Functional characterization of a Na+-coupled dicarboxylate transporter from Bacillus licheniformis

The Na+-coupled dicarboxylate transporter, SdcL, from Bacillus licheniformis is a member of the divalent anion/Na+ symporter (DASS) family that includes the bacterial Na+/dicarboxylate cotransporter SdcS (from Staphyloccocus aureus) and the mammalian Na+/dicarboxylate cotransporters, NaDC1 and NaDC3. The transport properties of SdcL produced in Escherichia coli are similar to those of its prokaryotic and eukaryotic counterparts, involving the Na+-dependent transport of dicarboxylates such as succinate or malate across the cytoplasmic membrane with a Km of ∼ 6 μM. SdcL may also transport aspartate, α-ketoglutarate and oxaloacetate with low affinity. The cotransport of Na+ and dicarboxylate by SdcL has an apparent stoichiometry of 2:1, and a K0.5 for Na+ of 0.9 mM. Our findings represent the characterization of another prokaryotic protein of the DASS family with transport properties similar to its eukaryotic counterparts, but with a broader substrate specificity than other prokaryotic DASS family members. The broader range of substrates carried by SdcL may provide insight into domains of the protein that allow a more flexible or larger substrate binding pocket.