The liquid fraction from hydrothermal pretreatment of wheat straw provides lytic polysaccharide monooxygenases with both electrons and H2O2 co-substrate

Riin Kont; Ville Pihlajaniemi; Anna S Borisova; Nina Aro; Kaisa Marjamaa; Judith Loogen; Jochen Büchs; Vincent G H Eijsink; Kristiina Kruus; Priit Väljamäe

doi:10.1186/s13068-019-1578-5

The liquid fraction from hydrothermal pretreatment of wheat straw provides lytic polysaccharide monooxygenases with both electrons and H₂O₂ co-substrate

Biotechnol Biofuels. 2019 Oct 8:12:235. doi: 10.1186/s13068-019-1578-5. eCollection 2019.

Authors

Affiliations

¹ 1Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia.
² 2VTT Technical Research Centre of Finland Ltd, Espoo, Finland.
³ 3Department of Biochemical Engineering (AVT.BioVT), RWTH Aachen University, Aachen, Germany.
⁴ 4Norwegian University of Life Sciences (NMBU), Ås, Norway.

Abstract

Background: Enzyme-aided valorization of lignocellulose represents a green and sustainable alternative to the traditional chemical industry. The recently discovered lytic polysaccharide monooxygenases (LPMOs) are important components of the state-of-the art enzyme cocktails for cellulose conversion. Yet, these monocopper enzymes are poorly characterized in terms of their kinetics, as exemplified by the growing evidence for that H₂O₂ may be a more efficient co-substrate for LPMOs than O₂. LPMOs need external electron donors and one key question of relevance for bioprocess development is whether the required reducing power may be provided by the lignocellulosic substrate.

Results: Here, we show that the liquid fraction (LF) resulting from hydrothermal pretreatment of wheat straw supports LPMO activity on both chitin and cellulose. The initial, transient activity burst of the LPMO reaction was caused by the H₂O₂ present in the LF before addition of LPMO, while the steady-state rate of LPMO reaction was limited by the LPMO-independent production of H₂O₂ in the LF. H₂O₂ is an intermediate of LF oxidation as evidenced by a slow H₂O₂ accumulation in LF, despite high H₂O₂ production rates. This H₂O₂ scavenging ability of LF is important since high concentrations of H₂O₂ may lead to irreversible inactivation of LPMOs.

Conclusions: Our results support the growing understanding that fine-tuned control over the rates of H₂O₂ production and consumption in different, enzymatic and non-enzymatic reactions is essential for harnessing the full catalytic potential of LPMOs in lignocellulose valorization.

Keywords: Cellulose; Chitin; Hydrogen peroxide; Hydrothermal pretreatment; Lytic polysaccharide monooxygenase; Oxidation; Phenolic compounds; Serratia marcescens LPMO10A; Trichoderma reesei LPMO9A; Wheat straw.