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Basis of substrate binding and conservation of selectivity in the CLC family of channels and transporters.

TitleBasis of substrate binding and conservation of selectivity in the CLC family of channels and transporters.
Publication TypeJournal Article
Year of Publication2009
AuthorsPicollo A, Malvezzi M, Houtman JCD, Accardi A
JournalNat Struct Mol Biol
Volume16
Issue12
Pagination1294-301
Date Published2009 Dec
ISSN1545-9985
KeywordsAmino Acid Substitution, Anions, Binding Sites, Chloride Channels, Chlorine, Escherichia coli Proteins, Models, Molecular, Mutagenesis, Site-Directed, Nitrates, Protein Binding, Protein Conformation, Protein Structure, Tertiary, Substrate Specificity
Abstract

Ion binding to secondary active transporters triggers a cascade of conformational rearrangements resulting in substrate translocation across cellular membranes. Despite the fundamental role of this step, direct measurements of binding to transporters are rare. We investigated ion binding and selectivity in CLC-ec1, a H(+)-Cl(-) exchanger of the CLC family of channels and transporters. Cl(-) affinity depends on the conformation of the protein: it is highest with the extracellular gate removed and weakens as the transporter adopts the occluded configuration and with the intracellular gate removed. The central ion-binding site determines selectivity in CLC transporters and channels. A serine-to-proline substitution at this site confers NO(3)(-) selectivity upon the Cl(-)-specific CLC-ec1 transporter and CLC-0 channel. We propose that CLC-ec1 operates through an affinity-switch mechanism and that the bases of substrate specificity are conserved in the CLC channels and transporters.

DOI10.1038/nsmb.1704
Alternate JournalNat. Struct. Mol. Biol.
PubMed ID19898476
PubMed Central IDPMC2920496
Grant List1R01GM085232 / GM / NIGMS NIH HHS / United States
R01 GM085232-01A1 / GM / NIGMS NIH HHS / United States