Structure, function, and genomic organization of human Na(+)-dependent high-affinity dicarboxylate transporter.
We have cloned and functionally characterized the human Na(+)-dependent high-affinity dicarboxylate transporter (hNaDC3) from placenta. The hNaDC3 cDNA codes for a protein of 602 amino acids with 12 transmembrane domains. When expressed in mammalian cells, the cloned transporter mediates the transport of succinate in the presence of Na(+) [concentration of substrate necessary for half-maximal transport (K(t)) for succinate = 20+/-1 microM]. Dimethylsuccinate also interacts with hNaDC3. The Na(+)-to-succinate stoichiometry is 3:1 and concentration of Na(+) necessary for half-maximal transport (K(Na(+))(0.5)) is 49+/-1 mM as determined by uptake studies with radiolabeled succinate. When expressed in Xenopus laevis oocytes, hNaDC3 induces Na(+)-dependent inward currents in the presence of succinate and dimethylsuccinate. At a membrane potential of -50 mV, K(Suc)(0.5) is 102+/-20 microM and K(Na(+))(0.5) is 22+/-4 mM as determined by the electrophysiological approach. Simultaneous measurements of succinate-evoked charge transfer and radiolabeled succinate uptake in hNaDC3-expressing oocytes indicate a charge-to-succinate ratio of 1:1 for the transport process, suggesting a Na(+)-to-succinate stoichiometry of 3:1. pH titration of citrate-induced currents shows that hNaDC3 accepts preferentially the divalent anionic form of citrate as a substrate. Li(+) inhibits succinate-induced currents in the presence of Na(+). Functional analysis of rat-human and human-rat NaDC3 chimeric transporters indicates that the catalytic domain of the transporter lies in the carboxy-terminal half of the protein. The human NaDC3 gene is located on chromosome 20q12-13.1, as evidenced by fluorescent in situ hybridization. The gene is >80 kbp long and consists of 13 exons and 12 introns.
Wang
H
H
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA.
Fei
Y J
YJ
Kekuda
R
R
Yang-Feng
T L
TL
Devoe
L D
LD
Leibach
F H
FH
Prasad
P D
PD
Ganapathy
V
V
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002874:Chromosome Mapping; D002890:Chromosomes, Human, Pair 20 / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D029382:Dicarboxylic Acid Transporters; D003998:Dicarboxylic Acids / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D018076:DNA, Complementary; D029382:Dicarboxylic Acid Transporters; D003998:Dicarboxylic Acids; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D011993:Recombinant Fusion Proteins; C092524:SLC13A2 protein, human; C490478:Slc13a2 protein, rat; D027981:Symporters; D012964:Sodium