Comparative Analysis of Polyethylene-Oxidizing Laccases: Redox Properties and Enzyme-Polyethylene Interaction Mechanism

Laccases that oxidize low-density polyethylene (LDPE) represent a promising strategy for bioremediation purposes. To rationalize or optimize their PE-oxidative activity, two fundamental factors must be considered: the enzyme's redox potential and its binding affinity/mode towards LDPE. Indeed, a stable laccase-PE complex may facilitate a thermodynamically unfavorable electron transfer, even without redox mediators. In this study, we compared the redox potential and the LDPE-binding properties of three different PE-oxidizing laccases: a fungal high-redox potential laccase from Trametes versicolor, a bacterial low-redox potential laccase from Bacillus subtilis, and the recently characterized LMCO2 from Rhodococcus opacus R7. First, we measured that LMCO2 has a low potential (E°=413 mV), consistent with other bacterial variants. Using computational tools, we simulated the interactions of these laccases with a large LDPE model and highlighted the key role of hydrophobic residues surrounding the T1 site. Notably, a methionine-rich loop in LMCO2 appears to enhance the formation of a stable complex with LDPE, potentially facilitating electron transfer. This study underscores the necessity for comprehensive computational strategies to analyze enzyme-polymer interactions beyond simplistic models, uncovering critical binding determinants and informing future mutagenesis experiments, in order to enhance laccase performance and rationalize variations in enzymatic activity.