Expression cloning and characterization of a novel sodium-dicarboxylate cotransporter from winter flounder kidney.
A cDNA coding for a Na+-dicarboxylate cotransporter, fNaDC-3, from winter flounder (Pseudopleuronectes americanus) kidney was isolated by functional expression in Xenopus laevis oocytes. The fNaDC-3 cDNA is 2384 nucleotides long and encodes a protein of 601 amino acids with a calculated molecular mass of 66.4 kDa. Secondary structure analysis predicts at least eight membrane-spanning domains. Transport of succinate by fNaDC-3 was sodium-dependent, could be inhibited by lithium, and evoked an inward current. The apparent affinity constant (Km) of fNaDC-3 for succinate of 30 microM resembles that of Na+-dicarboxylate transport in the basolateral membrane of mammalian renal proximal tubules. The substrates specific for the basolateral transporter, 2,3-dimethylsuccinate and cis-aconitate, not only inhibited succinate uptake but also evoked inward currents, proving that they are transported by fNaDC-3. Succinate transport via fNaDC-3 decreased by lowering pH, as did citrate transport, although much more moderately. These characteristics suggest that fNaDC-3 is a new type of Na+-dicarboxylate transporter that most likely corresponds to the Na+-dicarboxylate cotransporter in the basolateral membrane of mammalian renal proximal tubules.
Abteilung Nephrologie und Rheumatologie, Georg-August-Universität Göttingen, Robert-Koch-Strasse 40, D-37075 Göttingen, Germany. jsteffgen@veg-physiol.med.uni-goettingen.de
J
J
Steffgen
B C
BC
Burckhardt
C
C
Langenberg
L
L
Kühne
G A
GA
Müller
G
G
Burckhardt
N A
NA
Wolff
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D029382:Dicarboxylic Acid Transporters; D005432:Flounder; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D029363:Organic Anion Transporters, Sodium-Dependent; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D018076:DNA, Complementary; D029382:Dicarboxylic Acid Transporters; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; C092524:SLC13A2 protein, human; D027981:Symporters