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Issue 2, 2019
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Mechanism of hydrogen peroxide formation by lytic polysaccharide monooxygenase

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Abstract

Lytic polysaccharide monooxygenases (LPMOs) are copper-containing metalloenzymes that can cleave the glycosidic link in polysaccharides. This could become crucial for production of energy-efficient biofuels from recalcitrant polysaccharides. Although LPMOs are considered oxygenases, recent investigations have shown that H2O2 can also act as a co-substrate for LPMOs. Intriguingly, LPMOs generate H2O2 in the absence of a polysaccharide substrate. Here, we elucidate a new mechanism for H2O2 generation starting from an AA10-LPMO crystal structure with an oxygen species bound, using QM/MM calculations. The reduction level and protonation state of this oxygen-bound intermediate has been unclear. However, this information is crucial to the mechanism. We therefore investigate the oxygen-bound intermediate with quantum refinement (crystallographic refinement enhanced with QM calculations), against both X-ray and neutron data. Quantum refinement calculations suggest a Cu(II)–O2 system in the active site of the AA10-LPMO and a neutral protonated –NH2 state for the terminal nitrogen atom, the latter in contrast to the original interpretation. Our QM/MM calculations show that H2O2 generation is possible only from a Cu(I) center and that the most favourable reaction pathway is to involve a nearby glutamate residue, adding two electrons and two protons to the Cu(II)–O2 system, followed by dissociation of H2O2.

Graphical abstract: Mechanism of hydrogen peroxide formation by lytic polysaccharide monooxygenase

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Article information


Submitted
07 Sep 2018
Accepted
18 Oct 2018
First published
19 Oct 2018

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 576-586
Article type
Edge Article

Mechanism of hydrogen peroxide formation by lytic polysaccharide monooxygenase

O. Caldararu, E. Oksanen, U. Ryde and E. D. Hedegård, Chem. Sci., 2019, 10, 576
DOI: 10.1039/C8SC03980A

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