Mining Thermophile Genomes for New PETases with Exceptional Thermostabilities using Sequence Similarity Networks.

Enzymatic hydrolysis of polyethylene terephthalate (PET) is a promising technology for advancing a circular PET economy. Several PET-degrading α/β hydrolases have been identified, but the full potential of this enzyme family to catalyze PET hydrolysis remains largely unexplored. To address this, sequence similarity networks were employed to investigate the α/β hydrolase fold-5 subfamily (IPR029059) for new PETases. Priority was given to sequences from thermophiles, as thermostable enzymes are likely more suitable for industrial applications. Ten enzymes with ~20% sequence identity to the well-known LCC-PETase were identified, and seven were successfully overexpressed and purified for in vitro characterization. Each enzyme catalyzed the hydrolysis of p-nitrophenyl butyrate, a mimic of trimeric PET, and emulsified PET nanoparticles. Notably, three enzymes were also capable of hydrolyzing PET films. Novel PETases exhibited melting temperatures (Tm) exceeding 55 °C and only modest losses of activity after incubation at 70 °C for 24 hours. The crystal structure of AroC (Tm = 85 °C) was resolved to 2.2 Å, revealing several salt bridges that likely confer thermostability, and a unique loop that is conserved amongst the PETases described here. These novel enzymes will enable engineering campaigns to generate thermostable and catalytically efficient PETases for use as industrial biocatalysts.