Enhanced degradation of thermoplastic polyurethane plastics based on engineering lignin peroxidase

Thermoplastic polyurethane (TPU) with complex physical crosslinking is difficult to degrade under natural environmental conditions. Current degradation methods, particularly for aromatic TPU, suffer from poor degradation efficiency. This study investigated the degradation performance of lignin peroxidase (LiP) on aromatic TPU through protein engineering and multi-enzyme system construction. Results indicated that wild-type LiP (WT-LiP), expressed from the recombinant Pichia pastoris GS115, exhibited a certain degradation effect on aromatic TPU. By using molecular docking techniques to identify key mutation sites, three LiP mutants (F46W, H47W, and H175R) were successfully constructed. Under optimal conditions (30°C, pH 2.5, 1 mM H₂O₂, and 5 U/mg enzyme), the F46W mutant achieved a molecular weight degradation rate of 11.97 % after 3 days of degradation, which is 2.2 times higher than that of the WT-LiP with a weight loss of 2.22 %, and the degradation efficiency in 28 days was 26.59 %. Furthermore, the constructed multi-enzyme systems (LiP-manganese peroxidase-laccase and LiP-carboxylesterase) substantially improved the degradation efficiency of TPU. Specifically, the LiP-carboxylesterase system demonstrated superior performance, achieving molecular weight degradation rates of 29.20 % and weight loss of 5.07 % after 3 days of treatment. This study provides a green enzymatic approach for efficient aromatic TPU plastics degradation and offers more sustainable solutions for plastic waste management.