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Bhat S, Hasenhuetl PS, Kasture A, El-Kasaby A, Baumann MH, Blough BE, Sucic S, Sandtner W, Freissmuth M. Conformational state interactions provide clues to the pharmacochaperone potential of serotonin transporter partial substrates. J Biol Chem 2017; 292:16773-16786. [PMID: 28842491 PMCID: PMC5633137 DOI: 10.1074/jbc.m117.794081] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Revised: 07/25/2017] [Indexed: 12/15/2022] Open
Abstract
Point mutations in SLC6 transporters cause misfolding, which can be remedied by pharmacochaperones. The serotonin transporter (SERT/SLC6A4) has a rich pharmacology including inhibitors, releasers (amphetamines, which promote the exchange mode), and more recently, discovered partial substrates. We hypothesized that partial substrates trapped the transporter in one or several states of the transport cycle. This conformational trapping may also be conducive to folding. We selected naphthylpropane-2-amines of the phenethylamine library (PAL) including the partial substrate PAL1045 and its congeners PAL287 and PAL1046. We analyzed their impact on the transport cycle of SERT by biochemical approaches and by electrophysiological recordings; substrate-induced peak currents and steady-state currents monitored the translocation of substrate and co-substrate Na+ across the lipid bilayer and the transport cycle, respectively. These experiments showed that PAL1045 and its congeners bound with different affinities (ranging from nm to μm) to various conformational intermediates of SERT during the transport cycle. Consistent with the working hypothesis, PAL1045 was the most efficacious compound in restoring surface expression and transport activity to the folding-deficient mutant SERT-601PG602-AA. These experiments provide a proof-of-principle for a rational search for pharmacochaperones, which may be useful to restore function to clinically relevant folding-deficient transporter mutants.
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Affiliation(s)
- Shreyas Bhat
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Peter S Hasenhuetl
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Ameya Kasture
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Ali El-Kasaby
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Michael H Baumann
- the Translational Pharmacology Section, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224, and
| | - Bruce E Blough
- Center for Drug Discovery, Research Triangle Institute, Research Triangle Park, North Carolina 27709-1294
| | - Sonja Sucic
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Walter Sandtner
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Michael Freissmuth
- From the Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria,
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Sohail MI, Schmid D, Wlcek K, Spork M, Szakács G, Trauner M, Stockner T, Chiba P. Molecular Mechanism of Taurocholate Transport by the Bile Salt Export Pump, an ABC Transporter Associated with Intrahepatic Cholestasis. Mol Pharmacol 2017; 92:401-413. [PMID: 28784620 DOI: 10.1124/mol.117.108688] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Accepted: 07/31/2017] [Indexed: 12/12/2022] Open
Abstract
The bile salt export pump (BSEP/ABCB11) transports bile salts from hepatocytes into bile canaliculi. Its malfunction is associated with severe liver disease. One reason for functional impairment of BSEP is systemic administration of drugs, which as a side effect inhibit the transporter. Therefore, drug candidates are routinely screened for potential interaction with this transporter. Hence, understanding the functional biology of BSEP is of key importance. In this study, we engineered the transporter to dissect interdomain communication paths. We introduced mutations in noncanonical and in conserved residues of either of the two nucleotide binding domains and determined the effect on BSEP basal and substrate-stimulated ATPase activity as well as on taurocholate transport. Replacement of the noncanonical methionine residue M584 (Walker B sequence of nucleotide binding site 1) by glutamate imparted hydrolysis competency to this site. Importantly, this mutation was able to sustain 15% of wild-type transport activity, when the catalytic glutamate of the canonical nucleotide binding site 2 was mutated to glutamine. Kinetic modeling of experimental results for the ensuing M584E/E1244Q mutant suggests that a transfer of hydrolytic capacity from the canonical to the noncanonical nucleotide binding site results in loss of active and adoption of facilitative characteristics. This facilitative transport is ATP-gated. To the best of our knowledge, this result is unprecedented in ATP-binding cassette proteins with one noncanonical nucleotide binding site. Our study promotes an understanding of the domain interplay in BSEP as a basis for exploration of drug interactions with this transporter.
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Affiliation(s)
- Muhammad Imran Sohail
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Diethart Schmid
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Katrin Wlcek
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Matthias Spork
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Gergely Szakács
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Michael Trauner
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Thomas Stockner
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
| | - Peter Chiba
- Institute of Medical Chemistry, Center for Pathobiochemistry and Genetics (M.I.S., M.S., P.C.), Institute of Physiology, Center for Physiology and Pharmacology (D.S.), Institute of Cancer Research (G.S.), Hans Popper Laboratory of Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine III (M.T.), and Institute of Pharmacology, Center for Physiology and Pharmacology (T.S.), Medical University of Vienna, Vienna, Austria; Department of Zoology, Government College University Lahore, Lahore, Pakistan (M.I.S.); and Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria (K.W.)
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Li Y, Mayer FP, Hasenhuetl PS, Burtscher V, Schicker K, Sitte HH, Freissmuth M, Sandtner W. Occupancy of the Zinc-binding Site by Transition Metals Decreases the Substrate Affinity of the Human Dopamine Transporter by an Allosteric Mechanism. J Biol Chem 2017; 292:4235-4243. [PMID: 28096460 PMCID: PMC5354487 DOI: 10.1074/jbc.m116.760140] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 12/16/2016] [Indexed: 11/06/2022] Open
Abstract
The human dopamine transporter (DAT) has a tetrahedral Zn2+-binding site. Zn2+-binding sites are also recognized by other first-row transition metals. Excessive accumulation of manganese or of copper can lead to parkinsonism because of dopamine deficiency. Accordingly, we examined the effect of Mn2+, Co2+, Ni2+, and Cu2+ on transport-associated currents through DAT and DAT-H193K, a mutant with a disrupted Zn2+-binding site. All transition metals except Mn2+ modulated the transport cycle of wild-type DAT with affinities in the low micromolar range. In this concentration range, they were devoid of any action on DAT-H193K. The active transition metals reduced the affinity of DAT for dopamine. The affinity shift was most pronounced for Cu2+, followed by Ni2+ and Zn2+ (= Co2+). The extent of the affinity shift and the reciprocal effect of substrate on metal affinity accounted for the different modes of action: Ni2+ and Cu2+ uniformly stimulated and inhibited, respectively, the substrate-induced steady-state currents through DAT. In contrast, Zn2+ elicited biphasic effects on transport, i.e. stimulation at 1 μm and inhibition at 10 μm. A kinetic model that posited preferential binding of transition metal ions to the outward-facing apo state of DAT and a reciprocal interaction of dopamine and transition metals recapitulated all experimental findings. Allosteric activation of DAT via the Zn2+-binding site may be of interest to restore transport in loss-of-function mutants.
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Affiliation(s)
- Yang Li
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Felix P Mayer
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Peter S Hasenhuetl
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Verena Burtscher
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Klaus Schicker
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Harald H Sitte
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Michael Freissmuth
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
| | - Walter Sandtner
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13a, 1090 Vienna, Austria
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Li Y, Hasenhuetl PS, Schicker K, Sitte HH, Freissmuth M, Sandtner W. Dual Action of Zn2+ on the Transport Cycle of the Dopamine Transporter. J Biol Chem 2015; 290:31069-76. [PMID: 26504078 PMCID: PMC4692231 DOI: 10.1074/jbc.m115.688275] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Indexed: 11/21/2022] Open
Abstract
The dopamine transporter shapes dopaminergic neurotransmission by clearing extracellular dopamine and by replenishing vesicular stores. The dopamine transporter carries an endogenous binding site for Zn2+, but the nature of the Zn2+-dependent modulation has remained elusive: both, inhibition and stimulation of DAT have been reported. Here, we exploited the high time resolution of patch-clamp recordings to examine the effects of Zn2+ on the transport cycle of DAT: we recorded peak currents associated with substrate translocation and steady-state currents reflecting the forward transport mode of DAT. Zn2+ depressed the peak current but enhanced the steady-state current through DAT. The parsimonious explanation is preferential binding of Zn2+ to the outward facing conformation of DAT, which allows for an allosteric activation of DAT, in both, the forward transport mode and substrate exchange mode. We directly confirmed that Zn2+ dissociated more rapidly from the inward- than from the outward-facing state of DAT. Finally, we formulated a kinetic model for the action of Zn2+ on DAT that emulated all current experimental observations and accounted for all previous (in part contradictory) findings. Importantly, the model predicts that the intracellular Na+ concentration determines whether substrate uptake by DAT is stimulated or inhibited by Zn2+. This prediction was directly verified. The mechanistic framework provided by the current model is of relevance for the rational design of allosteric activators of DAT. These are of interest for treating de novo loss-of-function mutations of DAT associated with neuropsychiatric disorders such as attention deficit hyperactivity disorder (ADHD).
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Affiliation(s)
- Yang Li
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
| | - Peter S Hasenhuetl
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
| | - Klaus Schicker
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
| | - Harald H Sitte
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
| | - Michael Freissmuth
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
| | - Walter Sandtner
- From the Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Waehringerstrasse 13a, A-1090 Vienna, Austria
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5
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Sitte HH, Freissmuth M. Amphetamines, new psychoactive drugs and the monoamine transporter cycle. Trends Pharmacol Sci 2014; 36:41-50. [PMID: 25542076 PMCID: PMC4502921 DOI: 10.1016/j.tips.2014.11.006] [Citation(s) in RCA: 178] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Revised: 11/25/2014] [Accepted: 11/25/2014] [Indexed: 01/05/2023]
Abstract
In monoaminergic neurons, the vesicular transporters and the plasma membrane transporters operate in a relay. Amphetamine and its congeners target this relay to elicit their actions: most amphetamines are substrates, which pervert the relay to elicit efflux of monoamines into the synaptic cleft. However, some amphetamines act as transporter inhibitors. Both compound classes elicit profound psychostimulant effects, which render them liable to recreational abuse. Currently, a surge of new psychoactive substances occurs on a global scale. Chemists bypass drug bans by ingenuous structural variations, resulting in a rich pharmacology. A credible transport model must account for their distinct mode of action and link this to subtle differences in activity and undesired, potentially deleterious effects.
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Affiliation(s)
- Harald H Sitte
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13A, 1090 Vienna, Austria; Center for Addiction Research and Science (AddRess), Medical University Vienna, Waehringerstrasse 13A, 1090 Vienna, Austria.
| | - Michael Freissmuth
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University Vienna, Waehringerstrasse 13A, 1090 Vienna, Austria
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