Glucuronoyl esterases improve cellulose hydrolysis by lignocellulose degrading enzymes and enhance lignin extraction

Glucuronoyl esterases (GEs) catalyze cleavage of ester linkages between lignin and hemicellulose. This study investigates the role of GEs in the conversion of lignocellulosic biomass in combination with a minimal set of monocomponent cellulases (endo-1,4-glucanase, cellobiohydrolases 1 and 2, and beta-glucosidase) and a GH10 endo-xylanase. We clearly demonstrate how these enzymes promote the disassembly of lignocellulose by breaking some of the covalent bonds between lignin and xylan. By cleaving the ester-linked lignin-carbohydrate complexes, we demonstrate enhanced cellulose hydrolysis of untreated lignocellulosic biomass (hardwood, softwood, and cereals). The increase in glucose production from hydrolysis of untreated lignocellulose suggests an improvement in cellulase accessibility to cellulose fibers associated with ester bond cleavage and highlights how GEs complement cellulases and xylanases in breaking down the complex lignocellulosic matrix. Furthermore, we demonstrate how GEs facilitate lignin extraction in mild aldehyde-assisted fractionation, which results in a higher yield of aldehyde-protected lignins, which is desirable for high-value applications. This is the first direct evidence of improve lignin extraction by the action of GEs. GEs are important enzymes for the efficient deconstruction of lignocellulosic biomass and that the integration of GEs with other enzymes may lead to more sustainable and economically viable biomass conversion processes alongside extraction of high-quality lignin.