Understanding the inhibition effect of hemicellulosic sugars on the enzymatic hydrolysis of cellulose: A combined experimental and computational study.

Sugar-platform biorefinery, involving pretreatment and enzymatic hydrolysis, is the central part of efficient utilization of lignocellulosic biomass. However, hemicellulose-derived sugars generated during pretreatment impose specific inhibition on enzymatic hydrolysis of cellulose. With the growing industrial demand for complete utilization of fermentable sugars, the inhibition by high concentration of hemicellulosic sugars represents a major challenge for economically viable biorefinery. This study initially investigated the inhibition degree of hemicellulosic sugars (xylose and mannose) on the enzymatic hydrolysis of cellulose, revealing that the inhibition by hemicellulosic sugars was mainly affected by the hydrolysis of crystalline cellulose and further determined by the hydrolytic performance of CBHI. Then, the inhibition effect of hemicellulosic sugars on CBHI kinetics was analyzed by combining interfacial experiment and theoretical model, demonstrating that the inhibition on productive association and processive movement was the determining factors affecting the hydrolytic performance of CBHI. Further, molecular dynamic simulations were performed and suggested that xylose binds with CBHI steadily in its substrate-binding tunnel through hydrogen bonds and hydrophobic interactions, accounting for the impaired productive association and processive movement. Our study provides improved insight into the inhibition mechanism by hemicellulosic sugars, and offers avenues for engineering more efficient cellulase and achieving more economically viable biorefinery.