The use of LeuT as a model in elucidating binding sites for substrates and inhibitors in neurotransmitter transporters

• Published in: Biochimica et biophysica acta Vol. 1850; no. 3; pp. 500 - 510
• Main Author: Loland, Claus J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2015
• Subjects: Allosteric site; Alternating access mechanism; Amino Acid Transport Systems - chemistry; Amino Acid Transport Systems - metabolism; Animals; Antidepressant; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Binding site; Binding Sites; biophysics; crystal structure; crystallization; Crystallography, X-Ray; dopamine; Drosophila melanogaster; fluorescence emission spectroscopy; Humans; illicit drugs; LeuT; ligands; mammals; Models, Molecular; nervous system diseases; neurons; neurotransmitters; norepinephrine; nuclear magnetic resonance spectroscopy; Plasma Membrane Neurotransmitter Transport Proteins - chemistry; Plasma Membrane Neurotransmitter Transport Proteins - metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; serotonin; Sodium Symporter; structure-activity relationships; symporters; synaptic transmission; X-radiation; Antidepressant; Binding site; LeuT; Allosteric site; Sodium Symporter; Alternating access mechanism
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2014.04.011

The mammalian neurotransmitter transporters are complex proteins playing a central role in synaptic transmission between neurons by rapid reuptake of neurotransmitters. The proteins which transport dopamine, noradrenaline and serotonin belong to the Neurotransmitter:Sodium Symporters (NSS). Due to their important role, dysfunctions are associated with several psychiatric and neurological diseases and they also serve as targets for a wide range of therapeutic and illicit drugs. Despite the central physiological and pharmacological importance, direct evidence on structure–function relationships on mammalian NSS proteins has so far been unsuccessful. The crystal structure of the bacterial NSS protein, LeuT, has been a turning point in structural investigations. To provide an update on what is known about the binding sites for substrates and inhibitors in the LeuT. The different binding modes and binding sites will be discussed with special emphasis on the possible existence of a second substrate binding site. It is the goal to give an insight into how investigations on ligand binding in LeuT have provided basic knowledge about transporter conformations and translocation mechanism which can pave the road for a deeper understanding of drug binding and function of the mammalian transporters. The LeuT is a suitable model for the structural investigation of NSS proteins including the possible location of drug binding sites. It is still debated whether the LeuT is a suitable model for the molecular mechanisms behind substrate translocation. Structure and functional aspects of NSS proteins are central for understanding synaptic transmission. With the purification and crystallization of LeuT as well as the dopamine transporter from Drosophila melanogaster, the application of biophysical methods such as fluorescence spectroscopy, neutron- or x-ray scattering and NMR for understanding its function becomes increasingly available. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins. •LeuT is a suitable model for exploring S1 substrate binding sites in NSS proteins.•The existence of the S2 binding site in LeuT for substrates is still debated.•LeuT is less suitable for exploring binding sites for inhibitors at mammalian NSS.•The allosteric binding site is for TCAs and SSRIs is also present in LeuT.