Mechanism behind oxidase activity of cellulose-active AA10 lytic polysaccharide monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) are unique mono-copper enzymes that boost the degradation of different polysaccharides and play important roles in the sustainable production of biofuels, in human and plant pathogens and potentially also in plastic degradation. Their activity depends on a co-substrate, where recent results show that hydrogen peroxide is the preferred co-substrate. Under typical experimental conditions, no hydrogen peroxide is added and it is instead produced in situ by LPMOs themselves, which could possibly be the rate-limiting step. Previous theoretical investigations of the oxidase reaction have been highly inhomogeneous, and focused on different aspects of LPMO reactivity. In this paper, we systematically investigate how LPMOs generate hydrogen peroxide using accurate quantum mechanics/molecular mechanics (QM/MM) hybrid methods with extended QM regions. We find that protonation of a generated superoxide intermediate at the active-site is most likely, but that this requires further reduction of the superoxide.