Discovery of LPMO activity on hemicelluloses shows the importance of oxidative processes in plant cell wall degradation

Jane Wittrup Agger, Trine Isaksen, Anikó Várnai, Silvia Vidal-Melgosa, William G. T. Willats, Roland Ludwig, Svein J. Horn, Vincent G. H. Eijsink, Bjørge Westereng

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The recently discovered lytic polysaccharide monooxygenases (LPMOs) are known to carry out oxidative cleavage of glycoside bonds in chitin and cellulose, thus boosting the activity ofwell-known hydrolytic depolymerizing enzymes. Because biomass-degrading microorganisms tend to produce a plethora of LPMOs, and considering the complexity and copolymeric nature of the plant cell wall, it has been speculated that some LPMOs may act on other substrates, in particular the hemicelluloses that tether to cellulose microfibrils. We demonstrate that an LPMO from Neurospora crassa, NcLPMO9C, indeed degrades various hemicelluloses, in particular xyloglucan. This activity was discovered using a glycan microarray-based screening method for detection of substrate specificities of carbohydrate-active enzymes, and further explored using defined oligomeric hemicelluloses, isolated polymeric hemicelluloses and cell walls. Products generated by NcLPMO9C were analyzed using high performance anion exchange chromatography and multidimensional mass spectrometry. We show that NcLPMO9C generates oxidized products from a variety of substrates and that its product profile differs from those of hydrolytic enzymes acting on the same substrates. The enzyme particularly acts on the glucose backbone of xyloglucan, accepting various substitutions (xylose, galactose) in almost all positions. Because the attachment of xyloglucan to cellulose hampers depolymerization of the latter, it is possible that the beneficial effect of the LPMOs that are present in current commercial cellulase mixtures in part is due to hitherto undetected LPMO activities on recalcitrant hemicellulose structures.

Original languageEnglish
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Issue number17
Pages (from-to)6287-6292
ISSN0027-8424
DOIs
Publication statusPublished - 2014
Externally publishedYes

Keywords

  • Biorefinery
  • CBM33
  • GH61
  • Metallo enzymes

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