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

The SdcF transporter from Bacillus licheniformis (gene BL02343) is a member of the divalent anion sodium symporter (DASS)/SLC13 family that includes Na⁺/dicarboxylate transporters from bacteria to humans. SdcF was functionally expressed in Escherichia coli (BL21) and assayed in right side out membrane vesicles. ScdF catalyzed the sodium-coupled transport of succinate and α-ketoglutarate. Succinate transport was strongly inhibited by malate, fumarate, tartrate, oxaloacetate and l-aspartate. Similar to the other DASS transporters, succinate transport by SdcF was inhibited by anthranilic acids, N-(p-amylcinnamoyl) anthranilic acid and flufenamate. SdcF transport was cation-dependent, with a K _0.5 for sodium of ~1.5 mM and a K _0.5 for Li⁺ of ~40 mM. Succinate transport kinetics 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 succinate binds last. We conclude that SdcF is a secondary active transporter for four- and five-carbon dicarboxylates that can use Na⁺ or Li⁺ as a driving cation.