Nonsteroidal Anti-Inflammatory Drugs and Other Anthranilic Acids Inhibit the Na+/Dicarboxylate Symporter from Staphylococcus aureus

The Na+/dicarboxylate symporter from Staphylococcus aureus, named SdcS, is a member of the divalent anion sodium symporter (DASS) family that also includes the mammalian SLC13 Na+/dicarboxylate cotransporters, NaDC1 and NaCT. The mammalian members of the family are sensitive to inhibition by anthranilic acid derivatives such as N-(p-amylcinnamoyl)anthranilic acid (ACA), which act as slow inhibitors. This study shows that SdcS is inhibited by ACA as well as the fenamate nonsteroidal anti-inflammatory drugs, flufenamate and niflumate. The inhibition was rapid and reversible. The IC50 for ACA was approximately 55 mu M. Succinate kinetics by SdcS were sigmoidal, with a K-0.5 of 9 mu M and a Hill coefficient of 1.5. Addition of ACA decreased the V-max and increased the Hill coefficient without affecting the K-0.5, consistent with its activity as a negative modulator of SdcS activity. ACA inhibition was not correlated with the K-0.5 for succinate in SdcS mutants, and ACA did not affect the reactivity of the N108C mutant to the cysteine reagent, MTSET. We conclude that ACA and other anthranilic acid derivatives are effective allosteric inhibitors of SdcS. Furthermore, the mechanism of inhibition appears to be distinct from the mechanism observed in human NaDC1.