The chloride permeation pathway of a glutamate transporter and its proximity to the glutamate translocation pathway.
Excitatory amino acid transporters (EAATs) regulate glutamate concentrations in the brain to maintain normal excitatory synaptic transmission. A widely accepted view of transporters is that they consist of a pore with alternating access to the intracellular and extracellular solutions, which serves to couple ion movement to the movement of substrate. However, recent observations that EAATs, and also a number of other neurotransmitter transporters, can also function as ligand-gated chloride channels have blurred the distinctions between transporters and ion channels. Here we show that mutations in the second transmembrane domain (TM2) of EAAT1 alter anion permeation properties without affecting glutamate transport and that a number of TM2 residues are accessible to the external aqueous solution. Furthermore, we demonstrate that the extracellular edge of TM2 is in close proximity to a membrane-associated domain that influences glutamate transport. This study will provide the foundation for beginning to understand how transporters can function as both transporters and ion channels.
Ryan
Renae M
RM
Department of Pharmacology, Institute for Biomedical Research, University of Sydney, Sydney, New South Wales 2006, Australia.
Mitrovic
Ann D
AD
Vandenberg
Robert J
RJ
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001692:Biological Transport; D002463:Cell Membrane Permeability / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D027341:Excitatory Amino Acid Transporter 1 / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D014982:Xenopus laevis
D002712:Chlorides; D027341:Excitatory Amino Acid Transporter 1; D010446:Peptide Fragments; D011994:Recombinant Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid