title: Discovery and characterization of novel d-xylose-specific transporters from Neurospora crassa and Pichia stipitis.
abstract: Saccharomyces cerevisiae is considered one of the most promising organisms for ethanol production from lignocellulosic feedstock. Unfortunately, pentose sugars, which comprise up to 30% of lignocellulose, cannot be utilized by wild type S. cerevisiae. Heterologous pathways were introduced into S. cerevisiae to enable utilization of d-xylose, the most abundant pentose sugar. However, the resulting recombinant S. cerevisiae strains exhibited a slow growth rate and poor sugar utilization efficiency when grown on d-xylose as the sole carbon source. d-xylose uptake is the first step of d-xylose utilization. d-xylose can only enter yeast cells through hexose transporters, which have two orders of magnitude lower affinity towards d-xylose compared to hexoses. It was also shown that inefficient pentose uptake is the limiting step in some d-xylose metabolizing yeast strains. Here we report the cloning and characterization of two novel d-xylose-specific transporters from Neurospora crassa and Pichia stipitis. These two transporters were identified from a total of 18 putative pentose transporters. They were functionally expressed and properly localized in S. cerevisiae as indicated by HPLC analysis and fluorescence confocal microscopy, respectively. Kinetic parameters of the d-xylose-specific transporters were determined using a (14)C-labeled sugar uptake assay. Use of pentose-specific transporters should improve d-xylose consumption and ethanol production in fast d-xylose assimilating strains, thereby lowering the cost of lignocellulosic ethanol production.
authors: Energy Biosciences Institute, Institute for Genomic Biology, Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors: Jing
authors: J
authors: Du
authors: Sijin
authors: S
authors: Li
authors: Huimin
authors: H
authors: Zhao
mesh_terms: D050260:Carbohydrate Metabolism; D003001:Cloning, Molecular; D016681:Genome, Fungal / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009492:Neurospora crassa / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010843:Pichia / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D014994:Xylose / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D049452:Green Fluorescent Proteins; D014994:Xylose