Exploring how lignin structure influences the interaction between carbohydrate-binding module and lignin using AFM

Nonproductive adsorption of cellulase onto the residual lignin in substrate seriously hinders the enzymatic hy-drolysis. To understand how lignin structure affects lignin-cellulase interaction, the carbohydrate-binding module (CBM) functionalized atomic force microscope tip was used to measure CBM-lignin interaction by single-molecule dynamic force spectroscopy in this work. The results showed that sulfonated lignin (SL) has the greatest adhesion force to CBM (4.74 nN), while those of masson pine milled wood lignin (MWL), poplar MWL and herbaceous MWLs were 2.85, 1.03 and 0.27-0.61 nN, respectively. It provides direct quantitative evidence for the significance of lignin structure on lignin-cellulase interaction. The CBM-MWLs interaction decreased sharply to 0.054-0.083 nN while SL was added, indicating the primary mechanism of SL promoting lignocel-lulose hydrolysis was significantly reducing the nonproductive adsorption of substrate lignin on cellulase. Finally, the competitive adsorption mechanism was proposed to interpret why SL effectively promotes the enzymatic hydrolysis of lignin-containing substrates.

Automated summary

In this study, the interaction between lignin and cellulase was investigated using a carbohydrate-binding module (CBM) functionalized atomic force microscope tip. The results showed that sulfonated lignin (SL) had the strongest adhesion force to CBM, while other lignin samples had weaker adhesion forces. It was found that the primary mechanism by which SL promoted hydrolysis was by reducing the nonproductive adsorption of substrate lignin onto cellulase. The study also proposed a competitive adsorption mechanism to explain the effective promotion of enzymatic hydrolysis by SL in lignin-containing substrates.