Impact of Copper Saturation on Lytic Polysaccharide Monooxygenase Performance

Lytic polysaccharide monooxygenases (LPMOs) are important for the effective depolymerization of recalcitrant polysaccharides. Despite their recognized importance, reported synergies with hydrolytic enzymes are often modest. We show that the kinetics of the LPMO-catalyzed depolymerization of chitin and cellulose are strongly affected by copper availability and the degree of enzyme copper saturation. Importantly, reactions with non-copper-saturated LPMOs are relatively slow but stable, which may be beneficial under industrial biomass processing conditions, whereas reactions with copper-saturated LPMOs are fast, but may lead to rapid enzyme inactivation. We show that this relates to the release of copper by damaged LPMOs that may be scavenged by apo-LPMOs, which then become activated. These effects of copper and copper saturation vary with the substrate concentration, which affects the rate of oxidative damage. We conclude that management of LPMO copper saturation and, perhaps, the use of copper chelators provides opportunities for optimizing the use of these powerful enzymes.