Effect of poly(ethylene glycol) on enzymatic hydrolysis and adsorption of cellulase enzymes to pretreated lignocellulose

There is a need to develop the enzymatic hydrolysis of cellulose for production of ethanol from biomass. In recent years the inhibitory effects of lignin in lignocellulosic substrates has been the focus of several studies. This points to the importance of understanding the interactions between cellulose degrading enzymes and lignin. Surface active substances have been shown to adsorb to lignin surfaces resulting in reduction of unproductive enzyme binding. It is essential to understand the surface properties of both enzymes and lignin to develop pretreatment methods, surface active additives and engineering of cellulose degrading enzyme systems. This study investigates the PEG-lignin interaction as well as interactions between lignin and the enzyme modules of the Hypocrea jecorina (Trichoderma reesei) enzymes Cel7A and Cel7B. Interactions were monitored with C-14 labelled PEG 4000 and by measuring the enzymatic activity in solution. It was found that the dominating driving force of PEG adsorption on lignin is hydrophobic interaction. The effect of PEG addition on enzyme conversion of lignocellulose increased with higher temperature due to increased adsorption of PEG on lignin, thus resulting in a higher surface density of PEG on the surface. The hydrophobic adsorption of enzymes to lignin induces denaturation of enzymes on lignin surfaces. The addition of PEG to the enzyme hydrolysis at a temperature of 50 degrees C is suggested to hinder deactivation of enzymes by exclusion of enzymes from lignin surfaces. The adsorption of full-length Cel7B to lignin was stronger than for Cel7A. A more hydrophobic surface on the flat face of the cellulose binding module (CBM) together with an additional exposed aromatic residue on the rough face of Cel7B CBM compared to Cel7A CBM gives a higher affinity to lignin for the Cel7B enzyme. (c) 2007 Elsevier Inc. All rights reserved.