Reconstructing a chloride-binding site in a bacterial neurotransmitter transporter homologue

J Biol Chem. 2011 Jan 28;286(4):2834-42. doi: 10.1074/jbc.M110.186064. Epub 2010 Nov 29.


In ion-coupled transport proteins, occupation of selective ion-binding sites is required to trigger conformational changes that lead to substrate translocation. Neurotransmitter transporters, targets of abused and therapeutic drugs, require Na(+) and Cl(-) for function. We recently proposed a chloride-binding site in these proteins not present in Cl(-)-independent prokaryotic homologues. Here we describe conversion of the Cl(-)-independent prokaryotic tryptophan transporter TnaT to a fully functional Cl(-)-dependent form by a single point mutation, D268S. Mutations in TnaT-D268S, in wild type TnaT and in serotonin transporter provide direct evidence for the involvement of each of the proposed residues in Cl(-) coordination. In both SERT and TnaT-D268S, Cl(-) and Na(+) mutually increased each other's potency, consistent with electrostatic interaction through adjacent binding sites. These studies establish the site where Cl(-) binds to trigger conformational change during neurotransmitter transport.

Publication types

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

MeSH terms

  • Amino Acid Substitution
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Binding Sites
  • Biological Transport / physiology
  • Chlorides / metabolism
  • Gram-Positive Endospore-Forming Rods / chemistry*
  • Gram-Positive Endospore-Forming Rods / genetics
  • Gram-Positive Endospore-Forming Rods / metabolism
  • Humans
  • Mutation, Missense
  • Neurotransmitter Agents / chemistry
  • Neurotransmitter Agents / metabolism
  • Serotonin Plasma Membrane Transport Proteins / chemistry*
  • Serotonin Plasma Membrane Transport Proteins / genetics
  • Serotonin Plasma Membrane Transport Proteins / metabolism
  • Structural Homology, Protein


  • Bacterial Proteins
  • Chlorides
  • Neurotransmitter Agents
  • Serotonin Plasma Membrane Transport Proteins