After their release by synapses the action of a number of neurotransmitters
is terminated by their high affinity sodium-dependent reuptake into
presynaptic terminals by specific transport proteins [1,2,3,4]. These proteins
are the target of psychomotor stimulants such as amphetamines or cocaine. All
these proteins belong to a family, known  as the sodium:neurotransmitter
symporter family (SNF), that also include some transporters that function
outside the brain and carry related molecules. The SNF family is currently
known to consist of transporters for:
βine (also transports GABA).
GABA (four different forms of GABA transporters have been characterized).
Haemophilus hypothetical proteins HI0736 and HI1690.
Methanococcus jannaschii hypothetical MJ1319.
These transporters are glycoproteins of about 600 to 700 amino-acid residues.
The two bacterial proteins are smaller (457 to 508 residues). These proteins
seem to contain 12 transmembrane domains and both termini are predicted to be
located in the cytoplasm.
As signature patterns for these proteins we have selected two highly conserved
regions. The first region spans the C-terminal part of the first transmembrane
domain, a short extracellular loop, and the N-terminal part of the second
transmembrane domain. The second region is located in the largest
extracellular loop between the third and fourth transmembrane domains; this
region contains two conserved cysteines that could be involved in disulfide
bonds. We also developed a profile for this family of proteins.
December 2004 / Patterns and text revised.
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