title: Crystal structure of a bacterial homologue of Na+/Cl--dependent neurotransmitter transporters.
abstract: Na+/Cl--dependent transporters terminate synaptic transmission by using electrochemical gradients to drive the uptake of neurotransmitters, including the biogenic amines, from the synapse to the cytoplasm of neurons and glia. These transporters are the targets of therapeutic and illicit compounds, and their dysfunction has been implicated in multiple diseases of the nervous system. Here we present the crystal structure of a bacterial homologue of these transporters from Aquifex aeolicus, in complex with its substrate, leucine, and two sodium ions. The protein core consists of the first ten of twelve transmembrane segments, with segments 1-5 related to 6-10 by a pseudo-two-fold axis in the membrane plane. Leucine and the sodium ions are bound within the protein core, halfway across the membrane bilayer, in an occluded site devoid of water. The leucine and ion binding sites are defined by partially unwound transmembrane helices, with main-chain atoms and helix dipoles having key roles in substrate and ion binding. The structure reveals the architecture of this important class of transporter, illuminates the determinants of substrate binding and ion selectivity, and defines the external and internal gates.
authors.affiliation: Department of Biochemistry and Molecular Biophysics and.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Yamashita
authors.forename: Satinder K
authors.initials: SK
authors.lastname: Singh
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Kawate
authors.forename: Yan
authors.initials: Y
authors.lastname: Jin
authors.forename: Eric
authors.initials: E
authors.lastname: Gouaux
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism*; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D007930:Leucine / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018377:Neurotransmitter Agents / Q000378:metabolism*; D016415:Sequence Alignment; D012964:Sodium / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014867:Water / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002712:Chlorides; D026901:Membrane Transport Proteins; D018377:Neurotransmitter Agents; D014867:Water; D012964:Sodium; D007930:Leucine