Nanomechanics of Lignin–Cellulase Interactions in Aqueous Solutions

Abstract

Efficient enzymatic hydrolysis of cellulose in lignocellulose to glucose is one of the most critical steps for the production of biofuels. The nonproductive adsorption of lignin to expensive cellulase highly impedes the development of biorefinery. Understanding the lignin–cellulase interaction mechanism serves as a vital basis for reducing such nonproductive adsorption in their practical applications. Yet, limited report is available on the direct characterization of the lignin–cellulase interactions. Herein, for the first time, the nanomechanics of the biomacromolecules including lignin, cellulase, and cellulose were systematically investigated by using a surface force apparatus (SFA) at the nanoscale in aqueous solutions. Interestingly, a cation−π interaction was discovered and demonstrated between lignin and cellulase molecules through SFA measurements with the addition of different cations (Na+, K+, etc.). The complementary adsorption tests and theoretical calculations further confirmed the validity of the force measurement results. This finding further inspired the investigation of the interaction between lignin and other noncatalytic-hydrolysis protein (i.e., soy protein). Soy protein was demonstrated as an effective, biocompatible, and inexpensive lignin-blocker based on the molecular force measurements through the combined effects of electrostatic, cation−π, and hydrophobic interactions, which significantly improved the enzymatic hydrolysis efficiencies of cellulose in pretreated lignocellulosic substrates. Our results offer quantitative information on the fundamental understanding of the lignin–cellulase interaction mechanism. Such unraveled nanomechanics provides new insights into the development of advanced biotechnologies for addressing the nonproductive adsorption of lignin to cellulase, with great implications on improving the economics of lignocellulosic biorefinery.

Using poly(N-Vinylcaprolactam) to Improve the Enzymatic Hydrolysis Efficiency of Phenylsulfonic Acid-Pretreated Bamboo

“…In this pH range, the net surface charge of PSA lignin was also reported to be negative ( Chen et al, 2017 ; Luo et al, 2020a ). Therefore, we infer that electrostatic attraction ( Wang et al, 2013 ) and cation-π interaction ( Zheng et al, 2021 ) would be not the main factors governing the efficient blocking of PNVCL towards PSA lignin. Because of the negative surface charge, the PNVCL coating formed on the surface of PSA lignin may further inhibit the adsorption of cellulase via electrostatic repulsion.…”

“…This indicates that PNVCL can not only be adsorbed on the surface of the hydrophobic PSA lignin film, but also form a hydrophilic coating after shielding the PSA lignin. Previous studies have found that hydrophilic surfaces could be easily hydrated, which would facilitate the inhibition of protein fouling induced by the hydrophobic interaction ( Cai et al, 2017a ; Cai et al, 2017b ; Wang et al, 2020 ; Zheng et al, 2021 ).…”

“…The adsorption properties of cellulase and PNVCL on the PSA lignin film were evaluated by the quartz crystal microbalance (QCM) (Biolin Corp., Gothenburg, Sweden) ( Gong et al, 2021 ; Zheng et al, 2021 ). Initially, a PSA lignin film was prepared on the surface of the QCM gold sensor according to a reported spin-coating method ( Cai et al, 2017b ; Zheng et al, 2021 ). Sample solution was prepared by dissolving 0.5 g of cellulase or PNVCL in 1 L of acetate buffer solution (50 mmol/L and pH 5.0).…”

Graphene Oxide Functionalized Cottonseed-Lignin Resin with Enhanced Wet Adhesion for Woody Composites Application

“…These peaks were showed in the spectra of DCF/AL and DCF/AL@GO-0.03. No new peak was detected for DCF modified with AL or GO indicating that: (i) the cross-linking took place without the formation of the chemical bonds mentioned before; (ii) due to the large number of chemical bonds already present in the cottonseed protein, it was not possible to detect the formation of any additional new bonds due to the overlap of several peaks in the fingerprint regions; and (iii) the combination between lignin and cottonseed protein was the cation-π interaction [ 14 ]. However, the effects of AL or GO on cottonseed-based adhesives could be readily confirmed using other characterization techniques, including thermal stability, sol-gel analysis, and wet adhesion test.…”

“…Moreover, it was reported that lignin is readily combined with protein to form a hydrophobic aggregation. For example, enzymatic hydrolysis of lignocellulosic biomass was accelerated in the solution containing soybean protein and protease as a result of lignin can form a strong intermolecular force with proteins [ 13 , 14 ]. Besides, when lignin was added to the soybean-based adhesive, it displayed performances on improved thermal stability or reduced the pores and cracks on the surface, and thus enhanced water resistance [ 15 , 16 ].…”