Unraveling non-productive adsorption molecular mechanisms of lignin and cellulase during enzymatic hydrolysis process: Insights into binding dynamics and driving forces

The non-productive adsorption of cellulase onto lignin significantly impedes hydrolysis efficiency. At present, the underlying interaction mechanism and structure-activity relationship between lignin and cellulase remain unclear. In this work, lignin model compounds including p-coumaric acid (H), 4-propylguaiacol (G), guaiacol (GA), syringyl alcohol (S-OH), sinapyl alcohol (S), guaiacylglycerol-β-guaiacyl ether (GG), and syringylglycerol-β-guaiacyl ether (SG) were employed to investigate the interactions mechanisms between lignin and cellulase. Fluorescence spectroscopy, atomic force microscope, surface plasmon resonance and molecular docking were utilized to characterize these interactions. Results showed that the inhibitory effects on cellulase hydrolysis followed the order (values in parentheses represent hydrolysis yields): H (45.82%) > GG (59.81%) > SG (60.95%) > G (63.86%) > GA (67.32%) > S-OH (69.23%) > S (76.32%), decreasing with the number of side chains in lignin structural units. Hydrophobic interactions dominated the interactions for H, SG, G, and GA systems, while hydrogen bonding and van der Waals forces were predominant for GG, S-OH, and S systems. Molecular docking further revealed the distinct roles of lignin structural units and functional groups in their interactions with cellulase components. These findings demonstrate that the non-productive adsorption of lignin to cellulase is driven by a combination of multiple interaction forces. Overall, steric hindrance, methoxy groups, and aliphatic hydroxyl groups are the key factors governing these interactions, providing strategic insights into optimizing cellulase hydrolysis through the modulation of lignin structural features.