The Role of Ideonella sakaiensis PETase in the Degradation of PET Plastics: a Structural Comparison of the Wild Type and S238F/W159H Double Mutant

Abstract

Polyethylene terephthalate (PET), a synthetic polymer, is one of the most commonly used plastics today and can be found in over 97% of packaging materials. PET’s durability as a plastic also makes it resistant to biodegradation. According to the National Association for PET Container Resources, only 29.1% of PET packaging waste was recycled in 2018, resulting in 27 million tons of plastic in landfills. These alarming statistics indicate a need for new technology to process discarded PET. A recently discovered bacterium, Ideonella sakaiensis 201‐F6, expresses the enzyme PETase, which binds and hydrolyzes PET. The structure of PETase closely resembles enzymes in the cutinase and lipase families. Similar to cutinases, PETase has an a/β hydrolase fold, but with a more open active‐site cleft. The catalytic residues in the active site of PETase hydrolyze PET plastics into intermediates which are then further broken down by the enzyme MHETase. Wild type PETase breaks down crystalline PET inefficiently, due to the rigid and dense structure of this plastic. In an effort to improve PETase performance, scientists made amino acid substitutions to the PETase active site. As a result, they discovered that the S238F/W159H double mutant narrowed the binding cleft, making the enzyme more active and therefore more efficient. The Pingry School MSOE Center for BioMolecular Modeling MAPS Team used 3‐D modeling and printing technology to examine structure‐function relationships of the PETase wild‐type and S238F/W159H double mutant. These models give an in‐depth view of the structure of PETase and illustrate how it can be utilized to degrade the highly prevalent PET plastic that has littered our planet. Furthermore, comparison of the wild‐type and double mutant structures provides molecular level details about structural changes that can enhance the performance of this enzyme. Gaining this perspective on PETase enzymes could lead to further advances in biotechnology solutions to the degradation of PET and related polymers.