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Nepal B, Das S, Reith ME, Kortagere S. Overview of the structure and function of the dopamine transporter and its protein interactions. Front Physiol 2023; 14:1150355. [PMID: 36935752 PMCID: PMC10020207 DOI: 10.3389/fphys.2023.1150355] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 02/21/2023] [Indexed: 03/06/2023] Open
Abstract
The dopamine transporter (DAT) plays an integral role in dopamine neurotransmission through the clearance of dopamine from the extracellular space. Dysregulation of DAT is central to the pathophysiology of numerous neuropsychiatric disorders and as such is an attractive therapeutic target. DAT belongs to the solute carrier family 6 (SLC6) class of Na+/Cl- dependent transporters that move various cargo into neurons against their concentration gradient. This review focuses on DAT (SCL6A3 protein) while extending the narrative to the closely related transporters for serotonin and norepinephrine where needed for comparison or functional relevance. Cloning and site-directed mutagenesis experiments provided early structural knowledge of DAT but our contemporary understanding was achieved through a combination of crystallization of the related bacterial transporter LeuT, homology modeling, and subsequently the crystallization of drosophila DAT. These seminal findings enabled a better understanding of the conformational states involved in the transport of substrate, subsequently aiding state-specific drug design. Post-translational modifications to DAT such as phosphorylation, palmitoylation, ubiquitination also influence the plasma membrane localization and kinetics. Substrates and drugs can interact with multiple sites within DAT including the primary S1 and S2 sites involved in dopamine binding and novel allosteric sites. Major research has centered around the question what determines the substrate and inhibitor selectivity of DAT in comparison to serotonin and norepinephrine transporters. DAT has been implicated in many neurological disorders and may play a role in the pathology of HIV and Parkinson's disease via direct physical interaction with HIV-1 Tat and α-synuclein proteins respectively.
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Affiliation(s)
- Binod Nepal
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Sanjay Das
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Maarten E. Reith
- Department of Psychiatry, New York University School of Medicine, New York City, NY, United States
| | - Sandhya Kortagere
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA, United States
- *Correspondence: Sandhya Kortagere,
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2
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Ruchala I, Battisti UM, Nguyen VT, Chen RYT, Glennon RA, Eltit JM. Functional characterization of N-octyl 4-methylamphetamine variants and related bivalent compounds at the dopamine and serotonin transporters using Ca 2+ channels as sensors. Toxicol Appl Pharmacol 2021; 419:115513. [PMID: 33785354 PMCID: PMC8148225 DOI: 10.1016/j.taap.2021.115513] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 03/21/2021] [Accepted: 03/25/2021] [Indexed: 10/21/2022]
Abstract
The early characterization of ligands at the dopamine and serotonin transporters, DAT and SERT, respectively, is important for drug discovery, forensic sciences, and drug abuse research. 4-Methyl amphetamine (4-MA) is a good example of an abused drug whose overdose can be fatal. It is a potent substrate at DAT and SERT where its simplest secondary amine (N-methyl 4-MA) retains substrate activity at them. In contrast, N-n-butyl 4-MA is very weak, therefore it was categorized as inactive at these transporters. Here, N-octyl 4-MA and other related compounds were synthesized, and their activities were evaluated at DAT and SERT. To expedite this endeavor, cells expressing DAT or SERT were co-transfected with a voltage-gated Ca2+ channel and, the genetically-encoded Ca2+ sensor, GCaMP6s. Control compounds and the newly synthesized molecules were tested on these cells using an automated multi-well fluorescence plate reader; substrates and inhibitors were identified successfully at DAT and SERT. N-Octyl 4-MA and three bivalent compounds were inhibitors at these transporters. These findings were validated by measuring Ca2+-mobilization using quantitative fluorescence microscopy. The bivalent molecules were the most potent of the series and were further characterized in an uptake-inhibition assay. Compared to cocaine, they showed comparable potency inhibiting uptake at DAT and higher potency at SERT. These observations support a previous hypothesis that amphetamine-related (and, here, N-extended alkyl and) bivalent arylalkylamine molecules are active at monoamine transporters, showing potent activity as reuptake inhibitors, and implicate the involvement of a distant auxiliary binding feature to account for their actions at DAT and SERT.
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Affiliation(s)
- Iwona Ruchala
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, United States of America
| | - Umberto M Battisti
- Deparment of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, United States of America
| | - Vy T Nguyen
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, United States of America
| | - Rita Yu-Tzu Chen
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, United States of America
| | - Richard A Glennon
- Deparment of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, United States of America
| | - Jose M Eltit
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, United States of America.
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3
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Xu L, Chen LY. Identification of a New Allosteric Binding Site for Cocaine in Dopamine Transporter. J Chem Inf Model 2020; 60:3958-3968. [PMID: 32649824 PMCID: PMC7484383 DOI: 10.1021/acs.jcim.0c00346] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Dopamine (DA) transporter (DAT) is a major target for psychostimulant drugs of abuse such as cocaine that competitively binds to DAT, inhibits DA reuptake, and consequently increases synaptic DA levels. In addition to the central binding site inside DAT, the available experimental evidence suggests the existence of alternative binding sites on DAT, but detection and characterization of these sites are challenging by experiments alone. Here, we integrate multiple computational approaches to probe the potential binding sites on the wild-type Drosophila melanogaster DAT and identify a new allosteric site that displays high affinity for cocaine. This site is located on the surface of DAT, and binding of cocaine is primarily dominated by interactions with hydrophobic residues surrounding the site. We show that cocaine binding to this new site allosterically reduces the binding of DA/cocaine to the central binding pocket, and simultaneous binding of two cocaine molecules to a single DAT seems infeasible. Furthermore, we find that binding of cocaine to this site stabilizes the conformation of DAT but alters the conformational population and thereby reduces the accessibility by DA, providing molecular insights into the inhibitory mechanism of cocaine. In addition, our results indicate that the conformations induced by cocaine binding to this site may be relevant to the oligomerization of DAT, highlighting a potential role of this new site in modulating the function of DAT.
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Affiliation(s)
- Liang Xu
- Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
| | - Liao Y Chen
- Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, United States
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4
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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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5
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Mikelman SR, Guptaroy B, Schmitt KC, Jones KT, Zhen J, Reith MEA, Gnegy ME. Tamoxifen Directly Interacts with the Dopamine Transporter. J Pharmacol Exp Ther 2018; 367:119-128. [PMID: 30108161 PMCID: PMC7250473 DOI: 10.1124/jpet.118.248179] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 07/26/2018] [Indexed: 11/22/2022] Open
Abstract
The selective estrogen receptor modulator tamoxifen increases extracellular dopamine in vivo and acts as a neuroprotectant in models of dopamine neurotoxicity. We investigated the effect of tamoxifen on dopamine transporter (DAT)-mediated dopamine uptake, dopamine efflux, and [3H]WIN 35,428 [(-)-2-β-carbomethoxy-3-β-(4-fluorophenyl)tropane] binding in rat striatal tissue. Tamoxifen dose-dependently blocked dopamine uptake (54% reduction at 10 μM) and amphetamine-stimulated efflux (59% reduction at 10 μM) in synaptosomes. It also produced a small but significant reduction in [3H]WIN 35,428 binding in striatal membranes, indicating a weak interaction with the substrate binding site in the DAT. Biotinylation and cysteine accessibility studies indicated that tamoxifen stabilizes the outward-facing conformation of the DAT in a cocaine-like manner and does not affect surface expression of the DAT. Additional studies with mutant DAT constructs D476A and I159A suggested a direct interaction between tamoxifen and a secondary substrate binding site of the transporter. Locomotor studies revealed that tamoxifen attenuates amphetamine-stimulated hyperactivity in rats but has no depressant or stimulant activity in the absence of amphetamine. These results suggest a complex mechanism of action for tamoxifen as a regulator of the DAT. Due to its effectiveness against amphetamine actions and its central nervous system permeant activity, the tamoxifen structure represents an excellent starting point for a structure-based drug-design program to develop a pharmacological therapeutic for psychostimulant abuse.
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Affiliation(s)
- Sarah R Mikelman
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Bipasha Guptaroy
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Kyle C Schmitt
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Kymry T Jones
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Juan Zhen
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Maarten E A Reith
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
| | - Margaret E Gnegy
- Gnegy Laboratory, Department of Pharmacology, University of Michigan School of Medicine, Ann Arbor, Michigan (S.R.M., B.G., M.E.G.); and Reith Laboratory, Department of Psychiatry, University of New York School of Medicine, New York, New York (K.C.S., K.T.J., J.Z., M.E.A.R.)
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6
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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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7
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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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8
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Wang P, Fu T, Zhang X, Yang F, Zheng G, Xue W, Chen Y, Yao X, Zhu F. Differentiating physicochemical properties between NDRIs and sNRIs clinically important for the treatment of ADHD. Biochim Biophys Acta Gen Subj 2017; 1861:2766-2777. [PMID: 28757337 DOI: 10.1016/j.bbagen.2017.07.022] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 07/23/2017] [Accepted: 07/26/2017] [Indexed: 12/25/2022]
Abstract
BACKGROUND Drugs available for treating attention-deficit hyperactivity disorder (ADHD) are mainly selective norepinephrine (sNRIs) and dual norepinephrine-dopamine (NDRIs) reuptake inhibitors. The major problem of sNRIs lines in their delayed onset of action and partial- or non-responses, which makes NDRIs distinguished in drug efficacy. Understanding of the differential binding modes of these 2 types of drugs to their corresponding targets can give great insights into the discovery of privileged drug-like scaffolds with improved efficacy. So far, no such study has been carried out. METHODS A combinatorial computational strategy, integrating homology modeling, molecular docking, molecular dynamics (MD) and binding free energy calculation, was employed to analyze the binding modes of 8 clinically important ADHD drugs in their targets. RESULTS Binding modes of 2 types of ADHD drugs (sNRIs and NDRIs) in their targets was identified for the first time by MD simulation, and 15 hot spot residues were discovered as crucial for NDRIs' binding in hNET and hDAT. Comparing to sNRIs, a clear reduction in the hydrophobic property of NDRIs' one functional group was observed, and the depth of drugs' aromatic ring stretched into the pocket of both targets was further identified as key contributors to drugs' selectivity. CONCLUSIONS The hydrophobic property of NDRI ADHD drugs' one functional group contributes to their selectivity when bind hNET and hDAT. GENERAL SIGNIFICANCE These results provide insights into NDRI ADHD drugs' binding mechanisms, which could be utilized as structural blueprints for assessing and discovering more efficacious drugs for ADHD therapy.
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Affiliation(s)
- Panpan Wang
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; College of Chemistry and Pharmaceutical Engineering, Huanghuai University, Zhumadian 463000, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Tingting Fu
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Xiaoyu Zhang
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Fengyuan Yang
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Guoxun Zheng
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Weiwei Xue
- School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China.
| | - Yuzong Chen
- Bioinformatics and Drug Design Group, Department of Pharmacy, National University of Singapore, Singapore 117543, Singapore
| | - Xiaojun Yao
- State Key Laboratory of Applied Organic Chemistry, Department of Chemistry, Lanzhou University, Lanzhou 730000, China
| | - Feng Zhu
- Innovative Drug Research and Bioinformatics Group, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China; School of Pharmaceutical Sciences and Collaborative Innovation Center for Brain Science, Chongqing University, Chongqing 401331, China.
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9
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Rives ML, Javitch JA, Wickenden AD. Potentiating SLC transporter activity: Emerging drug discovery opportunities. Biochem Pharmacol 2017; 135:1-11. [DOI: 10.1016/j.bcp.2017.02.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 02/13/2017] [Indexed: 12/12/2022]
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10
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Wang P, Zhang X, Fu T, Li S, Li B, Xue W, Yao X, Chen Y, Zhu F. Differentiating Physicochemical Properties between Addictive and Nonaddictive ADHD Drugs Revealed by Molecular Dynamics Simulation Studies. ACS Chem Neurosci 2017; 8:1416-1428. [PMID: 28557437 DOI: 10.1021/acschemneuro.7b00173] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Attention-deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed mental disorder of children and adolescents. Although psychostimulants are currently the first-line drugs for ADHD, their highly addictive profile raises great abuse concerns. It is known that psychostimulants' addictiveness is largely attributed to their interaction with dopamine transporter (DAT) and their binding modes in DAT can thus facilitate the understanding of the mechanism underlining drugs' addictiveness. However, no DAT residue able to discriminate ADHD drugs' addictiveness is identified, and the way how different drug structures affect their abuse liability is still elusive. In this study, multiple computational methods were integrated to differentiate binding modes between approved psychostimulants and ADHD drugs of little addictiveness. As a result, variation in energy contribution of 8 residues between addictive and nonaddictive drugs was observed, and a reduction in hydrophobicity of drugs' 2 functional groups was identified as the indicator of drugs' addictiveness. This finding agreed well with the physicochemical properties of 8 officially reported controlled substances. The identified variations in binding mode can shed light on the mechanism underlining drugs' addictiveness, which may thus facilitate the discovery of improved ADHD therapeutics with reduced addictive profile.
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Affiliation(s)
- Panpan Wang
- College of Pharmaceutical
Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Xiaoyu Zhang
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Tingting Fu
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Shuang Li
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Bo Li
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Weiwei Xue
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
| | - Xiaojun Yao
- State Key Laboratory of Applied Organic
Chemistry and Department of Chemistry, Lanzhou University, Lanzhou 730000, China
| | - Yuzong Chen
- Bioinformatics and
Drug Design Group, Department of Pharmacy, National University of Singapore, Singapore 117543, Singapore
| | - Feng Zhu
- College of Pharmaceutical
Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
- Innovative Drug Research and Bioinformatics
Group, School of Pharmaceutical Sciences and Collaborative Innovation
Center for Brain Science, Chongqing University, Chongqing 401331, China
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11
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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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12
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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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13
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Nikolic K, Mavridis L, Djikic T, Vucicevic J, Agbaba D, Yelekci K, Mitchell JBO. Drug Design for CNS Diseases: Polypharmacological Profiling of Compounds Using Cheminformatic, 3D-QSAR and Virtual Screening Methodologies. Front Neurosci 2016; 10:265. [PMID: 27375423 PMCID: PMC4901078 DOI: 10.3389/fnins.2016.00265] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 05/25/2016] [Indexed: 11/13/2022] Open
Abstract
HIGHLIGHTSMany CNS targets are being explored for multi-target drug design New databases and cheminformatic methods enable prediction of primary pharmaceutical target and off-targets of compounds QSAR, virtual screening and docking methods increase the potential of rational drug design
The diverse cerebral mechanisms implicated in Central Nervous System (CNS) diseases together with the heterogeneous and overlapping nature of phenotypes indicated that multitarget strategies may be appropriate for the improved treatment of complex brain diseases. Understanding how the neurotransmitter systems interact is also important in optimizing therapeutic strategies. Pharmacological intervention on one target will often influence another one, such as the well-established serotonin-dopamine interaction or the dopamine-glutamate interaction. It is now accepted that drug action can involve plural targets and that polypharmacological interaction with multiple targets, to address disease in more subtle and effective ways, is a key concept for development of novel drug candidates against complex CNS diseases. A multi-target therapeutic strategy for Alzheimer‘s disease resulted in the development of very effective Multi-Target Designed Ligands (MTDL) that act on both the cholinergic and monoaminergic systems, and also retard the progression of neurodegeneration by inhibiting amyloid aggregation. Many compounds already in databases have been investigated as ligands for multiple targets in drug-discovery programs. A probabilistic method, the Parzen-Rosenblatt Window approach, was used to build a “predictor” model using data collected from the ChEMBL database. The model can be used to predict both the primary pharmaceutical target and off-targets of a compound based on its structure. Several multi-target ligands were selected for further study, as compounds with possible additional beneficial pharmacological activities. Based on all these findings, it is concluded that multipotent ligands targeting AChE/MAO-A/MAO-B and also D1-R/D2-R/5-HT2A-R/H3-R are promising novel drug candidates with improved efficacy and beneficial neuroleptic and procognitive activities in treatment of Alzheimer's and related neurodegenerative diseases. Structural information for drug targets permits docking and virtual screening and exploration of the molecular determinants of binding, hence facilitating the design of multi-targeted drugs. The crystal structures and models of enzymes of the monoaminergic and cholinergic systems have been used to investigate the structural origins of target selectivity and to identify molecular determinants, in order to design MTDLs.
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Affiliation(s)
- Katarina Nikolic
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade Belgrade, Serbia
| | - Lazaros Mavridis
- School of Biological and Chemical Sciences, Queen Mary University of London London, UK
| | - Teodora Djikic
- Department of Bioinformatics and Genetics, Faculty of Engineering and Natural Sciences, Kadir Has University Istanbul, Turkey
| | - Jelica Vucicevic
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade Belgrade, Serbia
| | - Danica Agbaba
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade Belgrade, Serbia
| | - Kemal Yelekci
- Department of Bioinformatics and Genetics, Faculty of Engineering and Natural Sciences, Kadir Has University Istanbul, Turkey
| | - John B O Mitchell
- EaStCHEM School of Chemistry and Biomedical Sciences Research Complex, University of St Andrews St Andrews, UK
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14
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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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15
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Stuhr-Hansen N, Andersen J, Thygesen MB, Strømgaard K. Synthesis of Symmetrical and Non-Symmetrical Bivalent Neurotransmitter Ligands. ChemistrySelect 2016. [DOI: 10.1002/slct.201600116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Nicolai Stuhr-Hansen
- Department of Drug Design and Pharmacology; University of Copenhagen; Universitetsparken 2 DK-2100 Copenhagen Denmark
- Department of Chemistry; Chemical Biology Section; University of Copenhagen; Thorvaldsensvej 40 1871 Frederiksberg C Denmark
| | - Jacob Andersen
- Department of Drug Design and Pharmacology; University of Copenhagen; Universitetsparken 2 DK-2100 Copenhagen Denmark
| | - Mikkel B. Thygesen
- Department of Chemistry; Chemical Biology Section; University of Copenhagen; Thorvaldsensvej 40 1871 Frederiksberg C Denmark
| | - Kristian Strømgaard
- Department of Drug Design and Pharmacology; University of Copenhagen; Universitetsparken 2 DK-2100 Copenhagen Denmark
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16
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Zhu R, Sinwel D, Hasenhuetl PS, Saha K, Kumar V, Zhang P, Rankl C, Holy M, Sucic S, Kudlacek O, Karner A, Sandtner W, Stockner T, Gruber HJ, Freissmuth M, Newman AH, Sitte HH, Hinterdorfer P. Nanopharmacological Force Sensing to Reveal Allosteric Coupling in Transporter Binding Sites. Angew Chem Int Ed Engl 2015; 55:1719-22. [PMID: 26695726 DOI: 10.1002/anie.201508755] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 11/11/2015] [Indexed: 11/11/2022]
Abstract
Controversy regarding the number and function of ligand binding sites in neurotransmitter/sodium symporters arose from conflicting data in crystal structures and molecular pharmacology. Here, we have designed novel tools for atomic force microscopy that directly measure the interaction forces between the serotonin transporter (SERT) and the S- and R-enantiomers of citalopram on the single molecule level. This approach is based on force spectroscopy, which allows for the extraction of dynamic information under physiological conditions thus inaccessible via X-ray crystallography. Two distinct populations of characteristic binding strengths of citalopram 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 when accessed in a physiological context. Competition experiments revealed that these two sites are allosterically coupled and exert reciprocal modulation.
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Affiliation(s)
- Rong Zhu
- Institute for Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria
| | - Doris Sinwel
- Institute for Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria.,Christian Doppler Laboratory for Nanoscopic Methods in Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria
| | - Peter S Hasenhuetl
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Kusumika Saha
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Vivek Kumar
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Peng Zhang
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Christian Rankl
- Keysight Technologies Austria GmbH, Mooslackengasse 17, 1190, Vienna, Austria
| | - Marion Holy
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Sonja Sucic
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Oliver Kudlacek
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Andreas Karner
- Institute for Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria.,Center for Advanced Bioanalysis, Gruberstrasse 40, 4020, Linz, Austria
| | - Walter Sandtner
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Thomas Stockner
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Hermann J Gruber
- Institute for Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria
| | - Michael Freissmuth
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Amy Hauck Newman
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Harald H Sitte
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090, Vienna, Austria
| | - Peter Hinterdorfer
- Institute for Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria. .,Christian Doppler Laboratory for Nanoscopic Methods in Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020, Linz, Austria. .,Center for Advanced Bioanalysis, Gruberstrasse 40, 4020, Linz, Austria.
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17
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Cheng MH, Block E, Hu F, Cobanoglu MC, Sorkin A, Bahar I. Insights into the Modulation of Dopamine Transporter Function by Amphetamine, Orphenadrine, and Cocaine Binding. Front Neurol 2015; 6:134. [PMID: 26106364 PMCID: PMC4460958 DOI: 10.3389/fneur.2015.00134] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 05/26/2015] [Indexed: 12/29/2022] Open
Abstract
Human dopamine (DA) transporter (hDAT) regulates dopaminergic signaling in the central nervous system by maintaining the synaptic concentration of DA at physiological levels, upon reuptake of DA into presynaptic terminals. DA translocation involves the co-transport of two sodium ions and the channeling of a chloride ion, and it is achieved via alternating access between outward-facing (OF) and inward-facing states of DAT. hDAT is a target for addictive drugs, such as cocaine, amphetamine (AMPH), and therapeutic antidepressants. Our recent quantitative systems pharmacology study suggested that orphenadrine (ORPH), an anticholinergic agent and anti-Parkinson drug, might be repurposable as a DAT drug. Previous studies have shown that DAT-substrates like AMPH or -blockers like cocaine modulate the function of DAT in different ways. However, the molecular mechanisms of modulation remained elusive due to the lack of structural data on DAT. The newly resolved DAT structure from Drosophila melanogaster opens the way to a deeper understanding of the mechanism and time evolution of DAT–drug/ligand interactions. Using a combination of homology modeling, docking analysis, molecular dynamics simulations, and molecular biology experiments, we performed a comparative study of the binding properties of DA, AMPH, ORPH, and cocaine and their modulation of hDAT function. Simulations demonstrate that binding DA or AMPH drives a structural transition toward a functional form predisposed to translocate the ligand. In contrast, ORPH appears to inhibit DAT function by arresting it in the OF open conformation. The analysis shows that cocaine and ORPH competitively bind DAT, with the binding pose and affinity dependent on the conformational state of DAT. Further assays show that the effect of ORPH on DAT uptake and endocytosis is comparable to that of cocaine.
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Affiliation(s)
- Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA
| | - Ethan Block
- Department of Cell Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA
| | - Feizhuo Hu
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA ; Department of Pharmacology and Pharmaceutical Sciences, School of Medicine, Tsinghua University , Beijing , China
| | - Murat Can Cobanoglu
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA
| | - Alexander Sorkin
- Department of Cell Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA
| | - Ivet Bahar
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh , Pittsburgh, PA , USA
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18
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Loland CJ. The use of LeuT as a model in elucidating binding sites for substrates and inhibitors in neurotransmitter transporters. Biochim Biophys Acta Gen Subj 2014; 1850:500-10. [PMID: 24769398 DOI: 10.1016/j.bbagen.2014.04.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2014] [Revised: 04/09/2014] [Accepted: 04/11/2014] [Indexed: 01/24/2023]
Abstract
BACKGROUND The mammalian neurotransmitter transporters are complex proteins playing a central role in synaptic transmission between neurons by rapid reuptake of neurotransmitters. The proteins which transport dopamine, noradrenaline and serotonin belong to the Neurotransmitter:Sodium Symporters (NSS). Due to their important role, dysfunctions are associated with several psychiatric and neurological diseases and they also serve as targets for a wide range of therapeutic and illicit drugs. Despite the central physiological and pharmacological importance, direct evidence on structure-function relationships on mammalian NSS proteins has so far been unsuccessful. The crystal structure of the bacterial NSS protein, LeuT, has been a turning point in structural investigations. SCOPE OF REVIEW To provide an update on what is known about the binding sites for substrates and inhibitors in the LeuT. The different binding modes and binding sites will be discussed with special emphasis on the possible existence of a second substrate binding site. It is the goal to give an insight into how investigations on ligand binding in LeuT have provided basic knowledge about transporter conformations and translocation mechanism which can pave the road for a deeper understanding of drug binding and function of the mammalian transporters. MAJOR CONCLUSIONS The LeuT is a suitable model for the structural investigation of NSS proteins including the possible location of drug binding sites. It is still debated whether the LeuT is a suitable model for the molecular mechanisms behind substrate translocation. GENERAL SIGNIFICANCE Structure and functional aspects of NSS proteins are central for understanding synaptic transmission. With the purification and crystallization of LeuT as well as the dopamine transporter from Drosophila melanogaster, the application of biophysical methods such as fluorescence spectroscopy, neutron- or x-ray scattering and NMR for understanding its function becomes increasingly available. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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Affiliation(s)
- Claus J Loland
- Molecular Neuropharmacology Laboratory, Department of Neuroscience and Pharmacology, The Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
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19
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Yim JCH, Bexrud JA, Ayinla RO, Leitch DC, Schafer LL. Bis(amidate)bis(amido) Titanium Complex: A Regioselective Intermolecular Alkyne Hydroamination Catalyst. J Org Chem 2014; 79:2015-28. [DOI: 10.1021/jo402668q] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Jacky C.-H. Yim
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, British
Columbia V6T 1Z1, Canada
| | - Jason A. Bexrud
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, British
Columbia V6T 1Z1, Canada
| | - Rashidat O. Ayinla
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, British
Columbia V6T 1Z1, Canada
| | - David C. Leitch
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, British
Columbia V6T 1Z1, Canada
| | - Laurel L. Schafer
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, British
Columbia V6T 1Z1, Canada
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20
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Schmitt KC, Rothman RB, Reith MEA. Nonclassical pharmacology of the dopamine transporter: atypical inhibitors, allosteric modulators, and partial substrates. J Pharmacol Exp Ther 2013; 346:2-10. [PMID: 23568856 DOI: 10.1124/jpet.111.191056] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The dopamine transporter (DAT) is a sodium-coupled symporter protein responsible for modulating the concentration of extraneuronal dopamine in the brain. The DAT is a principle target of various psychostimulant, nootropic, and antidepressant drugs, as well as certain drugs used recreationally, including the notoriously addictive stimulant cocaine. DAT ligands have traditionally been divided into two categories: cocaine-like inhibitors and amphetamine-like substrates. Whereas inhibitors block monoamine uptake by the DAT but are not translocated across the membrane, substrates are actively translocated and trigger DAT-mediated release of dopamine by reversal of the translocation cycle. Because both inhibitors and substrates increase extraneuronal dopamine levels, it is often assumed that all DAT ligands possess an addictive liability equivalent to that of cocaine. However, certain recently developed ligands, such as atypical benztropine-like DAT inhibitors with reduced or even a complete lack of cocaine-like rewarding effects, suggest that addictiveness is not a constant property of DAT-affecting compounds. These atypical ligands do not conform to the classic preconception that all DAT inhibitors (or substrates) are functionally and mechanistically alike. Instead, they suggest the possibility that the DAT exhibits some of the ligand-specific pleiotropic functional qualities inherent to G-protein-coupled receptors. That is, ligands with different chemical structures induce specific conformational changes in the transporter protein that can be differentially transduced by the cell, ultimately eliciting unique behavioral and psychological effects. The present overview discusses compounds with conformation-specific activity, useful not only as tools for studying the mechanics of dopamine transport, but also as leads for medication development in addictive disorders.
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Affiliation(s)
- Kyle C Schmitt
- Department of Neurosurgery, New York University School of Medicine, 455 First Ave., Public Health Laboratories (8th Floor), New York, New York 10016, USA.
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21
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Stockner T, Montgomery TR, Kudlacek O, Weissensteiner R, Ecker GF, Freissmuth M, Sitte HH. Mutational analysis of the high-affinity zinc binding site validates a refined human dopamine transporter homology model. PLoS Comput Biol 2013; 9:e1002909. [PMID: 23436987 PMCID: PMC3578762 DOI: 10.1371/journal.pcbi.1002909] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Accepted: 12/16/2012] [Indexed: 11/24/2022] Open
Abstract
The high-resolution crystal structure of the leucine transporter (LeuT) is frequently used as a template for homology models of the dopamine transporter (DAT). Although similar in structure, DAT differs considerably from LeuT in a number of ways: (i) when compared to LeuT, DAT has very long intracellular amino and carboxyl termini; (ii) LeuT and DAT share a rather low overall sequence identity (22%) and (iii) the extracellular loop 2 (EL2) of DAT is substantially longer than that of LeuT. Extracellular zinc binds to DAT and restricts the transporter‚s movement through the conformational cycle, thereby resulting in a decrease in substrate uptake. Residue H293 in EL2 praticipates in zinc binding and must be modelled correctly to allow for a full understanding of its effects. We exploited the high-affinity zinc binding site endogenously present in DAT to create a model of the complete transmemberane domain of DAT. The zinc binding site provided a DAT-specific molecular ruler for calibration of the model. Our DAT model places EL2 at the transporter lipid interface in the vicinity of the zinc binding site. Based on the model, D206 was predicted to represent a fourth co-ordinating residue, in addition to the three previously described zinc binding residues H193, H375 and E396. This prediction was confirmed by mutagenesis: substitution of D206 by lysine and cysteine affected the inhibitory potency of zinc and the maximum inhibition exerted by zinc, respectively. Conversely, the structural changes observed in the model allowed for rationalizing the zinc-dependent regulation of DAT: upon binding, zinc stabilizes the outward-facing state, because its first coordination shell can only be completed in this conformation. Thus, the model provides a validated solution to the long extracellular loop and may be useful to address other aspects of the transport cycle. The dopamine transporter (DAT) regulates dopaminergic neurotransmission in the brain and is implicated in numerous human disease states. DAT is unique among the monoamine neurotransmitter transporter family because its substrate transport is inhibited by extracellular zinc. DAT homology models rely upon the crystal structure of LeuT solved in 2005. LeuT and DAT share a relatively low overall sequence identity of 22%. In addition, the length of the second extracellular loop of DAT exceeds that of LeuT by 21 residues. The zinc binding site cannot be directly modeled from the LeuT template alone because of these differences. Current available homology models of DAT focused on substrate or inhibitor binding rather than on the second extracellular loop. We exploited the specificity of the zinc binding site to build and calibrate a DAT homology model of the complete transmembrane domain. Our model predicted that the zinc binding site in DAT consists of four zinc co-ordinating residues rather than three that had been previously identified. We verified this hypothesis by site-directed mutagenesis and uptake inhibition studies.
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Affiliation(s)
- Thomas Stockner
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University Vienna, Vienna, Austria
| | - Therese R. Montgomery
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University Vienna, Vienna, Austria
| | - Oliver Kudlacek
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University Vienna, Vienna, Austria
| | | | - Gerhard F. Ecker
- Department of Medicinal Chemistry, University of Vienna, Vienna, Austria
| | - Michael Freissmuth
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University Vienna, Vienna, Austria
| | - Harald H. Sitte
- Center of Physiology and Pharmacology, Institute of Pharmacology, Medical University Vienna, Vienna, Austria
- * E-mail:
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22
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Sotomayor-Zárate R, Quiroz G, Araya KA, Abarca J, Ibáñez MR, Montecinos A, Guajardo C, Núñez G, Fierro A, Moya PR, Iturriaga-Vásquez P, Gómez-Molina C, Gysling K, Reyes-Parada M. 4-Methylthioamphetamine Increases Dopamine in the Rat Striatum and has Rewarding EffectsIn Vivo. Basic Clin Pharmacol Toxicol 2012; 111:371-9. [DOI: 10.1111/j.1742-7843.2012.00926.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 06/07/2012] [Indexed: 11/26/2022]
Affiliation(s)
- Ramón Sotomayor-Zárate
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
- Departamento de Fisiología, Facultad de Ciencias; Universidad de Valparaíso; Valparaíso Chile
| | - Gabriel Quiroz
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Katherine A. Araya
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Jorge Abarca
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - María R. Ibáñez
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Alejandro Montecinos
- Faculty of Chemistry and Biology; University of Santiago de Chile; Santiago Chile
| | - Carlos Guajardo
- Faculty of Chemistry and Biology; University of Santiago de Chile; Santiago Chile
| | - Gabriel Núñez
- PhD Program in Biotechnology, Faculty of Chemistry and Biology; University of Santiago de Chile; Santiago Chile
| | - Angélica Fierro
- Faculty of Chemistry and Biology; University of Santiago de Chile; Santiago Chile
- Millennium Institute for Cell Dynamics and Biotechnology; Santiago Chile
| | - Pablo R. Moya
- Laboratory of Clinical Science; National Institute of Mental Health; Bethesda MD USA
| | - Patricio Iturriaga-Vásquez
- Millennium Institute for Cell Dynamics and Biotechnology; Santiago Chile
- Department of Chemistry, Faculty of Sciences; University of Chile; Santiago Chile
| | | | - Katia Gysling
- Millennium Science Nucleus in Stress and Addiction and Department of Cell and Molecular Biology, Faculty of Biological Sciences; Pontificia Universidad Católica de Chile; Santiago Chile
| | - Miguel Reyes-Parada
- Millennium Institute for Cell Dynamics and Biotechnology; Santiago Chile
- Faculty of Medical Sciences; School of Medicine, University of Santiago de Chile; Santiago Chile
- Facultad de Ciencias de la Salud; Universidad Autónoma de Chile; Santiago Chile
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23
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Manepalli S, Surratt CK, Madura JD, Nolan TL. Monoamine transporter structure, function, dynamics, and drug discovery: a computational perspective. AAPS JOURNAL 2012; 14:820-31. [PMID: 22918625 DOI: 10.1208/s12248-012-9391-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 07/09/2012] [Indexed: 11/30/2022]
Abstract
With the breakthrough crystallization of the bacterial leucine transporter protein LeuT, the first available X-ray structure for the neurotransmitter/sodium symporter family, development of 3-D computational models is suddenly essential for structure-function studies on the plasmalemmal monoamine transporters (MATs). LeuT-based MAT models have been used to guide elucidation of substrate and inhibitor binding pockets, and molecular dynamics simulations using these models are providing insight into conformations involved in the substrate translocation cycle. With credible MAT models finally in hand, structure-based virtual screening for novel ligands is yielding lead compounds toward the development of new medications for psychostimulant dependence, attention deficit hyperactivity, depression, anxiety, schizophrenia, and other disorders associated with dopamine, norepinephrine, or serotonin dysregulation.
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Affiliation(s)
- Sankar Manepalli
- Department of Chemistry and Biochemistry, Center for Computational Sciences, Duquesne University, Pittsburgh, Pennsylvania, USA
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24
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Reith MEA, Ali S, Hashim A, Sheikh IS, Theddu N, Gaddiraju NV, Mehrotra S, Schmitt KC, Murray TF, Sershen H, Unterwald EM, Davis FA. Novel C-1 substituted cocaine analogs unlike cocaine or benztropine. J Pharmacol Exp Ther 2012; 343:413-25. [PMID: 22895898 DOI: 10.1124/jpet.112.193771] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Despite a wealth of information on cocaine-like compounds, there is no information on cocaine analogs with substitutions at C-1. Here, we report on (R)-(-)-cocaine analogs with various C-1 substituents: methyl (2), ethyl (3), n-propyl (4), n-pentyl (5), and phenyl (6). Analog 2 was equipotent to cocaine as an inhibitor of the dopamine transporter (DAT), whereas 3 and 6 were 3- and 10-fold more potent, respectively. None of the analogs, however, stimulated mouse locomotor activity, in contrast to cocaine. Pharmacokinetic assays showed compound 2 occupied mouse brain rapidly, as cocaine itself; moreover, 2 and 6 were behaviorally active in mice in the forced-swim test model of depression and the conditioned place preference test. Analog 2 was a weaker inhibitor of voltage-dependent Na+ channels than cocaine, although 6 was more potent than cocaine, highlighting the need to assay future C-1 analogs for this activity. Receptorome screening indicated few significant binding targets other than the monoamine transporters. Benztropine-like "atypical" DAT inhibitors are known to display reduced cocaine-like locomotor stimulation, presumably by their propensity to interact with an inward-facing transporter conformation. However, 2 and 6, like cocaine, but unlike benztropine, exhibited preferential interaction with an outward-facing conformation upon docking in our DAT homology model. In summary, C-1 cocaine analogs are not cocaine-like in that they are not stimulatory in vivo. However, they are not benztropine-like in binding mechanism and seem to interact with the DAT similarly to cocaine. The present data warrant further consideration of these novel cocaine analogs for antidepressant or cocaine substitution potential.
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Affiliation(s)
- Maarten E A Reith
- Department of Psychiatry, New York University School of Medicine, 450 E 29th Street, Alexandria Building Room 803, New York, NY 10016, USA.
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25
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Rothman RB, Partilla JS, Baumann MH, Lightfoot-Siordia C, Blough BE. Studies of the biogenic amine transporters. 14. Identification of low-efficacy "partial" substrates for the biogenic amine transporters. J Pharmacol Exp Ther 2012; 341:251-62. [PMID: 22271821 DOI: 10.1124/jpet.111.188946] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Several compounds have been identified that display low-efficacy, "partial substrate" activity. Here, we tested the hypothesis that the mechanism of this effect is a slower rate of induced neurotransmitter efflux than that produced by full substrates. Biogenic amine transporter release assays were carried out in rat brain synaptosomes and followed published procedures. [(3)H]1-methyl-4-phenylpyridinium (MPP(+)) was used to assess release from dopamine (DA) and norepinephrine nerve terminals, whereas [(3)H]5-hydroxytryptamine (5-HT) was used to assess release from 5-HT nerve terminals. A detailed time-course evaluation of DA transporter (DAT)-mediated efflux was conducted by measuring the efflux of [(3)H]MPP(+) after the addition of various test compounds. In vivo microdialysis experiments compared the effects of the full substrates [(±)-1-(2-naphthyl)propan-2-amine (PAL-287) and (S)-N-methyl-1-(2-naphthyl)propan-2-amine (PAL-1046)], to that of a partial DAT/5-HT transporter substrate [(S)-N-ethyl-1-(2-naphthyl)propan-2-amine (PAL-1045)] on extracellular DA and 5-HT in the nucleus accumbens of the rat. The in vitro release assays demonstrated that partial substrate activity occurs at all three transporters. In the DAT efflux experiments, D-amphetamine (full substrate) promoted a fast efflux (K1 = 0.24 min(-1)) and a slow efflux (K2 = 0.008 min(-1)). For the partial DAT substrates, K1 = ∼0.04 min(-1), and K2 approximated zero. The in vivo microdialysis experiments showed that the partial substrate (PAL-1045) was much less effective in elevating extracellular DA and 5-HT than the comparator full substrates. We conclude that low-efficacy partial DAT substrates promote efflux at a slower rate than full substrates, and "partiality" reflects the ultra-slow K2 constant, which functionally limits the ability of these compounds to increase extracellular DA. We speculate that partial biogenic amine transporter substrates bind to the transporter but are less effective in inducing conformational changes required for reverse transport activity.
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Affiliation(s)
- Richard B Rothman
- Translational Pharmacology Section, Intramural Research Program, National Institute on Drug Abuse, 333 Cassell Drive, Suite 4500, Baltimore, MD 21224, USA.
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26
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Wildling L, Rankl C, Haselgrübler T, Gruber HJ, Holy M, Newman AH, Zou MF, Zhu R, Freissmuth M, Sitte HH, Hinterdorfer P. Probing binding pocket of serotonin transporter by single molecular force spectroscopy on living cells. J Biol Chem 2011; 287:105-113. [PMID: 22033932 PMCID: PMC3249061 DOI: 10.1074/jbc.m111.304873] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
The serotonin transporter (SERT) terminates neurotransmission by removing serotonin from the synaptic cleft. In addition, it is the site of action of antidepressants (which block the transporter) and of amphetamines (which induce substrate efflux). The interaction energies involved in binding of such compounds to the transporter are unknown. Here, we used atomic force microscopy (AFM) to probe single molecular interactions between the serotonin transporter and MFZ2-12 (a potent cocaine analog) in living CHOK1 cells. For the AFM measurements, MFZ2-12 was immobilized on AFM tips by using a heterobifunctional cross-linker. By varying the pulling velocity in force distance cycles drug-transporter complexes were ruptured at different force loadings allowing for mapping of the interaction energy landscape. We derived chemical rate constants from these recordings and compared them with those inferred from inhibition of transport and ligand binding: koff values were in good agreement with those derived from uptake experiments; in contrast, the kon values were scaled down when determined by AFM. Our observations generated new insights into the energy landscape of the interaction between SERT and inhibitors. They thus provide a useful framework for molecular dynamics simulations by exploring the range of forces and energies that operate during the binding reaction.
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Affiliation(s)
- Linda Wildling
- Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstrasse 69, 4040 Linz, Austria
| | - Christian Rankl
- Agilent Technologies, Austria GmbH, Aubrunnerweg 11, 4040 Linz, Austria
| | | | - Hermann J Gruber
- Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstrasse 69, 4040 Linz, Austria
| | - Marion Holy
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Amy Hauck Newman
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224
| | - Mu-Fa Zou
- Medicinal Chemistry Section, Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224
| | - Rong Zhu
- Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstrasse 69, 4040 Linz, Austria
| | - Michael Freissmuth
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Harald H Sitte
- Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Peter Hinterdorfer
- Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstrasse 69, 4040 Linz, Austria; Center for Advanced Bioanalysis, Scharitzerstrasse 6-8, 4020 Linz, Austria.
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27
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The atypical stimulant and nootropic modafinil interacts with the dopamine transporter in a different manner than classical cocaine-like inhibitors. PLoS One 2011; 6:e25790. [PMID: 22043293 PMCID: PMC3197159 DOI: 10.1371/journal.pone.0025790] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 09/11/2011] [Indexed: 11/19/2022] Open
Abstract
Modafinil is a mild psychostimulant with pro-cognitive and antidepressant effects. Unlike many conventional stimulants, modafinil has little appreciable potential for abuse, making it a promising therapeutic agent for cocaine addiction. The chief molecular target of modafinil is the dopamine transporter (DAT); however, the mechanistic details underlying modafinil's unique effects remain unknown. Recent studies suggest that the conformational effects of a given DAT ligand influence the magnitude of the ligand's reinforcing properties. For example, the atypical DAT inhibitors benztropine and GBR12909 do not share cocaine's notorious addictive liability, despite having greater binding affinity. Here, we show that the binding mechanism of modafinil is different than cocaine and similar to other atypical inhibitors. We previously established two mutations (W84L and D313N) that increase the likelihood that the DAT will adopt an outward-facing conformational state—these mutations increase the affinity of cocaine-like inhibitors considerably, but have little or opposite effect on atypical inhibitor binding. Thus, a compound's WT/mutant affinity ratio can indicate whether the compound preferentially interacts with a more outward- or inward-facing conformational state. Modafinil displayed affinity ratios similar to those of benztropine, GBR12909 and bupropion (which lack cocaine-like effects in humans), but far different than those of cocaine, β-CFT or methylphenidate. Whereas treatment with zinc (known to stabilize an outward-facing transporter state) increased the affinity of cocaine and methylphenidate two-fold, it had little or no effect on the binding of modafinil, benztropine, bupropion or GBR12909. Additionally, computational modeling of inhibitor binding indicated that while β-CFT and methylphenidate stabilize an “open-to-out” conformation, binding of either modafinil or bupropion gives rise to a more closed conformation. Our findings highlight a mechanistic difference between modafinil and cocaine-like stimulants and further demonstrate that the conformational effects of a given DAT inhibitor influence its phenomenological effects.
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28
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Molecular determinants for selective recognition of antidepressants in the human serotonin and norepinephrine transporters. Proc Natl Acad Sci U S A 2011; 108:12137-42. [PMID: 21730142 DOI: 10.1073/pnas.1103060108] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inhibitors of the serotonin transporter (SERT) and norepinephrine transporter (NET) are widely used in the treatment of major depressive disorder. Although SERT/NET selectivity is a key determinant for the therapeutic properties of these drugs, the molecular determinants defining SERT/NET selectivity are poorly understood. In this study, the structural basis for selectivity of the SERT selective inhibitor citalopram and the structurally closely related NET selective inhibitor talopram is delineated. A systematic structure-activity relationship study allowed identification of the substituents that control activity and selectivity toward SERT and NET and revealed a common pattern showing that SERT and NET have opposite preference for the stereochemical configuration of these inhibitors. Mutational analysis of nonconserved SERT/NET residues within the central substrate binding site was performed to determine the molecular basis for inhibitor selectivity. Changing only five residues in NET to the complementary residues in SERT transferred a SERT-like affinity profile for R- and S-citalopram into NET, showing that the selectivity of these compounds is determined by amino acid differences in the central binding site of the transporters. In contrast, the activity of R- and S-talopram was largely unaffected by any mutations within the central substrate binding site of SERT and NET and in the outer vestibule of NET, suggesting that citalopram and talopram bind to distinct sites on SERT and NET. Together, these findings provide important insight into the molecular basis for SERT/NET selectivity of antidepressants, which can be used to guide rational development of unique transporter inhibitors with fine-tuned transporter selectivity.
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29
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Clinical and molecular characterisation of hereditary dopamine transporter deficiency syndrome: an observational cohort and experimental study. Lancet Neurol 2010; 10:54-62. [PMID: 21112253 PMCID: PMC3002401 DOI: 10.1016/s1474-4422(10)70269-6] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
BACKGROUND dopamine transporter deficiency syndrome is the first identified parkinsonian disorder caused by genetic alterations of the dopamine transporter. We describe a cohort of children with mutations in the gene encoding the dopamine transporter (SLC6A3) with the aim to improve clinical and molecular characterisation, reduce diagnostic delay and misdiagnosis, and provide insights into the pathophysiological mechanisms. METHODS 11 children with a biochemical profile suggestive of dopamine transporter deficiency syndrome were enrolled from seven paediatric neurology centres in the UK, Germany, and the USA from February, 2009, and studied until June, 2010. The syndrome was characterised by detailed clinical phenotyping, biochemical and neuroradiological studies, and SLC6A3 mutation analysis. Mutant constructs of human dopamine transporter were used for in-vitro functional analysis of dopamine uptake and cocaine-analogue binding. FINDINGS children presented in infancy (median age 2·5 months, range 0·5-7) with either hyperkinesia (n=5), parkinsonism (n=4), or a mixed hyperkinetic and hypokinetic movement disorder (n=2). Seven children had been initially misdiagnosed with cerebral palsy. During childhood, patients developed severe parkinsonism-dystonia associated with an eye movement disorder and pyramidal tract features. All children had raised ratios of homovanillic acid to 5-hydroxyindoleacetic acid in cerebrospinal fluid, of range 5·0-13·2 (normal range 1·3-4·0). Homozygous or compound heterozygous SLC6A3 mutations were detected in all cases. Loss of function in all missense variants was recorded from in-vitro functional studies, and was supported by the findings of single photon emission CT DaTSCAN imaging in one patient, which showed complete loss of dopamine transporter activity in the basal nuclei. INTERPRETATION dopamine transporter deficiency syndrome is a newly recognised, autosomal recessive disorder related to impaired dopamine transporter function. Careful characterisation of patients with this disorder should provide novel insights into the complex role of dopamine homoeostasis in human disease, and understanding of the pathophysiology could help to drive drug development.
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30
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Sarker S, Weissensteiner R, Steiner I, Sitte HH, Ecker GF, Freissmuth M, Sucic S. The high-affinity binding site for tricyclic antidepressants resides in the outer vestibule of the serotonin transporter. Mol Pharmacol 2010; 78:1026-35. [PMID: 20829432 DOI: 10.1124/mol.110.067538] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
Abstract
The structure of the bacterial leucine transporter from Aquifex aeolicus (LeuT(Aa)) has been used as a model for mammalian Na(+)/Cl(-)-dependent transporters, in particular the serotonin transporter (SERT). The crystal structure of LeuT(Aa) liganded to tricyclic antidepressants predicts simultaneous binding of inhibitor and substrate. This is incompatible with the mutually competitive inhibition of substrates and inhibitors of SERT. We explored the binding modes of tricyclic antidepressants by homology modeling and docking studies. Two approaches were used subsequently to differentiate between three clusters of potential docking poses: 1) a diagnostic SERT(Y95F) mutation, which greatly reduced the affinity for [(3)H]imipramine but did not affect substrate binding; 2) competition binding experiments in the presence and absence of carbamazepine (i.e., a tricyclic imipramine analog with a short side chain that competes with [(3)H]imipramine binding to SERT). Binding of releasers (para-chloroamphetamine, methylene-dioxy-methamphetamine/ecstasy) and of carbamazepine were mutually exclusive, but Dixon plots generated in the presence of carbamazepine yielded intersecting lines for serotonin, MPP(+), paroxetine, and ibogaine. These observations are consistent with a model, in which 1) the tricyclic ring is docked into the outer vestibule and the dimethyl-aminopropyl side chain points to the substrate binding site; 2) binding of amphetamines creates a structural change in the inner and outer vestibule that precludes docking of the tricyclic ring; 3) simultaneous binding of ibogaine (which binds to the inward-facing conformation) and of carbamazepine is indicative of a second binding site in the inner vestibule, consistent with the pseudosymmetric fold of monoamine transporters. This may be the second low-affinity binding site for antidepressants.
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Affiliation(s)
- Subhodeep Sarker
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Waehringer Strasse 13a, Vienna, Austria
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31
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Courville P, Quick M, Reimer RJ. Structure-function studies of the SLC17 transporter sialin identify crucial residues and substrate-induced conformational changes. J Biol Chem 2010; 285:19316-23. [PMID: 20424173 PMCID: PMC2885210 DOI: 10.1074/jbc.m110.130716] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 04/26/2010] [Indexed: 11/06/2022] Open
Abstract
Salla disease and infantile sialic acid storage disorder are human diseases caused by loss of function of sialin, a lysosomal transporter that mediates H(+)-coupled symport of acidic sugars N-acetylneuraminic acid and glucuronic acid out of lysosomes. Along with the closely related vesicular glutamate transporters, sialin belongs to the SLC17 transporter family. Despite their critical role in health and disease, these proteins remain poorly understood both structurally and mechanistically. Here, we use substituted cysteine accessibility screening and radiotracer flux assays to evaluate experimentally a computationally generated three-dimensional structure model of sialin. According to this model, sialin consists of 12 transmembrane helices (TMs) with an overall architecture similar to that of the distantly related glycerol 3-phosphate transporter GlpT. We show that TM4 in sialin lines a large aqueous cavity that forms a part of the substrate permeation pathway and demonstrate substrate-induced alterations in accessibility of substituted cysteine residues in TM4. In addition, we demonstrate that one mutant, F179C, has a dramatically different effect on the apparent affinity and transport rate for N-acetylneuraminic acid and glucuronic acid, suggesting that it may be directly involved in substrate recognition and/or translocation. These findings offer a basis for further defining the transport mechanism of sialin and other SLC17 family members.
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Affiliation(s)
- Pascal Courville
- From the Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California 94305 and
| | - Matthias Quick
- the Center for Molecular Recognition, Department of Psychiatry, Columbia University College of Physicians and Surgeons, and Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032
| | - Richard J. Reimer
- From the Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California 94305 and
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32
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Nyola A, Karpowich NK, Zhen J, Marden J, Reith ME, Wang DN. Substrate and drug binding sites in LeuT. Curr Opin Struct Biol 2010; 20:415-22. [PMID: 20739005 DOI: 10.1016/j.sbi.2010.05.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Revised: 05/14/2010] [Accepted: 05/20/2010] [Indexed: 01/13/2023]
Abstract
LeuT is a member of the neurotransmitter/sodium symporter family, which includes the neuronal transporters for serotonin, norepinephrine, and dopamine. The original crystal structure of LeuT shows a primary leucine-binding site at the center of the protein. LeuT is inhibited by different classes of antidepressants that act as potent inhibitors of the serotonin transporter. The newly determined crystal structures of LeuT-antidepressant complexes provide opportunities to probe drug binding in the serotonin transporter, of which the exact position remains controversial. Structure of a LeuT-tryptophan complex shows an overlapping binding site with the primary substrate site. A secondary substrate binding site was recently identified, where the binding of a leucine triggers the cytoplasmic release of the primary substrate. This two binding site model presents opportunities for a better understanding of drug binding and the mechanism of inhibition for mammalian transporters.
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Affiliation(s)
- Ajeeta Nyola
- Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
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