Structure-Guided Terminal Modifications Enhance the Efficiency of PET Degradation

Poly(ethylene terephthalate) (PET) is a widely used plastic whose persistence and improper disposal pose serious environmental and health risks. In this study, three novel PET hydrolases TbPETase, AbPETase, and AfPETase were identified from Thermoanaerobacterales, Acidimicrobiales, and Actinokineospora fastidiosa, respectively. Among these, TbPETase exhibited the highest enzymatic activity and thermostability. Based on structural analysis, we performed semirational truncations targeting the intrinsically disordered N- and C-terminal regions of TbPETase, generating two improved variants ΔN36 and ΔC4. The double mutant, TbPETaseΔN36/ΔC4, demonstrated a 2.3-fold increase in overall enzymatic activity and a 2.6-fold improvement in catalytic efficiency (kcat/Km) compared to the wild-type enzyme, along with significantly enhanced thermal stability. Molecular dynamics simulations revealed that the removal of flexible terminal regions increased the overall structural rigidity of TbPETaseΔN36/ΔC4. This structural stabilization was associated with the formation of a hydrogen bond at T215 and a π-π stacking interaction at W193. In a 100 mL one-pot reaction system, the combination of TbPETaseΔN36/ΔC4 with an engineered BMHETase variant, BMHETase6M, achieved 81.2% degradation of semicrystalline PET powder at 60 °C over 60 h, yielding terephthalic acid as the major product. These findings demonstrate the potential of TbPETaseΔN36/ΔC4 as a highly efficient and industrially applicable biocatalyst for PET degradation.