Thermostable protein Nanocage-Based scaffold for robust polyester depolymerization

The accumulation of polyester plastics poses a major challenge for efficient recycling strategies. Enzymatic depolymerization is a promising biotechnological approach, but it is often limited by enzyme instability and the need for costly purification procedures. Here, we report a thermostable self-assembling protein nanocage scaffold derived from the C-terminal domain of the Escherichia coli BetT protein (BetTC) for polyester depolymerization. A poly(ethylene terephthalate) (PET) hydrolase variant (ICCG, an engineered cutinase) was genetically fused to the nanocage through rationally designed linkers to construct a biohybrid nanocatalyst. Systematic evaluation of different linker architectures revealed that enzyme presentation on the nanocage critically influences catalytic activity. In particular, the rigid proline-glycine (PG) linker construct exhibited approximately a twofold higher PET degradation rate compared to free ICCG, while also showing enhanced activity toward poly(butylene adipate-co-terephthalate) (PBAT). The nanocage also conferred exceptional thermal robustness, maintaining structural integrity after prolonged incubation at 50 °C. Notably, the nanocatalyst remained active in unpurified E. coli lysates, enabling a simplified, purification-free biocatalytic process. Overall, this work establishes the BetTC nanocage as an effective and engineerable protein scaffold for developing robust biocatalysts in polyester depolymerization, a key step towards recycling.