title: Engineering of an endogenous hexose transporter into a specific D-xylose transporter facilitates glucose-xylose co-consumption in Saccharomyces cerevisiae.
abstract: BACKGROUND
  Engineering of Saccharomyces cerevisiae for the simultaneous utilization of hexose and pentose sugars is vital for cost-efficient cellulosic bioethanol production. This yeast lacks specific pentose transporters and depends on endogenous hexose transporters for low affinity pentose uptake. Consequently, engineered xylose-fermenting yeast strains first utilize D-glucose before D-xylose can be transported and metabolized.
  
  
  RESULTS
  We have used an evolutionary engineering approach that depends on a quadruple hexokinase deletion xylose-fermenting S. cerevisiae strain to select for growth on D-xylose in the presence of high D-glucose concentrations. This resulted in D-glucose-tolerant growth of the yeast of D-xylose. This could be attributed to mutations at N367 in the endogenous chimeric Hxt36 transporter, causing a defect in D-glucose transport while still allowing specific uptake of D-xylose. The Hxt36-N367A variant transports D-xylose with a high rate and improved affinity, enabling the efficient co-consumption of D-glucose and D-xylose.
  
  
  CONCLUSIONS
  Engineering of yeast endogenous hexose transporters provides an effective strategy to construct glucose-insensitive xylose transporters that are well integrated in the carbon metabolism regulatory network, and that can be used for efficient lignocellulosic bioethanol production.
authors.affiliation: Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology, University of Groningen, Zernike Institute for Advanced Materials and Kluyver Centre for Genomics of Industrial Fermentation, Groningen, The Netherlands.
authors.forename: Jeroen G
authors.initials: JG
authors.lastname: Nijland
authors.affiliation: Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology, University of Groningen, Zernike Institute for Advanced Materials and Kluyver Centre for Genomics of Industrial Fermentation, Groningen, The Netherlands.
authors.forename: Hyun Yong
authors.initials: HY
authors.lastname: Shin
authors.affiliation: DSM Biotechnology Center, Alexander Fleminglaan 1, 2613 AX Delft, The Netherlands.
authors.forename: René M
authors.initials: RM
authors.lastname: de Jong
authors.affiliation: DSM Biotechnology Center, Alexander Fleminglaan 1, 2613 AX Delft, The Netherlands.
authors.forename: Paul P
authors.initials: PP
authors.lastname: de Waal
authors.affiliation: DSM Biotechnology Center, Alexander Fleminglaan 1, 2613 AX Delft, The Netherlands.
authors.forename: Paul
authors.initials: P
authors.lastname: Klaassen
authors.affiliation: Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology, University of Groningen, Zernike Institute for Advanced Materials and Kluyver Centre for Genomics of Industrial Fermentation, Groningen, The Netherlands.
authors.forename: Arnold Jm
authors.initials: AJ
authors.lastname: Driessen
keywords: Bioethanol; Evolutionary engineering; Sugar transporter; Xylose transporter; Yeast