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Fig. 1. Sequence and topology of the sodium/proton exchanger, NHE3 from Aedes
aegypti. (A) Canonical translation of Aedes NHE3 (AF187723)
aligned with Anopheles NHE3 (AY170874) and their close relatives in
Drosophila, crab and vertebrates. DmNHE3a (AAF60313) refers to the
full-length Drosophila NHE3 homolog, whereas DmNHE3b (AY048581) and
DmNHE3c (AY128467) refer to possible splice variants identified by
high-throughput cDNA sequencing and by RT-PCR analysis, respectively.
Identical residues are shaded in red and conserved residues are boxed. DmNHE2
from the original annotation (Giannakou
and Dow, 2001) is here assigned to the NHE3 family.
AeNHE3 ORF is encoded by 21 exons; asterisks indicate the position of
introns. (B) Predicted transmembrane topology and potential phosphorylation
sites in AeNHE3. The positions of residues at the beginning and end
of predicted transmembrane helices are numbered. Putative phosphorylation
sites and ERK-D domains are given in green and blue, respectively. (C)
Comparison of amiloride binding sites in NHEs. A critical leucine (arrow)
within the pocket renders amiloride sensitivity to vertebrate NHE1, 2 and 4.
The corresponding residue in AeNHE3 is phenylalanine (F313).
Substitution of leucine to phenylalanine in vertebrate NHE1 and 2 removes the
amiloride sensitivity in these NHEs (see Discussion). Conserved residues are
shown in red whereas semi-conservative substitutions are back-shadowed in
blue. (D) Calcineurin B homologous protein (CHP) binding site is conserved in
insect NHE3. The conserved hydrophobic residues (green) are required for
efficient transport function of plasma membrane NHEs. Note that the shorter
AeNHE3 (AeNHE3-2.8kb) contains only half-site for CHP binding. Ae, Ag
and Hs refer to Aedes aegypti, Anopheles gambiae and human,
respectively. Accession numbers (GenBank; right) and amino acid positions
(left) are indicated.
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