Depolymerization of polyurethane by Cladosporium sp. CP25 via two thermotolerant cutinases with distinct catalytic properties.

Abstract

Polyurethanes (PU) are extensively used in industrial products, but their end-of-life recycling has been a long-standing research challenge due to the intrinsic structural stability. PU depolymerization by biological enzymes represents a feasible strategy with promising attention. However, examples of robust depolymerization enzymes are lacking despite extensive research scale-up to a laboratory-relevant level. Here, we reported two cutinases CpLCut1 and CpLCut2 derived from Cladosporium sp. CP25 that demonstrated thermotolerant properties and efficient depolymerization of polyester-PU materials. After 21-days incubation at 25 °C, CP25 degraded up to 72% of commercial PU foam, as supported by changes in foam structure and the detection of degradation products. CpLCut1 and CpLCut2 possessed significant ability to hydrolyze PU into adipic acid by ester bond cleavage. Notably, CpLCut2 exhibited remarkable thermal stability, retaining 93% of its initial activity after incubation at 55 °C for 12 h, which could be attributed to the enhanced conformational stability and more persistent enzyme-substrate interactions from molecular dynamics simulations. Molecular docking, along with product distribution, elucidated a special substrate-binding mode of CpLCut1 and CpLCut2 with a plastic substrate analogue. Overall, our results expand the repertoire of PU-degrading cutinases, and provide promising enzyme candidates for future end-of-life recycling of PU waste.