Polyethylene terephthalate (PET) is one of the most widely used plastic polymers in the world. PET waste leads to the creation of micro- and nanosized plastic particles that have been linked to cell damage and inflammation in humans. Despite this worldwide environmental and health threat, accumulation of PET waste increases yearly. Reports of PET-degrading enzymes fuel circular economy concepts and a need to optimize these enzymes to achieve higher turnover rates for industrial applications. Here, we study PETase and MHETase from I. sakaiensis using molecular dynamics simulations with the Drude-2019 polarizable force field. To this end, we developed parameters to describe PET polymer and its derived monomers that are compatible with the Drude force field, allowing us to study both enzymes in their bound and unbound forms. Model molecules, such as methylbenzoate, 2-hydroxyethylbenzoate and benzoate were parametrized and later used to build the PET monomer (bis(2-hydroxyethyl) terephthalate, BHET). Dipole moments and molecular polarizabilities calculated via high-level QM methods were targeted alongside relevant water interactions. Dihedral parameters were fit to reproduce QM torsional energy profiles. Self-consistency of BHET parameters was assessed by checking dimer interaction energies based on PET crystal packing. Moreover, protein side-chain analogues were used to probe interactions with the aromatic ring portion of the PET monomer and, when necessary, NBFIXes were applied to correct interactions. In addition, electronic properties of BHET were studied in multiple solvents with different dielectric properties to better understand the substrate polarization when bound to the enzyme. Electric field calculations allowed us to show how PETase and MHETase organize electric fields that facilitate catalysis. Overall, these results highlight the interplay between electronic properties of PET-degrading enzymes and their conformational dynamics, opening new avenues for enzyme engineering efforts.

Modulation of polyethylene terephthalate (PET) electronic properties by PET-degrading enzymes

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