Microscopic Characterization of the Chloride Permeation Pathway in the Human Excitatory Amino Acid Transporter 1 (EAAT1)

Shashank Pant, Qianyi Wu, Renae Ryan, Emad Tajkhorshid

Research output: Contribution to journalArticlepeer-review


Excitatory amino acid transporters (EAATs) are glutamate transporters that belong to the solute carrier 1A (SLC1A) family. They couple glutamate transport to the cotransport of three sodium (Na+) ions and one proton (H+) and the counter-transport of one potassium (K+) ion. In addition to this coupled transport, binding of cotransported species to EAATs activates a thermodynamically uncoupled chloride (Cl-) conductance. Structures of SLC1A family members have revealed that these transporters use a twisting elevator mechanism of transport, where a mobile transport domain carries substrate and coupled ions across the membrane, while a static scaffold domain anchors the transporter in the membrane. We recently demonstrated that the uncoupled Cl-conductance is activated by the formation of an aqueous pore at the domain interface during the transport cycle in archaeal GltPh. However, a pathway for the uncoupled Cl-conductance has not been reported for the EAATs, and it is unclear if such a pathway is conserved. Here, we employ all-atom molecular dynamics (MD) simulations combined with enhanced sampling, free-energy calculations, and experimental mutagenesis to approximate large-scale conformational changes during the transport process and identified a Cl--conducting conformation in human EAAT1 (hEAAT1). Sampling the large-scale structural transitions in hEAAT1 allowed us to capture an intermediate conformation formed during the transport cycle with a continuous aqueous pore at the domain interface. The free-energy calculations performed for the conduction of Cl-and Na+ions through the captured conformation highlight the presence of two hydrophobic gates that control low-barrier movement of Cl-through the aqueous pathway. Overall, our findings provide insights into the mechanism by which a human neurotransmitter transporter supports functional duality of active transport and passive Cl-permeation and confirm the commonality of this mechanism in different members of the SLC1A family.

Original languageEnglish (US)
Pages (from-to)776-785
Number of pages10
JournalACS Chemical Neuroscience
Issue number6
StatePublished - Mar 16 2022


  • chloride channel
  • electrophysiology
  • excitatory amino acid transporter (EAAT)
  • glutamate transporter
  • molecular dynamics
  • structural transition

ASJC Scopus subject areas

  • Cognitive Neuroscience
  • Biochemistry
  • Physiology
  • Cell Biology


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