Understanding and engineering cellulase-lignin interactions

The high cost of hydrolytic enzymes is a barrier to the commercial production of lignocellulosic biofuels. One strategy for decreasing this cost is the recycling of enzymes in batch processes, or countercurrent enzyme adsorption for continuous or semi-continuous processes. Lignin is a major biomass component, making up 15-30% of biomass dry weight, and remains present in biomass after all industrially-relevant pretreatment methods. Numerous studies have demonstrated an inverse correlation between the rate of biomass hydrolysis and the lignin content. Lignin has been shown to inhibit enzymatic hydrolysis and enzyme recovery not only by physically blocking cellulose, but also by nonproductively binding cellulases and contributing to enzyme denaturation.

Despite the numerous studies documenting cellulase adsorption to lignin, few attempts have been made to engineer enzymes for reduced lignin affinity. In this work, we are using alanine-scanning mutagenesis to identify residues in T. reesei carbohydrate binding modules that contribute to lignin binding. We are screening each mutant for binding to lignin and cellulose, and lignin inhibition. This work will identify residues to target for engineering reduced lignin binding.