Polyethylene terephthalate (PET) is the synthetic juggernaut of the modern world—strong, lightweight, and seemingly indestructible. Yet, this durability is a double-edged sword. PET waste lingers in landfills, oceans, and ecosystems for centuries, accumulating like an unstoppable plastic zombie apocalypse.
Nature, however, has begun to fight back. Certain microorganisms have evolved enzymes capable of breaking down PET into its constituent monomers, terephthalic acid (TPA) and ethylene glycol (EG). The discovery of Ideonella sakaiensis and its PETase enzyme in 2016 marked a turning point—proof that biology could tackle synthetic polymers.
Natural PETase is slow—too slow for industrial use. Scientists have turned to protein engineering to create faster, more efficient versions. Two primary strategies dominate:
By mimicking natural selection in the lab, researchers subject PETase to iterative rounds of mutation and screening. The best-performing mutants are selected and further optimized. Notable improvements include:
Using structural biology and computational modeling, scientists pinpoint key amino acids influencing PETase performance. Strategic mutations enhance substrate binding, catalytic efficiency, and stability. For example:
Why settle for one enzyme when you can combine them? Researchers have engineered fusion proteins, such as PETase-MHETase chimeras, which degrade PET more efficiently by keeping intermediate products close to the active site.
A 2020 study engineered a PETase-MHETase hybrid capable of depolymerizing PET at 6x the rate of wild-type PETase. This mutant not only chews through plastic faster but also operates at higher temperatures—ideal for industrial scalability.
The dream? Giant bioreactors where shredded PET waste is fed to engineered enzymes, producing pure TPA and EG for repolymerization. Challenges remain:
Real-world PET varies in crystallinity, additives, and contamination. Enzymes must be robust enough to handle dirty, mixed plastics.
Enzyme production must be cheap enough to compete with virgin PET. Fermentation optimization and cell-free systems are being explored.
Separating TPA and EG from the enzymatic slurry requires energy-efficient purification methods.
If engineered enzymes can make PET recycling as efficient as aluminum can recycling, we might finally break free from the disposable plastic nightmare. The question isn’t "Can we?"—it’s "How soon?"
The race is on—plastic versus protein. And this time, biology might just win.