Fluoride resistance and transport by riboswitch-controlled CLC antiporters

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, a...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2012-09, Vol.109 (38), p.15289-15294
Main Authors: Stockbridge, Randy B, Lim, Hyun-Ho, Otten, Renee, Williams, Carole, Shane, Tania, Weinberg, Zasha, Miller, Christopher
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Anions
Antiporters
Antiporters - chemistry
Bacteria
Bacterial proteins
binding sites
Biological Sciences
Catalysis
Chloride Channels - chemistry
Cytotoxicity
E coli
Escherichia coli
Escherichia coli - metabolism
Fluorides
Fluorides - chemistry
Fluorine - chemistry
glutamic acid
Ions
Kinetics
Light scattering
lipid bilayers
Lipid Bilayers - chemistry
Lipids
Liposomes
Liposomes - chemistry
Lysosomes - chemistry
Magnetic Resonance Spectroscopy - methods
Molecular Sequence Data
nuclear magnetic resonance spectroscopy
Osmosis
Phylogenetics
Phylogeny
Proteins
Riboswitch - genetics
sequence alignment
Sequence Homology, Amino Acid
Stoichiometry
toxicity
valine
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Summary: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 ¹⁹F 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 Fs lack conserved residues that form the anion binding site in canonical CLCs. Second, CLC Fs exhibit high anion selectivity for F ⁻ over Cl ⁻. Third, at a residue thought to distinguish CLC channels and transporters, CLC Fs 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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1210896109