Identification and analysis of sugar transporters capable of co-transporting glucose and xylose simultaneously.

Simultaneous co-fermentation of glucose and xylose is a key desired trait of engineered Saccharomyces cerevisiae for efficient and rapid production of biofuels and chemicals. However, glucose strongly inhibits xylose transport by endogenous hexose transporters of S. cerevisiae. We identified structurally distant sugar transporters (Lipomyces starkeyi LST1_205437 and Arabidopsis thaliana AtSWEET7) capable of co-transporting glucose and xylose from previously unexplored oleaginous yeasts and plants. Kinetic analysis showed that LST1_205437 had lenient glucose inhibition on xylose transport and AtSWEET7 transported glucose and xylose simultaneously with no inhibition. Modelling studies of LST1_205437 revealed that Ala335 residue at sugar binding site can accommodates both glucose and xylose. Docking studies with AtSWEET7 revealed that Trp59, Trp183, Asn145, and Asn179 residues stabilized the interactions with sugars, allowing both xylose and glucose to be co-transported. In addition, we altered sugar preference of LST1_205437 by single amino acid mutation at Asn365. Our findings provide a new mechanistic insight on glucose and xylose transport mechanism of sugar transporters and the identified sugar transporters can be employed to develop engineered yeast strains for producing cellulosic biofuels and chemicals. GRAPHICAL ABSTRACT LAY SUMMARY: Simultaneous co-fermentation of glucose and xylose, the two most abundant sugars in cellulosic biomass, is a key trait for efficient production of biofuels and chemicals. In this study, the authors identified and characterized two structurally distant transporters with 7 and 12 transmembrane (TM) facilitated partial and complete co-transportation of glucose and xylose. This work not only contributes to the understanding of the sugar co-transport mechanism in yeast and plant, but also enables rapid and efficient co-utilization of cellulosic sugars for the production of biofuels and chemicals.