Evidence for a third sodium-binding site in glutamate transporters suggests an ion/substrate coupling model

H. Peter Larsson, Xiaoyu Wang, Bogdan Lev, Isabelle Baconguis, David A. Caplan, Nicholas P. Vyleta, Hans P. Koch, Ana Diez-Sampedro, Sergei Y. Noskov

Research output: Contribution to journalArticle

60 Scopus citations

Abstract

Excitatory amino acid transporters (EAATs) remove glutamate from synapses. They maintain an efficient synaptic transmission and prevent glutamate from reaching neurotoxic levels. Glutamate transporters couple the uptake of one glutamate to the cotransport of three sodium ions and one proton and the countertransport of one potassium ion. The molecular mechanism for this coupled uptake of glutamate and its co- and counter-transported ions is not known. In a crystal structure of the bacterial glutamate transporter homolog, Glt Ph, only two cations are bound to the transporter, and there is no indication of the location of the third sodium site. In experiments using voltage clamp fluorometry and simulations based on molecular dynamics combined with grand canonical Monte Carlo and free energy simulations performed on different isoforms of GltPh as well on a homology model of EAAT3,wesought to locate the third sodium-binding site in EAAT3. Both experiments and computer simulations suggest that T370 and N451 (T314 and N401 in GltPh) form part of the third sodium-binding site. Interestingly, the sodium bound at T370 forms part of the binding site for the amino acid substrate, perhaps explaining both the strict coupling of sodium transport to uptake of glutamate and the ion selectivity of the affinity for the transported amino acid in EAATs.

Original languageEnglish (US)
Pages (from-to)13912-13917
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume107
Issue number31
DOIs
Publication statusPublished - Aug 3 2010

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Keywords

  • Excitatory amino acid transporters
  • Fluorescence
  • Simulations
  • The sodium/aspartate symporter from Pyrococcus horikoshii (Glt)

ASJC Scopus subject areas

  • General

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