Comparison of Polyethylene Terephthalate (PET) Degrading Cutinases from Bacteria and Fungi: Structural Characterization and Molecular Docking Analysis.

Polyethylene terephthalate (PET) is one of the major plastics specified in the Plastics Identification System, which has been proven harmful to living organisms. The degradation of PET is made possible by microbial enzymes such as cutinases. Cutinase can be found in both bacteria and fungi, however, the degradation rate might be different. In this study, the known structures of fifteen fungal and bacterial cutinases were investigated using computational analysis. To compare the ability of these cutinases in PET degradation, a molecular docking analysis between the dimer unit of PET monomer (di-PET) and the enzymes was conducted using AutoDock Vina, resulting in predicted binding affinities and molecular interactions. Computational analysis of the enzymes identified a high aliphatic index indicative of high thermal stability. The analyses of the secondary and tertiary structures of cutinases showed their overall high stability and regions of flexibility. According to molecular docking analysis, Thermobifida genus cutinases showed the highest binding affinity for di-PET in comparison to other bacterial species and fungi. In particular, the calcium-bound cutinase Est119 from Thermobifida alba was predicted to bind di-PET with an affinity of - 6.4 kcal/mol at a position close to the Ser-residue of the catalytic triad that is involved in the first step of ester hydrolysis. Furthermore, among fungi, the strongest binding affinities between the cutinases and di-PET were observed in the Fusarium genus and Humicola insolens with - 5.7 kcal/mol. This study indicates the possibilities for further engineering of these enzymes for more efficient PET degradation, industrial recycling and upcycling, and improved waste management.