Functional Characterization of SdcF from Bacillus licheniformis, a Homolog of the SLC13 Na+/Dicarboxylate Transporters

The SdcF transporterfrom Bacillus licheniformis(gene BL02343) is a member of the divalent anion sodium symporter(DASS)/SLC13 family that includes Na+/dicarboxylate transportersfrom bacteria to humans. SdcF was functionally expressed in Escherichia coli (BL21) and assayed in right side out membrane vesicles. ScdF catalyzed the sodium-coupled transportof succinateand α-ketoglutarate. Succinate transportwas strongly inhibited by malate, fumarate, tartrate, oxaloacetate and l-aspartate. Similar to the other DASS transporters, succinate transportby SdcF was inhibited by anthranilic acids, N-(p-amylcinnamoyl) anthranilic acidand flufenamate. SdcF transportwas cation-dependent, with a K 0.5 for sodium of ~1.5 mM and a K 0.5 for Li+ of ~40 mM. Succinate transportkinetics by SdcF were sigmoidal, suggesting that SdcF may contain two cooperative substrate binding sites. The results support an ordered binding mechanism for SdcF in which sodium binds first and succinatebinds last. We conclude that SdcF is a secondary active transporterfor four- and five-carbon dicarboxylates that can use Na+ or Li+ as a driving cation.