Engineered PET Hydrolase: Plastic Depolymerization

Reaction Conditions

Temperature 50 °C

Enzyme loading 20 molecules

Crystallinity 35%

Live Readouts

PET degraded

0.0%

Relative activity

—

Degradation rate

0.0 units/min

Monomers released (TPA + EG)

How it works

An engineered PET hydrolase (modeled after FAST-PETase / LCC-ICCG variants) is a surface-erosion biocatalyst: it cannot dissolve into the solid polymer, so it can only cleave ester bonds on chains it can physically reach at the crystal surface. Amorphous PET chains are loosely packed and accessible; crystalline regions pack tightly and resist attack, so degradation eats into a solid block from the outside in and prefers the amorphous fraction.

Ester-bond hydrolysis (per cleavage event):
  –[OC-C6H4-CO-O-CH2-CH2-O]–n + H2O
        →  HOOC-C6H4-COOH (TPA)  +  HO-CH2-CH2-OH (EG)

Temperature-dependent activity (Daniel–Danson equilibrium model):
  k_cat(T)   = A · exp(−Ea / R·T)            (Arrhenius catalytic step)
  F_active(T)= 1 / (1 + exp(−(ΔH_eq/R)·(1/T_eq − 1/T)))   (reversible unfolding)
  rate(T)    = k_cat(T) · F_active(T)        → bell-shaped optimum near T_eq

Temperature — raises the catalytic rate constant like any Arrhenius reaction, but past the enzyme's melting equilibrium (T_eq, here ≈55 °C) an increasing fraction of the population reversibly unfolds and stops working, producing a realistic thermal optimum rather than "hotter is always faster".
Enzyme loading — more enzyme molecules diffusing over the surface means more simultaneous attack sites, raising throughput roughly linearly until the exposed surface itself becomes the bottleneck.
Crystallinity — the fraction of polymer units flagged as crystalline (tan/rigid) versus amorphous (green/soft); crystalline units are cleaved far more slowly, matching the well-documented resistance of high-crystallinity PET (bottles, textile fiber) to enzymatic recycling.
Each successful cleavage removes one lattice unit and releases one terephthalic acid (TPA) + ethylene glycol (EG) monomer pair, shown drifting away from the block — this is the same reaction biofoundries use to depolymerize waste PET back into monomers for closed-loop "bio-recycling".

Amorphous PET (degradable) Crystalline PET (resistant) Enzyme molecule TPA / EG monomer

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