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.