down plastic into its soluble components,” explains Francesco Colizzi, one of the study’s lead authors.
Ania Di Pede-Mattatelli, a co-author of the study, highlights that “these enzymes could also be utilized to treat PET microplastics that result from washing microfleece textiles and subsequently end up in sewage treatment plants. This application would contribute to the preservation of the marine environment.”
Experiments and 3D simulations
In a recent publication in the journal ACS Catalysis, the authors of the study have successfully unraveled the intricate mechanism of biocatalytic PET degradation at the atomic level. To achieve this, they devised a glass matrix that stabilized the intermediates of the enzymatic reaction, enabling real-time detection through magnetic resonance spectroscopy experiments. By analyzing the spectroscopic data using molecular calculations on a supercomputer, they generated a comprehensive 3D molecular model of the enzymatic process involved in PET degradation.
The binding and interaction of PET with these enzymes have been the subject of intense research, leading to conflicting hypotheses. Some theories suggested that a substantial portion of PET needed to bind to the enzyme for effective breakdown of the plastic polymer into its constituent components.
Contrary to these assumptions, the study demonstrates that the enzyme can cleave the polymer with the interaction of only 2 PET subunits. Furthermore, it unveils the intriguing capability of the enzyme to “walk” or slide along the PET chain, facilitating movement between successive cuts.
“Understanding the precise interactions between PET and the enzyme is crucial for guiding the development of improved systems for recycling. Nature itself provides us with the raw materials to combat plastic pollution, but it is our responsibility to utilize them wisely,” concludes Colizzi.
In summary, this research provides a groundbreaking insight into the PET degradation process, shedding light on the minimal PET-enzyme interaction required for effective enzymatic breakdown. These findings have significant implications for the design of more efficient recycling methods, emphasizing the importance of sustainable utilization of nature’s resources to mitigate plastic pollution.