title: Chloride binding site of neurotransmitter sodium symporters.
abstract: Neurotransmitter:sodium symporters (NSSs) play a critical role in signaling by reuptake of neurotransmitters. Eukaryotic NSSs are chloride-dependent, whereas prokaryotic NSS homologs like LeuT are chloride-independent but contain an acidic residue (Glu290 in LeuT) at a site where eukaryotic NSSs have a serine. The LeuT-E290S mutant displays chloride-dependent activity. We show that, in LeuT-E290S cocrystallized with bromide or chloride, the anion is coordinated by side chain hydroxyls from Tyr47, Ser290, and Thr254 and the side chain amide of Gln250. The bound anion and the nearby sodium ion in the Na1 site organize a connection between their coordinating residues and the extracellular gate of LeuT through a continuous H-bond network. The specific insights from the structures, combined with results from substrate binding studies and molecular dynamics simulations, reveal an anion-dependent occlusion mechanism for NSS and shed light on the functional role of chloride binding.
authors: Department of Molecular Biology and Genetics, Aarhus University, DK-8000 Aarhus C, Denmark.
authors: Adriana K
authors: AK
authors: Kantcheva
authors: Matthias
authors: M
authors: Quick
authors: Lei
authors: L
authors: Shi
authors: Anne-Marie Lund
authors: AM
authors: Winther
authors: Sebastian
authors: S
authors: Stolzenberg
authors: Harel
authors: H
authors: Weinstein
authors: Jonathan A
authors: JA
authors: Javitch
authors: Poul
authors: P
authors: Nissen
mesh_terms: D001419:Bacteria / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D001965:Bromides / Q000737:chemistry / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D050480:Plasma Membrane Neurotransmitter Transport Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001965:Bromides; D002712:Chlorides; D050480:Plasma Membrane Neurotransmitter Transport Proteins
keywords: SLC6; X-ray crystallography; antidepressant; membrane transport; psychostimulant
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