Development of Cellulosome-based Enzyme Complexes as a Enhanced Hydrolysis Platform for Bioethanol Production from Lignocellulosic Biomass by Yeast

Heterogeneous structure of lignin imparts plants with structural rigidity and also serves to protect cellulose and hemicellulose from degradation. Thus, prior to fermentative production of ethanol from the cellulose by yeast strains, the materials are degraded and hydrolyzed to release monomeric sugars. The use of complexed enzyme systems is one of the strategies for effective lignocellulosic biomass hydrolysis. Enzyme complexes were formed via the interaction of a dockerin domain with cohesin modules in the scaffolding protein. In this study, designer cellulosome was assembled in yeast Saccharomyces cerevisiae for utilizing of cellulose as the substrate. For utilizing of cellulose part in lignocellulosic biomass by simultaneous saccharification and fermentation, a recombinant scaffolding protein from Clostridium cellulovorans and a chimeric endoglucanase E from Clostridium thermocellum were assembled as complex system. Compared to the results for single subunit, assembly of cellulosome-based enzyme complexes caused a noticeable increase such as 2.1-fold-higher in the level of enzyme activity. The resulting strain was able to ferment cellulose part in pretreated barley straw into ethanol with the aid of beta-glucosidase A from C. thermocellum. In the fermentation assay at 10 g/L initial substrate, approximately 2.1-folds higher ethanol than that of wild type was produced. Accelerating the biological degradation of lignocellulosic materials will benefit from the development of useful recombinant enzymes with hydrolysis ability. In future research, construction of designer enzyme complexes containing other lignin degrading enzymes could be used to develop biocatalysts that can completely degrade lignocellulose into single sugars.