Selective Cleavage of Lignin β-O-4 Aryl Ether Bond by β-Etherase of the White-Rot Fungus Dichomitus squalens.

Mila Marinović,Miia R Mäkelä,Ronald P De Vries,Robin Moore,Jussi Kontro,Adiphol Dilokpimol,Jussi Sipilä,Paula Nousiainen,Kristiina Hildén

doi:10.1021/acssuschemeng.7b03619

Abstract

Production of value-added compounds from a renewable aromatic polymer, lignin, has proven to be challenging. Chemical procedures, involving harsh reaction conditions, are costly and often result in nonselective degradation of lignin linkages. Therefore, enzymatic catalysis with selective cleavage of lignin bonds provides a sustainable option for lignin valorization. In this study, we describe the first functionally characterized fungal intracellular β-etherase from the wood-degrading white-rot basidiomycete Dichomitus squalens. This enzyme, Ds-GST1, from the glutathione-S-transferase superfamily selectively cleaved the β-O-4 aryl ether bond of a dimeric lignin model compound in a glutathione-dependent reaction. Ds-GST1 also demonstrated activity on polymeric synthetic lignin fractions, shown by a decrease in molecular weight distribution of the laccase-oxidized guaiacyl dehydrogenation polymer. In addition to a possible role of Ds-GST1 in intracellular catabolism of lignin-derived aromatic compounds, the cleavage of the most abundant linkages in lignin under mild reaction conditions makes this biocatalyst an attractive green alternative in biotechnological applications.

Highlights

Lignin is the largest renewable resource of aromatics with the production of approximately 100 million tons per year.[1]
We show that an intracellular GSH-dependent βetherase Ds-GST1 from the white-rot fungus D. squalens catalyzes selective cleavage of β-O-4 bond in a racemic β-O-4 aryl ether lignin model (1)
Ds-GST1 is the first functionally characterized fungal β-etherase with known gene sequence, and it can be classified into the fungal specific glutathione-Stransferase fungal specific class A (GSTFuA) class of GST enzymes

Summary

■ INTRODUCTION

Lignin is the largest renewable resource of aromatics with the production of approximately 100 million tons per year.[1]. We show here that an intracellular GST of D. squalens, DsGST1, selectively cleaves the β-O-4 bond of a dimeric lignin model compound and acts on a synthetic lignin dehydrogenation polymer. This is the first characterization of a functional intracellular β-etherase from a lignin-degrading basidiomycete fungus. Reaction mixtures containing oxidized G-DHP, 12 mM reduced GSH (Sigma-Aldrich) and 8 mg/mL Ds-GST1 or 4 mg/mL LigF were mixed (Eppendorf ThermoMixer C, 450 rpm) for 48 h at 25 °C, and acidified by two drops of 2 M HCl. Microcrystalline cellulose (200 mg, Fluka) was added to assist the handling of the material. The chromatograms are based on dioxane lignin extracts and were normalized against the highest peak in the chromatogram

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES