Electrogenic Steps Associated with Substrate Binding to the Neuronal Glutamate Transporter EAAC1

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Glutamate transporters facilitate glutamate uptake via sodium co-transport.
• The binding site's location suggests potential voltage dependence of glutamate binding.

Purpose of the Study:

• To investigate whether glutamate binding to transporters is electrogenic.
• To elucidate the role of transmembrane potential in glutamate transport.

Main Methods:

• Utilized photo-release of caged glutamate to rapidly apply it to cells expressing EAAC1.
• Employed electrophysiology to measure currents in wild-type and mutant (A334E) EAAC1 transporters.
• Performed electrostatic calculations to predict glutamate binding valence.

Main Results:

• Wild-type EAAC1 showed inward currents upon glutamate application, consistent with electrogenic uptake.
• Mutant EAAC1 (A334E) exhibited outward currents, indicating electrogenic binding of negatively charged glutamate.
• Results align with electrostatic predictions of a -0.27 valence for glutamate binding.
• The A334E mutation isolated electrogenic binding by inhibiting translocation/Na+ binding.

Conclusions:

• Glutamate binding to EAAC1 is an electrogenic process influenced by transmembrane potential.
• Electrogenic binding is a crucial factor in understanding voltage-dependent glutamate uptake and synaptic buffering.
• This finding necessitates re-evaluation of transporter models to include voltage-dependent binding steps.