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Mechanism of hydrogen peroxide formation by lytic polysaccharide monooxygenase

Caldararu, Octav LU ; Oksanen, Esko LU ; Ryde, Ulf LU and Hedegård, Erik D. LU (2019) In Chemical Science 10(2). p.576-586
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... (More)

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)-O-2 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)-O-2 system, followed by dissociation of H2O2.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Chemical Science
volume
10
issue
2
pages
11 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85059561976
ISSN
2041-6520
DOI
10.1039/c8sc03980a
language
English
LU publication?
yes
id
d4a0055f-6dba-49f5-8299-71f330ba68d4
date added to LUP
2019-01-21 14:13:47
date last changed
2019-05-21 04:17:42
@article{d4a0055f-6dba-49f5-8299-71f330ba68d4,
  abstract     = {<p>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 H<sub>2</sub>O<sub>2</sub> can also act as a co-substrate for LPMOs. Intriguingly, LPMOs generate H<sub>2</sub>O<sub>2</sub> in the absence of a polysaccharide substrate. Here, we elucidate a new mechanism for H<sub>2</sub>O<sub>2</sub> 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)-O-2 system in the active site of the AA10-LPMO and a neutral protonated -NH<sub>2</sub> state for the terminal nitrogen atom, the latter in contrast to the original interpretation. Our QM/MM calculations show that H<sub>2</sub>O<sub>2</sub> 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)-O-2 system, followed by dissociation of H<sub>2</sub>O<sub>2</sub>.</p>},
  author       = {Caldararu, Octav and Oksanen, Esko and Ryde, Ulf and Hedegård, Erik D.},
  issn         = {2041-6520},
  language     = {eng},
  number       = {2},
  pages        = {576--586},
  publisher    = {Royal Society of Chemistry},
  series       = {Chemical Science},
  title        = {Mechanism of hydrogen peroxide formation by lytic polysaccharide monooxygenase},
  url          = {http://dx.doi.org/10.1039/c8sc03980a},
  volume       = {10},
  year         = {2019},
}