Accelerating Depolymerization of Poly(ethylene terephthalate) Using Chemically Modified Cutinase and Ionic Liquids

Enzymatic depolymerization of poly(ethylene terephthalate) [PET] has shown great promise as a biocatalytic route for closing the loop on PET plastic recycling. However, there is often a trade-off between the stability of hydrolytic enzymes and the activity of the enzyme toward PET in aqueous environments near the polymer glass transition temperatures. While there have been improvements in the thermal stability of PET hydrolytic enzymes through mutagenesis, there are still significant issues with the long-term operational stability of these systems at elevated temperatures. Herein, we present a chemical modification strategy that allowed for the solubilization of a PET-active cutinase from Thermobifida fusca (TfCut) in ionic liquids. This allowed the engineered hydrolytic enzyme to operate at 120 °C with linear kinetics over 7 days, ultimately resulting in a 9.52-fold improvement in total turnovers relative to the native enzyme in aqueous media. Overall, our work shows the potential of considering biocatalyst stabilization alongside solvent reaction engineering that can serve as a blueprint to dramatically improve the utility of PET-degrading enzymes for plastic upcycling.