title: Structure and mechanism of an amino acid antiporter.
abstract: Virulent enteric pathogens such as Escherichia coli strain O157:H7 rely on acid-resistance (AR) systems to survive the 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 A 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.
authors.affiliation: State Key Laboratory of Bio-membrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Gao
authors.forename: Feiran
authors.initials: F
authors.lastname: Lu
authors.forename: Lijun
authors.initials: L
authors.lastname: Zhou
authors.forename: Shangyu
authors.initials: S
authors.lastname: Dang
authors.forename: Linfeng
authors.initials: L
authors.lastname: Sun
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Li
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
mesh_terms: D000376:Agmatine / Q000378:metabolism; D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017920:Antiporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D001120:Arginine / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019453:Escherichia coli O157 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation
chemical_list: C476528:AdiC protein, E coli; D026905:Amino Acid Transport Systems; D017920:Antiporters; D029968:Escherichia coli Proteins; D000376:Agmatine; D001120:Arginine