Grinen, A. | bioRxiv Science

bioRxiv2026

MPNN-guided redesign of PET hydrolases with enhanced catalytic activity below the PET glass transition temperature

Enzymatic depolymerization of polyethylene terephthalate (PET) presents a sustainable route for plastic circularity, but its industrial viability is disadvantaged by the need for thermostable enzymes active under mild, energy-efficient conditions. While Polyester Hydrolase Leipzig 7 (PHL7, also known as PES-H1) rapidly degrades amorphous PET near the glass transition temperature of this polymer (~65{degrees}C), its poor protein expression, inactivation above 60{degrees}C and slow depolymerization below 60{degrees}C limits its practical application. Here, we employ ProteinMPNN and LigandMPNN, structural and evolutionary information, to redesign the sequence of PHL7 and improve protein expression, thermostability and activity. We identified 2/36 experimentally tested variants (D5, D11) with enhanced PET depolymerization at 50{degrees}C, achieving the same efficiency as PHL7 at 70{degrees}C but with a shifted product profile, favoring mono-(2-hydroxyethyl) terephthalate (MHET) over terephthalate. Molecular dynamics revealed that these redesigns exhibit enhanced flexibility in active site regions, providing a mechanistic understanding of their low-temperature catalysis. These variants enable a potential route to resynthesize virgin PET via MHET polycondensation, offering an efficient circular economy pathway.

bioengineering↗

bioRxiv2026

Polar Marine Microbial Communities as Reservoirs of Polyester Degrading Enzymes

BackgroundPolyethylene terephthalate (PET) is one of the most widely used plastics and a major contributor to marine pollution. While the diversity of PET hydrolases (PETases), which degrade PET into mono(2-hydroxyethyl) terephthalate (MHET), terephthalate (TPA) and ethylene glycol, has been documented in temperate and tropical waters, their potential presence in polar oceans remain unascertained. ResultsHere, we systematically screened polar and non-polar marine metagenomes using Hidden Markov models (HMM) generated using experimentally validated PETases. We identified >680 putative PETase-like sequences, with Antarctic and Arctic candidates enriched in high-fidelity motifs associated with PETase-like activity. Phylogenetic and structural analyses defined a high-confidence PETase-like clade comprising both Type I and Type II enzymes, differing in thermostability-related features and PET-binding motifs. Experimental assays confirmed polyesterase activity in 5/9 candidates from this clade, including polar-derived variants active at 14-25{degrees}C. Downstream enzymes for PET consumption were also widespread, detecting 209 putative MHET hydrolases and 442 TPA-catabolyzing enzymes. Further, we reconstructed 112 metagenome-assembled genomes (MAGs) carrying at least one PETase-like gene, more than half from polar datasets. Notably, 15 MAGs encoded multiple PETase-like enzymes, and 1 Antarctic MAG harbored a complete PETase-MHETase-TPA pathway, evidencing a fully integrated degradation potential in cold-adapted taxa. ConclusionsTogether, these results demonstrate that polar oceans act as previously overlooked reservoirs of taxonomically and functionally diverse plastic-degrading enzymes. The enrichment of PETase-like enzymes and downstream pathways in polar microbial communities expands the global biogeography of plastic biodegradation and highlights cold-active enzymes as promising candidates for developing low-temperature plastic bioremediation strategies.

bioinformatics↗