Glucuronoyl Esterases: Key Players for Carbohydrate and Lignin Valorization

Glucuronoyl esterases (GEs) are enzymes capable of cleaving ester linkages between lignin and hemicellulose. This study investigates the role of GEs in the conversion of lignocellulosic biomass and how these enzymes promote the disassembly of lignocellulose by breaking some of the covalent bonds between lignin and xylan within plant cell walls. By cleaving the ester-linked lignin-carbohydrate complexes (LCCs), we demonstrate the synergistic potential of GEs in combination with a GH10 endo-xylanase and a minimal cellulase preparation (endo-1,4-glucanase, cellobiohydrolases 1 and 2, and beta-glucosidase) for enhanced cellulose hydrolysis of untreated lignocellulosic biomass (hardwood, softwood, and cereals). The obtained 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 the complementary action of GEs in breaking down the complex lignocellulosic matrix. Furthermore, GEs facilitate lignin extraction in mild aldehyde-assisted fractionation, resulting in a higher yield of aldehyde-protected lignins, which is desirable for high-value applications. The results suggest that 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.