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Proc Natl Acad Sci U S A. 2014 Apr 29;111(17):6287-92. doi: 10.1073/pnas.1323629111. Epub 2014 Apr 14.

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

Author information

1
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (NMBU), 1432 Aas, Norway.

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 of well-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.

KEYWORDS:

CBM33; GH61; biorefinery; metallo enzymes

PMID:
24733907
PMCID:
PMC4035949
DOI:
10.1073/pnas.1323629111
[Indexed for MEDLINE]
Free PMC Article

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