Enzyme that decomposes PET plastic: Leipzig scientists increase efficiency

"Our previous article on the discovery of this enzyme in summer 2021 has already made a big splash," says Dr Christian Sonnendecker, who played a major role in the initial publication. "This outstanding teamwork has become the most successful research article ever published in the journal ChemSusChem."

In order to understand how the biocatalyst works, the spatial structure of the enzyme was first elucidated by first author Konstantin Richter in his doctoral thesis with the help of crystals. "To a certain extent, we followed on from our determination of the first structure of a PET-degrading enzyme," says Prof Dr Norbert Sträter, who led the crystallographic investigations. "That was almost ten years ago, when Prof Dr Wolfgang Zimmermann established this biotechnological enzyme research in Leipzig. Back then, hardly anyone had it on their radar."

In order to unlock the secrets of the highly efficient reaction acceleration of enzyme PHL7 from the static crystal structures, Christian Sonnendecker has inspired other experts for his research. The working groups led by Georg Künze and Christian Wiebeler used computer simulations of protein dynamics and quantum chemical calculations to understand the reaction mechanism and, above all, the contributions of individual amino acids in the binding of the PET polymer and to design better enzymes. "These predictions and calculations are extremely helpful in rationally improving an enzyme," explains Sonnendecker, "but in the end, of course, it's the experiment that decides."

This showed a very good agreement between the experimental data and the theoretical calculations. "We realised the proposed changes to the enzyme using genetic engineering and were able to further increase both the activity and the stability, which is extremely important for technical applications." Too strong a binding of the enzyme to the polymeric plastic substrate is counterproductive, explains the biochemist with regard to the proposed sliding mechanism, according to which a binding channel guides the substrate to the active centre. "Sometimes less is more," says Sonnendecker.

When asked how the research will continue, Sonnendecker explains his plans in the interdisciplinary research network: "We want to use newly developed methods of nuclear magnetic resonance spectroscopy to investigate the binding of the enzyme to the polymer substrate with the expert Prof Dr Jörg Matysik. The experiments will bring us closer than ever to the real processes of interaction between protein and plastic."

Work is already continuing on the third generation of the enzyme, whereby rational design by humans is being expanded to include machine predictions using artificial intelligence (AI). "We have completely new screening methods at our disposal for this, such as the impedance spectroscopy platform recently developed by Ronny Frank, which feeds the AI with high-quality training data," explains Sonnendecker.

However, the young scientist from the Institute of Analytical Chemistry at Leipzig University sees the future primarily in bioplastics, which are based on renewable raw materials instead of earth-based ones and are also more easily biodegradable from the outset. The foundation of a company is in preparation for the technical realisation of his visions. "This will enable us to establish a technological alternative to the fossil-dominated plastics industry in the medium term and create artificial CO2 reservoirs," says Sonnendecker and sees "a bright future with regard to plant-based raw materials".

Scientific publication by "idw - Informationsdienst Wissenschaft" from 12 April 2023