Engineered Enzymes for Plastic Degradation
What are engineered enzymes?
Engineering enzymes involve the intricate and sophisticated process of modifying the amino acid sequences within these vital proteins. This modification can be achieved by either introducing or removing specific chemical groups from the amino acid chain, thereby altering the enzyme's structure and function.
One common method of enzyme modification is phosphorylation, where a phosphate group is added to the hydroxyl side chains of serine, threonine, or tyrosine residues. This often leads to significant changes in enzyme activity and regulation, effectively turning the enzyme "on" or "off." Another process is acetylation, which involves the addition of an acetyl group to lysine residues. This alteration can profoundly influence the interactions between proteins, therefore affecting various cellular mechanisms.
Methylation is another critical modification, where a methyl group is added to particular amino acids. This change can impact both the function and regulatory mechanisms of the enzyme. Furthermore, glycosylation, the attachment of sugar molecules to the enzyme, plays a vital role in protein stability and signaling. In addition to these chemical modifications, more targeted approaches like site-directed mutagenesis utilize genetic engineering to precisely alter specific amino acids at designated sites within the enzyme.
Another technique is PEGylation, which involves attaching polyethylene glycol (PEG) to the enzyme surface. This adaptation significantly increases the solubility and stability of the enzyme under various conditions, making it more effective in practical applications.
The goal of these engineering techniques is to tailor enzymes, creating variants that add specific properties not found in their natural counterparts. These engineered enzymes can be designed to function under extreme conditions, such as elevated or reduced temperatures and abnormal pH levels. On the contrary, unmodified enzymes may become denatured in these conditions, and cease functioning. Moreover, these modifications can also influence the specificity of enzyme-substrate interactions, determining which substrates the enzyme is capable of binding to and catalyzing reactions with. As a result, they are valuable tools in many industrial and medical applications, allowing for enhanced biochemical reactions and efficiency across various fields.
How are Engineered Enzymes Used for Plastic Degradation?
Engineered microbial enzymes degrade plastic into smaller molecules, which bacteria can utilize as a carbon source or repurpose for recycling. This process is called biocatalytic depolymerization and is a sustainable alternative to traditional plastic waste management. Enzymes are modified for this function because they are more efficient at breaking down the complex polymer chains of plastic, enabling faster and more effective recycling or biodegradation of plastic waste. Regular enzymes might not recognize plastic as a substrate, so modifications can improve their ability to bind and break down plastics. Plastic also takes an extremely long time to break down, but with an increase in catalytic activity, these new enzymes can break it down faster.
Most of the widely used plastics are either thermoplastic or thermosetting. Thermoplastics, such as acrylic, polyamide, and polyethylene, become soft and moldable at high temperatures and harden when cooled. This property makes them relatively easy to recycle because they can be softened and remolded into new products, although over time the quality declines. Thermosetting plastics, like polyurethane, epoxy resin, and melamine resin, harden when heated and are almost impossible to recycle.
Fortunately, in 2012, researchers at Osaka University discovered PETase (Polyethylene Terephthalate Dehydrogenase), an enzyme found in bacteria that can break down one of the world’s most used
plastics, PET (polyethylene terephthalate), used in beverage bottles, making it a promising candidate for large-scale plastic recycling.
Impacts
The development of modified enzymes for plastic degradation represents a significant advancement in addressing the global issue of plastic pollution. These enzymes offer a sustainable and effective method for recycling plastic waste by breaking it down into reusable components, which lessens plastic accumulation in landfills and oceans. This process fosters a circular economy where plastic can be continuously recycled and reused, reducing the demand for new materials. Unlike traditional chemical recycling methods, enzymatic degradation is more environmentally friendly, operating under milder conditions and potentially producing fewer harmful byproducts. By breaking down complex plastic polymers, these enzymes also enhance recycling processes, enabling the creation of new plastic products from recycled materials, thus mitigating the environmental damage caused by plastic pollution.
References
Duan, Shuyan, et al. “The structural and molecular mechanisms of type II PETases: a mini review.” ResearchGate, August 2023, https://www.researchgate.net/figure/PET-degradation-by-PETase-and-MHETase_fig1_372887856. Accessed 31 January 2025.
“Enzyme Engineering And Its Application.” Infinita Biotech, https://infinitabiotech.com/blog/application-of-enzyme-engineering/. Accessed 26 January 2025.
“Enzymes and the active site (article).” Khan Academy, https://www.khanacademy.org/science/ap-biology/cellular-energetics/enzyme-structure-and-catalysis/a/enzymes-and-the-active-site. Accessed 2 February 2025.
F, Roger. “Improved Endurance And Reduced Fatigue With EAA.” tennisnerd, 15 October 2024, https://www.tennisnerd.net/nutrition/improved-endurance-and-reduced-fatigue-with-eaa/41625. Accessed 2 February 2025.
Goddard, Julie. “Engineering enzymes to degrade microplastics in wastewater.” Cornell University Agricultural Experiment Station, 2023, https://cals.cornell.edu/agricultural-experiment-station/engineering-enzymes-degrade-microplastics-wastewater#:~:text=We%20have%20engineered%20new%20PETase,in%20the%20wastewater%20treatment%20process. Accessed 26 January 2025.
Sanford, Adam, and Rumiana Tenchov. “Can plastic eating super-enzymes solve our destructive plastic problem?” CAS, https://www.cas.org/resources/cas-insights/can-plastic-eating-super-enzymes-solve-our-destructive. Accessed 2 February 2025.