Sammanfattning

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 eta(1)-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 (eta(1)) 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.

Nyckelord

C-H activation; copper monooxygenase; GH61; CBM33; biofuels

Publicerad i

Proceedings of the National Academy of Sciences
2014, Volym: 111, nummer: 1, sidor: 149-154
Utgivare: NATL ACAD SCIENCES

SLU författare

• Ståhlberg, Jerry

  • Institutionen för molekylärbiologi, Sveriges lantbruksuniversitet
    
  • Norges miljø- og biovitenskapelige universitet (NMBU)

• Sandgren, Mats

  • Institutionen för molekylärbiologi, Sveriges lantbruksuniversitet
    

UKÄ forskningsämne

Förnyelsebar bioenergi
Strukturbiologi
Biokemi och molekylärbiologi


Publikationens identifierare

DOI: https://doi.org/10.1073/pnas.1316609111

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/60941