Enhanced enzyme activity for biomass degrading and bioethanol producing by introduction of cellulosome-based enzyme complexes in 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. Developing cellulosome-based enzyme complex will be useful for the efficient conversion of biomass to valuable products. [This work was supported by the New & Renewable Energy Technology Development Program of the Korea Institute of Energy  Technology Evaluation and Planning(KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No.20113010090040)]