Elucidating the nonproductive adsorption mechanism of cellulase with lignin fractions from hydrothermally pretreated poplar using multi-dimensional spectroscopic technologies

Abstract

An in situ investigation of the influence of pretreatment lignin distribution and interaction with enzymes can provide insights into the mechanism of lignin, limiting the enzymatic efficiency of cellulose. One of the main focuses of this study is to elucidate the differences in cellulase hydrolysis caused by surface lignin after pretreatment (including pseudo-lignin deposited on biomass surface lignin and soluble lignin) compared to residual lignin in the pretreated material. Particularly, the combination of different non-destructive spectroscopies (atomic force microscopy (AFM), surface plasmon resonance (SPR), and fluorescence spectrometry (FLS)) was used to examine the nonproductive adsorption mechanisms of cellulase with differing lignin fractions from pretreated poplar. The results showed that surface lignin (SL) from pretreated poplar had almost no inhibitory effect on the Avicel hydrolysis yield. In contrast, residual lignin (RL) in pretreated poplar significantly inhibited the Avicel hydrolysis yield from 74.6% to 50.94%. The characterization results revealed that SL has lower hydrophobicity, molecular weight, and linkage content (β-O-4, β–β and β-5), which is significantly different from the structure of RL. The multi-dimensional non-destructive spectroscopy indicated that the interaction forces between SL and cellulase fractions (0.044–2.04 nN) were smaller than that of RL and cellulase fractions (0.11–3.62 nN). The SL binds to cellulase mainly through hydrogen bonds and van der Waals forces, while the RL interacts mainly through hydrophobic forces. Furthermore, SL bound to cellulase is more likely to dissociate compared with RL. This study provides a fundamental understanding of lignin-cellulase interactions for effectively converting lignocellulose into biofuels.