title: Eukaryotic resistance to fluoride toxicity mediated by a widespread family of fluoride export proteins.
abstract: Fluorine is an abundant element and is toxic to organisms from bacteria to humans, but the mechanisms by which eukaryotes resist fluoride toxicity are unknown. The Escherichia coli gene crcB was recently shown to be regulated by a fluoride-responsive riboswitch, implicating it in fluoride response. There are >8,000 crcB homologs across all domains of life, indicating that it has an important role in biology. Here we demonstrate that eukaryotic homologs [renamed FEX (fluoride exporter)] function in fluoride export. FEX KOs in three eukaryotic model organisms, Neurospora crassa, Saccharomyces cerevisiae, and Candida albicans, are highly sensitized to fluoride (>200-fold) but not to other halides. Some of these KO strains are unable to grow in fluoride concentrations found in tap water. Using the radioactive isotope of fluoride, (18)F, we developed an assay to measure the intracellular fluoride concentration and show that the FEX deletion strains accumulate fluoride in excess of the external concentration, providing direct evidence of FEX function in fluoride efflux. In addition, they are more sensitive to lower pH in the presence of fluoride. These results demonstrate that eukaryotic FEX genes encode a previously unrecognized class of fluoride exporter necessary for survival in standard environmental conditions.
authors.affiliation: Departments of Molecular, Cellular and Developmental Biology, Chemistry, and Molecular Biophysics and Biochemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520.
authors.forename: Sanshu
authors.initials: S
authors.lastname: Li
authors.forename: Kathryn D
authors.initials: KD
authors.lastname: Smith
authors.forename: Jared H
authors.initials: JH
authors.lastname: Davis
authors.forename: Patricia B
authors.initials: PB
authors.lastname: Gordon
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Breaker
authors.forename: Scott A
authors.initials: SA
authors.lastname: Strobel
mesh_terms: D002176:Candida albicans / Q000235:genetics*; D004785:Environmental Pollutants / Q000378:metabolism* / Q000633:toxicity; D005459:Fluorides / Q000378:metabolism* / Q000633:toxicity; D005462:Fluorine Radioisotopes / Q000032:analysis; D055786:Gene Knockout Techniques; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009492:Neurospora crassa / Q000235:genetics*; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000235:genetics*
chemical_list: D004785:Environmental Pollutants; D005462:Fluorine Radioisotopes; D026901:Membrane Transport Proteins; D005459:Fluorides
keywords: dual membrane topology; environmental toxin; ion transport; toxicity resistance