1
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Duma L, Senicourt L, Rigaud B, Papadopoulos V, Lacapère JJ. Solid-state NMR study of structural heterogeneity of the apo WT mouse TSPO reconstituted in liposomes. Biochimie 2023; 205:73-85. [PMID: 36029902 DOI: 10.1016/j.biochi.2022.08.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 08/08/2022] [Accepted: 08/18/2022] [Indexed: 11/02/2022]
Abstract
In the last decades, ligand binding to human TSPO has been largely used in clinical neuroimaging, but little is known about the interaction mechanism. Protein conformational mobility plays a key role in the ligand recognition and both, ligand-free and ligand-bound structures, are mandatory for characterizing the molecular binding mechanism. In the absence of crystals for mammalian TSPO, we have exploited solid-state nuclear magnetic resonance (ssNMR) spectroscopy under magic-angle spinning (MAS) to study the apo form of recombinant mouse TSPO (mTSPO) reconstituted in lipids. This environment has been previously described to permit binding of its high-affinity drug ligand PK11195 and appears therefore favourable for the study of molecular dynamics. We have optimized the physical conditions to get the best resolution for MAS ssNMR spectra of the ligand-free mTSPO. We have compared and combined various ssNMR spectra to get dynamical information either for the lipids or for the mTSPO. Partial assignment of residue types suggests few agreements with the published solution NMR assignment of the PK11195-bound mTSPO in DPC detergent. Moreover, we were able to observe some lateral chains of aromatic residues that were not assigned in solution. 13C double-quantum NMR spectroscopy shows remarkable dynamics for ligand-free mTSPO in lipids which may have significant implications on the recognition of the ligand and/or other protein partners.
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Affiliation(s)
- Luminita Duma
- Champagne-Ardenne University, CNRS, ICMR UMR, 7312, Reims, France.
| | - Lucile Senicourt
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 Place Jussieu, F-75005, Paris, France
| | - Baptiste Rigaud
- CNRS Institut des Matériaux de Paris Centre (FR2482), 4 Place Jussieu, 75005, Paris, France
| | - Vassilios Papadopoulos
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA, 90089, USA
| | - Jean-Jacques Lacapère
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 Place Jussieu, F-75005, Paris, France
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2
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Hiser C, Montgomery BL, Ferguson-Miller S. TSPO protein binding partners in bacteria, animals, and plants. J Bioenerg Biomembr 2021; 53:463-487. [PMID: 34191248 PMCID: PMC8243069 DOI: 10.1007/s10863-021-09905-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 06/12/2021] [Indexed: 12/11/2022]
Abstract
The ancient membrane protein TSPO is phylogenetically widespread from archaea and bacteria to insects, vertebrates, plants, and fungi. TSPO’s primary amino acid sequence is only modestly conserved between diverse species, although its five transmembrane helical structure appears mainly conserved. Its cellular location and orientation in membranes have been reported to vary between species and tissues, with implications for potential diverse binding partners and function. Most TSPO functions relate to stress-induced changes in metabolism, but in many cases it is unclear how TSPO itself functions—whether as a receptor, a sensor, a transporter, or a translocator. Much evidence suggests that TSPO acts indirectly by association with various protein binding partners or with endogenous or exogenous ligands. In this review, we focus on proteins that have most commonly been invoked as TSPO binding partners. We suggest that TSPO was originally a bacterial receptor/stress sensor associated with porphyrin binding as its most ancestral function and that it later developed additional stress-related roles in eukaryotes as its ability to bind new partners evolved.
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Affiliation(s)
- Carrie Hiser
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA. .,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
| | - Beronda L Montgomery
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.,Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.,Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
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3
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Rivière G, Jaipuria G, Andreas LB, Leonov A, Giller K, Becker S, Zweckstetter M. Membrane-embedded TSPO: an NMR view. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2020; 50:173-180. [PMID: 33354729 PMCID: PMC8071791 DOI: 10.1007/s00249-020-01487-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Revised: 10/19/2020] [Accepted: 11/26/2020] [Indexed: 12/21/2022]
Abstract
Translocator Protein (18 kDa) (TSPO) is a mitochondrial transmembrane protein commonly used as a biomarker for neuroinflammation and is also a potential therapeutic target in neurodegenerative diseases. Despite intensive research efforts, the function of TSPO is still largely enigmatic. Deciphering TSPO structure in the native lipid environment is essential to gain insight into its cellular activities and to design improved diagnostic and therapeutic ligands. Here, we discuss the influence of lipid composition on the structure of mammalian TSPO embedded into lipid bilayers on the basis of solid-state NMR experiments. We further highlight that cholesterol can influence both the tertiary and quaternary TSPO structure and also influence TSPO localization in mitochondria-associated endoplasmic reticulum membranes.
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Affiliation(s)
- Gwladys Rivière
- Senior Research Group of Translational Structural Biology in Dementia, Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Von-Siebold-Str. 3a, 37075, Göttingen, Germany
- Department of Neurology, University Medical Center Göttingen, University of Göttingen, Waldweg 33, 37073, Göttingen, Germany
| | - Garima Jaipuria
- Senior Research Group of Translational Structural Biology in Dementia, Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Von-Siebold-Str. 3a, 37075, Göttingen, Germany
- Department of Neurology, University Medical Center Göttingen, University of Göttingen, Waldweg 33, 37073, Göttingen, Germany
| | - Loren B Andreas
- Department of NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Andrei Leonov
- Department of NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Karin Giller
- Department of NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Stefan Becker
- Department of NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Markus Zweckstetter
- Senior Research Group of Translational Structural Biology in Dementia, Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Von-Siebold-Str. 3a, 37075, Göttingen, Germany.
- Department of Neurology, University Medical Center Göttingen, University of Göttingen, Waldweg 33, 37073, Göttingen, Germany.
- Department of NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
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4
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Xia Y, Ledwitch K, Kuenze G, Duran A, Li J, Sanders CR, Manning C, Meiler J. A unified structural model of the mammalian translocator protein (TSPO). JOURNAL OF BIOMOLECULAR NMR 2019; 73:347-364. [PMID: 31243635 PMCID: PMC8006375 DOI: 10.1007/s10858-019-00257-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2019] [Accepted: 06/10/2019] [Indexed: 05/10/2023]
Abstract
The translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), is a membrane protein located on the outer mitochondrial membrane. Experimentally-derived structures of mouse TSPO (mTSPO) and its homologs from bacterial species have been determined by NMR spectroscopy and X-ray crystallography, respectively. These structures and ligand interactions within the TSPO binding pocket display distinct differences. Here, we leverage experimental and computational studies to derive a unified structural model of mTSPO in the presence and absence of the TSPO ligand, PK11195, and study the effects of DPC detergent micelles on the TSPO structure and ligand binding. From this work, we conclude that that the lipid-mimetic system used to solubilize mTSPO for NMR studies thermodynamically destabilizes the protein, introduces structural perturbations, and alters the characteristics of ligand binding. Furthermore, we used Rosetta to construct a unified mTSPO model that reconciles deviating features of the mammalian and bacterial TSPO. These deviating features are likely a consequence of the detergent system used for structure determination of mTSPO by NMR. The unified mTSPO model agrees with available experimental NMR data, appears to be physically realistic (i.e. thermodynamically not frustrated as judged by the Rosetta energy function), and simultaneously shares the structural features observed in sequence-conserved regions of the bacterial proteins. Finally, we identified the binding site for an imaging ligand VUIIS8310 that is currently positioned for clinical translation using NMR spectroscopy and propose a computational model of the VUIIS8310-mTSPO complex.
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Affiliation(s)
- Yan Xia
- Center for Structural Biology, Vanderbilt University, Nashville, TN, 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA
| | - Kaitlyn Ledwitch
- Center for Structural Biology, Vanderbilt University, Nashville, TN, 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA
| | - Georg Kuenze
- Center for Structural Biology, Vanderbilt University, Nashville, TN, 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA
| | - Amanda Duran
- Center for Structural Biology, Vanderbilt University, Nashville, TN, 37240, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA
| | - Jun Li
- Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Charles R Sanders
- Department of Biochemistry, Vanderbilt University, Nashville, TN, 37240, USA
| | - Charles Manning
- Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Jens Meiler
- Center for Structural Biology, Vanderbilt University, Nashville, TN, 37240, USA.
- Department of Chemistry, Vanderbilt University, Nashville, TN, 37235, USA.
- Department of Chemistry, Center for Structural Biology, Vanderbilt University, MRBIII 5144B, Nashville, TN, 37232, USA.
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5
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Iatmanen-Harbi S, Senicourt L, Papadopoulos V, Lequin O, Lacapere JJ. Characterization of the High-Affinity Drug Ligand Binding Site of Mouse Recombinant TSPO. Int J Mol Sci 2019; 20:ijms20061444. [PMID: 30901938 PMCID: PMC6470738 DOI: 10.3390/ijms20061444] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 03/18/2019] [Accepted: 03/19/2019] [Indexed: 02/08/2023] Open
Abstract
The optimization of translocator protein (TSPO) ligands for Positron Emission Tomography as well as for the modulation of neurosteroids is a critical necessity for the development of TSPO-based diagnostics and therapeutics of neuropsychiatrics and neurodegenerative disorders. Structural hints on the interaction site and ligand binding mechanism are essential for the development of efficient TSPO ligands. Recently published atomic structures of recombinant mammalian and bacterial TSPO1, bound with either the high-affinity drug ligand PK 11195 or protoporphyrin IX, have revealed the membrane protein topology and the ligand binding pocket. The ligand is surrounded by amino acids from the five transmembrane helices as well as the cytosolic loops. However, the precise mechanism of ligand binding remains unknown. Previous biochemical studies had suggested that ligand selectivity and binding was governed by these loops. We performed site-directed mutagenesis to further test this hypothesis and measured the binding affinities. We show that aromatic residues (Y34 and F100) from the cytosolic loops contribute to PK 11195 access to its binding site. Limited proteolytic digestion, circular dichroism and solution two-dimensional (2-D) NMR using selective amino acid labelling provide information on the intramolecular flexibility and conformational changes in the TSPO structure upon PK 11195 binding. We also discuss the differences in the PK 11195 binding affinities and the primary structure between TSPO (TSPO1) and its paralogous gene product TSPO2.
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Affiliation(s)
- Soria Iatmanen-Harbi
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 place Jussieu, F-75005 Paris, France.
| | - Lucile Senicourt
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 place Jussieu, F-75005 Paris, France.
| | - Vassilios Papadopoulos
- Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA 90089, USA.
| | - Olivier Lequin
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 place Jussieu, F-75005 Paris, France.
| | - Jean-Jacques Lacapere
- Sorbonne Université, Ecole Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules (LBM), 4 place Jussieu, F-75005 Paris, France.
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6
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Calevro A, Cotel MC, Natesan S, Modo M, Vernon AC, Mondelli V. Effects of chronic antipsychotic drug exposure on the expression of Translocator Protein and inflammatory markers in rat adipose tissue. Psychoneuroendocrinology 2018; 95:28-33. [PMID: 29793094 DOI: 10.1016/j.psyneuen.2018.05.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 05/14/2018] [Accepted: 05/15/2018] [Indexed: 01/09/2023]
Abstract
The precise effect of antipsychotic drugs on either central or peripheral inflammation remains unclear. An important issue in this debate is to what extent the known peripheral metabolic effects of antipsychotics, including increased adiposity, may contribute to increased inflammation. Adipose tissue is known to contribute to the development of systemic inflammation, which can eventually lead to insulin resistance and metabolic dysregulation. As a first step to address this question, we evaluated whether chronic exposure to clinically comparable doses of haloperidol or olanzapine resulted in the immune activation of rat adipose tissue. Samples of visceral adipose tissue were sampled from male Sprague-Dawley rats exposed to, haloperidol, olanzapine or vehicle (all n = 8), for 8 weeks. From these we measured a cytokine profile, protein expression of F4/80 (a phenotypic macrophage marker) and translocator protein (TSPO), a target for radiotracers putatively indicating microgliosis in clinical neuroimaging studies. Chronic olanzapine exposure resulted in significantly higher adipose IL-6 levels compared with vehicle-controls (ANOVA p = 0.008, Bonferroni post-hoc test p = 0.006); in parallel, animals exposed to olanzapine had significantly higher F4/80 expression when compared with vehicle-controls (Mann Whitney Test, p = 0.014), whereas there was no difference between haloperidol and vehicle groups (Mann Whitney test, p = 0.1). There were no significant effects of either drug on adipose TSPO protein levels. Nevertheless, we found a positive correlation between F4/80 and TSPO adipose protein levels in the olanzapine-exposed rats (Spearman's rho = 0.76, p = 0.037). Our data suggest that chronic exposure to olanzapine, but not haloperidol, increases production of the pro-inflammatory cytokine IL-6 in adipose tissue and increased macrophages expression (F4/80), in the absence of measurable changes in TSPO with respect to vehicle. This may have potentially important consequences in terms of metabolic dysregulation associated with long-term antipsychotic treatment.
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Affiliation(s)
- Anita Calevro
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Psychological Medicine, London, UK
| | - Marie-Caroline Cotel
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Basic and Clinical Neuroscience, London, UK
| | - Sridhar Natesan
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Basic and Clinical Neuroscience, London, UK
| | - Michel Modo
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Basic and Clinical Neuroscience, London, UK; Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Anthony C Vernon
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Basic and Clinical Neuroscience, London, UK; MRC Centre for Neurodevelopmental Disorders, King's College London, London SE1 1UL, UK
| | - Valeria Mondelli
- King's College London, Institute of Psychiatry, Psychology and Neuroscience, Department of Psychological Medicine, London, UK.
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7
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Senicourt L, Duma L, Papadopoulos V, Lacapere JJ. Solid-State NMR of Membrane Protein Reconstituted in Proteoliposomes, the Case of TSPO. Methods Mol Biol 2017; 1635:329-344. [PMID: 28755378 DOI: 10.1007/978-1-4939-7151-0_18] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Structural studies of membrane proteins (MP) in a native or native-like environment remain a challenge. X-ray crystallography of three-dimensional crystals of MP in lipids and cryo-electron microscopy of two-dimensional crystals also in lipids have given atomic structures of several MP. Recent developments of solid-state NMR (ssNMR) provided structural data of MP in lipids and should give access to the dynamic behavior of MP's in a native-like environment. Preparation of samples for ssNMR is not trivial with overexpressed proteins since purified recombinant MP have to be reincorporated in proteoliposomes and concentrated in the small volume of the rotor used for ssNMR studies. We present here the protocol that we have used to study the recombinant mouse TSPO1, an integral membrane protein of 20 kDa mostly found in the outer membrane of mitochondria and overexpressed in E. coli bacteria.
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Affiliation(s)
- Lucile Senicourt
- Sorbonne Universités-UPMC University of Paris 06, Département de Chimie, École Normale Supérieure-PSL Research University, CNRS UMR 7203 LBM, 4 Place Jussieu, 75005, Paris Cedex 05, France
| | - Luminita Duma
- CNRS Enzyme and Cell Engineering Laboratory, Sorbonne Universités, Université de Technologie de Compiègne, Rue Roger Couttolenc, CS 60319, 60203, Compiègne Cedex, France
| | - Vassilios Papadopoulos
- The Research Institute of the McGill, University Health Center, Montreal, QC, Canada, H4A 3J1.,Department of Medicine, McGill University, Montreal, QC, Canada, H4A 3J1
| | - Jean-Jacques Lacapere
- Sorbonne Universités-UPMC University of Paris 06, Département de Chimie, École Normale Supérieure-PSL Research University, CNRS UMR 7203 LBM, 4 Place Jussieu, 75005, Paris Cedex 05, France.
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8
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TSPO: kaleidoscopic 18-kDa amid biochemical pharmacology, control and targeting of mitochondria. Biochem J 2016; 473:107-21. [PMID: 26733718 DOI: 10.1042/bj20150899] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The 18-kDa translocator protein (TSPO) localizes in the outer mitochondrial membrane (OMM) of cells and is readily up-regulated under various pathological conditions such as cancer, inflammation, mechanical lesions and neurological diseases. Able to bind with high affinity synthetic and endogenous ligands, its core biochemical function resides in the translocation of cholesterol into the mitochondria influencing the subsequent steps of (neuro-)steroid synthesis and systemic endocrine regulation. Over the years, however, TSPO has also been linked to core cellular processes such as apoptosis and autophagy. It interacts and forms complexes with other mitochondrial proteins such as the voltage-dependent anion channel (VDAC) via which signalling and regulatory transduction of these core cellular events may be influenced. Despite nearly 40 years of study, the precise functional role of TSPO beyond cholesterol trafficking remains elusive even though the recent breakthroughs on its high-resolution crystal structure and contribution to quality-control signalling of mitochondria. All this along with a captivating pharmacological profile provides novel opportunities to investigate and understand the significance of this highly conserved protein as well as contribute the development of specific therapeutics as presented and discussed in the present review.
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9
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Abstract
The 3D structure of the 18-kDa transmembrane (TM) protein TSPO (translocator protein)/PBR (peripheral benzodiazepine receptor), which contains a binding site for benzodiazepines, is important to better understand its function and regulation by endogenous and synthetic ligands. We have recently determined the structure of mammalian TSPO/PBR in complex with the diagnostic ligand PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide; Jaremko et al. (2014) Science 343: , 1363-1366], providing for the first time atomic-level insight into the conformation of this protein, which is up-regulated in various pathological conditions including Alzheimer's disease and Parkinson's disease. Here, we review the studies which have probed the structural properties of mammalian TSPO/PBR as well as the homologues bacterial tryptophan-rich sensory proteins (TspOs) over the years and provide detailed insight into the 3D structure of mouse TSPO (mTSPO)/PBR in complex with PK11195.
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10
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Enigmatic Translocator protein (TSPO) and cellular stress regulation. Trends Biochem Sci 2015; 40:497-503. [PMID: 26228316 DOI: 10.1016/j.tibs.2015.07.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/25/2015] [Accepted: 07/06/2015] [Indexed: 11/23/2022]
Abstract
Translocator proteins (TSPOs) are conserved, ubiquitous membrane proteins identified initially as benzodiazepine-binding proteins in mammalian cells. Recent genetic and biochemical studies have challenged the accepted model that TSPOs are essential and required for steroidogenesis in animal cells. Instead, evidence from different kingdoms of life suggests that TSPOs are encoded by nonessential genes that are temporally upregulated in cells encountering conditions of oxidative stress, including inflammation and tissue injury. Here we discuss how TSPOs may be involved in complex homeostasis signaling mechanisms. We suggest that the main physiological role of TSPOs may be to modulate oxidative stress, irrespective of the cell type or subcellular localization, in part through the subtle regulation of tetrapyrrole metabolism.
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11
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Chua SW, Kassiou M, Ittner LM. The translocator protein as a drug target in Alzheimer's disease. Expert Rev Neurother 2014; 14:439-48. [PMID: 24625007 DOI: 10.1586/14737175.2014.896201] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The translocator protein (TSPO) recently emerged as a potential drug target in Alzheimer's disease (AD). This has been fuelled mainly by positron emission topography studies that show the upregulation of TSPO in AD, especially in relation to microgliosis and astrogliosis in amyloid-β and tau pathology. Although data as to the exact role of TSPO in AD is still inconclusive, TSPO appears to be involved in neuroinflammatory processes and AD has been shown to involve substantial inflammation. Therefore, further development and investigation of the pharmacological effect of TSPO ligands in AD pathology are warranted.
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Affiliation(s)
- Sook W Chua
- Dementia Research Unit, School of Medical Sciences, Wallace Wurth Building, University of New South Wales, Sydney, NSW 2052, Australia
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12
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Liu G, Middleton RJ, Hatty CR, Kam WW, Chan R, Pham T, Harrison‐Brown M, Dodson E, Veale K, Banati RB. The 18 kDa translocator protein, microglia and neuroinflammation. Brain Pathol 2014; 24:631-53. [PMID: 25345894 PMCID: PMC8029074 DOI: 10.1111/bpa.12196] [Citation(s) in RCA: 166] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 08/19/2014] [Indexed: 12/17/2022] Open
Abstract
The 18 kDa translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, is expressed in the injured brain. It has become known as an imaging marker of "neuroinflammation" indicating active disease, and is best interpreted as a nondiagnostic biomarker and disease staging tool that refers to histopathology rather than disease etiology. The therapeutic potential of TSPO as a drug target is mostly based on the understanding that it is an outer mitochondrial membrane protein required for the translocation of cholesterol, which thus regulates the rate of steroid synthesis. This pivotal role together with the evolutionary conservation of TSPO has underpinned the belief that any loss or mutation of TSPO should be associated with significant physiological deficits or be outright incompatible with life. However, against prediction, full Tspo knockout mice are viable and across their lifespan do not show the phenotype expected if cholesterol transport and steroid synthesis were significantly impaired. Thus, the "translocation" function of TSPO remains to be better substantiated. Here, we discuss the literature before and after the introduction of the new nomenclature for TSPO and review some of the newer findings. In light of the controversy surrounding the function of TSPO, we emphasize the continued importance of identifying compounds with confirmed selectivity and suggest that TSPO expression is analyzed within specific disease contexts rather than merely equated with the reified concept of "neuroinflammation."
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Affiliation(s)
- Guo‐Jun Liu
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Ryan J. Middleton
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Claire R. Hatty
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Winnie Wai‐Ying Kam
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Ronald Chan
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Tien Pham
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Meredith Harrison‐Brown
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Eoin Dodson
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
| | - Kelly Veale
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
| | - Richard B. Banati
- Life SciencesAustralian Nuclear Science and Technology OrganisationNSWAustralia
- Brain & Mind Research InstituteThe University of SydneyNSWAustralia
- Discipline of Medical Imaging & Radiation SciencesFaculty of Health SciencesThe University of SydneyNSWAustralia
- National Imaging Facility and Ramaciotti Brain Imaging CentreSydneyNSWAustralia
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13
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Hinsen K, Vaitinadapoule A, Ostuni MA, Etchebest C, Lacapere JJ. Construction and validation of an atomic model for bacterial TSPO from electron microscopy density, evolutionary constraints, and biochemical and biophysical data. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:568-80. [PMID: 25450341 DOI: 10.1016/j.bbamem.2014.10.028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 10/01/2014] [Accepted: 10/20/2014] [Indexed: 11/30/2022]
Abstract
The 18 kDa protein TSPO is a highly conserved transmembrane protein found in bacteria, yeast, animals and plants. TSPO is involved in a wide range of physiological functions, among which the transport of several molecules. The atomic structure of monomeric ligand-bound mouse TSPO in detergent has been published recently. A previously published low-resolution structure of Rhodobacter sphaeroides TSPO, obtained from tubular crystals with lipids and observed in cryo-electron microscopy, revealed an oligomeric structure without any ligand. We analyze this electron microscopy density in view of available biochemical and biophysical data, building a matching atomic model for the monomer and then the entire crystal. We compare its intra- and inter-molecular contacts with those predicted by amino acid covariation in TSPO proteins from evolutionary sequence analysis. The arrangement of the five transmembrane helices in a monomer of our model is different from that observed for the mouse TSPO. We analyze possible ligand binding sites for protoporphyrin, for the high-affinity ligand PK 11195, and for cholesterol in TSPO monomers and/or oligomers, and we discuss possible functional implications.
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Affiliation(s)
- Konrad Hinsen
- Centre de Biophysique Moléculaire (CNRS), Rue Charles Sadron, 45071 Orléans Cedex, France; Synchrotron SOLEIL, Division Expériences, Saint Aubin, B.P. 48, 91192 Gif-sur-Yvette Cedex, France.
| | - Aurore Vaitinadapoule
- INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France; National Centre for Biological Sciences (NCBS), Tata Institute for Fundamental Research, GKVK Campus, Bangalore, Karnataka, India; Dynamique des Structures et des Interactions des des Macromolécules Biologiques, France.
| | - Mariano A Ostuni
- INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France.
| | - Catherine Etchebest
- INSERM, UMR-S1134, 6 rue Alexandre Cabanel, Université Paris 7 Denis Diderot, F-75015 Paris, France; Université Paris Diderot, Sorbonne Paris Cité, Paris, France; Institut National de la Transfusion Sanguine (INTS), Paris, France; GR-Ex, Laboratoire d'Excellence, Paris, France; Dynamique des Structures et des Interactions des des Macromolécules Biologiques, France.
| | - Jean-Jacques Lacapere
- Sorbonne Universités, UPMC Univ Paris 06, Laboratoire de Biomolécules (LBM), 4 Place Jussieu, F-75005 Paris, France; Ecole Normale Supérieure - PSL Research University, Département de Chimie, 24, rue Lhomond, 75005 Paris, France; CNRS, UMR 7203 LBM, F-75005 Paris, France.
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14
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Jaremko L, Jaremko M, Becker S, Zweckstetter M. Toward the functional oligomerization state of tryptophan-rich sensory proteins. Protein Sci 2014; 23:1154-60. [PMID: 24817333 DOI: 10.1002/pro.2487] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 05/07/2014] [Accepted: 05/07/2014] [Indexed: 11/06/2022]
Abstract
A conserved family of tryptophan-rich sensory proteins (TspO) mediates the transport of heme degradation intermediates across membranes. In eukaryotes, the homologous mitochondrial translocator protein (TSPO) binds cholesterol and radioligands as monomer. On the basis of the mammalian TSPO structure, bioinformatic analysis, and a 10 Å resolution electron microscopy map of TspO from Rhodobacter sphaeroides, we developed a model of the tertiary and quaternary structure of TspO that is in agreement with available mutagenesis data. Our study provides insight into the conformational basis for the restricted interaction of bacterial TspO with radioligands and the functional oligomerization state of bacterial TspO proteins.
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Affiliation(s)
- Lukasz Jaremko
- Max-Planck-Institut für Biophysikalische Chemie, 37077, Göttingen, Germany; Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), 37077, Göttingen, Germany
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15
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Morohaku K, Pelton SH, Daugherty DJ, Butler WR, Deng W, Selvaraj V. Translocator protein/peripheral benzodiazepine receptor is not required for steroid hormone biosynthesis. Endocrinology 2014; 155:89-97. [PMID: 24174323 PMCID: PMC3868810 DOI: 10.1210/en.2013-1556] [Citation(s) in RCA: 186] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Molecular events that regulate cellular biosynthesis of steroid hormones have been a topic of intense research for more than half a century. It has been established that transport of cholesterol into the mitochondria forms the rate-limiting step in steroid hormone production. In current models, both the steroidogenic acute regulatory protein (StAR) and the translocator protein (TSPO) have been implicated to have a concerted and indispensable effort in this cholesterol transport. Deletion of StAR in mice resulted in a critical failure of steroid hormone production, but deletion of TSPO in mice was found to be embryonic lethal. As a result, the role of TSPO in cholesterol transport has been established only using pharmacologic and genetic tools in vitro. To allow us to explore in more detail the function of TSPO in cell type-specific experimental manipulations in vivo, we generated mice carrying TSPO floxed alleles (TSPOfl/fl). In this study we made conditional knockout mice (TSPOcΔ/Δ) with TSPO deletion in testicular Leydig cells by crossing with an anti-Mullerian hormone receptor type II cre/+ mouse line. Genetic ablation of TSPO in steroidogenic Leydig cells in mice did not affect testosterone production, gametogenesis, and reproduction. Expression of StAR, cytochrome P450 side chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase type I, and TSPO2 in TSPOcΔ/Δ testis was unaffected. These results challenge the prevailing dogma that claims an essential role for TSPO in steroid hormone biosynthesis and force reexamination of functional interpretations made for this protein. This is the first study examining conditional TSPO gene deletion in mice. The results show that TSPO function is not essential for steroid hormone biosynthesis.
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Affiliation(s)
- Kanako Morohaku
- Department of Animal Science, College of Agriculture and Life Sciences (K.M., S.H.P., W.R.B., V.S.), Cornell University, Ithaca, New York 14853; and Department of Biochemistry and Molecular Medicine, School of Medicine (D.J.D., W.D.), University of California at Davis, Sacramento, California 95618
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16
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Hatty CR, Le Brun AP, Lake V, Clifton LA, Liu GJ, James M, Banati RB. Investigating the interactions of the 18kDa translocator protein and its ligand PK11195 in planar lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:1019-30. [PMID: 24374318 DOI: 10.1016/j.bbamem.2013.12.013] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 12/16/2013] [Accepted: 12/18/2013] [Indexed: 12/20/2022]
Abstract
The functional effects of a drug ligand may be due not only to an interaction with its membrane protein target, but also with the surrounding lipid membrane. We have investigated the interaction of a drug ligand, PK11195, with its primary protein target, the integral membrane 18kDa translocator protein (TSPO), and model membranes using Langmuir monolayers, quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR). We found that PK11195 is incorporated into lipid monolayers and lipid bilayers, causing a decrease in lipid area/molecule and an increase in lipid bilayer rigidity. NR revealed that PK11195 is incorporated into the lipid chain region at a volume fraction of ~10%. We reconstituted isolated mouse TSPO into a lipid bilayer and studied its interaction with PK11195 using QCM-D, which revealed a larger than expected frequency response and indicated a possible conformational change of the protein. NR measurements revealed a TSPO surface coverage of 23% when immobilised to a modified surface via its polyhistidine tag, and a thickness of 51Å for the TSPO layer. These techniques allowed us to probe both the interaction of TSPO with PK11195, and PK11195 with model membranes. It is possible that previously reported TSPO-independent effects of PK11195 are due to incorporation into the lipid bilayer and alteration of its physical properties. There are also implications for the variable binding profiles observed for TSPO ligands, as drug-membrane interactions may contribute to the apparent affinity of TSPO ligands.
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Affiliation(s)
- Claire R Hatty
- Medical Imaging & Radiation Sciences Faculty Research Group, Faculty of Health Sciences, The University of Sydney, c/o Brain & Mind Research Institute, 94 Mallett Street, Camperdown, NSW 2050, Australia
| | - Anton P Le Brun
- Bragg Institute, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - Vanessa Lake
- Bragg Institute, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - Luke A Clifton
- ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK
| | - Guo Jun Liu
- Medical Imaging & Radiation Sciences Faculty Research Group, Faculty of Health Sciences, The University of Sydney, c/o Brain & Mind Research Institute, 94 Mallett Street, Camperdown, NSW 2050, Australia; Life Sciences, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
| | - Michael James
- Bragg Institute, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia; School of Chemistry, University of New South Wales, Kensington NSW 2052, Australia
| | - Richard B Banati
- Medical Imaging & Radiation Sciences Faculty Research Group, Faculty of Health Sciences, The University of Sydney, c/o Brain & Mind Research Institute, 94 Mallett Street, Camperdown, NSW 2050, Australia; Life Sciences, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia.
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17
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Issop L, Rone MB, Papadopoulos V. Organelle plasticity and interactions in cholesterol transport and steroid biosynthesis. Mol Cell Endocrinol 2013; 371:34-46. [PMID: 23246788 DOI: 10.1016/j.mce.2012.12.003] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 12/04/2012] [Accepted: 12/04/2012] [Indexed: 12/20/2022]
Abstract
Steroid biosynthesis is a multi-step process controlled by pituitary hormones, which, via cAMP-dependent signaling pathways, drive tissue-specific steroid formation. Steroidogenesis begins with the transport of the substrate, cholesterol, from intracellular stores into the inner mitochondrial membrane, where the steroidogenic enzyme CYP11A1 converts cholesterol to pregnenolone. This process is accelerated by hormones and involves a number of proteins and protein-protein interactions. Indeed, cholesterol, stored in lipid droplets and membranes, is transferred through a hormone-induced complex of proteins derived from the cytosol, mitochondria, and other organelles termed the transduceosome to the outer mitochondrial membrane. From there, cholesterol reaches CYP11A1 through outer/inner membrane contact sites. Thus, cholesterol transfer is likely achieved through a hormone-dependent reorganization of organelles and protein distribution and interactions. The findings reviewed herein suggest the presence of a hormone-dependent organelle communication network mediated by protein-protein interactions and inter-organelle trafficking, resulting in the efficient and timely delivery of cholesterol into mitochondria for steroid synthesis.
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Affiliation(s)
- Leeyah Issop
- Research Institute of the McGill University Health Centre, Department of Medicine, McGill University, Montreal, Quebec, Canada H3G 1A4
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