Excitatory amino acid transporters (EAATs) in the CNS maintain extracellular glutamate concentrations below excitotoxic levels and contribute to the clearance of glutamate released during neurotransmission. Over the previous grant period our laboratory identified and characterized five distinct human glutamate carrier subtypes, EAATs1-5. Transport of substrates by these carriers is thermodynamically coupled to the co-transport of two to three sodium ions, one proton, and the countertransport of a potassium ion; thus, this process is electrogenic. However, the amount of charge moved when substrates are applied is greater than would be predicted from the flux of coupled ions and substrate: we have also shown that this current elicited during substrate application arises from an uncoupled anion flux. Taking advantage of a highly functional cysteine-less version of EAAT1, we will continue to identify the structural and topological features required for substrate transport and ion permeation using cysteine substitutions together with sulfhydryl-modifying reagents. Studies will now begin to emphasize the electrophysiological analyses of currents associated with EAAT1 mutants using two electrode voltage clamp techniques in Xenopus oocytes. In addition, we will use two bacterial homologs of the mammalian EAATs as models for determining the structure of glutamate transporters with a view towards obtaining higher resolution structural information. Using high-resolution cryo-electron microscopic techniques we will image the bacterial carriers in lipid bilayers to determine gross structural features, including possible oligomeric state. Fluorescence and electron paramagnetic resonance (EPR) spectroscopy experiments will be used to refine structural models and analyze translocation-related conformational changes in purified bacterial carriers. The importance of understanding the structure, function, and regulation of different excitatory amino acid transporters is underscored by clinical and experimental studies, which have implicated abnormal transmitter reaccummulation in degenerative disorders such as ALS, Huntington's disease, ischemia-induced neurotoxicity, and Alzheimer's dementia.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS033273-08
Application #
6800512
Study Section
Special Emphasis Panel (ZRG1-MDCN-4 (01))
Program Officer
Stewart, Randall R
Project Start
1995-06-01
Project End
2006-08-31
Budget Start
2004-09-01
Budget End
2005-08-31
Support Year
8
Fiscal Year
2004
Total Cost
$211,613
Indirect Cost
Name
University of Pittsburgh
Department
Biology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Leighton, Barbara H; Seal, Rebecca P; Watts, Spencer D et al. (2006) Structural rearrangements at the translocation pore of the human glutamate transporter, EAAT1. J Biol Chem 281:29788-96
Shimamoto, Keiko; Sakai, Ryuichi; Takaoka, Kiyo et al. (2004) Characterization of novel L-threo-beta-benzyloxyaspartate derivatives, potent blockers of the glutamate transporters. Mol Pharmacol 65:1008-15
Cheng, Chialin; Glover, Greta; Banker, Gary et al. (2002) A novel sorting motif in the glutamate transporter excitatory amino acid transporter 3 directs its targeting in Madin-Darby canine kidney cells and hippocampal neurons. J Neurosci 22:10643-52
Leighton, Barbara H; Seal, Rebecca P; Shimamoto, Keiko et al. (2002) A hydrophobic domain in glutamate transporters forms an extracellular helix associated with the permeation pathway for substrates. J Biol Chem 277:29847-55
Shigeri, Y; Shimamoto, K; Yasuda-Kamatani, Y et al. (2001) Effects of threo-beta-hydroxyaspartate derivatives on excitatory amino acid transporters (EAAT4 and EAAT5). J Neurochem 79:297-302
Seal, R P; Leighton, B H; Amara, S G (2000) A model for the topology of excitatory amino acid transporters determined by the extracellular accessibility of substituted cysteines. Neuron 25:695-706
Fairman, W A; Sonders, M S; Murdoch, G H et al. (1998) Arachidonic acid elicits a substrate-gated proton current associated with the glutamate transporter EAAT4. Nat Neurosci 1:105-13
Eliasof, S; Arriza, J L; Leighton, B H et al. (1998) Excitatory amino acid transporters of the salamander retina: identification, localization, and function. J Neurosci 18:698-712
Seal, R P; Amara, S G (1998) A reentrant loop domain in the glutamate carrier EAAT1 participates in substrate binding and translocation. Neuron 21:1487-98
Eliasof, S; Arriza, J L; Leighton, B H et al. (1998) Localization and function of five glutamate transporters cloned from the salamander retina. Vision Res 38:1443-54

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