Structural Elucidation of Lignosulfonate–Cellulase Complexes: Formation, Composition, and Spatial Reconstruction

Lignosulfonate (LS) can enhance lignocellulose saccharification by forming complexes with cellulase. However, the composition and spatial structure of lignosulfonate-cellulase complexes (LCCs) are not clear. This study employed quartz crystal microbalance with dissipation monitoring, surface plasmon resonance, and small-angle X-ray scattering (SAXS) to investigate the composition and spatial arrangement of LCCs. Results revealed that LS molecules self-assemble into aggregates in buffer (pH 4.8), which subsequently form distinct complexes with cellulase depending on the molar ratio. At LS:cellulase ratios of 4:1 or higher, one LS aggregate binds to a single cellulase molecule, while at lower ratios, one LS aggregate binds to multiple cellulase molecules. SAXS analysis revealed that cellulase's adsorption domain interacts with LS aggregates, suggesting a mechanism to reduce nonproductive binding to lignin. Ionic strength was found to influence the complex formation through electrostatic interactions. These findings elucidate the structural basis for LS-mediated saccharification, providing insights for optimizing lignocellulosic biomass conversion.