Abstract
BackgroundMany fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic polysaccharide monooxygenases (LPMOs). The application of LPMOs is expected to contribute to ecologically friendly conversion of biomass into fuels and chemicals. Moreover, applications of LPMO-modified cellulose-based products may be envisaged within the food or material industry.ResultsHere, we show an up to 75-fold improvement in LPMO-driven cellulose degradation using polyphenol oxidase-activated lignin building blocks. This concerted enzymatic process involves the initial conversion of monophenols into diphenols by the polyphenol oxidase MtPPO7 from Myceliophthora thermophila C1 and the subsequent oxidation of cellulose by MtLPMO9B. Interestingly, MtPPO7 shows preference towards lignin-derived methoxylated monophenols. Sequence analysis of genomes of 336 Ascomycota and 208 Basidiomycota reveals a high correlation between MtPPO7 and AA9 LPMO genes.ConclusionsThe activity towards methoxylated phenolic compounds distinguishes MtPPO7 from well-known PPOs, such as tyrosinases, and ensures that MtPPO7 is an excellent redox partner of LPMOs. The correlation between MtPPO7 and AA9 LPMO genes is indicative for the importance of the coupled action of different monooxygenases in the concerted degradation of lignocellulosic biomass. These results will contribute to a better understanding in both lignin deconstruction and enzymatic lignocellulose oxidation and potentially improve the exploration of eco-friendly routes for biomass utilization in a circular economy.
Highlights
Many fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic poly‐ saccharide monooxygenases (LPMOs)
MtPPO7 addition improves cellulose oxidation by MtLPMO9B Our previous results have shown that reducing agents with a 1,2-benzenediol or 1,2,3-benzenetriol moiety gave the highest release of non-oxidized and C1-oxidized gluco-oligosaccharides from regenerated amorphous cellulose (RAC) incubated with three MtLPMOs compared to the incubation with compounds comprising only a single hydroxyl group [13]
Genome analysis Based on genome analysis, we found a positive correlation between genes encoding AA9 LPMOs and MtPPO7like enzymes in Ascomycota and Basidiomycota, which has not been shown previously
Summary
Many fungi boost the deconstruction of lignocellulosic plant biomass via oxidation using lytic poly‐ saccharide monooxygenases (LPMOs). Applications of LPMO-modified cellulose-based products may be envisaged within the food or material industry. Fungal carbohydrate converting enzymes are considered important for eco-friendly application in plant biomass degradation. The resulting carbohydrates are sources for the production of biochemicals or biofuels and new enzymatically modified cellulose-based products are envisaged for the future. Phenolic compounds are major components of lignocellulosic plant biomass. Phenolic compounds are present either as free molecules or in conjugated form as part of lignin or bound to carbohydrates. Lignin is one of the major constituents of (secondary) plant cell walls, together with the polysaccharides cellulose and hemicellulose. Hemicellulose interacts with lignin through ester and ether linkages, thereby forming a network that embeds the cellulose microfibrils [1, 2]
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