title: Fluoride resistance and transport by riboswitch-controlled CLC antiporters.
abstract: A subclass of bacterial CLC anion-transporting proteins, phylogenetically distant from long-studied CLCs, was recently shown to be specifically up-regulated by F(-). We establish here that a set of randomly selected representatives from this "CLC(F)" clade protect Escherichia coli from F(-) toxicity, and that the purified proteins catalyze transport of F(-) in liposomes. Sequence alignments and membrane transport experiments using (19)F NMR, osmotic response assays, and planar lipid bilayer recordings reveal four mechanistic traits that set CLC(F) proteins apart from all other known CLCs. First, CLC(F)s lack conserved residues that form the anion binding site in canonical CLCs. Second, CLC(F)s exhibit high anion selectivity for F(-) over Cl(-). Third, at a residue thought to distinguish CLC channels and transporters, CLC(F)s bear a channel-like valine rather than a transporter-like glutamate, and yet are F(-)/H(+) antiporters. Finally, F(-)/H(+) exchange occurs with 1:1 stoichiometry, in contrast to the usual value of 2:1.
authors.affiliation: Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA.
authors.forename: Randy B
authors.initials: RB
authors.lastname: Stockbridge
authors.forename: Hyun-Ho
authors.initials: HH
authors.lastname: Lim
authors.forename: Renee
authors.initials: R
authors.lastname: Otten
authors.forename: Carole
authors.initials: C
authors.lastname: Williams
authors.forename: Tania
authors.initials: T
authors.lastname: Shane
authors.forename: Zasha
authors.initials: Z
authors.lastname: Weinberg
authors.forename: Christopher
authors.initials: C
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D000838:Anions; D017920:Antiporters / Q000737:chemistry*; D002384:Catalysis; D018118:Chloride Channels / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism*; D005459:Fluorides / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008247:Lysosomes / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D009995:Osmosis; D010802:Phylogeny; D058928:Riboswitch / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D000838:Anions; D017920:Antiporters; D018118:Chloride Channels; D008051:Lipid Bilayers; D008081:Liposomes; D058928:Riboswitch; D005461:Fluorine; D005459:Fluorides