Biochem. J. (2006) 395
(543–549) (Printed in Great Britain)
Two glucose/xylose transporter genes from the yeast Candida intermedia: first molecular characterization of a yeast xylose–H+ symporter
Maria José LEANDRO, Paula GONÇALVES1 and Isabel SPENCER-MARTINS
Centro de Recursos Microbiológicos (CREM), Biotechnology Unit, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal
Candida intermedia PYCC 4715 was previously shown to grow well on xylose and to transport this sugar by two different transport systems: high-capacity and low-affinity facilitated diffusion and a high-affinity xylose–proton symporter, both of which accept glucose as a substrate. Here we report the isolation of genes encoding both transporters, designated GXF1 (glucose/xylose facilitator 1) and GXS1 (glucose/xylose symporter 1) respectively. Although GXF1 was isolated by functional complementation of an HXT-null (where Hxt refers to hexose transporters) Saccharomyces cerevisiae strain, isolation of the GXS1 cDNA required partial purification and micro-sequencing of the transporter, identified by its relative abundance in cells grown on low xylose concentrations. Both genes were expressed in S. cerevisiae and the kinetic parameters of glucose and xylose transport were determined. Gxs1 is the first yeast xylose/glucose–H+ symporter to be characterized at the molecular level. Comparison of its amino acid sequence with available sequence data revealed the existence of a family of putative monosaccharide–H+ symporters encompassing proteins from several yeasts and filamentous fungi.
Key words: Candida intermedia, membrane protein, sugar transport, xylose/glucose–H+ symport.
Abbreviations used: GXF, glucose/xylose facilitator; GXS, glucose/xylose symporter; ORF, open reading frame; PGK, phosphoglycerate kinase; RACE, rapid amplification of cDNA ends; RLM-RACE, RNA ligase-mediated RACE; RT, reverse transcriptase; XDH, xylose dehydrogenase; XR, xylitol reductase.
1To whom correspondence should be addressed (email pmz@fct.unl.pt).
The DNA sequence data reported will appear in DDBJ, EMBL, GenBank® and GSDB Nucleotide Sequence Databases under the accession numbers AJ937350 and AJ875406.
Received 5 September 2005/3 January 2006; accepted 11 January 2006
Published as BJ Immediate Publication 11 January 2006, doi:10.1042/BJ20051465
The Biochemical Society, London ©2006
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