title: Selective high-affinity transport of aspartate by a Drosophila homologue of the excitatory amino-acid transporters.
abstract: Excitatory amino-acid transporters (EAATs) are structurally related plasma membrane proteins that mediate the high-affinity uptake of the acidic amino acids glutamate and aspartate released at excitatory synapses, and maintain the extracellular concentrations of these neurotransmitters below excitotoxic levels [1] [2] [3] [4]. Several members of the EAAT family have been described previously. So far, all known EAATs have been reported to transport glutamate and aspartate with a similar affinity. Here, we report that dEAAT2 - a nervous tissue-specific EAAT homologue that we recently identified in the fruit fly Drosophila [5] - is a selective Na(+)-dependent high-affinity aspartate transporter (K(m) = 30 microM). We found that dEAAT2 can also transport L-glutamate but with a much lower affinity (K(m) = 185 microM) and a 10- to 15-fold lower relative efficacy (V(max)/K(m)). Competition experiments showed that the binding of glutamate to this transporter is much weaker than the binding of D- or L-aspartate. As dEAAT2 is the first known EAAT to show this substrate selectivity, it suggests that aspartate may play a specific role in the Drosophila nervous system.
authors.affiliation: Laboratoire de Neurobiologie Cellulaire et Fonctionnelle, CNRS, Marseille, F-13402, France.
authors.forename: M T
authors.initials: MT
authors.lastname: Besson
authors.forename: L
authors.initials: L
authors.lastname: Soustelle
authors.forename: S
authors.initials: S
authors.lastname: Birman
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D001692:Biological Transport; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism; D027342:Excitatory Amino Acid Transporter 2; D018698:Glutamic Acid / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D017981:Receptors, Neurotransmitter / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
chemical_list: D027342:Excitatory Amino Acid Transporter 2; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D018698:Glutamic Acid; D012964:Sodium; D011188:Potassium