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Cell. 2015 Jan 29;160(3):542-53. doi: 10.1016/j.cell.2014.12.035.

Mechanisms of anion conduction by coupled glutamate transporters.

Author information

1
Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52428 Jülich, Germany; Institut für Neurophysiologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany; Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany. Electronic address: jan-philipp.machtens@gmx.de.
2
Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52428 Jülich, Germany.
3
Institut für Neurophysiologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany.
4
School of Engineering, Physics, and Mathematics and Division of Computational Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
5
Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
6
Institute of Complex Systems, Zelluläre Biophysik (ICS-4), Forschungszentrum Jülich, 52428 Jülich, Germany. Electronic address: c.fahlke@fz-juelich.de.

Abstract

Excitatory amino acid transporters (EAATs) are essential for terminating glutamatergic synaptic transmission. They are not only coupled glutamate/Na(+)/H(+)/K(+) transporters but also function as anion-selective channels. EAAT anion channels regulate neuronal excitability, and gain-of-function mutations in these proteins result in ataxia and epilepsy. We have combined molecular dynamics simulations with fluorescence spectroscopy of the prokaryotic homolog GltPh and patch-clamp recordings of mammalian EAATs to determine how these transporters conduct anions. Whereas outward- and inward-facing GltPh conformations are nonconductive, lateral movement of the glutamate transport domain from intermediate transporter conformations results in formation of an anion-selective conduction pathway. Fluorescence quenching of inserted tryptophan residues indicated the entry of anions into this pathway, and mutations of homologous pore-forming residues had analogous effects on GltPh simulations and EAAT2/EAAT4 measurements of single-channel currents and anion/cation selectivities. These findings provide a mechanistic framework of how neurotransmitter transporters can operate as anion-selective and ligand-gated ion channels.

PMID:
25635461
DOI:
10.1016/j.cell.2014.12.035
[Indexed for MEDLINE]
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