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Ion binding and permeation at the GABA transporter GAT1
S Mager1, N Kleinberger-Doron, G I Keshet
1Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Summary
The GABA transporter GAT1 requires sodium (Na+) and chloride (Cl-) binding for efficient synaptic transmitter removal. Specific mutations or blockers can "lock" Na+ onto GAT1, impacting substrate release and transport rates.
Area of Science:
- Neuroscience
- Molecular Biology
- Biophysics
Background:
- The gamma-aminobutyric acid (GABA) transporter GAT1 is crucial for regulating GABAergic neurotransmission.
- Understanding the ion and substrate binding mechanisms of GAT1 is essential for comprehending its function in synaptic plasticity and neurological disorders.
Purpose of the Study:
- To investigate the role of ion binding, specifically Na+ and Cl-, in the functional mechanism of the GABA transporter GAT1.
- To elucidate how substrate permeation and transport are influenced by ion interactions and specific mutations or blockers.
Main Methods:
- GAT1 was expressed in Xenopus oocytes and mammalian cells.
- Electrophysiological recordings and [3H]GABA/[3H]tiagabine binding assays were performed.
- Voltage jumps, ion concentration jumps, and blocker exposure were used to study charge movements and transport kinetics.
Main Results:
- Charge movements indicate that two Na+ ions bind to GAT1 even without GABA, and Cl- facilitates Na+ binding.
- The initial Na+-GAT1 interaction is a rate-limiting step at saturating GABA concentrations.
- High-affinity blockers and the W68L mutation trap Na+ on the transporter, hindering substrate release.
Conclusions:
- Efficient synaptic GABA removal by GAT1 depends on prior Na+ and Cl- binding.
- The conserved transmembrane domain 1 plays a critical role in interacting with permeant substrates and ions.