Insight into lignin-carbohydrate ester change in pretreated corn bran and its enzymatic hydrolysis by three glucuronoyl esterases from Sordaria brevicollis.

Lignin-carbohydrate esters (LC-esters) formed by glucuronoarabinoxylan and lignin are a key factor for the recalcitrance of corn bran, understanding LC-esters change during pretreatment and enzymatic hydrolysis by glucuronoyl esterases (GEs) is essential to the sustainable utilization of corn bran. Herein, hydrolysis performances of three GEs, SbGE15A, SbGE15B, and SbGE15C from Sordaria brevicollis with different subclades and modularity, and changes in enzyme-reachable LC-esters during different pretreatments of corn bran have been comprehensively compared. F enzymes, SbGE15B and SbGE15C showed higher catalytic activity towards model and natural substrates than F enzyme, SbGE15A. Particularly, SbGE15C harboring carbohydrate-binding module 1 (CBM1) exhibited much superior catalytic performance and synergistic effect with GH10 endo-xylanase EpXYN1 from Eupenicillium parvum on pretreated residues than SbGE15A and SbGE15B without CBM1. Autohydrolysis and DES (ChCl-LA) pretreatment could decrease the content of enzyme-reachable LC-esters and depolymerize its structure, transitioning from Lignin-(Me)GlcA-Xylan to Lignin-(Me)GlcA-XOS, and eventually to Lignin-(Me)GlcA with increasing pretreatment time. These changes consequently cause a decrease in synergy between SbGE15s and EpXYN1 or commercial enzyme cocktails on pretreated residues. The findings provide new insights into significant changes in enzyme-reachable LC-esters depending on the pretreatment method and intensity and the consequent influence of these changes on the catalytic action of GEs.