Structure and Mechanism of an Amino Acid Antiporter

¹ State Key Laboratory of Bio-membrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China.; Center for Structural Biology, Department of Biological Sciences & Biotechnology, Tsinghua University, Beijing 100084, China.
² Center for Structural Biology, Department of Biological Sciences & Biotechnology, Tsinghua University, Beijing 100084, China.; School of Medicine, Tsinghua University, Beijing 100084, China.

These author contributed equally to this work.

Virulent enteric pathogens such as Escherichia coli strain O157:H7 rely on acid resistance (AR) systems to survive acidic environment in the stomach. A major component of AR is an arginine-dependent arginine:agmatine antiporter that expels intracellular protons. Here, we report the crystal structure of AdiC, the arginine:agmatine antiporter from E. coli O157:H7 and a member of the amino acid/polyamine/organocation (APC) superfamily of transporters at 3.6 Å resolution. The overall fold is similar to that of several Na⁺-coupled symporters. AdiC contains 12 transmembrane segments, forms a homodimer, and exists in an outward-facing, open conformation in the crystals. A conserved, acidic pocket opens to the periplasm. Structural and biochemical analysis reveals the essential ligand-binding residues, defines the transport route, and suggests a conserved mechanism for the antiporter activity.

^{来源：http://www.sciencemag.org/cgi/content/abstract/sci;1173654v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Structure+and+Mechanism+of+an+Amino+Acid+Antiporter&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT}