title: A mechanism for intracellular release of Na+ by neurotransmitter/sodium symporters.
abstract: Neurotransmitter/sodium symporters (NSSs) terminate synaptic signal transmission by Na+-dependent reuptake of released neurotransmitters. Key conformational states have been reported for the bacterial homolog LeuT and an inhibitor-bound Drosophila dopamine transporter. However, a coherent mechanism of Na+-driven transport has not been described. Here, we present two crystal structures of MhsT, an NSS member from Bacillus halodurans, in occluded inward-facing states with bound Na+ ions and L-tryptophan, providing insight into the cytoplasmic release of Na+. The switch from outward- to inward-oriented states is centered on the partial unwinding of transmembrane helix 5, facilitated by a conserved GlyX9Pro motif that opens an intracellular pathway for water to access the Na2 site. We propose a mechanism, based on our structural and functional findings, in which solvation through the TM5 pathway facilitates Na+ release from Na2 and the transition to an inward-open state.
authors.affiliation: 1] Danish Research Institute of Translational Neuroscience (DANDRITE), Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark. [2] Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors.forename: Lina
authors.initials: L
authors.lastname: Malinauskaite
authors.affiliation: 1] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York, USA.
authors.forename: Matthias
authors.initials: M
authors.lastname: Quick
authors.affiliation: 1] Danish Research Institute of Translational Neuroscience (DANDRITE), Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark. [2] Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors.forename: Linda
authors.initials: L
authors.lastname: Reinhard
authors.affiliation: 1] Danish Research Institute of Translational Neuroscience (DANDRITE), Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark. [2] Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors.forename: Joseph A
authors.identifier: 0000000302184862
authors.initials: JA
authors.lastname: Lyons
authors.affiliation: Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Yano
authors.affiliation: 1] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York, USA. [4] Department of Pharmacology, Columbia University College of Physicians and Surgeons, New York, New York, USA.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Javitch
authors.affiliation: 1] Danish Research Institute of Translational Neuroscience (DANDRITE), Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Aarhus, Denmark. [2] Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors.forename: Poul
authors.identifier: 0000000309486628
authors.initials: P
authors.lastname: Nissen
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D001692:Biological Transport; D002414:Cations, Monovalent; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D015870:Gene Expression; D007700:Kinetics; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D012964:Sodium / Q000737:chemistry*; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D002414:Cations, Monovalent; D011994:Recombinant Proteins; D014364:Tryptophan; D012964:Sodium