Researchers Enhance Effectiveness of Enzyme Degrading PET Plastic

Polyethylene terephthalate, commonly known as PET, stands out as one of the most extensively used plastics globally. You encounter it daily, especially in the familiar form of reusable PET drink bottles. When a product with PET reaches the end of its life, opting for the environmentally savvy reuse of PET components through enzyme-driven processes emerges as a compelling alternative to burning, burying, or relying solely on chemical recycling. It's a smart move both economically and ecologically.

Researchers from Leipzig University cracked the code on how an enzyme capable of breaking down PET operates. What's more, they amped up the efficiency of this biocatalyst. The scoop on their discoveries is in the latest edition of the journal Nature Communications.

Dr. Christian Sonnendecker, a pivotal figure in our earlier article unveiling this enzyme in the summer of 2021, reflects, "Our previous piece caused quite a stir. It turned out to be the most successful research article in the journal ChemSusChem to date. The teamwork behind it was truly exceptional."

Cracking the code on how the biocatalyst operates started with lead author Konstantin Richter using crystals to unveil the enzyme's spatial structure during his doctoral thesis. Professor Norbert Sträter, in charge of the crystallographic investigations, notes, "In a sense, we were building on the groundwork laid almost 10 years ago when Wolfgang Zimmermann kickstarted biotechnological enzyme research in Leipzig by determining the first structure of a PET-degrading enzyme. Back then, it wasn't on many people's radars."

To unravel the mysteries behind PHL7's remarkable reaction acceleration from the motionless crystal structures, Christian Sonnendecker brought in expertise from fellow researchers. Teams led by Georg Künze and Christian Wiebeler dove into computer simulations of protein dynamics and quantum chemical calculations. Their goal: decoding the reaction mechanism and understanding how individual amino acids contribute to binding the PET polymer, all in the quest to craft superior enzymes. Sonnendecker emphasizes, "While predictions and calculations guide us in enhancing an enzyme logically, the final verdict, of course, rests with the experiments."

The experimental data and theoretical calculations aligned significantly. "We implemented the suggested modifications to the enzyme through genetic engineering, resulting in a substantial boost in both its activity and stability—crucial for practical applications," notes Sonnendecker. He points out the importance of avoiding overly tight binding to the plastic substrate, as per the proposed sliding mechanism, where a binding channel guides the substrate to the active center. "In this case, less is more," emphasizes Sonnendecker.

Sonnendecker outlines the future trajectory of the research, sharing plans for the interdisciplinary network: "Teaming up with expert Jörg Matysik, we aim to employ recently developed nuclear resonance spectroscopy methods to delve into how the enzyme binds to the polymer substrate. This promises to bring our experiments even closer to the actual dynamics of protein-plastic interaction."

The team is currently in the process of developing the third generation of the enzyme, taking a leap in innovation by incorporating machine prediction through artificial intelligence into human rational design. Sonnendecker sheds light on the advancements, saying, "We now have cutting-edge screening methods in play, like the newly devised impedance spectroscopy platform by Ronny Frank, supplying top-notch training data for the AI."

Yet, the budding researcher from the Institute of Analytical Chemistry at Leipzig University envisions the future predominantly in bioplastics. These are crafted from renewable resources instead of petroleum, making them inherently more biodegradable. Taking steps to materialize this vision, a company is in the works.

Sonnendecker envisions a "green future with a focus on plant-based raw materials," expressing plans to forge a technological alternative to the fossil-centric plastics industry in the near future. He aims not just for innovation but also to contribute to artificial CO2 storage.