Lignin-derived inhibition of monocomponent cellulases and a xylanase in the hydrolysis of lignocellulosics

Non-productive enzyme binding onto lignin is the major inhibitory mechanism, which reduces hydrolysis rates and yields and prevents efficient enzyme recycling in the hydrolysis of lignocellulosics. The detailed mechanisms of binding are still poorly understood. Enzyme-lignin interactions were investigated by comparing the structural properties and binding behaviour of fungal monocomponent enzymes, cellobiohydrolases TrCel7A and TrCel6A, endoglucanases TrCel7B and TrCel5A, a xylanase TrXyn11 and a β-glucosidase AnCel3A, onto lignins isolated from steam pretreated spruce and wheat straw. The enzymes exhibited decreasing affinity onto lignin model films in the following order: TrCel7B > TrCel6A > TrCel5A > AnCel3A > TrCel7A > TrXyn11. As analysed in Avicel hydrolysis, TrCel6A and TrCel7B were most inhibited by lignin isolated from pretreated spruce. This could be partially explained by adsorption of the enzyme onto the lignin surface. Enzyme properties, such as enzyme surface charge, thermal stability or surface hydrophobicity could not alone explain the adsorption behaviour.