Design of Plastic Binding\nLytic Polysaccharide Monooxygenases\nvia Modular Engineering

The worldwide accumulation of plastic\nwaste in the environment,\nalong with its lifespan of hundreds of years, represents a serious\nthreat to ecosystems. Enzymatic recycling of plastic waste offers\na promising solution, but the high chemical inertness and hydrophobicity\nof plastics pose several challenges to enzymes. In nature, lytic polysaccharide\nmonooxygenases (LPMOs) can act at the surface of recalcitrant biopolymers,\ntaking advantage of their solvent-exposed active sites and appended\ncarbohydrate-binding modules (CBMs). LPMOs can disrupt the densely\npacked chains of polysaccharides (e.g., cellulose) by the oxidation\nof C–H bonds. Given the similarities between these natural\nand artificial polymers, we aimed here at promoting plastic-binding\nproperties to LPMOs, by swapping their CBM with three natural, surface-active\naccessory modules displaying different amphipathic properties. The\npolymer binding capacity of the resulting LPMO chimeras was assessed\non a library of synthetic polymers, including polyester, polyamide,\nand polyolefin substrates. We demonstrated that the plastic binding\nproperties of these engineered LPMOs are polymer-dependent and can\nbe tuned by playing on the nature of the accessory module and reaction\nconditions. Remarkably, we gained full binding for some chimera LPMOs\nwith striking results for polyhydroxyalkanoates (PHA). In the long\nterm perspective of harnessing the unique copper chemistry of LPMOs\nto degrade plastics, we also provided the first evidence of LPMO-dependent\nmodification of the PHA polymer, as supported by enzyme assays, gel\npermeation chromatography, and scanning electron microscopy. Altogether,\nour study provides the first roadmap for engineering plastic-binding\nability in LPMOs, constituting a crucial first step on the evolutionary\npath toward efficient interfacial catalysis of plastic-active enzymes.