A CLC-type F -/H + antiporter in ion-swapped conformations

Nat Struct Mol Biol. 2018 Jul;25(7):601-606. doi: 10.1038/s41594-018-0082-0. Epub 2018 Jun 25.

Abstract

Fluoride/proton antiporters of the CLCF family combat F- toxicity in bacteria by exporting this halide from the cytoplasm. These transporters belong to the widespread CLC superfamily but display transport properties different from those of the well-studied Cl-/H+ antiporters. Here, we report a structural and functional investigation of these F--transport proteins. Crystal structures of a CLCF homolog from Enterococcus casseliflavus are captured in two conformations with simultaneous accessibility of F- and H+ ions via separate pathways on opposite sides of the membrane. Manipulation of a key glutamate residue critical for H+ and F- transport reverses the anion selectivity of transport; replacement of the glutamate with glutamine or alanine completely inhibits F- and H+ transport while allowing for rapid uncoupled flux of Cl-. The structural and functional results lead to a 'windmill' model of CLC antiport wherein F- and H+ simultaneously move through separate ion-specific pathways that switch sidedness during the transport cycle.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Antiporters / chemistry*
  • Antiporters / genetics
  • Antiporters / metabolism*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Crystallography, X-Ray
  • Enterococcus / genetics
  • Enterococcus / metabolism
  • Fluorides / metabolism*
  • Glutamic Acid / chemistry
  • Ion Transport
  • Kinetics
  • Models, Biological
  • Mutagenesis, Site-Directed
  • Protein Conformation
  • Protein Subunits
  • Protons

Substances

  • Antiporters
  • Bacterial Proteins
  • Protein Subunits
  • Protons
  • Glutamic Acid
  • Fluorides