1
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Mena S, Cruikshank A, Best J, Nijhout HF, Reed MC, Hashemi P. Modulation of serotonin transporter expression by escitalopram under inflammation. Commun Biol 2024; 7:710. [PMID: 38851804 PMCID: PMC11162477 DOI: 10.1038/s42003-024-06240-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 04/24/2024] [Indexed: 06/10/2024] Open
Abstract
Selective serotonin reuptake inhibitors (SSRIs) are widely used for depression based on the monoamine deficiency hypothesis. However, the clinical use of these agents is controversial, in part because of their variable clinical efficacy and in part because of their delayed onset of action. Because of the complexities involved in replicating human disease and clinical dosing in animal models, the scientific community has not reached a consensus on the reasons for these phenomena. In this work, we create a theoretical hippocampal model incorporating escitalopram's pharmacokinetics, pharmacodynamics (competitive and non-competitive inhibition, and serotonin transporter (SERT) internalization), inflammation, and receptor dynamics. With this model, we simulate chronic oral escitalopram in mice showing that days to weeks are needed for serotonin levels to reach steady-state. We show escitalopram's chemical efficacy is diminished under inflammation. Our model thus offers mechanisms for how chronic escitalopram affects brain serotonin, emphasizing the importance of optimized dose and time for future antidepressant discoveries.
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Affiliation(s)
- Sergio Mena
- Department of Bioengineering, Imperial College London, London, SW7 2AZ, UK
| | | | - Janet Best
- Department of Mathematics, The Ohio State University, Columbus, OH, USA
| | - H F Nijhout
- Department of Biology, Duke University, Durham, NC, USA
| | - Michael C Reed
- Department of Mathematics, Duke University, Durham, NC, USA
| | - Parastoo Hashemi
- Department of Bioengineering, Imperial College London, London, SW7 2AZ, UK.
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2
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Nguyen H, Cheng MH, Lee JY, Aggarwal S, Mortensen OV, Bahar I. Allosteric modulation of serotonin and dopamine transporters: New insights from computations and experiments. Curr Res Physiol 2024; 7:100125. [PMID: 38836245 PMCID: PMC11148570 DOI: 10.1016/j.crphys.2024.100125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Revised: 03/13/2024] [Accepted: 03/14/2024] [Indexed: 06/06/2024] Open
Abstract
Human monoamine transporters (MATs) are critical to regulating monoaminergic neurotransmission by translocating their substrates from the synaptic space back into the presynaptic neurons. As such, their primary substrate binding site S1 has been targeted by a wide range of compounds for treating neuropsychiatric and neurodegenerative disorders including depression, ADHD, neuropathic pain, and anxiety disorders. We present here a comparative study of the structural dynamics and ligand-binding properties of two MATs, dopamine transporter (DAT) and serotonin transporter (SERT), with focus on the allosteric modulation of their transport function by drugs or substrates that consistently bind a secondary site S2, proposed to serve as an allosteric site. Our systematic analysis of the conformational space and dynamics of a dataset of 50 structures resolved for DAT and SERT in the presence of one or more ligands/drugs reveals the specific residues playing a consistent role in coordinating the small molecules bound to subsites S2-I and S2-II within S2, such as R476 and Y481 in dDAT and E494, P561, and F556 in hSERT. Further analysis reveals how DAT and SERT differ in their two principal modes of structural changes, PC1 and PC2. Notably, PC1 underlies the transition between outward- and inward-facing states of the transporters as well as their gating; whereas PC2 supports the rearrangements of TM helices near the S2 site. Finally, the examination of cross-correlations between structural elements lining the respective sites S1 and S2 point to the crucial role of coupled motions between TM6a and TM10. In particular, we note the involvement of hSERT residues F335 and G338, and E493-E494-T497 belonging to these two respective helices, in establishing the allosteric communication between S1 and S2. These results help understand the molecular basis of the action of drugs that bind to the S2 site of DAT or SERT. They also provide a basis for designing allosteric modulators that may provide better control of specific interactions and cellular pathways, rather than indiscriminately inhibiting the transporter by targeting its orthosteric site.
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Affiliation(s)
- Hoang Nguyen
- Laufer Center for Physical and Quantitative Biology and, USA
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY, 11794, USA
| | | | - Ji Young Lee
- Laufer Center for Physical and Quantitative Biology and, USA
| | - Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University School of Medicine, Philadelphia, PA, 19102, USA
| | - Ole Valente Mortensen
- Department of Pharmacology and Physiology, Drexel University School of Medicine, Philadelphia, PA, 19102, USA
| | - Ivet Bahar
- Laufer Center for Physical and Quantitative Biology and, USA
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY, 11794, USA
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3
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Salomon K, Abramyan AM, Plenge P, Wang L, Bundgaard C, Bang-Andersen B, Loland CJ, Shi L. Dynamic extracellular vestibule of human SERT: Unveiling druggable potential with high-affinity allosteric inhibitors. Proc Natl Acad Sci U S A 2023; 120:e2304089120. [PMID: 37792512 PMCID: PMC10576121 DOI: 10.1073/pnas.2304089120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 08/15/2023] [Indexed: 10/06/2023] Open
Abstract
The serotonin transporter (SERT) tightly regulates synaptic serotonin levels and has been the primary target of antidepressants. Binding of inhibitors to the allosteric site of human SERT (hSERT) impedes the dissociation of antidepressants bound at the central site and may enhance the efficacy of such antidepressants to potentially reduce their dosage and side effects. Here, we report the identification of a series of high-affinity allosteric inhibitors of hSERT in a unique scaffold, with the lead compound, Lu AF88273 (3-(1-(2-(1H-indol-3-yl)ethyl)piperidin-4-yl)-6-chloro-1H-indole), having 2.1 nM allosteric potency in inhibiting imipramine dissociation. In addition, we find that Lu AF88273 also inhibits serotonin transport in a noncompetitive manner. The binding pose of Lu AF88273 in the allosteric site of hSERT is determined with extensive molecular dynamics simulations and rigorous absolute binding free energy perturbation (FEP) calculations, which show that a part of the compound occupies a dynamically formed small cavity. The predicted binding location and pose are validated by site-directed mutagenesis and can explain much of the structure-activity relationship of these inhibitors using the relative binding FEP calculations. Together, our findings provide a promising lead compound and the structural basis for the development of allosteric drugs targeting hSERT. Further, they demonstrate that the divergent allosteric sites of neurotransmitter transporters can be selectively targeted.
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Affiliation(s)
- Kristine Salomon
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200Copenhagen N, Denmark
| | - Ara M. Abramyan
- Computational Chemistry and Molecular Biophysics Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse - Intramural Research Program, NIH, Baltimore, MD21224
- Schrödinger, Inc., San Diego, CA92121
| | - Per Plenge
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200Copenhagen N, Denmark
| | | | - Christoffer Bundgaard
- Medicinal Chemistry and Translational DMPK, H. Lundbeck A/S, DK-2500Copenhagen-Valby, Denmark
| | - Benny Bang-Andersen
- Medicinal Chemistry and Translational DMPK, H. Lundbeck A/S, DK-2500Copenhagen-Valby, Denmark
| | - Claus J. Loland
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200Copenhagen N, Denmark
| | - Lei Shi
- Computational Chemistry and Molecular Biophysics Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse - Intramural Research Program, NIH, Baltimore, MD21224
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4
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Niello M, Sideromenos S, Gradisch R, O´Shea R, Schwazer J, Maier J, Kastner N, Sandtner W, Jäntsch K, Lupica CR, Hoffman AF, Lubec G, Loland CJ, Stockner T, Pollak DD, Baumann MH, Sitte HH. Persistent binding at dopamine transporters determines sustained psychostimulant effects. Proc Natl Acad Sci U S A 2023; 120:e2114204120. [PMID: 36730201 PMCID: PMC9963675 DOI: 10.1073/pnas.2114204120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 12/28/2022] [Indexed: 02/03/2023] Open
Abstract
Psychostimulants interacting with the dopamine transporter (DAT) can be used illicitly or for the treatment of specific neuropsychiatric disorders. However, they can also produce severe and persistent adverse events. Often, their pharmacological properties in vitro do not fully correlate to their pharmacological profile in vivo. Here, we investigated the pharmacological effects of enantiomers of pyrovalerone, α-pyrrolidinovalerophenone, and 3,4-methylenedioxypyrovalerone as compared to the traditional psychostimulants cocaine and methylphenidate, using a variety of in vitro, computational, and in vivo approaches. We found that in vitro drug-binding kinetics at DAT correlate with the time-course of in vivo psychostimulant action in mice. In particular, a slow dissociation (i.e., slow koff) of S-enantiomers of pyrovalerone analogs from DAT predicts their more persistent in vivo effects when compared to cocaine and methylphenidate. Overall, our findings highlight the critical importance of drug-binding kinetics at DAT for determining the in vivo profile of effects produced by psychostimulant drugs.
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Affiliation(s)
- Marco Niello
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Spyridon Sideromenos
- Center for Physiology and Pharmacology, Department of Neurophysiology and Neuropharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Ralph Gradisch
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Ronan O´Shea
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Jakob Schwazer
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Julian Maier
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Nina Kastner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Walter Sandtner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Kathrin Jäntsch
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Carl R. Lupica
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Alexander F. Hoffman
- Electrophysiology Research Section, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Gert Lubec
- Department of Neuroproteomics, Paracelsus Medical University, 5020Salzburg, Austria
| | - Claus J. Loland
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200Copenhagen, Denmark
| | - Thomas Stockner
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Daniela D. Pollak
- Center for Physiology and Pharmacology, Department of Neurophysiology and Neuropharmacology, Medical University of Vienna, 1090Vienna, Austria
| | - Michael H. Baumann
- Designer Drug Research Unit, Intramural Research Program, National Institute on Drug Abuse, NIH, Baltimore, MD21224
| | - Harald H. Sitte
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, 1090Vienna, Austria
- AddRess, Center for Addiction Research and Science, Medical University of Vienna, 1090Vienna, Austria
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5
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Aggarwal S, Mortensen OV. Discovery and Development of Monoamine Transporter Ligands. ADVANCES IN NEUROBIOLOGY 2023; 30:101-129. [PMID: 36928847 PMCID: PMC10074400 DOI: 10.1007/978-3-031-21054-9_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
Monoamine transporters (MATs) are targets of a wide range of compounds that have been developed as therapeutic treatments for various neuropsychiatric and neurodegenerative disorders such as depression, ADHD, neuropathic pain, anxiety disorders, stimulant use disorders, epilepsy, and Parkinson's disease. The MAT family is comprised of three main members - the dopamine transporter (DAT), the norepinephrine transporter (NET), and the serotonin transporter (SERT). These transporters are through reuptake responsible for the clearance of their respective monoamine substrates from the extracellular space. The determination of X-ray crystal structures of MATs and their homologues bound with various substrates and ligands has resulted in a surge of structure-function-based studies of MATs to understand the molecular basis of transport function and the mechanism of various ligands that ultimately result in their behavioral effects. This review focusses on recent examples of ligand-based structure-activity relationship studies trying to overcome some of the challenges associated with previously developed MAT inhibitors. These studies have led to the discovery of unique and novel structurally diverse MAT ligands including allosteric modulators. These novel molecular scaffolds serve as leads for designing more effective therapeutic interventions by modulating the activities of MATs and ultimately their associated neurotransmission and behavioral effects.
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Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, USA.
| | - Ole Valente Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, USA.
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6
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Liu H, Wu Y, Li C, Tang Q, Zhang YW. Molecular docking and biochemical validation of (-)-syringaresinol-4-O-β-D-apiofuranosyl-(1→2)-β-D-glucopyranoside binding to an allosteric site in monoamine transporters. Front Pharmacol 2022; 13:1018473. [PMID: 36386236 PMCID: PMC9649612 DOI: 10.3389/fphar.2022.1018473] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 10/17/2022] [Indexed: 06/11/2024] Open
Abstract
Albizia julibrissin Durazz is one of the most common herbs used for depression and anxiety treatment, but its mechanism of action as an antidepressant or anxiolytic drug have not been fully understood. We previously isolated and identified one lignan glycoside compound from Albizia Julibrissin Durazz, (-)-syringaresinol-4-O-β-D-apiofuranosyl-(1→2)-β-D-glucopyranoside (SAG), that inhibited all three monoamine transporters with a mechanism of action different from that of the conventional antidepressants. In this study, we generated homology models for human dopamine transporter and human norepinephrine transporter, based on the X-ray structure of Drosophila dopamine transporter, and conducted the molecular docking of SAG to all three human monoamine transporters. Our computational results indicated that SAG binds to an allosteric site (S2) that has been demonstrated to be formed by an aromatic pocket positioned in the scaffold domain in the extracellular vestibule connected to the central site (S1) in these monoamine transporters. In addition, we demonstrated that SAG stabilizes a conformation of serotonin transporter with both the extracellular and cytoplasmic pathways closed. Furthermore, we performed mutagenesis of the residues in both the allosteric and orthosteric sites to biochemically validate SAG binding in all three monoamine transporters. Our results are consistent with the molecular docking calculation and support the association of SAG with the allosteric site. We expect that this herbal molecule could become a lead compound for the development of new therapeutic agents with a novel mechanism of action.
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Affiliation(s)
- Hanhe Liu
- School of Life Sciences, Guangzhou University, Guangzhou, China
| | - Yingyao Wu
- School of Life Sciences, Guangzhou University, Guangzhou, China
| | - Chan Li
- School of Life Sciences, Guangzhou University, Guangzhou, China
| | - Qingfa Tang
- School of Traditional Chinese Medicine, Southern Medical University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Chinese Medicine Pharmaceutics, Guangzhou, China
| | - Yuan-Wei Zhang
- School of Life Sciences, Guangzhou University, Guangzhou, China
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7
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Islas ÁA, Scior T. Allosteric Binding of MDMA to the Human Serotonin Transporter (hSERT) via Ensemble Binding Space Analysis with ΔG Calculations, Induced Fit Docking and Monte Carlo Simulations. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27092977. [PMID: 35566327 PMCID: PMC9099856 DOI: 10.3390/molecules27092977] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 04/13/2022] [Accepted: 04/14/2022] [Indexed: 11/16/2022]
Abstract
Despite the recent promising results of MDMA (3,4-methylenedioxy-methamphetamine) as a psychotherapeutic agent and its history of misuse, little is known about its molecular mode of action. MDMA enhances monoaminergic neurotransmission in the brain and its valuable psychoactive effects are associated to a dual action on the 5-HT transporter (SERT). This drug inhibits the reuptake of 5-HT (serotonin) and reverses its flow, acting as a substrate for the SERT, which possesses a central binding site (S1) for antidepressants as well as an allosteric (S2) one. Previously, we characterized the spatial binding requirements for MDMA at S1. Here, we propose a structure-based mechanistic model of MDMA occupation and translocation across both binding sites, applying ensemble binding space analyses, electrostatic complementarity, and Monte Carlo energy perturbation theory. Computed results were correlated with experimental data (r = 0.93 and 0.86 for S1 and S2, respectively). Simulations on all hSERT available structures with Gibbs free energy estimations (ΔG) revealed a favourable and pervasive dual binding mode for MDMA at S2, i.e., adopting either a 5-HT or an escitalopram-like orientation. Intermediate ligand conformations were identified within the allosteric site and between the two sites, outlining an internalization pathway for MDMA. Among the strongest and more frequent interactions were salt bridges with Glu494 and Asp328, a H-bond with Thr497, a π-π with Phe556, and a cation-π with Arg104. Similitudes and differences with the allosteric binding of 5-HT and antidepressants suggest that MDMA may have a distinctive chemotype. Thus, our models may provide a framework for future virtual screening studies and pharmaceutical design and to develop hSERT allosteric compounds with a unique psychoactive MDMA-like profile.
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Affiliation(s)
- Ángel A. Islas
- Vicerrectoría de Investigación y Estudios de Posgrado, Benemérita Universidad Autónoma de Puebla, Puebla 72592, Mexico
- Laboratory of Computational Molecular Simulations, Departamento de Farmacia, Benemérita Universidad Autónoma de Puebla, Puebla 72592, Mexico;
- Correspondence:
| | - Thomas Scior
- Laboratory of Computational Molecular Simulations, Departamento de Farmacia, Benemérita Universidad Autónoma de Puebla, Puebla 72592, Mexico;
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8
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Camicia F, Vaca HR, Guarnaschelli I, Koziol U, Mortensen OV, Fontana ACK. Molecular characterization of the serotonergic transporter from the cestode Echinococcus granulosus: pharmacology and potential role in the nervous system. Parasitol Res 2022; 121:1329-1343. [PMID: 35169884 PMCID: PMC9487190 DOI: 10.1007/s00436-022-07466-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 02/08/2022] [Indexed: 10/19/2022]
Abstract
Echinococcus granulosus, the etiological agent of human cystic echinococcosis (formerly known as hydatid disease), represents a serious worldwide public health problem with limited treatment options. The essential role played by the neuromuscular system in parasite survival and the relevance of serotonin (5-HT) in parasite movement and development make the serotonergic system an attractive source of drug targets. In this study, we cloned and sequenced a cDNA coding for the serotonin transporter from E. granulosus (EgSERT). Bioinformatic analyses suggest that EgSERT has twelve transmembrane domains with highly conserved ligand and ionic binding sites but a less conserved allosteric site compared with the human orthologue (HsSERT). Modeling studies also suggest a good degree of conservation of the overall structure compared with HsSERT. Functional and pharmacological studies performed on the cloned EgSERT confirm that this protein is indeed a serotonin transporter. EgSERT is specific for 5-HT and does not transport other neurotransmitters. Typical monoamine transport inhibitors also displayed inhibitory activities towards EgSERT, but with lower affinity than for the human SERT (HsSERT), suggesting a high divergence of the cestode transporter compared with HsSERT. In situ hybridization studies performed in the larval protoscolex stage suggest that EgSERT is located in discrete regions that are compatible with the major ganglia of the serotonergic nervous system. The pharmacological properties, the amino acidic substitutions at important functional regions compared with the HsSERT, and the putative role of EgSERT in the nervous system suggest that it could be an important target for pharmacological intervention.
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Affiliation(s)
- Federico Camicia
- Laboratorio de Toxinopatología, Centro de Patología Experimental y Aplicada, Facultad de Medicina, Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
| | - Hugo R Vaca
- Departamento de Microbiología, Parasitología e Inmunología, Facultad de Medicina, Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina.,Universidad de Buenos Aires (UBA), CONICET, Instituto de Investigaciones en Microbiología y Parasitología Médica (IMPaM), Ciudad Autónoma de Buenos Aires, Argentina
| | - Ines Guarnaschelli
- Sección Biología Celular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Uriel Koziol
- Sección Biología Celular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Andreia C K Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA.
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9
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Xue W, Fu T, Deng S, Yang F, Yang J, Zhu F. Molecular Mechanism for the Allosteric Inhibition of the Human Serotonin Transporter by Antidepressant Escitalopram. ACS Chem Neurosci 2022; 13:340-351. [PMID: 35041375 DOI: 10.1021/acschemneuro.1c00694] [Citation(s) in RCA: 67] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Human serotine transporter (hSERT) is one of the most influential drug targets, and its allosteric modulators (e.g., escitalopram) have emerged to be the next-generation medication for psychiatric disorders. However, the molecular mechanism underlying the allosteric modulation of hSERT is still elusive. Here, the simulation strategies of conventional (cMD) and steered (SMD) molecular dynamics were applied to investigate this molecular mechanism from distinct perspectives. First, cMD simulations revealed that escitalopram's binding to hSERT's allosteric site simultaneously enhanced its binding to the orthosteric site. Then, SMD simulation identified that the occupation of hSERT's allosteric site by escitalopram could also block its dissociation from the orthosteric site. Finally, by comparing the simulated structures of two hSERT-escitalopram complexes with and without allosteric modulation, a new conformational coupling between an extracellular (Arg104-Glu494) and an intracellular (Lys490-Glu494) salt bridge was identified. In summary, this study explored the mechanism underlying the allosteric modulation of hSERT by collectively applying two MD simulation strategies, which could facilitate our understanding of the allosteric modulations of not only hSERT but also other clinically important therapeutic targets.
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Affiliation(s)
- Weiwei Xue
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
- Central Nervous System Drug Key Laboratory of Sichuan Province, Luzhou 646000, China
| | - Tingting Fu
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
| | - Shengzhe Deng
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
| | - Fengyuan Yang
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
| | - Jingyi Yang
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
| | - Feng Zhu
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, Innovative Drug Research Center, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China
- College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China
- Innovation Institute for Artificial Intelligence in Medicine of Zhejiang University, Alibaba-Zhejiang University Joint Research Center of Future Digital Healthcare, Hangzhou 330110, China
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10
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Frangos ZJ, Cantwell Chater RP, Vandenberg RJ. Glycine Transporter 2: Mechanism and Allosteric Modulation. Front Mol Biosci 2021; 8:734427. [PMID: 34805268 PMCID: PMC8602798 DOI: 10.3389/fmolb.2021.734427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 10/25/2021] [Indexed: 01/19/2023] Open
Abstract
Neurotransmitter sodium symporters (NSS) are a subfamily of SLC6 transporters responsible for regulating neurotransmitter signalling. They are a major target for psychoactive substances including antidepressants and drugs of abuse, prompting substantial research into their modulation and structure-function dynamics. Recently, a series of allosteric transport inhibitors have been identified, which may reduce side effect profiles, compared to orthosteric inhibitors. Allosteric inhibitors are also likely to provide different clearance kinetics compared to competitive inhibitors and potentially better clinical outcomes. Crystal structures and homology models have identified several allosteric modulatory sites on NSS including the vestibule allosteric site (VAS), lipid allosteric site (LAS) and cholesterol binding site (CHOL1). Whilst the architecture of eukaryotic NSS is generally well conserved there are differences in regions that form the VAS, LAS, and CHOL1. Here, we describe ligand-protein interactions that stabilize binding in each allosteric site and explore how differences between transporters could be exploited to generate NSS specific compounds with an emphasis on GlyT2 modulation.
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Affiliation(s)
- Zachary J Frangos
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
| | - Ryan P Cantwell Chater
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
| | - Robert J Vandenberg
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
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11
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The antidepressant drug vilazodone is an allosteric inhibitor of the serotonin transporter. Nat Commun 2021; 12:5063. [PMID: 34417466 PMCID: PMC8379219 DOI: 10.1038/s41467-021-25363-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 08/05/2021] [Indexed: 12/12/2022] Open
Abstract
Depression is a common mental disorder. The standard medical treatment is the selective serotonin reuptake inhibitors (SSRIs). All characterized SSRIs are competitive inhibitors of the serotonin transporter (SERT). A non-competitive inhibitor may produce a more favorable therapeutic profile. Vilazodone is an antidepressant with limited information on its molecular interactions with SERT. Here we use molecular pharmacology and cryo-EM structural elucidation to characterize vilazodone binding to SERT. We find that it exhibits non-competitive inhibition of serotonin uptake and impedes dissociation of [3H]imipramine at low nanomolar concentrations. Our SERT structure with bound imipramine and vilazodone reveals a unique binding pocket for vilazodone, expanding the boundaries of the extracellular vestibule. Characterization of the binding site is substantiated with molecular dynamics simulations and systematic mutagenesis of interacting residues resulting in decreased vilazodone binding to the allosteric site. Our findings underline the versatility of SERT allosteric ligands and describe the unique binding characteristics of vilazodone. Vilazodone (VLZ) is a drug for the treatment of major depressive disorders that targets the serotonin transporter (SERT). Here, the authors combine pharmacology measurements and cryo-EM structural analysis to characterize VLZ binding to SERT and observe that VLZ exhibits non-competitive inhibition of serotonin transport and binds with nanomolar affinity to an allosteric site in SERT.
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12
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Elucidating the Mechanism Behind Sodium-Coupled Neurotransmitter Transporters by Reconstitution. Neurochem Res 2021; 47:127-137. [PMID: 34347265 DOI: 10.1007/s11064-021-03413-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 07/01/2021] [Accepted: 07/27/2021] [Indexed: 10/20/2022]
Abstract
Sodium-coupled neurotransmitter transporters play a fundamental role in the termination of synaptic neurotransmission, which makes them a major drug target. The reconstitution of these secondary active transporters into liposomes has shed light on their molecular transport mechanisms. From the earliest days of the reconstitution technique up to today's single-molecule studies, insights from live functioning transporters have been indispensable for our understanding of their physiological impact. The two classes of sodium-coupled neurotransmitter transporters, the neurotransmitter: sodium symporters and the excitatory amino acid transporters, have vastly different molecular structures, but complementary proteoliposome studies have sought to unravel their ion-dependence and transport kinetics. Furthermore, reconstitution experiments have been used on both protein classes to investigate the role of e.g. the lipid environment, of posttranslational modifications, and of specific amino acid residues in transport. Techniques that allow the detection of transport at a single-vesicle resolution have been developed, and single-molecule studies have started to reveal single transporter kinetics, which will expand our understanding of how transport across the membrane is facilitated at protein level. Here, we review a selection of the results and applications where the reconstitution of the two classes of neurotransmitter transporters has been instrumental.
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13
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Extracellular loops of the serotonin transporter act as a selectivity filter for drug binding. J Biol Chem 2021; 297:100863. [PMID: 34118233 PMCID: PMC8253976 DOI: 10.1016/j.jbc.2021.100863] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 06/04/2021] [Accepted: 06/07/2021] [Indexed: 11/24/2022] Open
Abstract
The serotonin transporter (SERT) shapes serotonergic neurotransmission by retrieving its eponymous substrate from the synaptic cleft. Ligands that discriminate between SERT and its close relative, the dopamine transporter DAT, differ in their association rate constant rather than their dissociation rate. The structural basis for this phenomenon is not known. Here we examined the hypothesis that the extracellular loops 2 (EL2) and 4 (EL4) limit access to the ligand-binding site of SERT. We employed an antibody directed against EL4 (residues 388–400) and the antibody fragments 8B6 scFv (directed against EL2 and EL4) and 15B8 Fab (directed against EL2) and analyzed their effects on the transport cycle of and inhibitor binding to SERT. Electrophysiological recordings showed that the EL4 antibody and 8B6 scFv impeded the initial substrate-induced transition from the outward to the inward-facing conformation but not the forward cycling mode of SERT. In contrast, binding of radiolabeled inhibitors to SERT was enhanced by either EL4- or EL2-directed antibodies. We confirmed this observation by determining the association and dissociation rate of the DAT-selective inhibitor methylphenidate via electrophysiological recordings; occupancy of EL2 with 15B8 Fab enhanced the affinity of SERT for methylphenidate by accelerating its binding. Based on these observations, we conclude that (i) EL4 undergoes a major movement during the transition from the outward to the inward-facing state, and (ii) EL2 and EL4 limit access of inhibitors to the binding of SERT, thus acting as a selectivity filter. This insight has repercussions for drug development.
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14
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Aggarwal S, Cheng MH, Salvino JM, Bahar I, Mortensen OV. Functional Characterization of the Dopaminergic Psychostimulant Sydnocarb as an Allosteric Modulator of the Human Dopamine Transporter. Biomedicines 2021; 9:634. [PMID: 34199621 PMCID: PMC8227285 DOI: 10.3390/biomedicines9060634] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 05/29/2021] [Accepted: 05/29/2021] [Indexed: 02/06/2023] Open
Abstract
The dopamine transporter (DAT) serves a critical role in controlling dopamine (DA)-mediated neurotransmission by regulating the clearance of DA from the synapse and extrasynaptic regions and thereby modulating DA action at postsynaptic DA receptors. Major drugs of abuse such as amphetamine and cocaine interact with DATs to alter their actions resulting in an enhancement in extracellular DA concentrations. We previously identified a novel allosteric site in the DAT and the related human serotonin transporter that lies outside the central orthosteric substrate- and cocaine-binding pocket. Here, we demonstrate that the dopaminergic psychostimulant sydnocarb is a ligand of this novel allosteric site. We identified the molecular determinants of the interaction between sydnocarb and DAT at the allosteric site using molecular dynamics simulations. Biochemical-substituted cysteine scanning accessibility experiments have supported the computational predictions by demonstrating the occurrence of specific interactions between sydnocarb and amino acids within the allosteric site. Functional dopamine uptake studies have further shown that sydnocarb is a noncompetitive inhibitor of DAT in accord with the involvement of a site different from the orthosteric site in binding this psychostimulant. Finally, DA uptake studies also demonstrate that sydnocarb affects the interaction of DAT with both cocaine and amphetamine. In summary, these studies further strengthen the prospect that allosteric modulation of DAT activity could have therapeutic potential.
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Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA;
| | - Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.H.C.); (I.B.)
| | | | - Ivet Bahar
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.H.C.); (I.B.)
| | - Ole Valente Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA;
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15
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Pidathala S, Mallela AK, Joseph D, Penmatsa A. Structural basis of norepinephrine recognition and transport inhibition in neurotransmitter transporters. Nat Commun 2021; 12:2199. [PMID: 33850134 PMCID: PMC8044178 DOI: 10.1038/s41467-021-22385-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 03/01/2021] [Indexed: 12/23/2022] Open
Abstract
Norepinephrine is a biogenic amine neurotransmitter that has widespread effects on alertness, arousal and pain sensation. Consequently, blockers of norepinephrine uptake have served as vital tools to treat depression and chronic pain. Here, we employ the Drosophila melanogaster dopamine transporter as a surrogate for the norepinephrine transporter and determine X-ray structures of the transporter in its substrate-free and norepinephrine-bound forms. We also report structures of the transporter in complex with inhibitors of chronic pain including duloxetine, milnacipran and a synthetic opioid, tramadol. When compared to dopamine, we observe that norepinephrine binds in a different pose, in the vicinity of subsite C within the primary binding site. Our experiments reveal that this region is the binding site for chronic pain inhibitors and a determinant for norepinephrine-specific reuptake inhibition, thereby providing a paradigm for the design of specific inhibitors for catecholamine neurotransmitter transporters.
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Affiliation(s)
| | | | - Deepthi Joseph
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Aravind Penmatsa
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
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16
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Niello M, Gradisch R, Loland CJ, Stockner T, Sitte HH. Allosteric Modulation of Neurotransmitter Transporters as a Therapeutic Strategy. Trends Pharmacol Sci 2020; 41:446-463. [PMID: 32471654 PMCID: PMC7610661 DOI: 10.1016/j.tips.2020.04.006] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Revised: 04/21/2020] [Accepted: 04/22/2020] [Indexed: 12/11/2022]
Abstract
Neurotransmitter transporters (NTTs) are involved in the fine-tuning of brain neurotransmitter homeostasis. As such, they are implicated in a plethora of complex behaviors, including reward, movement, and cognition. During recent decades, compounds that modulate NTT functions have been developed. Some of them are in clinical use for the management of different neuropsychiatric conditions. The majority of these compounds have been found to selectively interact with the orthosteric site of NTTs. Recently, diverse allosteric sites have been described in a number of NTTs, modulating their function. A more complex NTT pharmacology may be useful in the development of novel therapeutics. Here, we summarize current knowledge on such modulatory allosteric sites, with specific focus on their pharmacological and therapeutic potential.
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Affiliation(s)
- Marco Niello
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ralph Gradisch
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Claus Juul Loland
- Laboratory for Membrane Protein Dynamics. Department of Neuroscience. University of Copenhagen, Copenhagen, Denmark
| | - Thomas Stockner
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Harald H Sitte
- Centre for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria; AddRess, Centre for Addiction Research and Science, Medical University of Vienna, Vienna, Austria.
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17
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Xue W, Fu T, Zheng G, Tu G, Zhang Y, Yang F, Tao L, Yao L, Zhu F. Recent Advances and Challenges of the Drugs Acting on Monoamine Transporters. Curr Med Chem 2020; 27:3830-3876. [DOI: 10.2174/0929867325666181009123218] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/03/2018] [Indexed: 01/06/2023]
Abstract
Background:
The human Monoamine Transporters (hMATs), primarily including hSERT,
hNET and hDAT, are important targets for the treatment of depression and other behavioral disorders
with more than the availability of 30 approved drugs.
Objective:
This paper is to review the recent progress in the binding mode and inhibitory mechanism of
hMATs inhibitors with the central or allosteric binding sites, for the benefit of future hMATs inhibitor
design and discovery. The Structure-Activity Relationship (SAR) and the selectivity for hit/lead compounds
to hMATs that are evaluated by in vitro and in vivo experiments will be highlighted.
Methods:
PubMed and Web of Science databases were searched for protein-ligand interaction, novel
inhibitors design and synthesis studies related to hMATs.
Results:
Literature data indicate that since the first crystal structure determinations of the homologous
bacterial Leucine Transporter (LeuT) complexed with clomipramine, a sizable database of over 100 experimental
structures or computational models has been accumulated that now defines a substantial degree
of structural variability hMATs-ligands recognition. In the meanwhile, a number of novel hMATs
inhibitors have been discovered by medicinal chemistry with significant help from computational models.
Conclusion:
The reported new compounds act on hMATs as well as the structures of the transporters
complexed with diverse ligands by either experiment or computational modeling have shed light on the
poly-pharmacology, multimodal and allosteric regulation of the drugs to transporters. All of the studies
will greatly promote the Structure-Based Drug Design (SBDD) of structurally novel scaffolds with high
activity and selectivity for hMATs.
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Affiliation(s)
- Weiwei Xue
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Tingting Fu
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Guoxun Zheng
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Gao Tu
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Yang Zhang
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Fengyuan Yang
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
| | - Lin Tao
- Key Laboratory of Elemene Class Anti-cancer Chinese Medicine of Zhejiang Province, School of Medicine, Hangzhou Normal University, Hangzhou 310036, China
| | - Lixia Yao
- Department of Health Sciences Research, Mayo Clinic, Rochester, MN 55905, United States
| | - Feng Zhu
- Innovative Drug Research and Bioinformatics Group, School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, China
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18
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Zhu R, Sandtner W, Ahiable JEA, Newman AH, Freissmuth M, Sitte HH, Hinterdorfer P. Allosterically Linked Binding Sites in Serotonin Transporter Revealed by Single Molecule Force Spectroscopy. Front Mol Biosci 2020; 7:99. [PMID: 32656227 PMCID: PMC7325972 DOI: 10.3389/fmolb.2020.00099] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 05/01/2020] [Indexed: 01/24/2023] Open
Abstract
Crystal structures and experiments relying on the tools of molecular pharmacology reported conflicting results on ligand binding sites in neurotransmitter/sodium symporters (NSS). We explored the number and functionality of ligand binding sites of NSS in a physiological setting by designing novel tools for atomic force microscopy (AFM). These allow for directly measuring the interaction forces between the serotonin transporter (SERT) and the antidepressant S-citalopram (S-CIT) on the single molecule level: the AFM cantilever tips were functionalized with S-CIT via a flexible polyethylene glycol (PEG) linker. The tip chemistry was validated by specific force measurements and recognition imaging on CHO cells. Two distinct populations of characteristic binding strengths of S-CIT binding to SERT were revealed in Na+-containing buffer. In contrast, in Li+-containing buffer, SERT showed only low force interactions. Conversely, the vestibular mutant SERT-G402H merely displayed the high force population. These observations provide physical evidence for the existence of two binding sites in SERT. The dissociation rate constant of both binding sites was extracted by varying the dynamics of the force-probing experiments. Competition experiments revealed that the two sites are allosterically coupled and exert reciprocal modulation.
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Affiliation(s)
- Rong Zhu
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Walter Sandtner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Joan E A Ahiable
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Amy Hauck Newman
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, Intramural Research Program, Baltimore, MD, United States
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Harald H Sitte
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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19
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Cheng B, Morstein J, Ladefoged LK, Maesen JB, Schiøtt B, Sinning S, Trauner D. A Photoswitchable Inhibitor of the Human Serotonin Transporter. ACS Chem Neurosci 2020; 11:1231-1237. [PMID: 32275382 DOI: 10.1021/acschemneuro.9b00521] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The human serotonin transporter (hSERT) terminates serotonergic signaling through reuptake of neurotransmitter into presynaptic neurons and is a target for many antidepressant drugs. We describe here the development of a photoswitchable hSERT inhibitor, termed azo-escitalopram, that can be reversibly switched between trans and cis configurations using light of different wavelengths. The dark-adapted trans isomer was found to be significantly less active than the cis isomer, formed upon irradiation.
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Affiliation(s)
- Bichu Cheng
- School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
| | - Johannes Morstein
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
| | - Lucy Kate Ladefoged
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
| | - Jannick Bang Maesen
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200 Aarhus N, Denmark
| | - Birgit Schiøtt
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
| | - Steffen Sinning
- Department of Forensic Medicine, Aarhus University, Palle Juul-Jensens Boulevard 99, 8200 Aarhus N, Denmark
| | - Dirk Trauner
- Department of Chemistry, New York University, 100 Washington Square East, New York, New York 10003, United States
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20
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The mechanism of a high-affinity allosteric inhibitor of the serotonin transporter. Nat Commun 2020; 11:1491. [PMID: 32198394 PMCID: PMC7083837 DOI: 10.1038/s41467-020-15292-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 02/24/2020] [Indexed: 11/08/2022] Open
Abstract
The serotonin transporter (SERT) terminates serotonin signaling by rapid presynaptic reuptake. SERT activity is modulated by antidepressants, e.g., S-citalopram and imipramine, to alleviate symptoms of depression and anxiety. SERT crystal structures reveal two S-citalopram binding pockets in the central binding (S1) site and the extracellular vestibule (S2 site). In this study, our combined in vitro and in silico analysis indicates that the bound S-citalopram or imipramine in S1 is allosterically coupled to the ligand binding to S2 through altering protein conformations. Remarkably, SERT inhibitor Lu AF60097, the first high-affinity S2-ligand reported and characterized here, allosterically couples the ligand binding to S1 through a similar mechanism. The SERT inhibition by Lu AF60097 is demonstrated by the potentiated imipramine binding and increased hippocampal serotonin level in rats. Together, we reveal a S1-S2 coupling mechanism that will facilitate rational design of high-affinity SERT allosteric inhibitors.
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21
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Monoamine transporters: structure, intrinsic dynamics and allosteric regulation. Nat Struct Mol Biol 2019; 26:545-556. [PMID: 31270469 DOI: 10.1038/s41594-019-0253-7] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Accepted: 05/14/2019] [Indexed: 12/31/2022]
Abstract
Monoamine transporters (MATs) regulate neurotransmission via the reuptake of dopamine, serotonin and norepinephrine from extra-neuronal regions and thus maintain neurotransmitter homeostasis. As targets of a wide range of compounds, including antidepressants, substances of abuse and drugs for neuropsychiatric and neurodegenerative disorders, their mechanism of action and their modulation by small molecules have long been of broad interest. Recent advances in the structural characterization of dopamine and serotonin transporters have opened the way for structure-based modeling and simulations, which, together with experimental data, now provide mechanistic understanding of their transport function and interactions. Here we review recent progress in the elucidation of the structural dynamics of MATs and their conformational landscape and transitions, as well as allosteric regulation mechanisms.
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22
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Schumann-Gillett A, Blyth MT, O’Mara ML. Is protein structure enough? A review of the role of lipids in SLC6 transporter function. Neurosci Lett 2019; 700:64-69. [DOI: 10.1016/j.neulet.2018.05.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 05/09/2018] [Accepted: 05/11/2018] [Indexed: 12/17/2022]
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23
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Niello M, Cintulova D, Hellsberg E, Jäntsch K, Holy M, Ayatollahi LH, Cozzi NV, Freissmuth M, Sandtner W, Ecker GF, Mihovilovic MD, Sitte HH. para-Trifluoromethyl-methcathinone is an allosteric modulator of the serotonin transporter. Neuropharmacology 2019; 161:107615. [PMID: 31028773 DOI: 10.1016/j.neuropharm.2019.04.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 04/17/2019] [Accepted: 04/19/2019] [Indexed: 11/15/2022]
Abstract
The transporters for dopamine (DAT) and serotonin (SERT) are important targets in the treatment of psychiatric disorders including major depression, anxiety and attention-deficit hyperactivity disorder. Drugs acting at these transporters can act as inhibitors or as releasers. In addition, it has been recently appreciated that some compounds are less efficacious releasers than amphetamine. Thus, they are classified as partial releasers. Compounds can act on both SERT and DAT or display exquisite selectivity for either SERT or DAT, but the structural basis for selectivity is poorly understood. The trifluoromethyl-substitution of methcathinone in the para-position has been shown to dramatically shift the selectivity of methcathinone (MCAT) towards SERT. Here, we examined MCAT, para-trifluoromethyl-methcathinone (pCF3MCAT) and other analogues to understand (i) the determinants of selectivity and (ii) the effects of the para-CF3-substitution of MCAT on the transport cycle. We systematically tested different para-substituted MCATs by biochemical, computational and electrophysiological approaches: addition of the pCF3group, but not of other substituents with larger van der Waal's volume, lipophilicity or polarity, converted the DAT-selective MCAT into a SERT-selective partial releaser. Electrophysiological and superfusion experiments, together with kinetic modelling, showed that pCF3MCAT, but not MCAT, trapped a fraction of SERTs in an inactive state by occupying the S2-site. These findings define a new mechanism of action for partial releasers, which is distinct from the other two known binding modes underlying partial release. Our observations highlight the fact that the substrate permeation pathway of monoamine transporters supports multiple binding modes, which can be exploited for drug design. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Affiliation(s)
- Marco Niello
- Institute of Pharmacology, Medical University, Vienna, Austria
| | | | - Eva Hellsberg
- Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | - Kathrin Jäntsch
- Institute of Pharmacology, Medical University, Vienna, Austria
| | - Marion Holy
- Institute of Pharmacology, Medical University, Vienna, Austria
| | | | - Nicholas V Cozzi
- Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, USA
| | | | - Walter Sandtner
- Institute of Pharmacology, Medical University, Vienna, Austria
| | - Gerhard F Ecker
- Department of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | | | - Harald H Sitte
- Institute of Pharmacology, Medical University, Vienna, Austria.
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24
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Möller IR, Slivacka M, Nielsen AK, Rasmussen SGF, Gether U, Loland CJ, Rand KD. Conformational dynamics of the human serotonin transporter during substrate and drug binding. Nat Commun 2019; 10:1687. [PMID: 30976000 PMCID: PMC6459873 DOI: 10.1038/s41467-019-09675-z] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 03/22/2019] [Indexed: 12/24/2022] Open
Abstract
The serotonin transporter (SERT), a member of the neurotransmitter:sodium symporter family, is responsible for termination of serotonergic signaling by re-uptake of serotonin (5-HT) into the presynaptic neuron. Its key role in synaptic transmission makes it a major drug target, e.g. for the treatment of depression, anxiety and post-traumatic stress. Here, we apply hydrogen-deuterium exchange mass spectrometry to probe the conformational dynamics of human SERT in the absence and presence of known substrates and targeted drugs. Our results reveal significant changes in dynamics in regions TM1, EL3, EL4, and TM12 upon binding co-transported ions (Na+/K+) and ligand-mediated changes in TM1, EL3 and EL4 upon binding 5-HT, the drugs S-citalopram, cocaine and ibogaine. Our results provide a comprehensive direct view of the conformational response of SERT upon binding both biologically relevant substrate/ions and ligands of pharmaceutical interest, thus advancing our understanding of the structure-function relationship in SERT.
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Affiliation(s)
- Ingvar R Möller
- Protein Analysis Group, Department of Pharmacy, University of Copenhagen, Copenhagen, 2100, Denmark
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark
| | - Marika Slivacka
- Protein Analysis Group, Department of Pharmacy, University of Copenhagen, Copenhagen, 2100, Denmark
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark
| | - Anne Kathrine Nielsen
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark
| | - Søren G F Rasmussen
- Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark
| | - Ulrik Gether
- Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark
| | - Claus J Loland
- Laboratory for Membrane Protein Dynamics, Department of Neuroscience, University of Copenhagen, Copenhagen, 2200, Denmark.
| | - Kasper D Rand
- Protein Analysis Group, Department of Pharmacy, University of Copenhagen, Copenhagen, 2100, Denmark.
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25
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Navratna V, Gouaux E. Insights into the mechanism and pharmacology of neurotransmitter sodium symporters. Curr Opin Struct Biol 2019; 54:161-170. [PMID: 30921707 DOI: 10.1016/j.sbi.2019.03.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 03/07/2019] [Accepted: 03/08/2019] [Indexed: 12/17/2022]
Abstract
Neurotransmitter sodium symporters (NSS) belong to the SLC6 family of solute carriers and play an essential role in neurotransmitter homeostasis throughout the body. In the past decade, structural studies employing bacterial orthologs of NSSs have provided insight into the mechanism of neurotransmitter transport. While the overall architecture of SLC6 transporters is conserved among species, in comparison to the bacterial homologs, the eukaryotic SLC6 family members harbor differences in amino acid sequence and molecular structure, which underpins their functional and pharmacological diversity, as well as their ligand specificity. Here, we review the structures and mechanisms of eukaryotic NSSs, focusing on the molecular basis for ligand recognition and on transport mechanism.
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Affiliation(s)
- Vikas Navratna
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Eric Gouaux
- Vollum Institute, Oregon Health & Science University, Portland, OR, United States; Howard Hughes Medical Institute, Oregon Health & Science University, Portland, OR, United States.
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26
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Substrate and inhibitor binding to the serotonin transporter: Insights from computational, crystallographic, and functional studies. Neuropharmacology 2019; 161:107548. [PMID: 30807752 DOI: 10.1016/j.neuropharm.2019.02.030] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 02/19/2019] [Accepted: 02/22/2019] [Indexed: 02/02/2023]
Abstract
The serotonin transporter (SERT) belongs to the monoamine transporter family, which also includes the dopamine and norepinephrine transporters. SERT is essential for regulating serotonergic signaling by the reuptake of serotonin from the synaptic cleft back into the presynaptic neuron. Dysregulation of SERT has been implicated in several major psychiatric disorders such as major depressive disorder (MDD). MDD was among the top five leading causes of years lived with disease in 2016 and is characterized as a major global burden. Several drugs have been developed to target SERT for use in the treatment of MDD, and their respective binding modes and locations within SERT have been studied. The elucidation of the first structure of a bacterial SERT homologue in 2005 has accelerated crystallographic, computational, and functional studies to further elucidate drug binding and method of action in SERT. Herein, we aim to highlight and compare these studies with an emphasis on what the different experimental methods conclude on substrate and inhibitor binding modes, and the potential caveats of using the different types of studies are discussed. We focus this review on the binding of cognate substrate and drugs belonging to the different families of antidepressants, including tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and multimodal drugs, as well as illicit drugs such as cocaine, amphetamines, and ibogaine. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Yarravarapu N, Geffert L, Surratt CK, Cascio M, Lapinsky DJ. Clickable photoaffinity ligands for the human serotonin transporter based on the selective serotonin reuptake inhibitor (S)-citalopram. Bioorg Med Chem Lett 2018; 28:3431-3435. [PMID: 30266542 DOI: 10.1016/j.bmcl.2018.09.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 09/20/2018] [Accepted: 09/22/2018] [Indexed: 12/16/2022]
Abstract
To date, the development of photoaffinity ligands targeting the human serotonin transporter (hSERT), a key protein involved in disease states such as depression and anxiety, have been radioisotope-based (i.e., 3H or 125I). This letter instead highlights three derivatives of the selective serotonin reuptake inhibitor (SSRI) (S)-citalopram that were rationally designed and synthesized to contain a photoreactive benzophenone or an aryl azide for protein target capture via photoaffinity labeling and a terminal alkyne or an aliphatic azide for click chemistry-based proteomics. Specifically, clickable benzophenone-based (S)-citalopram photoprobe 6 (hSERT Ki = 0.16 nM) displayed 11-fold higher binding affinity at hSERT when compared to (S)-citalopram (hSERT Ki = 1.77 nM), and was subsequently shown to successfully undergo tandem photoaffinity labeling-biorthogonal conjugation using purified hSERT. Given clickable photoprobes can be used for various applications depending on which reporter is attached by click chemistry subsequent to photoaffinity labeling, photoprobe 6 is expected to find value in structure-function studies and other research applications involving hSERT (e.g., imaging).
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Affiliation(s)
- Nageswari Yarravarapu
- Graduate School of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States
| | - Laura Geffert
- Graduate School of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States
| | - Christopher K Surratt
- Graduate School of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States
| | - Michael Cascio
- Bayer School of Natural and Environmental Sciences, Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States
| | - David J Lapinsky
- Graduate School of Pharmaceutical Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States.
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28
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Tomlinson MJ, Krout D, Pramod AB, Lever JR, Newman AH, Henry LK, Vaughan RA. Identification of the benztropine analog [ 125I]GA II 34 binding site on the human dopamine transporter. Neurochem Int 2018; 123:34-45. [PMID: 30125594 DOI: 10.1016/j.neuint.2018.08.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 08/10/2018] [Accepted: 08/14/2018] [Indexed: 12/21/2022]
Abstract
The dopamine transporter (DAT) is a neuronal membrane protein that is responsible for reuptake of dopamine (DA) from the synapse and functions as a major determinant in control of DA neurotransmission. Cocaine and many psychostimulant drugs bind to DAT and block reuptake, inducing DA overflow that forms the neurochemical basis for euphoria and addiction. Paradoxically, however, some ligands such as benztropine (BZT) bind to DAT and inhibit reuptake but do not produce these effects, and it has been hypothesized that differential mechanisms of binding may stabilize specific transporter conformations that affect downstream neurochemical or behavioral outcomes. To investigate the binding mechanisms of BZT on DAT we used the photoaffinity BZT analog [125I]N-[n-butyl-4-(4‴-azido-3‴-iodophenyl)]-4',4″-difluoro-3α-(diphenylmethoxy)tropane ([125I]GA II 34) to identify the site of cross-linking and predict the binding pose relative to that of previously-examined cocaine photoaffinity analogs. Biochemical findings show that adduction of [125I]GA II 34 occurs at residues Asp79 or Leu80 in TM1, with molecular modeling supporting adduction to Leu80 and a pharmacophore pose in the central S1 site similar to that of cocaine and cocaine analogs. Substituted cysteine accessibility method protection analyses verified these findings, but identified some differences in structural stabilization relative to cocaine that may relate to BZT neurochemical outcomes.
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Affiliation(s)
- Michael J Tomlinson
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, United States
| | - Danielle Krout
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, United States
| | - Akula Bala Pramod
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, United States
| | - John R Lever
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, 65201, United States; Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, MO 65211, United States
| | - Amy Hauck Newman
- Medicinal Chemistry Section, National Institute on Drug Abuse - Intramural Research Program, Baltimore, MD 21224, United States
| | - L Keith Henry
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, United States.
| | - Roxanne A Vaughan
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, United States.
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Núñez-Vivanco G, Fierro A, Moya P, Iturriaga-Vásquez P, Reyes-Parada M. 3D similarities between the binding sites of monoaminergic target proteins. PLoS One 2018; 13:e0200637. [PMID: 30028869 PMCID: PMC6054423 DOI: 10.1371/journal.pone.0200637] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Accepted: 06/30/2018] [Indexed: 02/06/2023] Open
Abstract
The study of binding site similarities can be relevant to understand the interaction of different drugs at several molecular targets. The increasing availability of protein crystal structures and the development of novel algorithms designed to evaluate three-dimensional similarities, represent a great opportunity to explore the existence of electronic and shape features shared by clinically relevant proteins, which could assist drug design and discovery. Proteins involved in the recognition of monoaminergic neurotransmitters, such as monoamine transporters or monoamine oxidases (MAO) have been related to several psychiatric and neurological disorders such as depression or Parkinson’s disease. In this work, we evaluated the possible existence of similarities among the binding sites of the serotonin transporter (SERT), the dopamine transporter (DAT), MAO-A and MAO-B. This study was carried out using molecular simulation methodologies linked to the statistical algorithm PocketMatch, which was modified in order to obtain similarities profiles. Our results show that DAT and SERT exhibit a high degree of 3-D similarities all along the pathway that is presumably involved in the substrate transport process. Distinct differences, on the other hand, were found both at the extracellular and the intracellular ends of the transporters, which might be involved in the selective initial recognition of the corresponding substrate. Similarities were also found between the active (catalytic) site of MAO-A and the extracellular vestibule of SERT (the S2 binding site). These results suggest some degree of structural convergence for these proteins, which have different functions, tissue distribution and genetic origin, but which share the same endogenous ligand (serotonin). Beyond the functional implications, these findings are valuable for the design of both selective and non-selective ligands.
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Affiliation(s)
- Gabriel Núñez-Vivanco
- Centro de Bioinformática y Simulación Molecular, Universidad de Talca, Talca, Chile.,Escuela de Ingeniería Civil en Bioinformática, Universidad de Talca, Talca, Chile
| | | | - Pablo Moya
- Instituto de Fisiología, Universidad de Valparaíso, Valparaíso, Chile.,Centro Interdisciplinario de Neurociencia de Valparaíso CINV, Universidad de Valparaíso, Valparaíso, Chile
| | | | - Miguel Reyes-Parada
- School of Medicine, Faculty of Medical Sciences, University of Santiago de Chile, Santiago, Chile.,Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Talca, Chile
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Abramyan AM, Quick M, Xue C, Javitch JA, Shi L. Exploring Substrate Binding in the Extracellular Vestibule of MhsT by Atomistic Simulations and Markov Models. J Chem Inf Model 2018; 58:1244-1252. [PMID: 29851339 DOI: 10.1021/acs.jcim.8b00175] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Neurotransmitter:sodium symporters (NSS) terminate neurotransmission through Na+-driven reuptake of cognate neurotransmitters. Crystallographically, whereas both substrates and inhibitors have been found to bind in the central binding (S1) site of NSS, inhibitors were found to bind to a second binding (S2) site in the extracellular vestibule (EV) of transporters for leucine (LeuT) and serotonin. On the basis of computational and experimental studies, we proposed that substrates bind to the S2 site of LeuT as well and that substrate binding to the S2 site is essential for Na+-coupled symport. Recent binding experiments show that substrate (l-Trp) binding in the S2 site of MhsT, another bacterial NSS, is also central to the allosteric transport mechanism. Here, we used extensive molecular dynamics simulations combined with Markov state model analysis to investigate the interaction of l-Trp with the EV of MhsT and identified potential binding poses of l-Trp as well as induced conformational changes in the EV. Our computational findings were validated by experimental mutagenesis studies and shed light on the ligand binding characteristics of the EV of NSS, which may facilitate development of allosteric ligands targeting NSS.
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Affiliation(s)
- Ara M Abramyan
- Computational Chemistry and Molecular Biophysics Unit, National Institute on Drug Abuse - Intramural Research Program , National Institutes of Health , Baltimore , Maryland 21224 , United States
| | - Matthias Quick
- Division of Molecular Therapeutics , New York State Psychiatric Institute , New York , New York 10032 , United States
| | - Catherine Xue
- Computational Chemistry and Molecular Biophysics Unit, National Institute on Drug Abuse - Intramural Research Program , National Institutes of Health , Baltimore , Maryland 21224 , United States
| | - Jonathan A Javitch
- Division of Molecular Therapeutics , New York State Psychiatric Institute , New York , New York 10032 , United States
| | - Lei Shi
- Computational Chemistry and Molecular Biophysics Unit, National Institute on Drug Abuse - Intramural Research Program , National Institutes of Health , Baltimore , Maryland 21224 , United States
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31
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Structural basis for recognition of diverse antidepressants by the human serotonin transporter. Nat Struct Mol Biol 2018; 25:170-175. [PMID: 29379174 DOI: 10.1038/s41594-018-0026-8] [Citation(s) in RCA: 94] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Accepted: 12/27/2017] [Indexed: 12/22/2022]
Abstract
Selective serotonin reuptake inhibitors are clinically prescribed antidepressants that act by increasing the local concentrations of neurotransmitters at synapses and in extracellular spaces via blockade of the serotonin transporter. Here we report X-ray structures of engineered thermostable variants of the human serotonin transporter bound to the antidepressants sertraline, fluvoxamine, and paroxetine. The drugs prevent serotonin binding by occupying the central substrate-binding site and stabilizing the transporter in an outward-open conformation. These structures explain how residues within the central site orchestrate binding of chemically diverse inhibitors and mediate transporter drug selectivity.
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32
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Zhu R, Gruber HJ, Hinterdorfer P. Two Ligand Binding Sites in Serotonin Transporter Revealed by Nanopharmacological Force Sensing. Methods Mol Biol 2018; 1814:19-33. [PMID: 29956224 DOI: 10.1007/978-1-4939-8591-3_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The number of ligand binding sites in neurotransmitter-sodium symporters has been determined by crystal structure analysis and molecular pharmacology with controversial results. Here, we designed molecular tools to measure the interaction forces between the serotonin transporter (SERT) and S-citalopram on the single-molecule level by means of atomic force microscopy. Force spectroscopy allows for the extraction of dynamic information under physiological conditions which is inaccessible via X-ray crystallography. Two populations of distinctly different binding strength between S-citalopram and SERT were demonstrated in Na+-containing buffer. In Li+-containing buffer, SERT showed merely low-force interactions, whereas the vestibular mutant SERT-G402H only displayed the high force population. These observations provide physical evidence for the existence of two different binding sites in SERT when tested under near-physiological conditions.
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Affiliation(s)
- Rong Zhu
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Hermann J Gruber
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
| | - Peter Hinterdorfer
- Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria.
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Abstract
The dopamine (DAT), serotonin (SERT), and norepinephrine (NET) transporters, which are collectively referred to as monoamine transporters (MATs), play significant roles in regulating the neuronal response to these neurotransmitters. MATs terminate the action of these neurotransmitters by translocating them from the synaptic space into the presynaptic neurons. These three transmitters are responsible for controlling a number of physiological, emotional, and behavioral functions, with their transporters being the site of action of drugs employed for the treatment of a variety of conditions, including depression, anxiety, ADHD, schizophrenia, and psychostimulant abuse. Provided in this unit is information on the localization and regulation of MATs and the structural components of these proteins most responsible for the translocation process. Also included is a brief description of the evolution of ligands that interact with these transporters, as well as current theories concerning the pharmacological effects of substances that interact with these sites, including the molecular mechanisms of action of uptake inhibitors and allosteric modulators. Data relating to the presence, structure, and functions of allosteric modulators are included as well. The aim of this review is to provide background information on MATs to those who are new to this field, with a focus on the therapeutic potential of compounds that interact with these substrate transport sites. © 2017 by John Wiley & Sons, Inc.
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Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Pennsylvania
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Pennsylvania
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34
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Rannversson H, Andersen J, Bang-Andersen B, Strømgaard K. Mapping the Binding Site for Escitalopram and Paroxetine in the Human Serotonin Transporter Using Genetically Encoded Photo-Cross-Linkers. ACS Chem Biol 2017; 12:2558-2562. [PMID: 28910072 DOI: 10.1021/acschembio.7b00338] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In spite of the important role of the human serotonin transporter (hSERT) in depression treatment, the molecular details of how antidepressant drugs bind are still not completely understood, in particular those related to potential high- and low-affinity binding sites in hSERT. Here, we utilize amber codon suppression in hSERT to encode the photo-cross-linking unnatural amino acid p-azido-l-phenylalanine into the suggested high- and low-affinity binding sites. We then employ UV-induced cross-linking with azF to map the binding site of escitalopram and paroxetine, two prototypical selective serotonin reuptake inhibitors (SSRIs). We find that the two antidepressant drugs exclusively cross-link to azF incorporated at the high-affinity binding site of hSERT, while cross-linking is not observed at the low-affinity binding site. Combined with previous homology models and recent structural data on hSERT, our results provide important information to understand the molecular details of these clinical relevant binding sites.
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Affiliation(s)
- Hafsteinn Rannversson
- Center
for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen Ø, Denmark
| | - Jacob Andersen
- Center
for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen Ø, Denmark
| | | | - Kristian Strømgaard
- Center
for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Jagtvej 162, 2100 Copenhagen Ø, Denmark
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35
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Krout D, Pramod AB, Dahal RA, Tomlinson MJ, Sharma B, Foster JD, Zou MF, Boatang C, Newman AH, Lever JR, Vaughan RA, Henry LK. Inhibitor mechanisms in the S1 binding site of the dopamine transporter defined by multi-site molecular tethering of photoactive cocaine analogs. Biochem Pharmacol 2017; 142:204-215. [PMID: 28734777 DOI: 10.1016/j.bcp.2017.07.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 07/17/2017] [Indexed: 10/19/2022]
Abstract
Dopamine transporter (DAT) blockers like cocaine and many other abused and therapeutic drugs bind and stabilize an inactive form of the transporter inhibiting reuptake of extracellular dopamine (DA). The resulting increases in DA lead to the ability of these drugs to induce psychomotor alterations and addiction, but paradoxical findings in animal models indicate that not all DAT antagonists induce cocaine-like behavioral outcomes. How this occurs is not known, but one possibility is that uptake inhibitors may bind at multiple locations or in different poses to stabilize distinct conformational transporter states associated with differential neurochemical endpoints. Understanding the molecular mechanisms governing the pharmacological inhibition of DAT is therefore key for understanding the requisite interactions for behavioral modulation and addiction. Previously, we leveraged complementary computational docking, mutagenesis, peptide mapping, and substituted cysteine accessibility strategies to identify the specific adduction site and binding pose for the crosslinkable, photoactive cocaine analog, RTI 82, which contains a photoactive azide attached at the 2β position of the tropane pharmacophore. Here, we utilize similar methodology with a different cocaine analog N-[4-(4-azido-3-I-iodophenyl)-butyl]-2-carbomethoxy-3-(4-chlorophenyl)tropane, MFZ 2-24, where the photoactive azide is attached to the tropane nitrogen. In contrast to RTI 82, which crosslinked into residue Phe319 of transmembrane domain (TM) 6, our findings show that MFZ 2-24 adducts to Leu80 in TM1 with modeling and biochemical data indicating that MFZ 2-24, like RTI 82, occupies the central S1 binding pocket with the (+)-charged tropane ring nitrogen coordinating with the (-)-charged carboxyl side chain of Asp79. The superimposition of the tropane ring in the three-dimensional binding poses of these two distinct ligands provides strong experimental evidence for cocaine binding to DAT in the S1 site and the importance of the tropane moiety in competitive mechanisms of DA uptake inhibition. These findings set a structure-function baseline for comparison of typical and atypical DAT inhibitors and how their interactions with DAT could lead to the loss of cocaine-like behaviors.
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Affiliation(s)
- Danielle Krout
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - Akula Bala Pramod
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - Rejwi Acharya Dahal
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - Michael J Tomlinson
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - Babita Sharma
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - James D Foster
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA
| | - Mu-Fa Zou
- Medicinal Chemistry Section, National Institute on Drug Abuse - Intramural Research Program, Baltimore, MD 21224, USA
| | - Comfort Boatang
- Medicinal Chemistry Section, National Institute on Drug Abuse - Intramural Research Program, Baltimore, MD 21224, USA
| | - Amy Hauck Newman
- Medicinal Chemistry Section, National Institute on Drug Abuse - Intramural Research Program, Baltimore, MD 21224, USA
| | - John R Lever
- Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO, 65201, USA; Department of Radiology and Radiopharmaceutical Sciences Institute, University of Missouri, Columbia, MO 65211, USA
| | - Roxanne A Vaughan
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA.
| | - L Keith Henry
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, 1301 North Columbia Road, Grand Forks, ND 58202, USA.
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Fluorinated phenmetrazine "legal highs" act as substrates for high-affinity monoamine transporters of the SLC6 family. Neuropharmacology 2017; 134:149-157. [PMID: 28988906 DOI: 10.1016/j.neuropharm.2017.10.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 09/29/2017] [Accepted: 10/04/2017] [Indexed: 02/06/2023]
Abstract
A variety of new psychoactive substances (NPS) are appearing in recreational drug markets worldwide. NPS are compounds that target various receptors and transporters in the central nervous system to achieve their psychoactive effects. Chemical modifications of existing drugs can generate NPS that are not controlled by current legislation, thereby providing legal alternatives to controlled substances such as cocaine or amphetamine. Recently, 3-fluorophenmetrazine (3-FPM), a derivative of the anorectic compound phenmetrazine, appeared on the recreational drug market and adverse clinical effects have been reported. Phenmetrazine is known to elevate extracellular monoamine concentrations by an amphetamine-like mechanism. Here we tested 3-FPM and its positional isomers, 2-FPM and 4-FPM, for their abilities to interact with plasma membrane monoamine transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). We found that 2-, 3- and 4-FPM inhibit uptake mediated by DAT and NET in HEK293 cells with potencies comparable to cocaine (IC50 values < 2.5 μM), but display less potent effects at SERT (IC50 values >80 μM). Experiments directed at identifying transporter-mediated reverse transport revealed that FPM isomers induce efflux via DAT, NET and SERT in HEK293 cells, and this effect is augmented by the Na+/H+ ionophore monensin. Each FPM evoked concentration-dependent release of monoamines from rat brain synaptosomes. Hence, this study reports for the first time the mode of action for 2-, 3- and 4-FPM and identifies these NPS as monoamine releasers with marked potency at catecholamine transporters implicated in abuse and addiction. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'
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Erol I, Aksoydan B, Kantarcioglu I, Salmas RE, Durdagi S. Identification of novel serotonin reuptake inhibitors targeting central and allosteric binding sites: A virtual screening and molecular dynamics simulations study. J Mol Graph Model 2017; 74:193-202. [DOI: 10.1016/j.jmgm.2017.02.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 01/26/2017] [Accepted: 02/02/2017] [Indexed: 10/19/2022]
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38
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Topiol S, Bang-Andersen B, Sanchez C, Plenge P, Loland CJ, Juhl K, Larsen K, Bregnedal P, Bøgesø KP. X-ray structure based evaluation of analogs of citalopram: Compounds with increased affinity and selectivity compared with R-citalopram for the allosteric site (S2) on hSERT. Bioorg Med Chem Lett 2017; 27:470-478. [DOI: 10.1016/j.bmcl.2016.12.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 12/12/2016] [Accepted: 12/14/2016] [Indexed: 01/25/2023]
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39
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Ferraro M, Masetti M, Recanatini M, Cavalli A, Bottegoni G. Mapping Cholesterol Interaction Sites on Serotonin Transporter through Coarse-Grained Molecular Dynamics. PLoS One 2016; 11:e0166196. [PMID: 27907003 PMCID: PMC5132266 DOI: 10.1371/journal.pone.0166196] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Accepted: 10/24/2016] [Indexed: 12/19/2022] Open
Abstract
Serotonin transporter (SERT) modulates serotonergic signaling via re-uptake of serotonin in pre-synaptic cells. The inclusion in cholesterol-enriched membrane domains is crucial for SERT activity, suggesting a cross-talk between the protein and the sterol. Here, we develop a protocol to identify potential cholesterol interaction sites coupling statistical analysis to multi-microsecond coarse-grained molecular dynamics simulations of SERT in a previously validated raft-like membrane model. Six putative sites were found, including a putative CRAC motif on TM4 and a CARC motif on TM10. Among them, four hot-spots near regions related to ion binding, transport, and inhibition were detected. Our results encourage prospective studies to unravel mechanistic features of the transporter and related drug discovery implications.
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Affiliation(s)
| | - Matteo Masetti
- Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum - Università di Bologna, Bologna, Italy
- * E-mail: (MM); (GB)
| | - Maurizio Recanatini
- Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum - Università di Bologna, Bologna, Italy
| | - Andrea Cavalli
- CompuNet, Istituto Italiano di Tecnologia, Genova, Italy
- Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum - Università di Bologna, Bologna, Italy
| | - Giovanni Bottegoni
- CompuNet, Istituto Italiano di Tecnologia, Genova, Italy
- BiKi Technologies s.r.l., Genova, Italy
- * E-mail: (MM); (GB)
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Talbot JN, Geffert LM, Jorvig JE, Goldstein RI, Nielsen CL, Wolters NE, Amos ME, Munro CA, Dallman E, Mereu M, Tanda G, Katz JL, Indarte M, Madura JD, Choi H, Leak RK, Surratt CK. Rapid and sustained antidepressant properties of an NMDA antagonist/monoamine reuptake inhibitor identified via transporter-based virtual screening. Pharmacol Biochem Behav 2016; 150-151:22-30. [DOI: 10.1016/j.pbb.2016.08.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 08/23/2016] [Accepted: 08/24/2016] [Indexed: 01/08/2023]
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Andersen J, Ladefoged LK, Kristensen TNB, Munro L, Grouleff J, Stuhr-Hansen N, Kristensen AS, Schiøtt B, Strømgaard K. Interrogating the Molecular Basis for Substrate Recognition in Serotonin and Dopamine Transporters with High-Affinity Substrate-Based Bivalent Ligands. ACS Chem Neurosci 2016; 7:1406-1417. [PMID: 27425420 DOI: 10.1021/acschemneuro.6b00164] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The transporters for the neurotransmitters serotonin and dopamine (SERT and DAT, respectively) are targets for drugs used in the treatment of mental disorders and widely used drugs of abuse. Studies of prokaryotic homologues have advanced our structural understanding of SERT and DAT, but it still remains enigmatic whether the human transporters contain one or two high-affinity substrate binding sites. We have designed and employed 24 bivalent ligands possessing a highly systematic combination of substrate moieties (serotonin and/or dopamine) and aliphatic or poly(ethylene glycol) spacers to reveal insight into substrate recognition in SERT and DAT. An optimized bivalent ligand comprising two serotonin moieties binds SERT with 3,800-fold increased affinity compared to that of serotonin, suggesting that the human transporters have two distinct substrate binding sites. We show that the bivalent ligands are inhibitors of SERT and an experimentally validated docking model suggests that the bivalent compounds bind with one substrate moiety in the central binding site (the S1 site), whereas the other substrate moiety binds in a distinct binding site (the S2 site). A systematic study of nonconserved SERT/DAT residues surrounding the proposed binding region showed that nonconserved binding site residues do not contribute to selective recognition of substrates in SERT or DAT. This study provides novel insight into the molecular basis for substrate recognition in human transporters and provides an improved foundation for the development of new drugs targeting SERT and DAT.
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Affiliation(s)
- Jacob Andersen
- Department
of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Lucy Kate Ladefoged
- Interdisciplinary
Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Trine N. Bjerre Kristensen
- Interdisciplinary
Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Lachlan Munro
- Department
of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Julie Grouleff
- Interdisciplinary
Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Nicolai Stuhr-Hansen
- Department
of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Anders S. Kristensen
- Department
of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
| | - Birgit Schiøtt
- Interdisciplinary
Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Kristian Strømgaard
- Department
of Drug Design and Pharmacology, University of Copenhagen, DK-2100 Copenhagen, Denmark
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42
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Sealover NR, Felts B, Kuntz CP, Jarrard RE, Hockerman GH, Lamb PW, Barker EL, Henry LK. The external gate of the human and Drosophila serotonin transporters requires a basic/acidic amino acid pair for 3,4-methylenedioxymethamphetamine (MDMA) translocation and the induction of substrate efflux. Biochem Pharmacol 2016; 120:46-55. [PMID: 27638414 DOI: 10.1016/j.bcp.2016.09.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 09/08/2016] [Indexed: 11/24/2022]
Abstract
The substituted amphetamine, 3,4-methylenedioxy-methamphetamine (MDMA, ecstasy), is a widely used drug of abuse that induces non-exocytotic release of serotonin, dopamine, and norepinephrine through their cognate transporters as well as blocking the reuptake of neurotransmitter by the same transporters. The resulting dramatic increase in volume transmission and signal duration of neurotransmitters leads to psychotropic, stimulant, and entactogenic effects. The mechanism by which amphetamines drive reverse transport of the monoamines remains largely enigmatic, however, promising outcomes for the therapeutic utility of MDMA for post-traumatic stress disorder and the long-time use of the dopaminergic and noradrenergic-directed amphetamines in treatment of attention-deficit hyperactivity disorder and narcolepsy increases the importance of understanding this phenomenon. Previously, we identified functional differences between the human and Drosophila melanogaster serotonin transporters (hSERT and dSERT, respectively) revealing that MDMA is an effective substrate for hSERT but not dSERT even though serotonin is a potent substrate for both transporters. Chimeric dSERT/hSERT transporters revealed that the molecular components necessary for recognition of MDMA as a substrate was linked to regions of the protein flanking transmembrane domains (TM) V through IX. Here, we performed species-scanning mutagenesis of hSERT, dSERT and C. elegans SERT (ceSERT) along with biochemical and electrophysiological analysis and identified a single amino acid in TM10 (Glu394, hSERT; Asn484, dSERT, Asp517, ceSERT) that is primarily responsible for the differences in MDMA recognition. Our findings reveal that an acidic residue is necessary at this position for MDMA recognition as a substrate and serotonin releaser.
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Affiliation(s)
- Natalie R Sealover
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University College of Pharmacy, West Lafayette, IN 47907, United States
| | - Bruce Felts
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202, United States
| | - Charles P Kuntz
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University College of Pharmacy, West Lafayette, IN 47907, United States
| | - Rachel E Jarrard
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University College of Pharmacy, West Lafayette, IN 47907, United States
| | - Gregory H Hockerman
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University College of Pharmacy, West Lafayette, IN 47907, United States
| | | | - Eric L Barker
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University College of Pharmacy, West Lafayette, IN 47907, United States.
| | - L Keith Henry
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58202, United States.
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43
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Exploration of insights, opportunities and caveats provided by the X-ray structures of hSERT. Bioorg Med Chem Lett 2016; 26:5058-5064. [PMID: 27624075 DOI: 10.1016/j.bmcl.2016.08.087] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 08/24/2016] [Accepted: 08/26/2016] [Indexed: 01/16/2023]
Abstract
The recently reported X-ray structures of the human serotonin (5-HT) transporter SERT with bound inhibitors open new opportunities for drug discovery at SERT, selectivity design with respect to other neurotransmitter sodium transporters, and enhanced understanding of the molecular events involved in SERT action. Through computational and structural analyses, we explore the binding and migration of 5-HT at SERT. Consistent with earlier studies of leucine migration at the bacterial homolog of SERT, LeuT, we find multiple potential 'stopover' sites for 5-HT binding at SERT including the two (transmembrane S1 and extracellular vestibule S2) seen in the binding of the SSRI (S)-citalopram (S-Cit) to SERT, as well as other sites. Docking studies reveal the possibility of both hetero- (S-Cit+5-HT) and homo-dimeric (5-HT+5-HT) co-binding at both these sites which may explain earlier published allosteric activity observations and provide novel design strategies. Comparisons with substrate bound X-ray structures of the dopamine transporter reveal a number of potential sources of selectivity, some of which may be 'artificial' including target based, species related, experimental design related, and ligand dependent examples including substrate versus inhibitor related features.
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44
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Zhen J, Reith MEA. Impact of disruption of secondary binding site S2 on dopamine transporter function. J Neurochem 2016; 138:694-9. [PMID: 27315582 DOI: 10.1111/jnc.13704] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 06/09/2016] [Accepted: 06/10/2016] [Indexed: 11/30/2022]
Abstract
The structures of the leucine transporter, drosophila dopamine transporter, and human serotonin transporter show a secondary binding site (designated S2 ) for drugs and substrate in the extracellular vestibule toward the membrane exterior in relation to the primary substrate recognition site (S1 ). The present experiments are aimed at disrupting S2 by mutating Asp476 and Ile159 to Ala. Both mutants displayed a profound decrease in [(3) H]DA uptake compared with wild-type associated with a reduced turnover rate kcat . This was not caused by a conformational bias as the mutants responded to Zn(2+) (10 μM) similarly as WT. The dopamine transporters with either the D476A or I159A mutation both displayed a higher Ki for dopamine for the inhibition of [3H](-)-2-β-carbomethoxy-3-β-(4-fluorophenyl)tropane binding than did the WT transporter, in accordance with an allosteric interaction between the S1 and S2 sites. The results provide evidence in favor of a general applicability of the two-site allosteric model of the Javitch/Weinstein group from LeuT to dopamine transporter and possibly other monoamine transporters. X-ray structures of transporters closely related to the dopamine (DA) transporter show a secondary binding site S2 in the extracellular vestibule proximal to the primary binding site S1 which is closely linked to one of the Na(+) binding sites. This work examines the relationship between S2 and S1 sites. We found that S2 site impairment severely reduced DA transport and allosterically reduced S1 site affinity for the cocaine analog [(3) H]CFT. Our results are the first to lend direct support for the application of the two-site allosteric model, advanced for bacterial LeuT, to the human DA transporter. The model states that, after binding of the first DA molecule (DA1 ) to the primary S1 site (along with Na(+) ), binding of a second DA (DA2 ) to the S2 site triggers, through an allosteric interaction, the release of DA1 and Na(+) into the cytoplasm.
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Affiliation(s)
- Juan Zhen
- Department of Psychiatry, New York University School of Medicine, New York City, New York, USA
| | - Maarten E A Reith
- Department of Psychiatry, New York University School of Medicine, New York City, New York, USA.,Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York City, New York, USA
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Mnie-Filali O, Lau T, Matthaeus F, Abrial E, Delcourte S, El Mansari M, Pershon A, Schloss P, Sánchez C, Haddjeri N. Protein Kinases Alter the Allosteric Modulation of the Serotonin Transporter In Vivo and In Vitro. CNS Neurosci Ther 2016; 22:691-9. [PMID: 27171685 DOI: 10.1111/cns.12562] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 04/14/2016] [Accepted: 04/17/2016] [Indexed: 01/17/2023] Open
Abstract
AIM Studies using S- and R-enantiomers of the SSRI citalopram have shown that R-citalopram exerts an antagonistic effect on the efficacy of the antidepressant S-citalopram (escitalopram) through an interaction at an allosteric modulator site on the serotonin transporter (SERT). Here, we show that protein kinase signaling systems are involved in the allosteric modulation of the SERT in vivo and in vitro. METHODS We assessed the effects of nonspecific protein kinase inhibitor staurosporine in the action of escitalopram and/or R-citalopram using electrophysiological and behavioral assays in rats and cell surface SERT expression measures in serotoninergic cells. RESULTS Acute administration of R-citalopram counteracted the escitalopram-induced suppression of the serotonin (5-HT) neuronal firing activity and increase of the head twitches number following L-5-hydroxytryptophan injection. Importantly, these counteracting effects of R-citalopram were abolished by prior systemic administration of staurosporine. Interestingly, the preventing effect of staurosporine on 5-HT neuronal firing activity was abolished by direct activation of protein kinase C with phorbol 12-myristate 13-acetate. Finally, in vitro, quantification of the amount of cell surface-expressed SERT molecules revealed that R-citalopram prevented escitalopram-induced SERT internalization that was completely altered by staurosporine. CONCLUSION Taken together, these results highlight for the first time an involvement of protein kinases in the allosteric modulation of SERT function.
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Affiliation(s)
- Ouissame Mnie-Filali
- Univ Lyon, Université Lyon 1, Inserm, Stem Cell and Brain Research Institute U1208, 69500 Bron, France.,Department of Integrative Neurophysiology, CNCR, Vrije Universiteit, Amsterdam, The Netherlands
| | - Thorsten Lau
- Biochemical Laboratory, Central Institute of Mental Health, Mannheim, Germany
| | | | - Erika Abrial
- Univ Lyon, Université Lyon 1, Inserm, Stem Cell and Brain Research Institute U1208, 69500 Bron, France
| | - Sarah Delcourte
- Univ Lyon, Université Lyon 1, Inserm, Stem Cell and Brain Research Institute U1208, 69500 Bron, France
| | - Mostafa El Mansari
- Institute of Mental Health Research, University of Ottawa, Ottawa, ON, Canada
| | - Alan Pershon
- Neuropharmacology, Lundbeck Research USA, Paramus, NJ, USA
| | - Patrick Schloss
- Biochemical Laboratory, Central Institute of Mental Health, Mannheim, Germany
| | - Connie Sánchez
- Neuropharmacology, Lundbeck Research USA, Paramus, NJ, USA
| | - Nasser Haddjeri
- Univ Lyon, Université Lyon 1, Inserm, Stem Cell and Brain Research Institute U1208, 69500 Bron, France
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Synthesis and inhibitory evaluation of 3-linked imipramines for the exploration of the S2 site of the human serotonin transporter. Bioorg Med Chem 2016; 24:2725-38. [PMID: 27160055 DOI: 10.1016/j.bmc.2016.04.039] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Revised: 04/16/2016] [Accepted: 04/20/2016] [Indexed: 01/10/2023]
Abstract
The human serotonin transporter is the primary target of several antidepressant drugs, and the importance of a primary, high affinity binding site (S1) for antidepressant binding is well documented. The existence of a lower affinity, secondary binding site (S2) has, however, been debated. Herein we report the synthesis of 3-position coupled imipramine ligands from clomipramine using a copper free Sonogashira reaction. Ligand design was inspired by results from docking and steered molecular dynamics simulations, and the ligands were utilized in a structure-activity relationship study of the positional relationship between the S1 and S2 sites. The computer simulations suggested that the S2 site does indeed exist although with lower affinity for imipramine than observed within the S1 site. Additionally, it was possible to dock the 3-linked imipramine analogs into positions which occupy the S1 and the S2 site simultaneously. The structure activity relationship study showed that the shortest ligands were the most potent, and mutations enlarging the proposed S2 site were found to affect the larger ligands positively, while the smaller ligands were mostly unaffected.
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47
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Genetically encoded photocrosslinkers locate the high-affinity binding site of antidepressant drugs in the human serotonin transporter. Nat Commun 2016; 7:11261. [PMID: 27089947 PMCID: PMC4838859 DOI: 10.1038/ncomms11261] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Accepted: 03/07/2016] [Indexed: 02/02/2023] Open
Abstract
Despite the well-established role of the human serotonin transporter (hSERT) in the treatment of depression, the molecular details of antidepressant drug binding are still not fully understood. Here we utilize amber codon suppression in a membrane-bound transporter protein to encode photocrosslinking unnatural amino acids (UAAs) into 75 different positions in hSERT. UAAs are incorporated with high specificity, and functionally active transporters have similar transport properties and pharmacological profiles compared with wild-type transporters. We employ ultraviolet-induced crosslinking with p-azido-L-phenylalanine (azF) at selected positions in hSERT to map the binding site of imipramine, a prototypical tricyclic antidepressant, and vortioxetine, a novel multimodal antidepressant. We find that the two antidepressants crosslink with azF incorporated at different positions within the central substrate-binding site of hSERT, while no crosslinking is observed at the vestibular-binding site. Taken together, our data provide direct evidence for defining the high-affinity antidepressant binding site in hSERT. Molecular details of how antidepressant drugs bind to the human serotonin transporter are not currently clear. Here, the authors introduce photo-cross-linkers into the protein and map the binding site of several antidepressants.
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48
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49
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Coleman JA, Green EM, Gouaux E. X-ray structures and mechanism of the human serotonin transporter. Nature 2016; 532:334-9. [PMID: 27049939 PMCID: PMC4898786 DOI: 10.1038/nature17629] [Citation(s) in RCA: 438] [Impact Index Per Article: 54.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 02/29/2016] [Indexed: 12/19/2022]
Abstract
The serotonin transporter (SERT) terminates serotonergic signaling through the sodium and chloride dependent reuptake of neurotransmitter into presynaptic neurons. SERT is a target for antidepressant and psychostimulant drugs, which block reuptake and prolong neurotransmitter signaling. Here we report x-ray crystallographic structures of human SERT at 3.15 Å resolution bound to the antidepressants (S)-citalopram or paroxetine. Antidepressants lock SERT in an outward-open conformation by lodging in the central binding site, located between transmembrane helices 1, 3, 6, 8, and 10, directly blocking serotonin binding. We further identify the location of an allosteric site in the complex as residing at the periphery of the extracellular vestibule, interposed between extracellular loops 4 and 6 and TMs 1, 6, 10, and 11. Occupancy of the allosteric site sterically hinders ligand unbinding from the central site, providing an explanation for the action of (S)-citalopram as an allosteric ligand. These structures define the mechanism of antidepressant action in SERT and provide blueprints for future drug design.
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Affiliation(s)
- Jonathan A Coleman
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Evan M Green
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
| | - Eric Gouaux
- Vollum Institute, Oregon Health &Science University, Portland, Oregon 97239, USA.,Howard Hughes Medical Institute, Oregon Health &Science University, Portland, Oregon 97239, USA
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50
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Davis BA, Nagarajan A, Forrest LR, Singh SK. Mechanism of Paroxetine (Paxil) Inhibition of the Serotonin Transporter. Sci Rep 2016; 6:23789. [PMID: 27032980 PMCID: PMC4817154 DOI: 10.1038/srep23789] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 03/15/2016] [Indexed: 11/11/2022] Open
Abstract
The serotonin transporter (SERT) is an integral membrane protein that exploits preexisting sodium-, chloride-, and potassium ion gradients to catalyze the thermodynamically unfavorable movement of synaptic serotonin into the presynaptic neuron. SERT has garnered significant clinical attention partly because it is the target of multiple psychoactive agents, including the antidepressant paroxetine (Paxil), the most potent selective serotonin reuptake inhibitor known. However, the binding site and orientation of paroxetine in SERT remain controversial. To provide molecular insight, we constructed SERT homology models based on the Drosophila melanogaster dopamine transporter and docked paroxetine to these models. We tested the predicted binding configurations with a combination of radioligand binding and flux assays on wild-type and mutant SERTs. Our data suggest that the orientation of paroxetine, specifically its fluorophenyl ring, in SERT’s substrate binding site directly depends on this pocket’s charge distribution, and thereby provide an avenue toward understanding and enhancing high-affinity antidepressant activity.
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Affiliation(s)
- Bruce A Davis
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520 USA
| | - Anu Nagarajan
- Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, 35 Convent Drive, Bethesda, MD 20892 USA
| | - Lucy R Forrest
- Computational Structural Biology Section, National Institute of Neurological Disorders and Stroke, 35 Convent Drive, Bethesda, MD 20892 USA
| | - Satinder K Singh
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520 USA
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