In-situ lignin drives lytic polysaccharide monooxygenases to enhance enzymatic saccharification

Recently low-molecular lignin was reported to activate lytic polysaccharide monooxygenases (LPMOs) to oxidize cellulose. However, whether lignin formed in cell wall can play the role as electron donor for LPMOs is still largely unknown due to the complex ultrastructure of lignocellulosic biomass. In this study, we presented a new strategy to elucidate in-situ lignin function in LPMOs reaction. A lignocellulosic mimicking model was used as substrate, which was equipped with a polysaccharide template of self-assembled bacterial cellulose film and synthesized lignin. Remarkably, it has been demonstrated that lignin polymer deposited on cellulose can reduce LPMOs in-situ for cellulose oxidation and then boost cellulose hydrolysis, and the cellulose conversion ratio of the mimicked lignocellulosic film was increased by 26.0%. More importantly, lignin in-situ might exceed the well-known reductant of ascorbic acid to drive LPMOs for cellulase enzymatic hydrolysis with equivalent cellulose oxidation efficiency and extremely lower H2O2 generation, avoiding the inactivation of enzymes. The maximum H2O2 yield from lignin-driven LPMO reaction was 75.8% lower than that from ascorbic acid-driven reaction. Therefore, by using the lignocellulosic mimicking model, we have elucidated the function of in-situ lignin in boosting enzymatic hydrolysis. Such understanding could significantly promote current utilization of LPMOs in lignocellulosic biorefinery.