A Lytic Polysaccharide Monooxygenase from a White-Rot Fungus Drives the Degradation of Lignin by a Versatile Peroxidase

Abstract

Lytic polysaccharide monooxygenases (LPMOs), a class of copper-dependent enzymes, play a crucial role in boosting the enzymatic decomposition of polysaccharides. Here, we reveal that LPMOs might be associated with a lignin degradation pathway. An LPMO from white-rot fungus Pleurotus ostreatus, LPMO9A (PoLPMO9A), was shown to be able to efficiently drive the activity of class II lignin-degrading peroxidases in vitro through H₂O₂ production regardless of the presence or absence of a cellulose substrate. An LPMO-driven peroxidase reaction can degrade β-O-4 and 5-5' types of lignin dimer with 46.5% and 37.7% degradation, respectively, as well as alter the structure of natural lignin and kraft lignin. H₂O₂ generated by PoLPMO9A was preferentially utilized for the peroxidase from Physisporinus sp. strain P18 (PsVP) reaction rather than cellulose oxidation, indicating that white-rot fungi may have a strategy for preferential degradation of resistant lignin. This discovery shows that LPMOs may be involved in lignin oxidation as auxiliary enzymes of lignin-degrading peroxidases during the white-rot fungal decay process.IMPORTANCE The enzymatic biodegradation of structural polysaccharides is affected by the degree of delignification of lignocellulose during the white-rot fungal decay process. The lignin matrix decreases accessibility to the substrates for LPMOs. H₂O₂ has been studied as a cosubstrate for LPMOs, but the formation and utilization of H₂O₂ in the reactions still represent an intriguing focus of current research. Lignin-degrading peroxidases and LPMOs usually coexist during fungal decay, and therefore, the relationship between H₂O₂-dependent lignin-degrading peroxidases and LPMOs should be considered during the wood decay process. The current study revealed that white-rot fungal LPMOs may be involved in the degradation of lignin through driving a versatile form of peroxidase activity in vitro and that H₂O₂ generated by PoLPMO9A was preferentially used for lignin oxidation by lignin-degrading peroxidase (PsVP). These findings reveal a potential relationship between LPMOs and lignin degradation, which will be of great significance for further understanding the contribution of LPMOs to the white-rot fungal decay process.

Keywords: LPMOs; driven; lignin degradation; lignin-degrading peroxidases.