Lytic polysaccharide monooxygenases from Myceliophthora thermophila C1 differ in substrate preference and reducing agent specificity

Matthias Frommhagen; Martijn J Koetsier; Adrie H Westphal; Jaap Visser; Sandra W A Hinz; Jean-Paul Vincken; Willem J H van Berkel; Mirjam A Kabel; Harry Gruppen

doi:10.1186/s13068-016-0594-y

Lytic polysaccharide monooxygenases from Myceliophthora thermophila C1 differ in substrate preference and reducing agent specificity

Biotechnol Biofuels. 2016 Aug 31;9(1):186. doi: 10.1186/s13068-016-0594-y. eCollection 2016.

Authors

Matthias Frommhagen¹, Martijn J Koetsier², Adrie H Westphal³, Jaap Visser⁴, Sandra W A Hinz², Jean-Paul Vincken¹, Willem J H van Berkel³, Mirjam A Kabel¹, Harry Gruppen¹

Affiliations

¹ Laboratory of Food Chemistry, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.
² DuPont Industrial Biosciences, Nieuwe Kanaal 7-S, 6709 PA Wageningen, The Netherlands.
³ Laboratory of Biochemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen, The Netherlands.
⁴ Fungal Genetics & Technology Consultancy, P.O. Box 39b, 6700 AJ Wageningen, The Netherlands.

Abstract

Background: Lytic polysaccharide monooxgygenases (LPMOs) are known to boost the hydrolytic breakdown of lignocellulosic biomass, especially cellulose, due to their oxidative mechanism. For their activity, LPMOs require an electron donor for reducing the divalent copper cofactor. LPMO activities are mainly investigated with ascorbic acid as a reducing agent, but little is known about the effect of plant-derived reducing agents on LPMOs activity.

Results: Here, we show that three LPMOs from the fungus Myceliophthora thermophila C1, MtLPMO9A, MtLPMO9B and MtLPMO9C, differ in their substrate preference, C1-/C4-regioselectivity and reducing agent specificity. MtLPMO9A generated C1- and C4-oxidized, MtLPMO9B C1-oxidized and MtLPMO9C C4-oxidized gluco-oligosaccharides from cellulose. The recently published MtLPMO9A oxidized, next to cellulose, xylan, β-(1 → 3, 1 → 4)-glucan and xyloglucan. In addition, MtLPMO9C oxidized, to a minor extent, xyloglucan and β-(1 → 3, 1 → 4)-glucan from oat spelt at the C4 position. In total, 34 reducing agents, mainly plant-derived flavonoids and lignin-building blocks, were studied for their ability to promote LPMO activity. Reducing agents with a 1,2-benzenediol or 1,2,3-benzenetriol moiety gave the highest release of oxidized and non-oxidized gluco-oligosaccharides from cellulose for all three MtLPMOs. Low activities toward cellulose were observed in the presence of monophenols and sulfur-containing compounds.

Conclusions: Several of the most powerful LPMO reducing agents of this study serve as lignin building blocks or protective flavonoids in plant biomass. Our findings support the hypothesis that LPMOs do not only vary in their C1-/C4-regioselectivity and substrate specificity, but also in their reducing agent specificity. This work strongly supports the idea that the activity of LPMOs toward lignocellulosic biomass does not only depend on the ability to degrade plant polysaccharides like cellulose, but also on their specificity toward plant-derived reducing agents in situ.

Keywords: Electron donor; Flavonoids; Glucan; Lignin; Phenolics; Xylan.