Quantum Mechanical Calculations Suggest that Lytic Polysaccharide Monooxygenases Use a Copper-Oxyl, Oxygen-Rebound Mechanism

Seonah Kim, Jerry Ståhlberg, Mats Sandgren, Robert S. Paton, Gregg T. Beckham

Research output: Contribution to journalArticlepeer-review

189 Scopus Citations

Abstract

Lytic polysaccharide monooxygenases (LPMOs) exhibit a mononuclear copper-containing active site and use dioxygen and a reducing agent to oxidatively cleave glycosidic linkages in polysaccharides. LPMOs represent a unique paradigm in carbohydrate turnover and exhibit synergy with hydrolytic enzymes in biomass depolymerization. To date, several features of copper binding to LPMOs have been elucidated, but the identity of the reactive oxygen species and the key steps in the oxidative mechanism have not been elucidated. Here, density functional theory calculations are used with an enzyme active site model to identify the reactive oxygen species and compare two hypothesized reaction pathways in LPMOs for hydrogen abstraction and polysaccharide hydroxylation; namely, a mechanism that employs a η1-superoxo intermediate, which abstracts a substrate hydrogen and a hydroperoxo species is responsible for substrate hydroxylation, and a mechanism wherein a copper- oxyl radical abstracts a hydrogen and subsequently hydroxylates the substrate via an oxygen-rebound mechanism. The results predict that oxygen binds end-on (η1) to copper, and that a copperoxyl- mediated, oxygen-rebound mechanism is energetically preferred. The N-terminal histidine methylation is also examined,which is thought to modify the structure and reactivity of the enzyme. Density functional theory calculations suggest that this posttranslational modification has only a minor effect on the LPMO active site structure or reactivity for the examined steps. Overall, this study suggests the steps in the LPMO mechanism for oxidative cleavage of glycosidic bonds.

Original languageAmerican English
Pages (from-to)149-154
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Issue number1
DOIs
StatePublished - 2014

NREL Publication Number

  • NREL/JA-5100-61467

Keywords

  • Biofuels
  • C-H activation
  • CBM33
  • Copper monooxygenase
  • GH61

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