Effect of Sugars on the Real-Time Adsorption of Expansin on Cellulose

Biological pretreatment is a safe and environmentally friendly method for disrupting recalcitrant lignocellulose structures. Expansin and expansin-like proteins are used to open up the cellulose structure and display significant synergism when mixed with cellulases that catalyze the breakdown of (hemi)cellulose into sugars. However, the adsorption behavior of expansin in the presence of sugar products is yet unknown. In this work, we monitored the effects of various sugars on the real-time adsorption of Bacillus subtilis expansin (BsEXLX1) onto cellulose films using a quartz crystal microbalance with dissipation. Cellobiose and xylose at low concentrations enhanced BsEXLX1 adsorption, whereas they disrupted adsorption at higher concentrations. Arabinose and mannose continuously inhibited expansin adsorption with increasing concentration. No obvious influence of glucose and galactose on BsEXLX1 adsorption was found. Contact angle measurements and atomic force microscopy of cellulose upon BsEXLX1 adsorption in the presence of sugars showed that both hydrophilicity and roughness increased with BsEXLX1 treatment. These results give us the ability to modulate and control expansin adsorption and provide insights into effective expansin use during enzymatic hydrolysis of lignocellulose in biorefineries.