101
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Deng D, Yan N. GLUT, SGLT, and SWEET: Structural and mechanistic investigations of the glucose transporters. Protein Sci 2016; 25:546-58. [PMID: 26650681 DOI: 10.1002/pro.2858] [Citation(s) in RCA: 179] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Revised: 11/20/2015] [Accepted: 12/01/2015] [Indexed: 12/12/2022]
Abstract
Glucose is the primary fuel to life on earth. Cellular uptake of glucose is a fundamental process for metabolism, growth, and homeostasis. Three families of secondary glucose transporters have been identified in human, including the major facilitator superfamily glucose facilitators GLUTs, the sodium-driven glucose symporters SGLTs, and the recently identified SWEETs. Structures of representative members or their prokaryotic homologs of all three families were obtained. This review focuses on the recent advances in the structural elucidation of the glucose transporters and the mechanistic insights derived from these structures, including the molecular basis for substrate recognition, alternating access, and stoichiometric coupling of co-transport.
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Affiliation(s)
- Dong Deng
- State Key Laboratory of Bio-Membrane and Membrane Biotechnology, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China
| | - Nieng Yan
- State Key Laboratory of Bio-Membrane and Membrane Biotechnology, Center for Structural Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China
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102
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Moses M, Hedegård P, Hatzakis N. Quantification of Functional Dynamics of Membrane Proteins Reconstituted in Nanodiscs Membranes by Single Turnover Functional Readout. Methods Enzymol 2016; 581:227-256. [DOI: 10.1016/bs.mie.2016.08.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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103
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Tracer Flux Measurements to Study Outward Transport by Monoamine Neurotransmitter Transporters. NEUROMETHODS 2016. [DOI: 10.1007/978-1-4939-3765-3_2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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104
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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 A, Sitte HH, Hinterdorfer P. Nanopharmacological Force Sensing to Reveal Allosteric Coupling in Transporter Binding Sites. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201508755] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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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105
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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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106
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Li M, Jørgensen SK, McMillan DGG, Krzemiński Ł, Daskalakis NN, Partanen RH, Tutkus M, Tuma R, Stamou D, Hatzakis NS, Jeuken LJC. Single Enzyme Experiments Reveal a Long-Lifetime Proton Leak State in a Heme-Copper Oxidase. J Am Chem Soc 2015; 137:16055-63. [PMID: 26618221 PMCID: PMC4697922 DOI: 10.1021/jacs.5b08798] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Heme-copper oxidases (HCOs) are key
enzymes in prokaryotes and
eukaryotes for energy production during aerobic respiration. They
catalyze the reduction of the terminal electron acceptor, oxygen,
and utilize the Gibbs free energy to transport protons across a membrane
to generate a proton (ΔpH) and electrochemical gradient termed
proton motive force (PMF), which provides the driving force for the
adenosine triphosphate (ATP) synthesis. Excessive PMF is known to
limit the turnover of HCOs, but the molecular mechanism of this regulatory
feedback remains relatively unexplored. Here we present a single-enzyme
study that reveals that cytochrome bo3 from Escherichia coli, an HCO closely homologous
to Complex IV in human mitochondria, can enter a rare, long-lifetime
leak state during which proton flow is reversed. The probability of
entering the leak state is increased at higher ΔpH. By rapidly
dissipating the PMF, we propose that this leak state may enable cytochrome bo3, and possibly other HCOs, to maintain a suitable
ΔpH under extreme redox conditions.
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Affiliation(s)
- Mengqiu Li
- School of Biomedical Sciences, University of Leeds , LS2 9JT Leeds, U.K
| | - Sune K Jørgensen
- Department of Chemistry, Nano-Science Center and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen , 2100 Copenhagen, Denmark
| | | | - Łukasz Krzemiński
- School of Biomedical Sciences, University of Leeds , LS2 9JT Leeds, U.K
| | | | - Riitta H Partanen
- School of Biomedical Sciences, University of Leeds , LS2 9JT Leeds, U.K
| | - Marijonas Tutkus
- Department of Chemistry, Nano-Science Center and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen , 2100 Copenhagen, Denmark
| | - Roman Tuma
- School of Molecular and Cellular Biology, University of Leeds , LS2 9JT Leeds, U.K
| | - Dimitrios Stamou
- Department of Chemistry, Nano-Science Center and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen , 2100 Copenhagen, Denmark
| | - Nikos S Hatzakis
- Department of Chemistry, Nano-Science Center and Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen , 2100 Copenhagen, Denmark
| | - Lars J C Jeuken
- School of Biomedical Sciences, University of Leeds , LS2 9JT Leeds, U.K
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107
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van Oijen AM, Dixon NE. Probing molecular choreography through single-molecule biochemistry. Nat Struct Mol Biol 2015; 22:948-52. [DOI: 10.1038/nsmb.3119] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Accepted: 10/06/2015] [Indexed: 01/09/2023]
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108
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Tavoulari S, Margheritis E, Nagarajan A, DeWitt DC, Zhang YW, Rosado E, Ravera S, Rhoades E, Forrest LR, Rudnick G. Two Na+ Sites Control Conformational Change in a Neurotransmitter Transporter Homolog. J Biol Chem 2015; 291:1456-71. [PMID: 26582198 DOI: 10.1074/jbc.m115.692012] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 12/13/2022] Open
Abstract
In LeuT, a prokaryotic homolog of neurotransmitter transporters, Na(+) stabilizes outward-open conformational states. We examined how each of the two LeuT Na(+) binding sites contributes to Na(+)-dependent closure of the cytoplasmic pathway using biochemical and biophysical assays of conformation. Mutating either of two residues that contribute to the Na2 site completely prevented cytoplasmic closure in response to Na(+), suggesting that Na2 is essential for this conformational change, whereas Na1 mutants retained Na(+) responsiveness. However, mutation of Na1 residues also influenced the Na(+)-dependent conformational change in ways that varied depending on the position mutated. Computational analyses suggest those mutants influence the ability of Na1 binding to hydrate the substrate pathway and perturb an interaction network leading to the extracellular gate. Overall, the results demonstrate that occupation of Na2 stabilizes outward-facing conformations presumably through a direct interaction between Na(+) and transmembrane helices 1 and 8, whereas Na(+) binding at Na1 influences conformational change through a network of intermediary interactions. The results also provide evidence that N-terminal release and helix motions represent distinct steps in cytoplasmic pathway opening.
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Affiliation(s)
| | | | - Anu Nagarajan
- the Computational Structural Biology Section, NINDS, National Institutes of Health, Rockville, Maryland 20852
| | - David C DeWitt
- Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and
| | | | | | | | - Elizabeth Rhoades
- Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and
| | - Lucy R Forrest
- the Computational Structural Biology Section, NINDS, National Institutes of Health, Rockville, Maryland 20852
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109
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Khelashvili G, Stanley N, Sahai MA, Medina J, LeVine MV, Shi L, De Fabritiis G, Weinstein H. Spontaneous inward opening of the dopamine transporter is triggered by PIP2-regulated dynamics of the N-terminus. ACS Chem Neurosci 2015; 6:1825-37. [PMID: 26255829 PMCID: PMC4653762 DOI: 10.1021/acschemneuro.5b00179] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
![]()
We
present the dynamic mechanism of concerted motions in a full-length
molecular model of the human dopamine transporter (hDAT), a member
of the neurotransmitter/sodium symporter (NSS) family, involved in
state-to-state transitions underlying function. The findings result
from an analysis of unbiased atomistic molecular dynamics simulation
trajectories (totaling >14 μs) of the hDAT molecule immersed
in lipid membrane environments with or without phosphatidylinositol
4,5-biphosphate (PIP2) lipids. The N-terminal region of
hDAT (N-term) is shown to have an essential mechanistic role in correlated
rearrangements of specific structural motifs relevant to state-to-state
transitions in the hDAT. The mechanism involves PIP2-mediated
electrostatic interactions between the N-term and the intracellular
loops of the transporter molecule. Quantitative analyses of collective
motions in the trajectories reveal that these interactions correlate
with the inward-opening dynamics of hDAT and are allosterically coupled
to the known functional sites of the transporter. The observed large-scale
motions are enabled by specific reconfiguration of the network of
ionic interactions at the intracellular end of the protein. The isomerization
to the inward-facing state in hDAT is accompanied by concomitant movements
in the extracellular vestibule and results in the release of an Na+ ion from the Na2 site and destabilization of the substrate
dopamine in the primary substrate binding S1 site. The dynamic mechanism
emerging from the findings highlights the involvement of the PIP2-regulated interactions between the N-term and the intracellular
loop 4 in the functionally relevant conformational transitions that
are also similar to those found to underlie state-to-state transitions
in the leucine transporter (LeuT), a prototypical bacterial homologue
of the NSS.
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Affiliation(s)
- George Khelashvili
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
| | - Nathaniel Stanley
- Computational
Biophysics Laboratory (GRIB-IMIM), Universitat Pompeu Fabra, Barcelona
Biomedical Research Park (PRBB), C/Doctor Aiguader 88, 08003 Barcelona, Spain
| | - Michelle A. Sahai
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
| | - Jaime Medina
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
| | - Michael V. LeVine
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
| | - Lei Shi
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
- HRH
Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational
Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York 10065, United States
| | - Gianni De Fabritiis
- Computational
Biophysics Laboratory (GRIB-IMIM), Universitat Pompeu Fabra, Barcelona
Biomedical Research Park (PRBB), C/Doctor Aiguader 88, 08003 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats, Passeig Lluis Companys 23, 08010 Barcelona, Spain
| | - Harel Weinstein
- Department
of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York 10065, United States
- HRH
Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational
Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York 10065, United States
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110
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Billesbølle CB, Krüger MB, Shi L, Quick M, Li Z, Stolzenberg S, Kniazeff J, Gotfryd K, Mortensen JS, Javitch JA, Weinstein H, Loland CJ, Gether U. Substrate-induced unlocking of the inner gate determines the catalytic efficiency of a neurotransmitter:sodium symporter. J Biol Chem 2015; 290:26725-38. [PMID: 26363074 DOI: 10.1074/jbc.m115.677658] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Indexed: 11/06/2022] Open
Abstract
Neurotransmitter:sodium symporters (NSSs) mediate reuptake of neurotransmitters from the synaptic cleft and are targets for several therapeutics and psychostimulants. The prokaryotic NSS homologue, LeuT, represents a principal structural model for Na(+)-coupled transport catalyzed by these proteins. Here, we used site-directed fluorescence quenching spectroscopy to identify in LeuT a substrate-induced conformational rearrangement at the inner gate conceivably leading to formation of a structural intermediate preceding transition to the inward-open conformation. The substrate-induced, Na(+)-dependent change required an intact primary substrate-binding site and involved increased water exposure of the cytoplasmic end of transmembrane segment 5. The findings were supported by simulations predicting disruption of an intracellular interaction network leading to a discrete rotation of transmembrane segment 5 and the adjacent intracellular loop 2. The magnitude of the spectroscopic response correlated inversely with the transport rate for different substrates, suggesting that stability of the intermediate represents an unrecognized rate-limiting barrier in the NSS transport mechanism.
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Affiliation(s)
- Christian B Billesbølle
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Mie B Krüger
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Lei Shi
- Department of Physiology and Biophysics and The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, New York 10065
| | - Matthias Quick
- Center for Molecular Recognition and Departments of Psychiatry and Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032
| | - Zheng Li
- Department of Physiology and Biophysics and
| | | | - Julie Kniazeff
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Kamil Gotfryd
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Jonas S Mortensen
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Jonathan A Javitch
- Center for Molecular Recognition and Departments of Psychiatry and Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032 Pharmacology, Columbia University College of Physicians and Surgeons, New York, New York 10032, and
| | - Harel Weinstein
- Department of Physiology and Biophysics and The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, New York 10065
| | - Claus J Loland
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Ulrik Gether
- From the Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark,
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111
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Claxton DP, Kazmier K, Mishra S, Mchaourab HS. Navigating Membrane Protein Structure, Dynamics, and Energy Landscapes Using Spin Labeling and EPR Spectroscopy. Methods Enzymol 2015; 564:349-87. [PMID: 26477257 DOI: 10.1016/bs.mie.2015.07.026] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
A detailed understanding of the functional mechanism of a protein entails the characterization of its energy landscape. Achieving this ambitious goal requires the integration of multiple approaches including determination of high-resolution crystal structures, uncovering conformational sampling under distinct biochemical conditions, characterizing the kinetics and thermodynamics of transitions between functional intermediates using spectroscopic techniques, and interpreting and harmonizing the data into novel computational models. With increasing sophistication in solution-based and ensemble-oriented biophysical approaches such as electron paramagnetic resonance (EPR) spectroscopy, atomic resolution structural information can be directly linked to conformational sampling in solution. Here, we detail how recent methodological and technological advances in EPR spectroscopy have contributed to the elucidation of membrane protein mechanisms. Furthermore, we aim to assist investigators interested in pursuing EPR studies by providing an introduction to the technique, a primer on experimental design, and a description of the practical considerations of the method toward generating high quality data.
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Affiliation(s)
- Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
| | - Kelli Kazmier
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Smriti Mishra
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
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112
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Substrate-modulated ADP/ATP-transporter dynamics revealed by NMR relaxation dispersion. Nat Struct Mol Biol 2015; 22:636-41. [PMID: 26167881 PMCID: PMC4527935 DOI: 10.1038/nsmb.3059] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2015] [Accepted: 06/16/2015] [Indexed: 12/02/2022]
Abstract
The ADP/ATP carrier (AAC) transports ADP and ATP across the inner mitochondrial membrane. Unlike most transporters that have 2-fold direct or inverted quasi-symmetry, AAC has the apparent 3-fold rotational symmetry. Further, its transport rate is fast for transporters that carry large solutes. Here, we perform comprehensive NMR relaxation dispersion measurements for the yeast AAC carrier 3, which provide residue-specific information on the protein conformational exchange. Our data indicate that AAC is predominantly in the cytosol-facing open state and converts to a lowly populated state in an asymmetric manner despite its three-fold structural symmetry. Binding of the substrate ADP significantly increases the rate of conformational exchange, whereas the inhibitor CATR slows the exchange. These results suggest that while the transporter catalyzes the translocation of substrate, the substrate also facilitates interconversion between alternating states that may be relevant to the transport function.
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113
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Zehnpfennig B, Wiriyasermkul P, Carlson DA, Quick M. Interaction of α-Lipoic Acid with the Human Na+/Multivitamin Transporter (hSMVT). J Biol Chem 2015; 290:16372-82. [PMID: 25971966 DOI: 10.1074/jbc.m114.622555] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Indexed: 11/06/2022] Open
Abstract
The human Na(+)/multivitamin transporter (hSMVT) has been suggested to transport α-lipoic acid (LA), a potent antioxidant and anti-inflammatory agent used in therapeutic applications, e.g. in the treatment of diabetic neuropathy and Alzheimer disease. However, the molecular basis of the cellular delivery of LA and in particular the stereospecificity of the transport process are not well understood. Here, we expressed recombinant hSMVT in Pichia pastoris and used affinity chromatography to purify the detergent-solubilized protein followed by reconstitution of hSMVT in lipid bilayers. Using a combined approach encompassing radiolabeled LA transport and equilibrium binding studies in conjunction with the stabilized R-(+)- and S-(-)-enantiomers and the R,S-(+/-) racemic mixture of LA or lipoamide, we identified the biologically active form of LA, R-LA, to be the physiological substrate of hSMVT. Interaction of R-LA with hSMVT is strictly dependent on Na(+). Under equilibrium conditions, hSMVT can simultaneously bind ~2 molecules of R-LA in a biphasic binding isotherm with dissociation constants (Kd) of 0.9 and 7.4 μm. Transport of R-LA in the oocyte and reconstituted system is exclusively dependent on Na(+) and exhibits an affinity of ~3 μm. Measuring transport with known amounts of protein in proteoliposomes containing hSMVT in outside-out orientation yielded a catalytic turnover number (kcat) of about 1 s(-1), a value that is well in agreement with other Na(+)-coupled transporters. Our data suggest that hSMVT-mediated transport is highly specific for R-LA at our tested concentration range, a finding with wide ramifications for the use of LA in therapeutic applications.
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Affiliation(s)
| | - Pattama Wiriyasermkul
- Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032
| | | | - Matthias Quick
- From the Center for Molecular Recognition and Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032, Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032
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114
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Wang KH, Penmatsa A, Gouaux E. Neurotransmitter and psychostimulant recognition by the dopamine transporter. Nature 2015; 521:322-7. [PMID: 25970245 DOI: 10.1038/nature14431] [Citation(s) in RCA: 311] [Impact Index Per Article: 34.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 03/23/2015] [Indexed: 12/17/2022]
Abstract
Na(+)/Cl(-)-coupled biogenic amine transporters are the primary targets of therapeutic and abused drugs, ranging from antidepressants to the psychostimulants cocaine and amphetamines, and to their cognate substrates. Here we determine X-ray crystal structures of the Drosophila melanogaster dopamine transporter (dDAT) bound to its substrate dopamine, a substrate analogue 3,4-dichlorophenethylamine, the psychostimulants d-amphetamine and methamphetamine, or to cocaine and cocaine analogues. All ligands bind to the central binding site, located approximately halfway across the membrane bilayer, in close proximity to bound sodium and chloride ions. The central binding site recognizes three chemically distinct classes of ligands via conformational changes that accommodate varying sizes and shapes, thus illustrating molecular principles that distinguish substrates from inhibitors in biogenic amine transporters.
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Affiliation(s)
- Kevin H Wang
- Vollum Institute, Oregon Health &Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA
| | - Aravind Penmatsa
- Vollum Institute, Oregon Health &Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA
| | - Eric Gouaux
- 1] Vollum Institute, Oregon Health &Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA [2] Howard Hughes Medical Institute, Oregon Health &Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA
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115
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LeVine MV, Weinstein H. AIM for Allostery: Using the Ising Model to Understand Information Processing and Transmission in Allosteric Biomolecular Systems. ENTROPY 2015; 17:2895-2918. [PMID: 26594108 PMCID: PMC4652859 DOI: 10.3390/e17052895] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In performing their biological functions, molecular machines must process and transmit information with high fidelity. Information transmission requires dynamic coupling between the conformations of discrete structural components within the protein positioned far from one another on the molecular scale. This type of biomolecular “action at a distance” is termed allostery. Although allostery is ubiquitous in biological regulation and signal transduction, its treatment in theoretical models has mostly eschewed quantitative descriptions involving the system's underlying structural components and their interactions. Here, we show how Ising models can be used to formulate an approach to allostery in a structural context of interactions between the constitutive components by building simple allosteric constructs we termed Allosteric Ising Models (AIMs). We introduce the use of AIMs in analytical and numerical calculations that relate thermodynamic descriptions of allostery to the structural context, and then show that many fundamental properties of allostery, such as the multiplicative property of parallel allosteric channels, are revealed from the analysis of such models. The power of exploring mechanistic structural models of allosteric function in more complex systems by using AIMs is demonstrated by building a model of allosteric signaling for an experimentally well-characterized asymmetric homodimer of the dopamine D2 receptor.
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Affiliation(s)
- Michael V. LeVine
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
- Author to whom correspondence should be addressed;
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116
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Stolzenberg S, Quick M, Zhao C, Gotfryd K, Khelashvili G, Gether U, Loland CJ, Javitch JA, Noskov S, Weinstein H, Shi L. Mechanism of the Association between Na+ Binding and Conformations at the Intracellular Gate in Neurotransmitter:Sodium Symporters. J Biol Chem 2015; 290:13992-4003. [PMID: 25869126 PMCID: PMC4447972 DOI: 10.1074/jbc.m114.625343] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Indexed: 11/16/2022] Open
Abstract
Neurotransmitter:sodium symporters (NSSs) terminate neurotransmission by Na+-dependent reuptake of released neurotransmitters. Previous studies suggested that Na+-binding reconfigures dynamically coupled structural elements in an allosteric interaction network (AIN) responsible for function-related conformational changes, but the intramolecular pathway of this mechanism has remained uncharted. We describe a new approach for the modeling and analysis of intramolecular dynamics in the bacterial NSS homolog LeuT. From microsecond-scale molecular dynamics simulations and cognate experimental verifications in both LeuT and human dopamine transporter (hDAT), we apply the novel method to identify the composition and the dynamic properties of their conserved AIN. In LeuT, two different perturbations disrupting Na+ binding and transport (i.e. replacing Na+ with Li+ or the Y268A mutation at the intracellular gate) affect the AIN in strikingly similar ways. In contrast, other mutations that affect the intracellular gate (i.e. R5A and D369A) do not significantly impair Na+ cooperativity and transport. Our analysis shows these perturbations to have much lesser effects on the AIN, underscoring the sensitivity of this novel method to the mechanistic nature of the perturbation. Notably, this set of observations holds as well for hDAT, where the aligned Y335A, R60A, and D436A mutations also produce different impacts on Na+ dependence. Thus, the detailed AIN generated from our method is shown to connect Na+ binding with global conformational changes that are critical for the transport mechanism. That the AIN between the Na+ binding sites and the intracellular gate in bacterial LeuT resembles that in eukaryotic hDAT highlights the conservation of allosteric pathways underlying NSS function.
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Affiliation(s)
- Sebastian Stolzenberg
- From the Department of Physiology and Biophysics and the Department of Physics, Cornell University, Ithaca, New York, 14850
| | - Matthias Quick
- the Departments of Psychiatry and the Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032
| | - Chunfeng Zhao
- the Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Kamil Gotfryd
- the Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark, and
| | | | - Ulrik Gether
- the Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark, and
| | - Claus J Loland
- the Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark, and
| | - Jonathan A Javitch
- the Departments of Psychiatry and the Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032, Pharmacology, Columbia University College of Physicians and Surgeons, New York, New York 10032
| | - Sergei Noskov
- the Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Harel Weinstein
- From the Department of Physiology and Biophysics and Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, New York, 10065,
| | - Lei Shi
- From the Department of Physiology and Biophysics and Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, New York, 10065, the Computational Chemistry and Molecular Biophysics Unit, NIDA, Intramural Research Program, National Institutes of Health, Baltimore, Maryland 21224
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117
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Functional mechanisms of neurotransmitter transporters regulated by lipid-protein interactions of their terminal loops. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1765-74. [PMID: 25847498 DOI: 10.1016/j.bbamem.2015.03.025] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 03/16/2015] [Accepted: 03/23/2015] [Indexed: 01/28/2023]
Abstract
The physiological functions of neurotransmitter:sodium symporters (NSS) in reuptake of neurotransmitters from the synapse into the presynaptic nerve have been shown to be complemented by their involvement, together with non-plasma membrane neurotransmitter transporters, in the reverse transport of substrate (efflux) in response to psychostimulants. Recent experimental evidence implicates highly anionic phosphatidylinositol 4,5-biphosphate (PIP(2)) lipids in such functions of the serotonin (SERT) and dopamine (DAT) transporters. Thus, for both SERT and DAT, neurotransmitter efflux has been shown to be strongly regulated by the presence of PIP(2) lipids in the plasma membrane, and the electrostatic interaction of the N-terminal region of DAT with the negatively charged PIP(2) lipids. We examine the experimentally established phenotypes in a structural context obtained from computational modeling based on recent crystallographic data. The results are shown to set the stage for a mechanistic understanding of physiological actions of neurotransmitter transporters in the NSS family of membrane proteins. This article is part of a Special Issue entitled: Lipid-protein interactions.
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118
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Abraham SJ, Cheng RC, Chew TA, Khantwal CM, Liu CW, Gong S, Nakamoto RK, Maduke M. 13C NMR detects conformational change in the 100-kD membrane transporter ClC-ec1. JOURNAL OF BIOMOLECULAR NMR 2015; 61:209-26. [PMID: 25631353 PMCID: PMC4398623 DOI: 10.1007/s10858-015-9898-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 01/13/2015] [Indexed: 05/03/2023]
Abstract
CLC transporters catalyze the exchange of Cl(-) for H(+) across cellular membranes. To do so, they must couple Cl(-) and H(+) binding and unbinding to protein conformational change. However, the sole conformational changes distinguished crystallographically are small movements of a glutamate side chain that locally gates the ion-transport pathways. Therefore, our understanding of whether and how global protein dynamics contribute to the exchange mechanism has been severely limited. To overcome the limitations of crystallography, we used solution-state (13)C-methyl NMR with labels on methionine, lysine, and engineered cysteine residues to investigate substrate (H(+)) dependent conformational change outside the restraints of crystallization. We show that methyl labels in several regions report H(+)-dependent spectral changes. We identify one of these regions as Helix R, a helix that extends from the center of the protein, where it forms the part of the inner gate to the Cl(-)-permeation pathway, to the extracellular solution. The H(+)-dependent spectral change does not occur when a label is positioned just beyond Helix R, on the unstructured C-terminus of the protein. Together, the results suggest that H(+) binding is mechanistically coupled to closing of the intracellular access-pathway for Cl(-).
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Affiliation(s)
- Sherwin J. Abraham
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Ricky C. Cheng
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Thomas A. Chew
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Chandra M. Khantwal
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Corey W. Liu
- Stanford Magnetic Resonance Laboratory, Stanford University School of Medicine, 299 Campus Drive West, D105 Fairchild Science Building, Stanford, CA 94305
| | - Shimei Gong
- Department of Molecular Physiology and Biological Physics, University of Virginia, PO Box 10011, Charlottesville, VA 22906-0011
| | - Robert K. Nakamoto
- Department of Molecular Physiology and Biological Physics, University of Virginia, PO Box 10011, Charlottesville, VA 22906-0011
| | - Merritt Maduke
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
- corresponding author, , tel (650)-723-9075, fax (650)-725-8021
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119
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Li J, Wen PC, Moradi M, Tajkhorshid E. Computational characterization of structural dynamics underlying function in active membrane transporters. Curr Opin Struct Biol 2015; 31:96-105. [PMID: 25913536 PMCID: PMC4476910 DOI: 10.1016/j.sbi.2015.04.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2015] [Revised: 04/06/2015] [Accepted: 04/07/2015] [Indexed: 11/21/2022]
Abstract
Active transport of materials across the cellular membrane is one the most fundamental processes in biology. In order to accomplish this task, membrane transporters rely on a wide range of conformational changes spanning multiple time and size scales. These molecular events govern key functional aspects in membrane transporters, namely, coordinated gating motions underlying the alternating access mode of operation, and coupling of uphill transport of substrate to various sources of energy, for example, transmembrane electrochemical gradients and ATP binding and hydrolysis. Computational techniques such as molecular dynamics simulations and free energy calculations have equipped us with a powerful repertoire of biophysical tools offering unparalleled spatial and temporal resolutions that can effectively complement experimental methodologies, and therefore help fill the gap of knowledge in understanding the molecular basis of function in membrane transporters.
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Affiliation(s)
- Jing Li
- Department of Biochemistry, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Po-Chao Wen
- Department of Biochemistry, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Mahmoud Moradi
- Department of Biochemistry, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Emad Tajkhorshid
- Department of Biochemistry, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
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120
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Singh SK, Pal A. Biophysical Approaches to the Study of LeuT, a Prokaryotic Homolog of Neurotransmitter Sodium Symporters. Methods Enzymol 2015; 557:167-98. [PMID: 25950965 DOI: 10.1016/bs.mie.2015.01.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ion-coupled secondary transport is utilized by multiple integral membrane proteins as a means of achieving the thermodynamically unfavorable translocation of solute molecules across the lipid bilayer. The chemical nature of these molecules is diverse and includes sugars, amino acids, neurotransmitters, and other ions. LeuT is a sodium-coupled, nonpolar amino acid symporter and eubacterial member of the solute carrier 6 (SLC6) family of Na(+)/Cl(-)-dependent neurotransmitter transporters. Eukaryotic counterparts encompass the clinically and pharmacologically significant transporters for γ-aminobutyric acid (GABA), glycine, serotonin (5-hydroxytryptamine, 5-HT), dopamine (DA), and norepinephrine (NE). Since the crystal structure of LeuT was first solved in 2005, subsequent crystallographic, binding, flux, and spectroscopic studies, complemented with homology modeling and molecular dynamic simulations, have allowed this protein to emerge as a remarkable mechanistic paradigm for both the SLC6 class as well as several other sequence-unrelated SLCs whose members possess astonishingly similar architectures. Despite yielding groundbreaking conceptual advances, this vast treasure trove of data has also been the source of contentious hypotheses. This chapter will present a historical scientific overview of SLC6s; recount how the initial and subsequent LeuT structures were solved, describing the insights they each provided; detail the accompanying functional techniques, emphasizing how they either supported or refuted the static crystallographic data; and assemble these individual findings into a mechanism of transport and inhibition.
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Affiliation(s)
- Satinder K Singh
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA.
| | - Aritra Pal
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA
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121
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Quick M, Shi L. The sodium/multivitamin transporter: a multipotent system with therapeutic implications. VITAMINS AND HORMONES 2015; 98:63-100. [PMID: 25817866 PMCID: PMC5530880 DOI: 10.1016/bs.vh.2014.12.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
The Na(+)/multivitamin transporter (SMVT) is a member of the solute:sodium symporter family that catalyzes the Na(+)-dependent uptake of the structurally diverse water-soluble vitamins pantothenic acid (vitamin B5) and biotin (vitamin H), α-lipoic acid-a vitamin-like substance with strong antioxidant properties-and iodide. The organic substrates of SMVT play central roles in the cellular metabolism and are, therefore, essential for normal human health and development. For example, biotin deficiency leads to growth retardation, dermatological disorders, and neurological disorders. Animal studies have shown that biotin deficiency during pregnancy is directly correlated to embryonic growth retardation, congenital malformation, and death of the embryo. This chapter focuses on the structural and functional features of the human isoform of SMVT (hSMVT); the discovery of which was greatly facilitated by the cloning and expression of hSMVT in tractable expression systems. Special emphasis will be given to mechanistic implications of the transport process of hSMVT that will inform our understanding of the molecular determinants of hSMVT-mediated transport in dynamic context to alleviate the development and optimization of hSMVT as a multipotent platform for drug delivery.
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Affiliation(s)
- Matthias Quick
- Department of Psychiatry, Division of Molecular Therapeutics, Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, New York, USA.
| | - Lei Shi
- Department of Physiology and Biophysics, Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, USA
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122
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Correlating charge movements with local conformational changes of a Na(+)-coupled cotransporter. Biophys J 2014; 106:1618-29. [PMID: 24739161 DOI: 10.1016/j.bpj.2014.02.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 02/13/2014] [Accepted: 02/28/2014] [Indexed: 11/23/2022] Open
Abstract
To gain insight into the steady-state and dynamic characteristics of structural rearrangements of an electrogenic secondary-active cotransporter during its transport cycle, two measures of conformational change (pre-steady-state current relaxations and intensity of fluorescence emitted from reporter fluorophores) were investigated as a function of membrane potential and external substrate. Cysteines were substituted at three believed-new sites in the type IIb Na(+)-coupled inorganic phosphate cotransporter (SLC34A2 flounder isoform) that were predicted to be involved in conformational changes. Labeling at one site resulted in substantial suppression of transport activity, whereas for the other sites, function remained comparable to the wild-type. For these mutants, the properties of the pre-steady-state charge relaxations were similar for each, whereas fluorescence intensity changes differed significantly. Fluorescence changes could be accounted for by simulations using a five-state model with a unique set of apparent fluorescence intensities assigned to each state according to the site of labeling. Fluorescence reported from one site was associated with inward and outward conformations, whereas for the other sites, including four previously indentified sites, emissions were associated principally with one or the other orientation of the transporter. The same membrane potential change induced complementary changes in fluorescence at some sites, which suggested that the microenvironments of the respective fluorophores experience concomitant changes in polarity. In response to step changes in voltage, the pre-steady-state current relaxation and the time course of change in fluorescence intensity were described by single exponentials. For one mutant the time constants matched well with and without external Na(+), providing direct evidence that this label reports conformational changes accompanying intrinsic charge movement and cation interactions.
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123
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Ma L, Yang F, Zheng J. Application of fluorescence resonance energy transfer in protein studies. J Mol Struct 2014; 1077:87-100. [PMID: 25368432 DOI: 10.1016/j.molstruc.2013.12.071] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Since the physical process of fluorescence resonance energy transfer (FRET) was elucidated more than six decades ago, this peculiar fluorescence phenomenon has turned into a powerful tool for biomedical research due to its compatibility in scale with biological molecules as well as rapid developments in novel fluorophores and optical detection techniques. A wide variety of FRET approaches have been devised, each with its own advantages and drawbacks. Especially in the last decade or so, we are witnessing a flourish of FRET applications in biological investigations, many of which exemplify clever experimental design and rigorous analysis. Here we review the current stage of FRET methods development with the main focus on its applications in protein studies in biological systems, by summarizing the basic components of FRET techniques, most established quantification methods, as well as potential pitfalls, illustrated by example applications.
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Affiliation(s)
- Linlin Ma
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, CA 95616, USA ; Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Fan Yang
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, CA 95616, USA
| | - Jie Zheng
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, CA 95616, USA
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124
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Bavishi K, Hatzakis NS. Shedding light on protein folding, structural and functional dynamics by single molecule studies. Molecules 2014; 19:19407-34. [PMID: 25429564 PMCID: PMC6272019 DOI: 10.3390/molecules191219407] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 11/07/2014] [Accepted: 11/12/2014] [Indexed: 11/16/2022] Open
Abstract
The advent of advanced single molecule measurements unveiled a great wealth of dynamic information revolutionizing our understanding of protein dynamics and behavior in ways unattainable by conventional bulk assays. Equipped with the ability to record distribution of behaviors rather than the mean property of a population, single molecule measurements offer observation and quantification of the abundance, lifetime and function of multiple protein states. They also permit the direct observation of the transient and rarely populated intermediates in the energy landscape that are typically averaged out in non-synchronized ensemble measurements. Single molecule studies have thus provided novel insights about how the dynamic sampling of the free energy landscape dictates all aspects of protein behavior; from its folding to function. Here we will survey some of the state of the art contributions in deciphering mechanisms that underlie protein folding, structural and functional dynamics by single molecule fluorescence microscopy techniques. We will discuss a few selected examples highlighting the power of the emerging techniques and finally discuss the future improvements and directions.
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Affiliation(s)
- Krutika Bavishi
- Plant Biochemistry Laboratory, Department of Plant and Environmental Sciences, Center for Synthetic Biology "bioSYNergy", Villum Research Center "Plant Plasticity", University of Copenhagen, Thorvaldsenvej 40, DK-1871 Frederiksberg C, Denmark.
| | - Nikos S Hatzakis
- Bio-Nanotechnology Laboratory, Department of Chemistry, Nano-Science Center, Lundbeck Foundation Center Biomembranes in Nanomedicine, University of Copenhagen, 2100 Copenhagen, Denmark.
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125
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Li Z, Lee ASE, Bracher S, Jung H, Paz A, Kumar JP, Abramson J, Quick M, Shi L. Identification of a second substrate-binding site in solute-sodium symporters. J Biol Chem 2014; 290:127-41. [PMID: 25398883 DOI: 10.1074/jbc.m114.584383] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The structure of the sodium/galactose transporter (vSGLT), a solute-sodium symporter (SSS) from Vibrio parahaemolyticus, shares a common structural fold with LeuT of the neurotransmitter-sodium symporter family. Structural alignments between LeuT and vSGLT reveal that the crystallographically identified galactose-binding site in vSGLT is located in a more extracellular location relative to the central substrate-binding site (S1) in LeuT. Our computational analyses suggest the existence of an additional galactose-binding site in vSGLT that aligns to the S1 site of LeuT. Radiolabeled galactose saturation binding experiments indicate that, like LeuT, vSGLT can simultaneously bind two substrate molecules under equilibrium conditions. Mutating key residues in the individual substrate-binding sites reduced the molar substrate-to-protein binding stoichiometry to ~1. In addition, the related and more experimentally tractable SSS member PutP (the Na(+)/proline transporter) also exhibits a binding stoichiometry of 2. Targeting residues in the proposed sites with mutations results in the reduction of the binding stoichiometry and is accompanied by severely impaired translocation of proline. Our data suggest that substrate transport by SSS members requires both substrate-binding sites, thereby implying that SSSs and neurotransmitter-sodium symporters share common mechanistic elements in substrate transport.
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Affiliation(s)
- Zheng Li
- From the Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, New York 10065
| | - Ashley S E Lee
- the Center for Molecular Recognition and Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032
| | - Susanne Bracher
- the Ludwig Maximilian University of Munich, Biocentre, Microbiology, Grosshaderner Strasse 2-4, Martinsried, D-82152, Germany
| | - Heinrich Jung
- the Ludwig Maximilian University of Munich, Biocentre, Microbiology, Grosshaderner Strasse 2-4, Martinsried, D-82152, Germany
| | - Aviv Paz
- the Department of Physiology, UCLA, Los Angeles, California 90095
| | - Jay P Kumar
- the Institute for Stem Cell Biology and Regenerative Medicine, NCBS Campus, GKVK Post, Bellary Road, Bangalore-560065, Karnataka, India
| | - Jeff Abramson
- the Department of Physiology, UCLA, Los Angeles, California 90095, the Institute for Stem Cell Biology and Regenerative Medicine, NCBS Campus, GKVK Post, Bellary Road, Bangalore-560065, Karnataka, India
| | - Matthias Quick
- the Center for Molecular Recognition and Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032, the Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032, and
| | - Lei Shi
- From the Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, New York 10065, the Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, New York 10021
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126
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Zomot E, Gur M, Bahar I. Microseconds simulations reveal a new sodium-binding site and the mechanism of sodium-coupled substrate uptake by LeuT. J Biol Chem 2014; 290:544-55. [PMID: 25381247 PMCID: PMC4281755 DOI: 10.1074/jbc.m114.617555] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The bacterial sodium-coupled leucine/alanine transporter LeuT is broadly used as a model system for studying the transport mechanism of neurotransmitters because of its structural and functional homology to mammalian transporters such as serotonin, dopamine, or norepinephrine transporters, and because of the resolution of its structure in different states. Although the binding sites (S1 for substrate, and Na1 and Na2 for two co-transported sodium ions) have been resolved, we still lack a mechanistic understanding of coupled Na(+)- and substrate-binding events. We present here results from extensive (>20 μs) unbiased molecular dynamics simulations generated using the latest computing technology. Simulations show that sodium binds initially the Na1 site, but not Na2, and, consistently, sodium unbinding/escape to the extracellular (EC) region first takes place at Na2, succeeded by Na1. Na2 diffusion back to the EC medium requires prior dissociation of substrate from S1. Significantly, Na(+) binding (and unbinding) consistently involves a transient binding to a newly discovered site, Na1″, near S1, as an intermediate state. A robust sequence of substrate uptake events coupled to sodium bindings and translocations between those sites assisted by hydration emerges from the simulations: (i) bindings of a first Na(+) to Na1″, translocation to Na1, a second Na(+) to vacated Na1″ and then to Na2, and substrate to S1; (ii) rotation of Phe(253) aromatic group to seclude the substrate from the EC region; and (iii) concerted tilting of TM1b and TM6a toward TM3 and TM8 to close the EC vestibule.
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Affiliation(s)
- Elia Zomot
- From the Department of Computational & Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Mert Gur
- From the Department of Computational & Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Ivet Bahar
- From the Department of Computational & Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
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127
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Dahal RA, Pramod AB, Sharma B, Krout D, Foster JD, Cha JH, Cao J, Newman AH, Lever JR, Vaughan RA, Henry LK. Computational and biochemical docking of the irreversible cocaine analog RTI 82 directly demonstrates ligand positioning in the dopamine transporter central substrate-binding site. J Biol Chem 2014; 289:29712-27. [PMID: 25179220 PMCID: PMC4207985 DOI: 10.1074/jbc.m114.571521] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 08/09/2014] [Indexed: 12/20/2022] Open
Abstract
The dopamine transporter (DAT) functions as a key regulator of dopaminergic neurotransmission via re-uptake of synaptic dopamine (DA). Cocaine binding to DAT blocks this activity and elevates extracellular DA, leading to psychomotor stimulation and addiction, but the mechanisms by which cocaine interacts with DAT and inhibits transport remain incompletely understood. Here, we addressed these questions using computational and biochemical methodologies to localize the binding and adduction sites of the photoactivatable irreversible cocaine analog 3β-(p-chlorophenyl)tropane-2β-carboxylic acid, 4'-azido-3'-iodophenylethyl ester ([(125)I]RTI 82). Comparative modeling and small molecule docking indicated that the tropane pharmacophore of RTI 82 was positioned in the central DA active site with an orientation that juxtaposed the aryliodoazide group for cross-linking to rat DAT Phe-319. This prediction was verified by focused methionine substitution of residues flanking this site followed by cyanogen bromide mapping of the [(125)I]RTI 82-labeled mutants and by the substituted cysteine accessibility method protection analyses. These findings provide positive functional evidence linking tropane pharmacophore interaction with the core substrate-binding site and support a competitive mechanism for transport inhibition. This synergistic application of computational and biochemical methodologies overcomes many uncertainties inherent in other approaches and furnishes a schematic framework for elucidating the ligand-protein interactions of other classes of DA transport inhibitors.
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Affiliation(s)
- Rejwi Acharya Dahal
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203
| | - Akula Bala Pramod
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203
| | - Babita Sharma
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203
| | - Danielle Krout
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203
| | - James D Foster
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203
| | - Joo Hwan Cha
- the Medicinal Chemistry Section, National Institute on Drug Abuse-Intramural Research Program, Baltimore, Maryland 21224
| | - Jianjing Cao
- the Medicinal Chemistry Section, National Institute on Drug Abuse-Intramural Research Program, Baltimore, Maryland 21224
| | - Amy Hauck Newman
- the Medicinal Chemistry Section, National Institute on Drug Abuse-Intramural Research Program, Baltimore, Maryland 21224
| | - John R Lever
- the Research Service, Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65201, and the Department of Radiology, Radiopharmaceutical Sciences Institute, and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri 65211
| | - Roxanne A Vaughan
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203,
| | - L Keith Henry
- From the Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203,
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128
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Pedersen AV, Andreassen TF, Loland CJ. A conserved salt bridge between transmembrane segments 1 and 10 constitutes an extracellular gate in the dopamine transporter. J Biol Chem 2014; 289:35003-14. [PMID: 25339174 DOI: 10.1074/jbc.m114.586982] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Neurotransmitter transporters play an important role in termination of synaptic transmission by mediating reuptake of neurotransmitter, but the molecular processes behind translocation are still unclear. The crystal structures of the bacterial homologue, LeuT, provided valuable insight into the structural and dynamic requirements for substrate transport. These structures support the existence of gating domains controlling access to a central binding site. On the extracellular side, access is controlled by the "thin gate" formed by an interaction between Arg-30 and Asp-404. In the human dopamine transporter (DAT), the corresponding residues are Arg-85 and Asp-476. Here, we present results supporting the existence of a similar interaction in DAT. The DAT R85D mutant has a complete loss of function, but the additional insertion of an arginine in opposite position (R85D/D476R), causing a charge reversal, results in a rescue of binding sites for the cocaine analogue [(3)H]CFT. Also, the coordination of Zn(2+) between introduced histidines (R85H/D476H) caused a ∼ 2.5-fold increase in [(3)H]CFT binding (Bmax). Importantly, Zn(2+) also inhibited [(3)H]dopamine transport in R85H/D476H, suggesting that a dynamic interaction is required for the transport process. Furthermore, cysteine-reactive chemistry shows that mutation of the gating residues causes a higher proportion of transporters to reside in the outward facing conformation. Finally, we show that charge reversal of the corresponding residues (R104E/E493R) in the serotonin transporter also rescues [(3)H](S)-citalopram binding, suggesting a conserved feature. Taken together, these data suggest that the extracellular thin gate is present in monoamine transporters and that a dynamic interaction is required for substrate transport.
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Affiliation(s)
- Anders V Pedersen
- From the Department of Neuroscience and Pharmacology, Molecular Neuropharmacology Laboratory, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Thorvald F Andreassen
- From the Department of Neuroscience and Pharmacology, Molecular Neuropharmacology Laboratory, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Claus J Loland
- From the Department of Neuroscience and Pharmacology, Molecular Neuropharmacology Laboratory, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen, Denmark
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129
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Cheng MH, Bahar I. Complete mapping of substrate translocation highlights the role of LeuT N-terminal segment in regulating transport cycle. PLoS Comput Biol 2014; 10:e1003879. [PMID: 25299050 PMCID: PMC4191883 DOI: 10.1371/journal.pcbi.1003879] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 08/26/2014] [Indexed: 11/19/2022] Open
Abstract
Neurotransmitter: sodium symporters (NSSs) regulate neuronal signal transmission by clearing excess neurotransmitters from the synapse, assisted by the co-transport of sodium ions. Extensive structural data have been collected in recent years for several members of the NSS family, which opened the way to structure-based studies for a mechanistic understanding of substrate transport. Leucine transporter (LeuT), a bacterial orthologue, has been broadly adopted as a prototype in these studies. This goal has been elusive, however, due to the complex interplay of global and local events as well as missing structural data on LeuT N-terminal segment. We provide here for the first time a comprehensive description of the molecular events leading to substrate/Na+ release to the postsynaptic cell, including the structure and dynamics of the N-terminal segment using a combination of molecular simulations. Substrate and Na+-release follows an influx of water molecules into the substrate/Na+-binding pocket accompanied by concerted rearrangements of transmembrane helices. A redistribution of salt bridges and cation-π interactions at the N-terminal segment prompts substrate release. Significantly, substrate release is followed by the closure of the intracellular gate and a global reconfiguration back to outward-facing state to resume the transport cycle. Two minimally hydrated intermediates, not structurally resolved to date, are identified: one, substrate-bound, stabilized during the passage from outward- to inward-facing state (holo-occluded), and another, substrate-free, along the reverse transition (apo-occluded).
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Affiliation(s)
- Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States of America
| | - Ivet Bahar
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, United States of America
- * E-mail:
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130
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Ghoneim M, Spies M. Direct correlation of DNA binding and single protein domain motion via dual illumination fluorescence microscopy. NANO LETTERS 2014; 14:5920-31. [PMID: 25204359 PMCID: PMC4189620 DOI: 10.1021/nl502890g] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
We report a dual illumination, single-molecule imaging strategy to dissect directly and in real-time the correlation between nanometer-scale domain motion of a DNA repair protein and its interaction with individual DNA substrates. The strategy was applied to XPD, an FeS cluster-containing DNA repair helicase. Conformational dynamics was assessed via FeS-mediated quenching of a fluorophore site-specifically incorporated into XPD. Simultaneously, binding of DNA molecules labeled with a spectrally distinct fluorophore was detected by colocalization of the DNA- and protein-derived signals. We show that XPD undergoes thermally driven conformational transitions that manifest in spatial separation of its two auxiliary domains. DNA binding does not strictly enforce a specific conformation. Interaction with a cognate DNA damage, however, stabilizes the compact conformation of XPD by increasing the weighted average lifetime of this state by 140% relative to an undamaged DNA. Our imaging strategy will be a valuable tool to study other FeS-containing nucleic acid processing enzymes.
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Affiliation(s)
- Mohamed Ghoneim
- Center
for Biophysics and Computational Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Department
of Biochemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Maria Spies
- Department
of Biochemistry, University of Iowa, Iowa City, Iowa 52242, United States
- E-mail: . Phone +1-319-335-3221
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131
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A mechanism for intracellular release of Na+ by neurotransmitter/sodium symporters. Nat Struct Mol Biol 2014; 21:1006-12. [PMID: 25282149 DOI: 10.1038/nsmb.2894] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2014] [Accepted: 08/26/2014] [Indexed: 12/11/2022]
Abstract
Neurotransmitter/sodium symporters (NSSs) terminate synaptic signal transmission by Na+-dependent reuptake of released neurotransmitters. Key conformational states have been reported for the bacterial homolog LeuT and an inhibitor-bound Drosophila dopamine transporter. However, a coherent mechanism of Na+-driven transport has not been described. Here, we present two crystal structures of MhsT, an NSS member from Bacillus halodurans, in occluded inward-facing states with bound Na+ ions and L-tryptophan, providing insight into the cytoplasmic release of Na+. The switch from outward- to inward-oriented states is centered on the partial unwinding of transmembrane helix 5, facilitated by a conserved GlyX9Pro motif that opens an intracellular pathway for water to access the Na2 site. We propose a mechanism, based on our structural and functional findings, in which solvation through the TM5 pathway facilitates Na+ release from Na2 and the transition to an inward-open state.
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132
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Simmons KJ, Jackson SM, Brueckner F, Patching SG, Beckstein O, Ivanova E, Geng T, Weyand S, Drew D, Lanigan J, Sharples DJ, Sansom MSP, Iwata S, Fishwick CWG, Johnson AP, Cameron AD, Henderson PJF. Molecular mechanism of ligand recognition by membrane transport protein, Mhp1. EMBO J 2014; 33:1831-44. [PMID: 24952894 PMCID: PMC4195764 DOI: 10.15252/embj.201387557] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The hydantoin transporter Mhp1 is a sodium-coupled secondary active transport protein of the nucleobase-cation-symport family and a member of the widespread 5-helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site-directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5-substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5-substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5-(2-naphthylmethyl)-L-hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1.
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Affiliation(s)
- Katie J Simmons
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Scott M Jackson
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Florian Brueckner
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Simon G Patching
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Oliver Beckstein
- Department of Physics, Arizona State University, Tempe, AZ, USA Department of Biochemistry, University of Oxford, Oxford, UK
| | - Ekaterina Ivanova
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Tian Geng
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Simone Weyand
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - David Drew
- Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK
| | - Joseph Lanigan
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - David J Sharples
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - So Iwata
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Colin W G Fishwick
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - A Peter Johnson
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Alexander D Cameron
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK School of Life Sciences, University of Warwick, Coventry, UK
| | - Peter J F Henderson
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
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133
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Juette MF, Terry DS, Wasserman MR, Zhou Z, Altman RB, Zheng Q, Blanchard SC. The bright future of single-molecule fluorescence imaging. Curr Opin Chem Biol 2014; 20:103-11. [PMID: 24956235 DOI: 10.1016/j.cbpa.2014.05.010] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Accepted: 05/09/2014] [Indexed: 11/13/2022]
Abstract
Single-molecule Förster resonance energy transfer (smFRET) is an essential and maturing tool to probe biomolecular interactions and conformational dynamics in vitro and, increasingly, in living cells. Multi-color smFRET enables the correlation of multiple such events and the precise dissection of their order and timing. However, the requirements for good spectral separation, high time resolution, and extended observation times place extraordinary demands on the fluorescent labels used in such experiments. Together with advanced experimental designs and data analysis, the development of long-lasting, non-fluctuating fluorophores is therefore proving key to progress in the field. Recently developed strategies for obtaining ultra-stable organic fluorophores spanning the visible spectrum are underway that will enable multi-color smFRET studies to deliver on their promise of previously unachievable biological insights.
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Affiliation(s)
- Manuel F Juette
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Daniel S Terry
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Michael R Wasserman
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Zhou Zhou
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Roger B Altman
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Qinsi Zheng
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States; Tri-Institutional Training Program in Chemical Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States
| | - Scott C Blanchard
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States; Tri-Institutional Training Program in Chemical Biology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, United States.
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134
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Heal DJ, Gosden J, Smith SL. Dopamine reuptake transporter (DAT) "inverse agonism"--a novel hypothesis to explain the enigmatic pharmacology of cocaine. Neuropharmacology 2014; 87:19-40. [PMID: 24953830 DOI: 10.1016/j.neuropharm.2014.06.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 05/07/2014] [Accepted: 06/09/2014] [Indexed: 12/20/2022]
Abstract
The long held view is cocaine's pharmacological effects are mediated by monoamine reuptake inhibition. However, drugs with rapid brain penetration like sibutramine, bupropion, mazindol and tesofensine, which are equal to or more potent than cocaine as dopamine reuptake inhibitors, produce no discernable subjective effects such as drug "highs" or euphoria in drug-experienced human volunteers. Moreover they are dysphoric and aversive when given at high doses. In vivo experiments in animals demonstrate that cocaine's monoaminergic pharmacology is profoundly different from that of other prescribed monoamine reuptake inhibitors, with the exception of methylphenidate. These findings led us to conclude that the highly unusual stimulant profile of cocaine and related compounds, eg methylphenidate, is not mediated by monoamine reuptake inhibition alone. We describe the experimental findings which suggest cocaine serves as a negative allosteric modulator to alter the function of the dopamine reuptake transporter (DAT) and reverse its direction of transport. This results in a firing-dependent, retro-transport of dopamine into the synaptic cleft. The proposed mechanism of cocaine is, therefore, different from other small molecule negative allostereric modulators of the monoamine reuptake transporters, eg SoRI-6238, which merely reduce the rate of inward transport. Because the physiological role of DAT is to remove dopamine from the synapse and the action of cocaine is the opposite of this, we have postulated that cocaine's effect is analogous to an inverse agonist. If this hypothesis is validated then cocaine is the prototypical compound that exemplifies a new class of monoaminergic drugs; DAT "inverse agonists". This article is part of the Special Issue entitled 'CNS Stimulants'.
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Affiliation(s)
- David J Heal
- RenaSci Limited, BioCity, Pennyfoot Street, Nottingham NG1 1GF, UK.
| | - Jane Gosden
- RenaSci Limited, BioCity, Pennyfoot Street, Nottingham NG1 1GF, UK
| | - Sharon L Smith
- RenaSci Limited, BioCity, Pennyfoot Street, Nottingham NG1 1GF, UK.
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135
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Mondal S, Khelashvili G, Weinstein H. Not just an oil slick: how the energetics of protein-membrane interactions impacts the function and organization of transmembrane proteins. Biophys J 2014; 106:2305-16. [PMID: 24896109 PMCID: PMC4052241 DOI: 10.1016/j.bpj.2014.04.032] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 03/31/2014] [Accepted: 04/23/2014] [Indexed: 01/12/2023] Open
Abstract
The membrane environment, its composition, dynamics, and remodeling, have been shown to participate in the function and organization of a wide variety of transmembrane (TM) proteins, making it necessary to study the molecular mechanisms of such proteins in the context of their membrane settings. We review some recent conceptual advances enabling such studies, and corresponding computational models and tools designed to facilitate the concerted experimental and computational investigation of protein-membrane interactions. To connect productively with the high resolution achieved by cognate experimental approaches, the computational methods must offer quantitative data at an atomistically detailed level. We show how such a quantitative method illuminated the mechanistic importance of a structural characteristic of multihelical TM proteins, that is, the likely presence of adjacent polar and hydrophobic residues at the protein-membrane interface. Such adjacency can preclude the complete alleviation of the well-known hydrophobic mismatch between TM proteins and the surrounding membrane, giving rise to an energy cost of residual hydrophobic mismatch. The energy cost and biophysical formulation of hydrophobic mismatch and residual hydrophobic mismatch are reviewed in the context of their mechanistic role in the function of prototypical members of multihelical TM protein families: 1), LeuT, a bacterial homolog of mammalian neurotransmitter sodium symporters; and 2), rhodopsin and the β1- and β2-adrenergic receptors from the G-protein coupled receptor family. The type of computational analysis provided by these examples is poised to translate the rapidly growing structural data for the many TM protein families that are of great importance to cell function into ever more incisive insights into mechanisms driven by protein-ligand and protein-protein interactions in the membrane environment.
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Affiliation(s)
- Sayan Mondal
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York; The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York.
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136
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Thomas JR, Gedeon PC, Madura JD. Structural dynamics of the monoamine transporter homolog LeuT from accelerated conformational sampling and channel analysis. Proteins 2014; 82:2289-302. [PMID: 24753369 DOI: 10.1002/prot.24588] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Revised: 03/29/2014] [Accepted: 04/10/2014] [Indexed: 01/28/2023]
Abstract
The bacterial leucine transporter LeuT retains significant secondary structure similarities to the human monoamine transporters (MAT) such as the dopamine and serotonin reuptake proteins. The primary method of computational study of the MATs has been through the use of the crystallized LeuT structure. Different conformations of LeuT can give insight into mechanistic details of the MAT family. A conformational sampling performed through accelerated molecular dynamics simulations testing different combinations of the leucine substrate and bound sodium ions revealed seven distinct conformational clusters. Further analysis has been performed to target salt-bridge residues R30-D404, Y108-F253, and R5-D369 and transmembrane domains on both the seven isolated structures and the total trajectories. In addition, solvent accessibility of LeuT and its substrate binding pockets has been analyzed using a program for calculating channel radii. Occupation of the Na2 site stabilizes the outward conformation and should bind to the open outward conformation before the leucine and Na1 sodium while two possible pathways were found to be available for intracellular transport.
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Affiliation(s)
- James R Thomas
- Department of Chemistry and Biochemistry and the Center for Computational Sciences, Duquesne University, Pittsburgh, Pennsylvania; Mylan School of Pharmacy, Duquesne University, Pittsburgh, Pennsylvania
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137
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Kazmier K, Sharma S, Quick M, Islam SM, Roux B, Weinstein H, Javitch JA, McHaourab HS. Conformational dynamics of ligand-dependent alternating access in LeuT. Nat Struct Mol Biol 2014; 21:472-9. [PMID: 24747939 PMCID: PMC4050370 DOI: 10.1038/nsmb.2816] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 03/27/2014] [Indexed: 12/12/2022]
Abstract
The leucine transporter (LeuT) from Aquifex aeolicus is a bacterial homolog of neurotransmitter/sodium symporters (NSSs) that catalyze reuptake of neurotransmitters at the synapse. Crystal structures of wild-type and mutants of LeuT have been interpreted as conformational states in the coupled transport cycle. However, the mechanistic identities inferred from these structures have not been validated, and the ligand-dependent conformational equilibrium of LeuT has not been defined. Here, we used distance measurements between spin-label pairs to elucidate Na(+)- and leucine-dependent conformational changes on the intracellular and extracellular sides of the transporter. The results identify structural motifs that underlie the isomerization of LeuT between outward-facing, inward-facing and occluded states. The conformational changes reported here present a dynamic picture of the alternating-access mechanism of LeuT and NSSs that is different from the inferences reached from currently available structural models.
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Affiliation(s)
- Kelli Kazmier
- 1] Chemical and Physical Biology Program, Vanderbilt University, Nashville, Tennessee, USA. [2]
| | - Shruti Sharma
- 1] Department of Molecular Physiology and Biophysics, Nashville, Tennessee, USA. [2]
| | - Matthias Quick
- 1] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] New York State Psychiatric Institute, Division of Molecular Therapeutics, New York, New York, USA
| | - Shahidul M Islam
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| | - Harel Weinstein
- 1] Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York, USA. [2] HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, New York, USA
| | - Jonathan A Javitch
- 1] Center for Molecular Recognition, Columbia University College of Physicians and Surgeons, New York, New York, USA. [2] Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York, USA. [3] New York State Psychiatric Institute, Division of Molecular Therapeutics, New York, New York, USA. [4] Department of Pharmacology, Columbia University College of Physicians and Surgeons, New York, New York, USA
| | - Hassane S McHaourab
- 1] Chemical and Physical Biology Program, Vanderbilt University, Nashville, Tennessee, USA. [2] Department of Molecular Physiology and Biophysics, Nashville, Tennessee, USA
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138
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LeVine MV, Weinstein H. NbIT--a new information theory-based analysis of allosteric mechanisms reveals residues that underlie function in the leucine transporter LeuT. PLoS Comput Biol 2014; 10:e1003603. [PMID: 24785005 PMCID: PMC4006702 DOI: 10.1371/journal.pcbi.1003603] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 03/24/2014] [Indexed: 11/23/2022] Open
Abstract
Complex networks of interacting residues and microdomains in the structures of biomolecular systems underlie the reliable propagation of information from an input signal, such as the concentration of a ligand, to sites that generate the appropriate output signal, such as enzymatic activity. This information transduction often carries the signal across relatively large distances at the molecular scale in a form of allostery that is essential for the physiological functions performed by biomolecules. While allosteric behaviors have been documented from experiments and computation, the mechanism of this form of allostery proved difficult to identify at the molecular level. Here, we introduce a novel analysis framework, called N-body Information Theory (NbIT) analysis, which is based on information theory and uses measures of configurational entropy in a biomolecular system to identify microdomains and individual residues that act as (i)-channels for long-distance information sharing between functional sites, and (ii)-coordinators that organize dynamics within functional sites. Application of the new method to molecular dynamics (MD) trajectories of the occluded state of the bacterial leucine transporter LeuT identifies a channel of allosteric coupling between the functionally important intracellular gate and the substrate binding sites known to modulate it. NbIT analysis is shown also to differentiate residues involved primarily in stabilizing the functional sites, from those that contribute to allosteric couplings between sites. NbIT analysis of MD data thus reveals rigorous mechanistic elements of allostery underlying the dynamics of biomolecular systems. We developed the new information theory-based analysis framework presented here, NbIT analysis, for the study of allosteric mechanisms in biomolecular systems from Molecular Dynamics trajectories. The illustrative application of NbIT to the analysis of the occluded state in the bacterial transporter LeuT, produced a quantitative representation of the allosteric behavior, and identified intramolecular channels that enable the long-distance information transmission. Our findings, identifying the roles of specific residues in the communication of the allosteric information, were validated by the recognition of residues that have been previously shown to play functional roles in this very well studied system. In addition, we show that application of NbIT analysis leads to the discrimination of functional roles by differentiating between residues that are essential to the dynamics within functional sites (e.g., the substrate binding sites), and residues whose role is to communicate between such functional sites. These results demonstrate that the information theoretical analysis presented here is a powerful tool for quantifying complex allosteric behavior in biomolecular systems and for identifying the crucial components underlying those behaviors.
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Affiliation(s)
- Michael V. LeVine
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York, United States of America
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University (WCMC), New York, New York, United States of America
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York, United States of America
- * E-mail:
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139
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Schnabel LV, Abratte CM, Schimenti JC, Felippe MJB, Cassano JM, Southard TL, Cross JA, Fortier LA. Induced pluripotent stem cells have similar immunogenic and more potent immunomodulatory properties compared with bone marrow-derived stromal cells in vitro. Regen Med 2014; 9:621-35. [PMID: 24773530 PMCID: PMC4352342 DOI: 10.2217/rme.14.29] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
AIM To evaluate the in vitro immunogenic and immunomodulatory properties of induced pluripotent stem cells (iPSCs) compared with bone marrow-derived mesenchymal stromal cells (MSCs). MATERIALS & METHODS Mouse embryonic fibroblasts (MEFs) were isolated from C3HeB/FeJ and C57BL/6J mice, and reprogrammed to generate iPSCs. Mixed leukocyte reactions were performed using MHC-matched and -mismatched responder leukocytes and stimulator leukocytes, iPSCs or MSCs. To assess immunogenic potential, iPSCs and MSCs were used as stimulator cells for responder leukocytes. To assess immunomodulatory properties, iPSCs and MSCs were cultured in the presence of stimulator and responder leukocytes. MEFs were used as a control. RESULTS iPSCs had similar immunogenic properties but more potent immunomodulatory effects than MSCs. Co-culture of MHC-mismatched leukocytes with MHC-matched iPSCs resulted in significantly less responder T-cell proliferation than observed for MHC-mismatched leukocytes alone and at more responder leukocyte concentrations than with MSCs. In addition, MHC-mismatched iPSCs significantly reduced responder T-cell proliferation when co-cultured with MHC-mismatched leukocytes, while MHC-mismatched MSCs did not. CONCLUSION These results provide important information when considering the use of iPSCs in place of MSCs in both regenerative and transplantation medicine.
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Affiliation(s)
- Lauren V Schnabel
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Christian M Abratte
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - John C Schimenti
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - M Julia Bevilaqua Felippe
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Jennifer M Cassano
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Teresa L Southard
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Jessica A Cross
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Lisa A Fortier
- Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
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140
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Schlessinger A, Khuri N, Giacomini KM, Sali A. Molecular modeling and ligand docking for solute carrier (SLC) transporters. Curr Top Med Chem 2014; 13:843-56. [PMID: 23578028 DOI: 10.2174/1568026611313070007] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 01/29/2013] [Accepted: 02/01/2013] [Indexed: 12/21/2022]
Abstract
Solute Carrier (SLC) transporters are membrane proteins that transport solutes, such as ions, metabolites, peptides, and drugs, across biological membranes, using diverse energy coupling mechanisms. In human, there are 386 SLC transporters, many of which contribute to the absorption, distribution, metabolism, and excretion of drugs and/or can be targeted directly by therapeutics. Recent atomic structures of SLC transporters determined by X-ray crystallography and NMR spectroscopy have significantly expanded the applicability of structure-based prediction of SLC transporter ligands, by enabling both comparative modeling of additional SLC transporters and virtual screening of small molecules libraries against experimental structures as well as comparative models. In this review, we begin by describing computational tools, including sequence analysis, comparative modeling, and virtual screening, that are used to predict the structures and functions of membrane proteins such as SLC transporters. We then illustrate the applications of these tools to predicting ligand specificities of select SLC transporters, followed by experimental validation using uptake kinetic measurements and other assays. We conclude by discussing future directions in the discovery of the SLC transporter ligands.
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Affiliation(s)
- Avner Schlessinger
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, 1700 4th Street, San Francisco, CA 94158, USA.
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141
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Abstract
Abstract The availability of high-resolution atomic structures for transport proteins provides unprecedented opportunities for understanding their mechanism of action. The details of conformational change can be deduced from these structures, especially when multiple conformations are available. However, the singular ability of transporters to couple the movement of one solute to that of another requires even more information than what is supplied by a crystal structure. This short commentary discusses how recent biochemical and biophysical studies are beginning to reveal how solute coupling is achieved.
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Affiliation(s)
- Gary Rudnick
- Department of Pharmacology, Yale University School of Medicine , New Haven, CT , USA
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142
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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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143
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Fraser R, Chen Y, Guptaroy B, Luderman KD, Stokes SL, Beg A, DeFelice LJ, Gnegy ME. An N-terminal threonine mutation produces an efflux-favorable, sodium-primed conformation of the human dopamine transporter. Mol Pharmacol 2014; 86:76-85. [PMID: 24753048 DOI: 10.1124/mol.114.091926] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The dopamine transporter (DAT) reversibly transports dopamine (DA) through a series of conformational transitions. Alanine (T62A) or aspartate (T62D) mutagenesis of Thr62 revealed T62D-human (h)DAT partitions in a predominately efflux-preferring conformation. Compared with wild-type (WT), T62D-hDAT exhibits reduced [(3)H]DA uptake and enhanced baseline DA efflux, whereas T62A-hDAT and WT-hDAT function in an influx-preferring conformation. We now interrogate the basis of the mutants' altered function with respect to membrane conductance and Na(+) sensitivity. The hDAT constructs were expressed in Xenopus oocytes to investigate if heightened membrane potential would explain the efflux characteristics of T62D-hDAT. In the absence of substrate, all constructs displayed identical resting membrane potentials. Substrate-induced inward currents were present in oocytes expressing WT- and T62A-hDAT but not T62D-hDAT, suggesting equal bidirectional ion flow through T62D-hDAT. Utilization of the fluorescent DAT substrate ASP(+) [4-(4-(dimethylamino)styryl)-N-methylpyridinium] revealed that T62D-hDAT accumulates substrate in human embryonic kidney (HEK)-293 cells when the substrate is not subject to efflux. Extracellular sodium (Na(+) e) replacement was used to evaluate sodium gradient requirements for DAT transport functions. The EC50 for Na(+) e stimulation of [(3)H]DA uptake was identical in all constructs expressed in HEK-293 cells. As expected, decreasing [Na(+)]e stimulated [(3)H]DA efflux in WT- and T62A-hDAT cells. Conversely, the elevated [(3)H]DA efflux in T62D-hDAT cells was independent of Na(+) e and commensurate with [(3)H]DA efflux attained in WT-hDAT cells, either by removal of Na(+) e or by application of amphetamine. We conclude that T62D-hDAT represents an efflux-willing, Na(+)-primed orientation-possibly representing an experimental model of the conformational impact of amphetamine exposure to hDAT.
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Affiliation(s)
- Rheaclare Fraser
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Yongyue Chen
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Bipasha Guptaroy
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Kathryn D Luderman
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Stephanie L Stokes
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Asim Beg
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Louis J DeFelice
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
| | - Margaret E Gnegy
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan (R.F., B.G., K.D.L., S.L.S., A.B., M.E.G.); and Departments of Psychiatry (Y.C.) and Physiology and Biophysics (L.J.D.), Virginia Commonwealth University, Richmond, Virginia
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144
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Drosophila melanogaster as a genetic model system to study neurotransmitter transporters. Neurochem Int 2014; 73:71-88. [PMID: 24704795 DOI: 10.1016/j.neuint.2014.03.015] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Revised: 03/20/2014] [Accepted: 03/24/2014] [Indexed: 12/30/2022]
Abstract
The model genetic organism Drosophila melanogaster, commonly known as the fruit fly, uses many of the same neurotransmitters as mammals and very similar mechanisms of neurotransmitter storage, release and recycling. This system offers a variety of powerful molecular-genetic methods for the study of transporters, many of which would be difficult in mammalian models. We review here progress made using Drosophila to understand the function and regulation of neurotransmitter transporters and discuss future directions for its use.
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145
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Cheng MH, Bahar I. Coupled global and local changes direct substrate translocation by neurotransmitter-sodium symporter ortholog LeuT. Biophys J 2014; 105:630-9. [PMID: 23931311 DOI: 10.1016/j.bpj.2013.06.032] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Revised: 06/12/2013] [Accepted: 06/14/2013] [Indexed: 01/01/2023] Open
Abstract
Significant advances have been made in recent years in characterizing neurotransmitter:sodium symporter (NSS) family structure and function. Yet, many time-resolved events and intermediates that control the various stages of transport cycle remain to be elucidated. Whether NSSs harbor one or two sites for binding their substrates (neurotransmitters or amino acids), and what the role of the secondary site S2 is, if any, are still unresolved. Using molecular modeling and simulations for LeuT, a bacterial NSS, we present a comprehensive account of substrate-binding and -stabilization events, and subsequently triggered interactions leading to substrate (alanine) release. LeuT instantaneous conformation as it reconfigures from substrate-receiving (outward-facing) to -releasing (inward-facing) state appears to be a determinant of its affinity to bind substrate at site S2. In the outward-facing state, S1 robustly binds alanine and regulates subsequent redistribution of interactions to trigger extracellular gate closure; whereas S2 is only a transient binding site. The substrate-binding affinity at S2 increases in an intermediate close to inward-facing state. LeuT harbors the two substrate-binding sites, and small displacements of second substrate near S2 are observed to induce concerted small translocations in the substrate bound to primary site S1, although complete release requires collective structural rearrangements that fully expose the intracellular vestibule to the cytoplasm.
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Affiliation(s)
- Mary Hongying Cheng
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pennsylvania, USA
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146
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Gabrielsen M, Kurczab R, Siwek A, Wolak M, Ravna AW, Kristiansen K, Kufareva I, Abagyan R, Nowak G, Chilmonczyk Z, Sylte I, Bojarski AJ. Identification of novel serotonin transporter compounds by virtual screening. J Chem Inf Model 2014; 54:933-43. [PMID: 24521202 PMCID: PMC3982395 DOI: 10.1021/ci400742s] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) plays an essential role in the termination of serotonergic neurotransmission by removing 5-HT from the synaptic cleft into the presynaptic neuron. It is also of pharmacological importance being targeted by antidepressants and psychostimulant drugs. Here, five commercial databases containing approximately 3.24 million drug-like compounds have been screened using a combination of two-dimensional (2D) fingerprint-based and three-dimensional (3D) pharmacophore-based screening and flexible docking into multiple conformations of the binding pocket detected in an outward-open SERT homology model. Following virtual screening (VS), selected compounds were evaluated using in vitro screening and full binding assays and an in silico hit-to-lead (H2L) screening was performed to obtain analogues of the identified compounds. Using this multistep VS/H2L approach, 74 active compounds, 46 of which had K(i) values of ≤1000 nM, belonging to 16 structural classes, have been identified, and multiple compounds share no structural resemblance with known SERT binders.
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Affiliation(s)
- Mari Gabrielsen
- Medical Pharmacology and Toxicology, Department of Medical Biology, Faculty of Health Sciences, UiT, The Arctic University of Norway , 9037 Tromsø, Norway
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147
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Conformational changes in dopamine transporter intracellular regions upon cocaine binding and dopamine translocation. Neurochem Int 2014; 73:4-15. [PMID: 24576496 DOI: 10.1016/j.neuint.2014.02.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 02/12/2014] [Accepted: 02/15/2014] [Indexed: 11/20/2022]
Abstract
The dopamine transporter (DAT), a member of the neurotransmitter:sodium symporter family, mediates the reuptake of dopamine at the synaptic cleft. DAT is the primary target for psychostimulants such as cocaine and amphetamine. We previously demonstrated that cocaine binding and dopamine transport alter the accessibility of Cys342 in the third intracellular loop (IL3). To study the conformational changes associated with the functional mechanism of the transporter, we made cysteine substitution mutants, one at a time, from Phe332 to Ser351 in IL3 of the background DAT construct, X7C, in which 7 endogenous cysteines were mutated. The accessibility of the 20 engineered cysteines to polar charged sulfhydryl reagents was studied in the absence and presence of cocaine or dopamine. Of the 11 positions that reacted with methanethiosulfonate ethyl ammonium, as evidenced by inhibition of ligand binding, 5 were protected against this inhibition by cocaine and dopamine (S333C, S334C, N336C, M342C and T349C), indicating that reagent accessibility is affected by conformational changes associated with inhibitor and substrate binding. In some of the cysteine mutants, transport activity is disrupted, but can be rescued by the presence of zinc, most likely because the distribution between inward- and outward-facing conformations is restored by zinc binding. The experimental data were interpreted in the context of molecular models of DAT in both the inward- and outward-facing conformations. Differences in the solvent accessible surface area for individual IL3 residues calculated for these states correlate well with the experimental accessibility data, and suggest that protection by ligand binding results from the stabilization of the outward-facing configuration. Changes in the residue interaction networks observed from the molecular dynamics simulations also revealed the critical roles of several positions during the conformational transitions. We conclude that the IL3 region of DAT undergoes significant conformational changes in transitions necessary for both cocaine binding and substrate transport.
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148
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Zheng Q, Juette MF, Jockusch S, Wasserman MR, Zhou Z, Altman RB, Blanchard SC. Ultra-stable organic fluorophores for single-molecule research. Chem Soc Rev 2014; 43:1044-56. [PMID: 24177677 PMCID: PMC3946787 DOI: 10.1039/c3cs60237k] [Citation(s) in RCA: 252] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Fluorescence provides a mechanism for achieving contrast in biological imaging that enables investigations of molecular structure, dynamics, and function at high spatial and temporal resolution. Small-molecule organic fluorophores have proven essential for such efforts and are widely used in advanced applications such as single-molecule and super-resolution microscopy. Yet, organic fluorophores, like all fluorescent species, exhibit instabilities in their emission characteristics, including blinking and photobleaching that limit their utility and performance. Here, we review the photophysics and photochemistry of organic fluorophores as they pertain to mitigating such instabilities, with a specific focus on the development of stabilized fluorophores through derivatization. Self-healing organic fluorophores, wherein the triplet state is intramolecularly quenched by a covalently attached protective agent, exhibit markedly improved photostabilities. We discuss the potential for further enhancements towards the goal of developing "ultra-stable" fluorophores spanning the visible spectrum and how such fluorophores are likely to impact the future of single-molecule research.
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Affiliation(s)
- Qinsi Zheng
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, USA.
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149
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Wang Y, Liu Y, Deberg HA, Nomura T, Hoffman MT, Rohde PR, Schulten K, Martinac B, Selvin PR. Single molecule FRET reveals pore size and opening mechanism of a mechano-sensitive ion channel. eLife 2014; 3:e01834. [PMID: 24550255 PMCID: PMC3925968 DOI: 10.7554/elife.01834] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The mechanosensitive channel of large conductance, which serves as a model system for mechanosensitive channels, has previously been crystallized in the closed form, but not in the open form. Ensemble measurements and electrophysiological sieving experiments show that the open-diameter of the channel pore is >25 Å, but the exact size and whether the conformational change follows a helix-tilt or barrel-stave model are unclear. Here we report measurements of the distance changes on liposome-reconstituted MscL transmembrane α-helices, using a ‘virtual sorting’ single-molecule fluorescence energy transfer. We observed directly that the channel opens via the helix-tilt model and the open pore reaches 2.8 nm in diameter. In addition, based on the measurements, we developed a molecular dynamics model of the channel structure in the open state which confirms our direct observations. DOI:http://dx.doi.org/10.7554/eLife.01834.001 Bacterial cells are full of fluid, and they will burst if they are not able to respond to a build up of pressure. Fortunately, the membrane of a bacterial cell contains channels that can detect the increased mechanical stress on the cell membrane and then open to relieve the pressure. In many bacterial cells, the last defence against the cell exploding is called the mechanosensitive channel of large conductance (MscL). This is made of five proteins, each of which consists of TM1 and TM2 helixes, which are responsible for opening and closing the channel. Two models have been proposed to explain how the channels are opened. In the barrel-stave model, the TM1 helix moves, while the TM2 helix remains stationary. This results in an open pore that is lined with TM1 and TM2 helixes in the same way that wooden staves line a barrel. In the helix-tilt model, both helixes tilt towards the membrane to open the channel. Wang et al. have now used a technique called single-molecule fluorescence resonance energy transfer (FRET) to explore the structure of the open channel in E. coli in order to determine which model is correct. In this technique an individual channel is labeled with two different fluorescent molecules. By illuminating the channel with light of a wavelength that excites the first fluorescent molecule, and measuring the strength of the fluorescence from the second molecule, it is possible to work out the distance between the two molecules. From this, the structure of the channel and how it opens and closes can be explored. Previous attempts to measure the diameters of open channels using fluorescence techniques have suffered from issues caused by the use of large numbers of fluorescent molecules. This has made it necessary to use computational modeling to extract the required data. By looking at a series of individual proteins, Wang et al. overcame these problems and found that the diameter of the fully open pore is 2.8 nm. The result provides strong support for the helix-tilt model. DOI:http://dx.doi.org/10.7554/eLife.01834.002
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Affiliation(s)
- Yong Wang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States
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150
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Okunola-Bakare OM, Cao J, Kopajtic T, Katz JL, Loland CJ, Shi L, Newman AH. Elucidation of structural elements for selectivity across monoamine transporters: novel 2-[(diphenylmethyl)sulfinyl]acetamide (modafinil) analogues. J Med Chem 2014; 57:1000-13. [PMID: 24494745 PMCID: PMC3954497 DOI: 10.1021/jm401754x] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
![]()
2-[(Diphenylmethyl)sulfinyl]acetamide
(modafinil, (±)-1) is a unique dopamine uptake inhibitor
that binds the dopamine
transporter (DAT) differently than cocaine and may have potential
for the treatment of psychostimulant abuse. To further investigate
structural requirements for this divergent binding mode, novel thio-
and sulfinylacetamide and ethanamine analogues of (±)-1 were synthesized wherein (1) the diphenyl rings were substituted
with methyl, trifluoromethyl, and halogen substituents and (2) substituents
were added to the terminal amide/amine nitrogen. Halogen substitution
of the diphenyl rings of (±)-1 gave several amide
analogues with improved binding affinity for DAT and robust selectivity
over the serotonin transporter (SERT), whereas affinity improved at
SERT over DAT for the p-halo-substituted amine analogues.
Molecular docking studies, using a subset of analogues with DAT and
SERT homology models, and functional data obtained with DAT (A480T)
and SERT (T497A) mutants defined a role for TM10 in the substrate/inhibitor
S1 binding sites of DAT and SERT.
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Affiliation(s)
- Oluyomi M Okunola-Bakare
- Medicinal Chemistry Section and ‡Psychobiology Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse-Intramural Research Program, National Institutes of Health , Baltimore, Maryland 21224, United States
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