title: Fluoride-dependent interruption of the transport cycle of a CLC Cl-/H+ antiporter.
abstract: Cl(-)/H(+) antiporters of the CLC superfamily transport anions across biological membranes in varied physiological contexts. These proteins are weakly selective among anions commonly studied, including Cl(-), Br(-), I(-), NO3(-) and SCN(-), but they seem to be very selective against F(-). The recent discovery of a new CLC clade of F(-)/H(+) antiporters, which are highly selective for F(-) over Cl(-), led us to investigate the mechanism of Cl(-)-over-F(-) selectivity by a CLC Cl(-)/H(+) antiporter, CLC-ec1. By subjecting purified CLC-ec1 to anion transport measurements, electrophysiological recording, equilibrium ligand-binding studies and X-ray crystallography, we show that F(-) binds in the Cl(-) transport pathway with affinity similar to Cl(-) but stalls the transport cycle. Examination of various mutant antiporters implies a 'lock-down' mechanism of F(-) inhibition, in which F(-), by virtue of its unique hydrogen-bonding chemistry, greatly retards a proton-linked conformational change essential for the transport cycle of CLC-ec1.
authors.affiliation: 1] Department of Biochemistry, Brandeis University, Waltham, Massachusetts, USA. [2] Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts, USA. [3].
authors.forename: Hyun-Ho
authors.initials: HH
authors.lastname: Lim
authors.forename: Randy B
authors.initials: RB
authors.lastname: Stockbridge
authors.forename: Christopher
authors.initials: C
authors.lastname: Miller
mesh_terms: D017920:Antiporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018118:Chloride Channels / Q000737:chemistry / Q000378:metabolism*; D002713:Chlorine / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D005459:Fluorides / Q000737:chemistry / Q000378:metabolism*; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular
chemical_list: D017920:Antiporters; D018118:Chloride Channels; D008024:Ligands; D002713:Chlorine; D006859:Hydrogen; D005459:Fluorides
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