Reductants fuel lytic polysaccharide monooxygenase activity in a pH‐dependent manner

• Published in: FEBS letters Vol. 597; no. 10; pp. 1363 - 1374
• Main Authors: Golten, Ole, Ayuso‐Fernández, Iván, Hall, Kelsi R., Stepnov, Anton A., Sørlie, Morten, Røhr, Åsmund Kjendseth, Eijsink, Vincent G. H.
• Format: Journal Article
• Language: English
• Published: England 01.05.2023
• Subjects: biomass conversion; Cysteine - metabolism; Hydrogen-Ion Concentration; LPMO; Mixed Function Oxygenases - chemistry; Oxidation-Reduction; Oxygen; peroxygenase; Polysaccharides - metabolism; Reducing Agents - pharmacology; reductant autooxidation; stopped‐flow; stopped-flow; biomass conversion; reductant autooxidation; LPMO; peroxygenase
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1002/1873-3468.14629

Polysaccharide‐degrading mono‐copper lytic polysaccharide monooxygenases (LPMOs) are efficient peroxygenases that require electron donors (reductants) to remain in the active Cu(I) form and to generate the H2O2 co‐substrate from molecular oxygen. Here, we show how commonly used reductants affect LPMO catalysis in a pH‐dependent manner. Between pH 6.0 and 8.0, reactions with ascorbic acid show little pH dependency, whereas reactions with gallic acid become much faster at increased pH. These dependencies correlate with the reductant ionization state, which affects its ability to react with molecular oxygen and generate H2O2. The correlation does not apply to l‐cysteine because, as shown by stopped‐flow kinetics, increased H2O2 production at higher pH is counteracted by increased binding of l‐cysteine to the copper active site. The findings highlight the importance of the choice of reductant and pH in LPMO reactions. Catalysis by lytic polysaccharide monooxygenases (LPMOs) requires a reductant to reduce the catalytic copper site and to generate the H2O2 co‐substrate from molecular oxygen. Using multiple reductants, this study shows that the pH dependency of reductant‐fueled LPMO reactions relates to the ionization state of the reductant, which affects the abiotic generation of H2O2 that limits the LPMO catalytic rate.