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Departments of Physiology and Pediatrics, Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia 30322
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.
cystic fibrosis transmembrane conductance regulator; chloride channel; selectivity; anion permeation
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