Identification of a region of strong discrimination in the pore of CFTR.
The variety of methods used to identify the structural determinants of anion selectivity in the cystic fibrosis transmembrane conductance regulator Cl(-) channel has made it difficult to assemble the data into a coherent framework that describes the three-dimensional structure of the pore. Here, we compare the relative importance of sites previously studied and identify new sites that contribute strongly to anion selectivity. We studied Cl(-) and substitute anions in oocytes expressing wild-type cystic fibrosis transmembrane conductance regulator or 12-pore-domain mutants to determine relative permeability and relative conductance for 9 monovalent anions and 1 divalent anion. The data indicate that the region of strong discrimination resides between T338 and S341 in transmembrane 6, where mutations affected selectivity between Cl(-) and both large and small anions. Mutations further toward the extracellular end of the pore only strongly affected selectivity between Cl(-) and larger anions. Only mutations at S341 affected selectivity between monovalent and divalent anions. The data are consistent with a narrowing of the pore between the extracellular end and a constriction near the middle of the pore.
McCarty
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Department of Physiology and Pediatrics, Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322, USA. nmcc@physio.emory.edu
Zhang
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ZR
D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution; D000818:Animals; D000838:Anions / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology*; D016296:Mutagenesis / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary; D014867:Water / Q000737:chemistry; D014981:Xenopus
D000838:Anions; D014867:Water; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000409:Alanine