Emerging Roles of PETase and MHETase in the Biodegradation of Plastic Wastes

Polyethylene terephthalate (PET) is extensively used in plastic products, and its accumulation in the environment has become a global concern. Being a non-degradable pollutant, a tremendous quantity of PET-bearing plastic materials have already accumulated in the environment, posing severe challenges towards the existence of various endangered species and consequently threatening the ecosystem and biodiversity. While conventional recycling and remediation methodologies so far have been ineffective in formulating a "green" degradation protocol, the bioremediation strategies-though nascent-are exhibiting greater promises towards achieving the target. Very recently, a novel bacterial strain called Ideonella sakaiensis 201-F6 has been discovered that produces a couple of unique enzymes, polyethylene terephthalate hydrolase and mono(2-hydroxyethyl) terephthalic acid hydrolase, enabling the bacteria to utilize PET as their sole carbon source. With a detailed understanding of the protein structure of these enzymes, possibilities for their optimization as PET degrading agents have started to emerge. In both proteins, several amino acids have been identified that are not only instrumental for catalysis but also provide avenues for the applications of genetic engineering strategies to improve the catalytic efficiencies of the enzymes. In this review, we focused on such unique structural features of these two enzymes and discussed their potential as molecular tools that can essentially become instrumental towards the development of sustainable bioremediation strategies. Degradation PET by wild type and genetically engineered PETase and MHETase. Effect of the MHETase-PETase chimeric protein and PETase expressed on the surface of yeast cells on PET degradation is also shown.