Plastic is a material designed to be resistant and recalcitrant to degradation, making it difficult to recycle. However, these characteristics make it similar to wood, a naturally recalcitrant material degraded by certain filamentous fungi using specialized enzymes.
A consortium of scientists from INRAE, the University of Bordeaux, and the University of Southern Brittany has successfully reprogrammed LPMO enzymes, which normally recognize the surface of cellulose fibers, the primary component of wood, to recognize different types of plastics.
These results, published in *ACS Chem&Bio Engineering*, open the door to the development of a biological toolbox for plastic recycling.
Plastic pollution is omnipresent in the environment, and plastic waste management is a global issue. Besides developing more thoughtful production and usage methods, one solution to this problem is to develop bio-recycling pathways. It is a significant scientific challenge because plastics are made of polymers that are highly resistant to degradation, as they were designed to be.
But this makes them similar to other naturally recalcitrant polymers, like wood cellulose, which can be degraded by filamentous fungi.
The secret of these fungi lies in secreting an arsenal of enzymes, specific proteins that facilitate chemical reactions. Notably, LPMOs (lytic polysaccharide monooxygenases) can degrade the surface of cellulose, weakening it to facilitate further degradation. These properties make them ideal candidates for evolving new functions, particularly in plastic degradation.
Chimeric enzymes that recognize plastics
LPMO enzymes are generally composed of two modules: a binding module that allows the enzyme to recognize and attach to a specific polymer—naturally, in this context, cellulose—and a catalytic module that degrades the surface of cellulose.
The scientists focused on the binding module, replacing it with other modules to grant the enzymes the ability to bind to different plastics using well-established protein engineering processes at an industrial scale. They successfully created chimeric LPMOs capable of recognizing and binding to various types of plastics. Some of them could even form holes on the surface of bio-sourced plastic, PHA (polyhydroxyalkanoate).
In the next phase of research, the scientists will evaluate the degradation capacity of these chimeric enzymes on different types of plastics in order to select the most efficient and combine them into enzymatic cocktails for plastic degradation. The goal is to create an enzymatic toolbox for plastic bio-recycling.
References:
Munzone A. et al. (2024). Design of Plastic Binding Lytic Polysaccharide Monooxygenases via Modular Engineering.
ACS Chem&Bio engineering
DOI:
https://doi.org/10.1021/cbe.4c00125