title: Mechanism of ammonia transport by Amt/MEP/Rh: structure of AmtB at 1.35 A.
abstract: The first structure of an ammonia channel from the Amt/MEP/Rh protein superfamily, determined to 1.35 angstrom resolution, shows it to be a channel that spans the membrane 11 times. Two structurally similar halves span the membrane with opposite polarity. Structures with and without ammonia or methyl ammonia show a vestibule that recruits NH4+/NH3, a binding site for NH4+, and a 20 angstrom-long hydrophobic channel that lowers the NH4+ pKa to below 6 and conducts NH3. Favorable interactions for NH3 are seen within the channel and use conserved histidines. Reconstitution of AmtB into vesicles shows that AmtB conducts uncharged NH3.
authors.affiliation: Department of Biochemistry and Biophysics, S412C Genentech Hall, University of California-San Francisco, 600 16th Street, San Francisco, CA 94143-2240, USA.
authors.forename: Shahram
authors.initials: S
authors.lastname: Khademi
authors.forename: Joseph
authors.initials: J
authors.lastname: O'Connell
authors.forename: Jonathan
authors.initials: J
authors.lastname: Remis
authors.forename: Yaneth
authors.initials: Y
authors.lastname: Robles-Colmenares
authors.forename: Larry J W
authors.initials: LJ
authors.lastname: Miercke
authors.forename: Robert M
authors.initials: RM
authors.lastname: Stroud
mesh_terms: D000595:Amino Acid Sequence; D000641:Ammonia / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008081:Liposomes; D008564:Membrane Potentials; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012204:Rh-Hr Blood-Group System / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D008081:Liposomes; D000644:Quaternary Ammonium Compounds; D012204:Rh-Hr Blood-Group System; D014867:Water; D000641:Ammonia