title: Uncoupling of a CLC Cl-/H+ exchange transporter by polyatomic anions.
abstract: CLC-ec1 is a bacterial archetype of CLC transporters, a ubiquitous class of proteins that catalyze transmembrane exchange of Cl- and H+ necessary for pH regulation of numerous physiological processes. Despite a profusion of high-resolution structures, the molecular mechanism of exchange remains unknown. Here, we rigorously demonstrate strict exchange stoichiometry of 2 Cl-/1 H+. In addition to Cl- and Br-, two non-halide ions, NO3- and SCN-, are shown to be transported by CLC-ec1, but with reduced H+ counter-transport. The loss of proton coupling to these anions is accompanied by an absence of bound anions in the central and external Cl- binding sites in the protein's anion selectivity region, as revealed by crystallographic comparison of Br- and SeCN- bound to this region.
authors.affiliation: Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA.
authors.forename: Wang
authors.initials: W
authors.lastname: Nguitragool
authors.forename: Christopher
authors.initials: C
authors.lastname: Miller
mesh_terms: D000838:Anions / Q000494:pharmacology*; D001665:Binding Sites; D001965:Bromides / Q000494:pharmacology; D018118:Chloride Channels / Q000737:chemistry / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000494:pharmacology; D017433:Protein Structure, Secondary; D011522:Protons; D013861:Thiocyanates / Q000494:pharmacology
chemical_list: D000838:Anions; D001965:Bromides; D018118:Chloride Channels; D002712:Chlorides; C508370:ClC protein, E coli; D029968:Escherichia coli Proteins; D009566:Nitrates; D011522:Protons; D013861:Thiocyanates