Structure and Mechanism of an Amino Acid Antiporter

Abstract

Antiporter Antics Bacteria that survive in the acidic environment of the stomach have mechanisms to maintain a high intracellular pH. In Escherichia coli , glutamate (Glu) and arginine (Arg) are decarboxylated intracellularly and the reaction products are exchanged with extracellular Glu and Arg. Gao et al. (p. 1565 , published online 28 May) now report a crystal structure of AdiC, an arginine:agmatine antiporter from E. coli . AdiC exhibits the same fold as that of the Na + -coupled symporters, including LeuT. It contains 12 transmembrane segments, forms a homodimer, and exists in an outward-facing, open conformation in the crystals. The structure, together with biochemical data, suggests how the antiporter senses the pH and responds to transport the reaction product agmatine out of the cell and Arg into the cell.