title: Biophysical Approaches to the Study of LeuT, a Prokaryotic Homolog of Neurotransmitter Sodium Symporters.
abstract: Ion-coupled secondary transport is utilized by multiple integral membrane proteins as a means of achieving the thermodynamically unfavorable translocation of solute molecules across the lipid bilayer. The chemical nature of these molecules is diverse and includes sugars, amino acids, neurotransmitters, and other ions. LeuT is a sodium-coupled, nonpolar amino acid symporter and eubacterial member of the solute carrier 6 (SLC6) family of Na(+)/Cl(-)-dependent neurotransmitter transporters. Eukaryotic counterparts encompass the clinically and pharmacologically significant transporters for γ-aminobutyric acid (GABA), glycine, serotonin (5-hydroxytryptamine, 5-HT), dopamine (DA), and norepinephrine (NE). Since the crystal structure of LeuT was first solved in 2005, subsequent crystallographic, binding, flux, and spectroscopic studies, complemented with homology modeling and molecular dynamic simulations, have allowed this protein to emerge as a remarkable mechanistic paradigm for both the SLC6 class as well as several other sequence-unrelated SLCs whose members possess astonishingly similar architectures. Despite yielding groundbreaking conceptual advances, this vast treasure trove of data has also been the source of contentious hypotheses. This chapter will present a historical scientific overview of SLC6s; recount how the initial and subsequent LeuT structures were solved, describing the insights they each provided; detail the accompanying functional techniques, emphasizing how they either supported or refuted the static crystallographic data; and assemble these individual findings into a mechanism of transport and inhibition.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA. Electronic address: satinder.k.singh@yale.edu.
authors.forename: Satinder K
authors.initials: SK
authors.lastname: Singh
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Aritra
authors.initials: A
authors.lastname: Pal
mesh_terms: D001419:Bacteria / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D019295:Computational Biology / Q000379:methods; D003460:Crystallization / Q000379:methods; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D008958:Models, Molecular; D050480:Plasma Membrane Neurotransmitter Transport Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D001426:Bacterial Proteins; D050480:Plasma Membrane Neurotransmitter Transport Proteins
keywords: Alternating access; Antidepressant; Detergent; Electron paramagnetic resonance; Flux kinetics; Lipid bilayer; Membrane protein crystallography; Scintillation proximity assay; Single-molecule fluorescence resonance energy transfer; Sodium-dependent neurotransmitter transporter