Perspectives on the Role of Enzymatic Biocatalysis for the Degradation of Plastic PET

Abstract

Plastics are highly durable and widely used materials. Current methodologies of plastic degradation, elimination, and recycling are flawed. In recent years, biodegradation (the usage of microorganisms for material recycling) has grown as a valid alternative to previously used methods. The evolution of bioengineering techniques and the discovery of novel microorganisms and enzymes with degradation ability have been key. One of the most produced plastics is PET, a long chain polymer of terephthalic acid (TPA) and ethylene glycol (EG) repeating monomers. Many enzymes with PET degradation activity have been discovered, characterized, and engineered in the last few years. However, classification and integrated knowledge of these enzymes are not trivial. Therefore, in this work we present a summary of currently known PET degrading enzymes, focusing on their structural and activity characteristics, and summarizing engineering efforts to improve activity. Although several high potential enzymes have been discovered, further efforts to improve activity and thermal stability are necessary.

Microbial Consortia and Mixed Plastic Waste: Pangenomic Analysis Reveals Potential for Degradation of Multiple Plastic Types via Previously Identified PET Degrading Bacteria

“…Though occurring at a slow pace, microbes are able to degrade these man-made polymers. Species of bacteria, including Pseudomonas and Bacillus , have been implicated in the biodegradation of PET plastic, but very few specific enzymes within these organisms have been identified and characterized [ 88 ] (ref). Here we use “omics” approaches and existing databases to elucidate the genetic basis of how a consortium of soil bacteria can cooperate to degrade PET plastic, a model for how this may be occurring in the environment.…”

An Overview into Polyethylene Terephthalate (PET) Hydrolases and Efforts in Tailoring Enzymes for Improved Plastic Degradation

“…MHETase contains a large lid domain comprising ~240 amino acid residues (Tyr252–Ala469) situated between the β-strand (β 7 ) and α-helix (α 17 ) of the α/β hydrolase fold, which is crucial for the hydrolysis of MHET ( Figure 2 c). This lid domain consists partly of catalytic residues (Ser225, His528, and Asp492) and a Ca2+ binding site [ 125 ], increasing lid domain stability. This lid domain also exhibits 32.5% similarity with the closest structural homolog of feruloyl esterase (FaeB) found in Aspergillus oryzae (PDB ID: 3WMT) with several additional loops that distinguish it from FaeB [ 126 ].…”

QM/MM Investigation to Identify the Hallmarks of Superior PET Biodegradation Activity of PETase over Cutinase

“…Currently, the biodegradation of plastics using enzymes has emerged as a promising method to recycle plastic waste . Various family of enzymes including hydrolases (such as cutinase), lipases, and esterases have demonstrated promising abilities to degrade PET into its building blocks and thus provide a sustainable approach to upcycle plastic waste to useful chemicals. , The recently discovered Ideonella sakaiensis strain 201-F6 bacterium showed a remarkable ability to grow on synthetic polymers by using it as a carbon and energy source through hydrolysis of PET at ambient temperature . This outstanding PET hydrolysis machinery contains two enzymes namely, Is PETase and MHETase, and works concomitantly to biodegrade PET via two subsequent steps.…”

“…Then, the deacylation stage includes the hydrolysis of the aminoacylate intermediate with the assistance of a water molecule, Scheme . Several computational studies on different PET-hydrolyzing enzymes have provided novel insights into this catalytic mechanism, but whether these two stages take place in a concerted or stepwise pathway is still unclear. ,− A number of these studies, however, support a multi-step pathway, yet full characterization of the metastable intermediates was not fully achieved. Therefore, it is important to further explore the mechanism and characterize all possible intermediates throughout the hydrolysis pathway of different PET hydrolases to identify critical features responsible for the superior hydrolytic activity of Is PETase over the homologous Tf Cut2.…”