Positive Charge Introduction on the Surface of Thermostabilized PET Hydrolase Facilitates PET Binding and Degradation

A thermostable enzyme PET2, found in a metagenome library, has been engineered to improve its hydrolytic activity against polyethylene terephthalate (PET). The PET2 wildtype (WT) showed a melting temperature of 69.0 degrees C and produced water-soluble reaction products at a rate of 0.40 min(-1) (2.4 mu M products from 0.1 mu M enzyme after 60 min reaction) from an amorphous PET film at 60 degrees C. Mutations for surface charge modification, backbone stabilization, and formation of additional disulfide bond were introduced into the PET2 WT, and the best mutant (PET2 7M) showed a melting temperature of 75.7 degrees C and hydrolytic activity of 1.3 min(-1) (7.8 mu M products from 0.1 mu M enzyme after 60 min reaction at 60 degrees C). X-ray crystal structures of PET2 mutants showed that introduced arginine and lysine residues oriented to the solvent, similar to a PET hydrolase from Ideonella sakaiensis 201-F6. Single-molecule fluorescence imaging revealed that these positively charged surface residues increased binding rate constant of PET2 7M to PET surface 2.7 times, compared with PET2 WT, and resulted in higher activity. Optimal temperature for amorphous PET hydrolysis by PET2 7M (68 degrees C) was 8 degrees C higher than that by PET2 WT (60 degrees C), and hydrolytic activity of PET2 7M at the optimal temperature (2.7 min(-1), 16.2 mu M products from 0.1 mu M enzyme after 60 min reaction) was 6.8 times higher than that of PET2 WT (0.40 min(-1)). Furthermore, PET2 7M generated reaction products with a constant rate for at least 24 h at 68 degrees C, indicating long-term thermal stability at the optimal temperature.

Automated summary

A thermostable enzyme PET2 was engineered for improved hydrolytic activity against polyethylene terephthalate (PET), with mutations in surface charge and formation of additional disulfide bond enhancing activity. The best mutant, PET2 7M, showed increased melting temperature and hydrolytic activity compared to wildtype PET2, with optimal temperature for hydrolysis being 8 degrees C higher and activity being 6.8 times higher at that temperature. These modifications led to enhanced binding rate and long-term thermal stability of PET2 7M at the optimal temperature.