IsPETase- and IsMHETase-Catalyzed Cascade Degradation Mechanism toward Polyethylene Terephthalate

Polyethylene terephthalate (PET) has caused serious environmental concerns. Recent studies show that a two-enzyme system in Ideonella sakaiensis is capable of degrading and upcycling PET. Here, with the molecular dynamics and quantum mechanics/molecular mechanics approaches, we systemically investigated the Ideonella sakaiensis PETase (IsPETase)- and Ideonella sakaiensis MHETase (IsMHETase)-catalyzed degradation processes. We reveal that both of the enzymes involve four elementary steps: (i) Ser-His-Asp-initiated nucleophilic attack, (ii) C–O bond cleavage, (iii) nucleophilic attack by water molecules, and (iv) IsPETase/IsMHETase deacylation. Statistical results from 20 independent conformations highlight that step (i) and (iv) are competitive for determining the turnover rate of IsPETase while step (iv) is the rate-determining step for IsMHETase. With the newly developed strategy, possible features (bonds, angles, dihedral angles, and charges) that influence the enzymatic catalysis were screened and identified. Robust relationship between active site features and activation energies were established. Distortion-interaction, hydrogen network, and noncovalent interaction analysis highlight the roles of distortion/interaction energy, hydrogen network, and weak interactions in the IsPETase- and IsMHETase-catalyzed cascade degradation of PET. These results deepen our understanding on the origin of the catalytic power of IsPETase and IsMHETase and may enhance the plastic recycling and sustainability at ambient temperature.