1. PINES, G., DANBOLT, N.C., BJORASS, M., ZHANG, Y.M., BENDAHAN, A., EIDE,
L., KOEPSELL, H., STORMMATHISEN, J., SEEBERG, E. AND KANNER, B.I.
Cloning and expression of a rat brain L-glutamate transporter.
NATURE 360 464-467 (1992).
2. KANAI, Y. AND HEDIGER, M.A.
Primary structure and functional characterization of a high affinity
NATURE 360 467-471 (1992).
3. TOLNER, B., POOLMAN, B. AND KONINGS, W.N.
Characterization and functional expression in Escherichia coli of the sodium
proton glutamate symport proteins of Bacillus stearothermophilus and Bacillus
MOL.MICROBIOL. 6(19) 2845-2856 (1992).
Synaptic transmission in vertebrates is thought to be terminated by
rapid transport of the neurotransmitter from the synaptic cleft into
presynaptic nerve terminals, or neuroglia, before it can reach neurotoxic
levels [1,2]. L-Glutamate, the main excitory transmitter in the brain,
is removed by a stereo-specific transporter that imports both sodium
ions and L-glutamate, and exports potassium ions : it is inhibited by
D-glutamate and high extracellular potassium ion concentration .
The structure of the transporter protein has been variously reported to
contain from 8 to 10 transmembrane (TM) regions, although 10 now seems to
be the accepted value. Abnormal neurotransmitter transport occurs in some
neurodegenerative diseases (anoxia and ischaemia), and this may reflect
problems with the transporter protein itself . Bacteria have several
different L-glutamate transport systems, one of which uses a protein
similar to the vertebrate brain L-glutamate transporter, greatest
conservation occurring in the TM regions . Both vertebrate brain and
bacterial L-glutamate transporters can also transport L-aspartate.
EDTRNSPORT is a 9-element fingerprint that provides a signature for the
glutamate-aspartate transporters. The fingerprint was derived from an
initial alignment of 3 sequences: motifs 1-6 encode the first six TM
regions, and motifs 7-9 encode the final three (TM domain 7 was not
sufficiently well-conserved to be included in the fingerprint) - motifs 3
and 7 include regions encoded by PROSITE patterns NA_DICARBOXYL_SYMP_1
(PS00713) and NA_DICARBOXYL_SYMP_2 (PS00714). Three iterations on OWL22.1
were required to reach convergence, at which point a true set comprising
10 sequences was identified. Three partial matches were also found,
DCTA_RHILE, DCTA_RHIME and DCTA_RHISN, which are members of the sodium
dicarboxylate symporter superfamily of which the glutamate-aspartate
transporters are members.
An update on SPTR37_9f identified a true set of 37 sequences, and 18