The access of Trichoderma reesei 6A to cellulose is blocked by isolated hemicelluloses and their derivatives in biomass hydrolysis

Abstract

During the conversion of lignocellulosic biomass to biochemical products, the end-products in the hydrolysate significantly inhibit cellulase efficiency and result in a low conversion yield. Our groups recently reported that cellobiohydrolase I (CBH I), the major enzyme in the cellulase mixture secreted by Trichoderma reesei, is susceptible to inhibition by xylan oligomers. In this work, effects of mannan with different structural properties, xylan and xylo-oligosaccharides (XOS) with different chain lengths on the hydrolytic action of CBHII, another key protein in commercial cellulase preparation, were investigated. Mannan and xylan oligomers blocked the adsorption of CBHII onto the cellulose surface and decreased the hydrolytic efficiency of CBHII. The ability of mannan in hindering the interaction of CBHII with cellulose varied with the physical properties of mannan. Mannan with high viscosity and galactose side units showed a stronger inhibitory effect on the efficiency of CBHII as compared with those with low viscosity and galactose side units. The inhibitory effect of XOS on the CBHII action decreased with the reduction of XOS chain length. Aside from CBHII, synergism between CBHI and CBHII was strongly inhibited by xylan and XOS. The results thus indicated the necessity of producing highly active CBHs that could minimize the product inhibition of cellulase in cellulose conversion to sugars.