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Fig. 1. Twenty-one sequences in the Drosophila genome are homologous to
SLC6 transporters. (A) Schematic illustration of the structure SLC6
family transporters (based on the crystal structure of
Yamashita et al., 2005).
Transmembrane domains are represented by grey rectangles and are numbered
according to Yamashita et al., while intracellular and extracellular loops are
represented by a thick dark line. Many metazoan SLC6 transporters have large
N-terminal and C-terminal extensions, represented by a broken thick line, and
most metazoan SLC6 transporters have a 10-50 amino acid extracellular loop
between TM3 and TM4, indicated by a thick broken line. Conserved intracellular
domains are indicated by white rectangles, and conserved extracellular domains
are indicated by black rectangles. The arrows indicate the position of the
beta sheet conformation predicted by Yamashita et al. Members of the orphan
neurotransmitter subfamily have divergent extracellular loops between TM7 and
TM8, and between TM11 and TM12 (dotted lines). (B) Multiple sequence alignment
generated in ClustalX using 21 putative Drosophila SLC6 transporters
and the leucine transporter from Aquifex aeolicus, manually adjusted
to maximize comparison to the Aquifex aeolicus transporter. Protein
domains are annotated at the top of each sequence block, indicating
transmembrane (TM) regions, intracellular linker regions (IL), extracellular
linker regions (EL) alpha helical structure (
), and beta-sheets
(arrows); designation of the protein domains is based on the published
alignment of Yamashita et al., with minor changes. The names of each protein
sequence are on the left (see Table S1 in supplementary material for accession
numbers), asterisks are used to mark 10 amino acid intervals, and the residue
numbers are indicated at far right. Amino acid residues are shaded according
to the degree of conservation (black=100%, dark grey=80%, light grey=60%;
amino acids with similar chemical properties are considered equivalent for the
purposes of determining conserved residues). Gaps are represented by dashes
and residues removed from the alignment for space reasons are indicated by
numbers in parentheses. Selected residues that were considered important for
transporter function by Yamashita et al. are indicated by symbols at the
bottom of each sequence block (
, charged residues at extracellular and
cytoplasmic entrances; 
,
,
residues important for coordinating sodium ions 1 and 2, respectively) and
residues considered to be strictly conserved by Yamashita et al. are indicated
as `Invariant' on the bottom line of each sequence block to facilitate
comparison between alignments.
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