Substrate-Binding Mode of a Thermophilic PET Hydrolase and Engineering the Enzyme to Enhance the Hydrolytic Efficacy

Polyethylene terephthalate (PET) is among the most extensively produced plastics, but huge amounts of PET wastes that have accumulated in the environment have become a serious threat to the ecosystem. Applying PET hydrolytic enzymes to depolymerize PET is an attractive measure to manage PET pollution, and searching for more effective enzymes is a prerequisite to achieve this goal. A thermostable cutinase that originates from the leaf-branch compost termed ICCG is the most effective PET hydrolase reported so far. Here, we illustrated the crystal structure of ICCG in complex with the PET analogue, mono(2-hydroxyethyl)terephthalic acid, to reveal the enzyme–substrate interaction network. Furthermore, we applied structure-based engineering to modify ICCG and screened for variants that exhibit higher efficacy than the parental enzyme. As a result, several variants with the measured melting temperature approaching 99 °C and elevated PET hydrolytic activity were obtained. Finally, crystallographic analyses were performed to reveal the structural stabilization effects mediated by the introduced mutations. These results are of importance in the context of understanding the mechanism of action of the thermostable PET hydrolytic enzyme and shall be beneficial to the development of PET biodegradation platforms.