Biologists Uncover Dual Structure Secret of Heat-Tolerant Enzymes to Revolutionize Industrial PET Plastic Recycling

Tokyo University of Science researchers reveal how a thermophilic enzyme balances rigidity and flexibility to break down PET plastic at 70°C.

By: AXL Media

Published: Apr 20, 2026, 9:01 AM EDT

Source: Information for this report was sourced from EurekAlert!

The Challenge of High Temperature Biorecycling

Biological recycling, or biorecycling, uses specialized enzymes to break down complex polymers like poly(ethylene terephthalate) (PET) into their original chemical building blocks. However, PET is most easily degraded at temperatures near 70°C, a point where the plastic becomes flexible. The primary industrial hurdle has been finding enzymes that don't unfold or lose functionality at these extreme heats. Typically, an enzyme is either rigid and heat-resistant or flexible and catalytic; achieving both is a significant engineering paradox.

Decoding the CtCut Enzyme

Led by Professor Tatsuya Nishino, researchers at the Tokyo University of Science (TUS) turned to Chaetomium thermophilum, a heat-loving fungus, to study its cutinase enzyme (CtCut). Cutinases are naturally designed to dissolve the waxy cuticle of plants, but their ability to target similar chemical bonds makes them ideal for plastic degradation. The study, published in the journal Crystals on March 24, 2026, utilized X-ray crystallography and differential scanning calorimetry to observe how the enzyme behaves as it is heated from 30°C to 100°C.

A Hybrid of Rigidity and Flexibility

The team discovered that CtCut utilizes a "functional division" in its architecture. It features a rock-solid $\alpha/\beta$-hydrolase core that provides the thermal stability needed to survive industrial conditions. Conversely, the active site is covered by a "lid loop"—a flexible region that remains mobile even when the rest of the protein is locked in place. This lid loop acts as a gatekeeper, changing shape to allow PET molecules to bind and undergo catalysis, effectively solving the trade-off between stability and activity.