Investigation of the functional role of aldose 1-epimerase in engineered cellobiose utilization.

Functional expression of a cellodextrin transporter and an intracellular β-glucosidase from Neurospora crassa in Saccharomyces cerevisiae enables simultaneous co-fermentation of cellobiose and non-glucose sugars such as xylose. Here we investigate the functional role of aldose 1-epimerase (AEP) in engineered cellobiose utilization. One AEP (Gal10) and two putative AEPs (Yhr210c and Ynr071c sharing 50.6% and 51.0% amino acid identity with Gal10, respectively) were selected. Deletion of GAL10 led to complete loss of both AEP activity and cell growth on cellobiose, while GAL10 complementation restored the AEP activity and cell growth. In addition, deletion of YHR210C or YNR071C resulted in improved cellobiose utilization. These results suggest that the intracellular mutarotation of β-glucose to α-glucose might be a rate controlling step and Gal10 play a crucial role in cellobiose fermentation by engineered S. cerevisiae.