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Moskalenko AV, Yarova PL, Gordeev SN, Smirnov SV. Single protein molecule mapping with magnetic atomic force microscopy. Biophys J 2010; 98:478-87. [PMID: 20141762 PMCID: PMC2814202 DOI: 10.1016/j.bpj.2009.10.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Revised: 10/06/2009] [Accepted: 10/15/2009] [Indexed: 02/04/2023] Open
Abstract
Understanding the structural organization and distribution of proteins in biological cells is of fundamental importance in biomedical research. The use of conventional fluorescent microscopy for this purpose is limited due to its relatively low spatial resolution compared to the size of a single protein molecule. Atomic force microscopy (AFM), on the other hand, allows one to achieve single-protein resolution by scanning the cell surface using a specialized ligand-coated AFM tip. However, because this method relies on short-range interactions, it is limited to the detection of binding sites that are directly accessible to the AFM tip. We developed a method based on magnetic (long-range) interactions and applied it to investigate the structural organization and distribution of endothelin receptors on the surface of smooth muscle cells. Endothelin receptors were labeled with 50-nm superparamagnetic microbeads and then imaged with magnetic AFM. Considering its high spatial resolution and ability to "see" magnetically labeled proteins at a distance of up to 150 nm, this approach may become an important tool for investigating the dynamics of individual proteins both on the cell membrane and in the submembrane space.
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Affiliation(s)
| | - Polina L. Yarova
- Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | | | - Sergey V. Smirnov
- Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
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Kobori T, Smith GD, Sandford R, Edwardson JM. The transient receptor potential channels TRPP2 and TRPC1 form a heterotetramer with a 2:2 stoichiometry and an alternating subunit arrangement. J Biol Chem 2010; 284:35507-13. [PMID: 19850920 DOI: 10.1074/jbc.m109.060228] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
There is functional evidence that polycystin-2 (TRPP2) interacts with other members of the transient receptor potential family, including TRPC1 and TRPV4. Here we have used atomic force microscopy to study the structure of the TRPP2 homomer and the interaction between TRPP2 and TRPC1. The molecular volumes of both Myc-tagged TRPP2 and V5-tagged TRPC1 isolated from singly transfected tsA 201 cells indicated that they assembled as homotetramers. The molecular volume of the protein isolated from cells expressing both TRPP2 and TRPC1 was intermediate between the volumes of the two homomers, suggesting that a heteromer was being formed. The distribution of angles between pairs of anti-Myc antibodies bound to TRPP2 particles had a large peak close to 90 degrees and a smaller peak close to 180 degrees , consistent with the assembly of TRPP2 as a homotetramer. In contrast, the corresponding angle distributions for decoration of the TRPP2-TRPC1 heteromer by either anti-Myc or anti-V5 antibodies had predominant peaks close to 180 degrees . This decoration pattern indicates a TRPP2:TRPC1 subunit stoichiometry of 2:2 and an alternating subunit arrangement.
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Affiliation(s)
- Toshiro Kobori
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD
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Functional variants of the serotonin receptor type 3A and B gene are associated with eating disorders. Pharmacogenet Genomics 2009; 19:790-9. [PMID: 19741568 DOI: 10.1097/fpc.0b013e32833132b3] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
OBJECTIVE As a key player in modulating both human physiological and behavioural functions including anxiety, perception and in particular appetite, serotonin (5-hydroxytryptamine, 5-HT) is likely to be involved in the aetiology of eating disorders. Studies showing serotonin receptor type 3 (5-HT3) receptors to mediate food intake depression (anorexic response) have triggered our interest in investigating the putative role of variants in the 5-HT3 receptor genes, HTR3A and HTR3B, in the susceptibility to anorexia nervosa (AN) and bulimia nervosa (BN). METHODS Two hundred and sixty-five patients with AN and 91 patients with BN as well as 191 healthy controls served as a pilot study group for mutational analysis by direct sequencing. Variants showing a significant association were subsequently genotyped in an independent Spanish cohort of 78 patients with AN and 119 patients with BN as well as 331 healthy controls for replication purposes. RESULTS In the pilot study, we found the coding HTR3B variant, p.Y129S, (rs1176744, P = 0.004, odds ratio = 2.06) to be associated with the restrictive subtype of AN. The association was confirmed in the Spanish study group (P = 0.034, odds ratio = 2.26). CONCLUSION Our study provides first evidence for an involvement of 5-HT3 variants in the aetiopathology of eating disorders in humans.
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Galeazzi S, Hermans TM, Paolino M, Anzini M, Mennuni L, Giordani A, Caselli G, Makovec F, Meijer EW, Vomero S, Cappelli A. Multivalent Supramolecular Dendrimer-Based Drugs. Biomacromolecules 2009; 11:182-6. [DOI: 10.1021/bm901055a] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Simone Galeazzi
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Thomas M. Hermans
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Marco Paolino
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Maurizio Anzini
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Laura Mennuni
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Antonio Giordani
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Gianfranco Caselli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Francesco Makovec
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - E. W. Meijer
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Salvatore Vomero
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
| | - Andrea Cappelli
- Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Università di Siena, Via A. Moro, 53100 Siena, Italy, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands, and Rottapharm S.p.A., Via Valosa di Sopra 7, 20052 Monza, Italy
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Sanghvi M, Hamouda AK, Davis MI, Morton RA, Srivastava S, Pandhare A, Duddempudi PK, Machu TK, Lovinger DM, Cohen JB, Blanton MP. Hydrophobic photolabeling studies identify the lipid-protein interface of the 5-HT3A receptor. Biochemistry 2009; 48:9278-86. [PMID: 19715355 DOI: 10.1021/bi901208j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A HEK-293 cell line that stably expresses mouse 5-HT(3A)Rs containing a C-terminal extension that confers high-affinity binding of alpha-bungarotoxin (alphaBgTx) was established (alphaBgTx-5-HT(3A)Rs) and used to purify alphaBgTx-5-HT(3A)Rs in a lipid environment for use in structural studies using photoaffinity labeling. alphaBgTx-5-HT(3A)Rs were expressed robustly (60 pmol of [(3)H]BRL-43694 binding sites (approximately 3 microg of receptor) per milligram of protein) and displayed the same functional properties as wild-type receptors (serotonin EC(50) = 5.3 +/- 0.04 microM). While [(125)I]alphaBgTx bound to the alphaBgTx-5-HT(3A)Rs with high affinity (K(d) = 11 nM), application of nonradioactive alphaBgTx (up to 300 microM) had no effect on serotonin-induced current responses. alphaBgTx-5-HT(3A)Rs were purified on an alphaBgTx-derivatized affinity column from detergent extracts in milligram quantities and at approximately 25% purity. The hydrophobic photolabel 3-trifluoromethyl-3-(m-[(125)I]iodophenyl)diazirine ([(125)I]TID) was used to identify the amino acids at the lipid-protein interface of purified and lipid-reconstituted alphaBgTx-5-HT(3A)Rs. [(125)I]TID photoincorporation into the alphaBgTx-5-HT(3A)R subunit was initially mapped to subunit proteolytic fragments of 8 kDa, containing the M4 transmembrane segment and approximately 60% of incorporated (125)I, and 17 kDa, containing the M1-M3 transmembrane segments. Within the M4 segment, [(125)I]TID labeled Ser(451), equivalent to the [(125)I]TID-labeled residue Thr(422) at the lipid-exposed face of the Torpedo nicotinic acetylcholine receptor (nAChR) alpha1M4 alpha-helix. These results provide a first definition of the surface of the 5-HT(3A)R M4 helix that is exposed to lipid and establish that this surface is equivalent to the surface exposed to lipid in the Torpedo nAChR.
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Affiliation(s)
- Mitesh Sanghvi
- Department of Pharmacology and Neuroscience and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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5-HT 3(5-hydroxytryptamine 3). Br J Pharmacol 2009. [DOI: 10.1111/j.1476-5381.2009.00502_2.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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LGIC. Br J Pharmacol 2009. [DOI: 10.1111/j.1476-5381.2009.00502.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Lange T, Jungmann P, Haberle J, Falk S, Duebbers A, Bruns R, Ebner A, Hinterdorfer P, Oberleithner H, Schillers H. Reduced number of CFTR molecules in erythrocyte plasma membrane of cystic fibrosis patients. Mol Membr Biol 2009; 23:317-23. [PMID: 16923725 DOI: 10.1080/09687860600738304] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Cystic fibrosis (CF), the most common genetic disease among Caucasians, is caused by mutations in the gene encoding CFTR (cystic fibrosis transmembrane conductance regulator). The most frequent mutation, DeltaF508, results in protein misfolding and, as a consequence, prevents CFTR from reaching its final location at the cell surface. CFTR is expressed in various cell types including red blood cells. The functional role of CFTR in erythrocytes is still unclear. Since the number of CFTR copies in a single erythrocyte of healthy donors and CF patients with a homozygous DeltaF508 mutation is unknown, we counted CFTR, localized in erythrocyte plasma membrane, at the single molecule level. A novel experimental approach combining atomic force microscopy with quantum-dot-labeled anti-CFTR antibodies, used as topographic surface markers, was employed to detect individual CFTR molecules. Analysis of erythrocyte plasma membranes taken from healthy donors and CF patients with a homozygous DeltaF508 mutation reveals mean (SEM) values of 698 (12.8) (n=542) and 172 (3.8) (n=538) CFTR molecules per red blood cell, respectively. We conclude that erythrocytes reflect the CFTR status of the organism and that quantification of CFTR in a blood sample could be useful in the diagnosis of CFTR related diseases.
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Affiliation(s)
- Tobias Lange
- Institute of Physiology II, University of Muenster, and Department of Pediatrics, University Hospitals of Muenster, Germany
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Zhang P, Luo Y, Chasan B, González-Perrett S, Montalbetti N, Timpanaro GA, Cantero MDR, Ramos AJ, Goldmann WH, Zhou J, Cantiello HF. The multimeric structure of polycystin-2 (TRPP2): structural-functional correlates of homo- and hetero-multimers with TRPC1. Hum Mol Genet 2009; 18:1238-51. [PMID: 19193631 DOI: 10.1093/hmg/ddp024] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Polycystin-2 (PC2, TRPP2), the gene product of PKD2, whose mutations cause autosomal dominant polycystic kidney disease (ADPKD), belongs to the superfamily of TRP channels. PC2 is a non-selective cation channel, with multiple subconductance states. In this report, we explored structural and functional properties of PC2 and whether the conductance substates represent monomeric contributions to the channel complex. A kinetic analysis of spontaneous channel currents of PC2 showed that four intrinsic, non-stochastic subconductance states, which followed a staircase behavior, were both pH- and voltage-dependent. To confirm the oligomeric contributions to PC2 channel function, heteromeric PC2/TRPC1 channel complexes were also functionally assessed by single channel current analysis. Low pH inhibited the PC2 currents in PC2 homomeric complexes, but failed to affect PC2 currents in PC2/TRPC1 heteromeric complexes. Amiloride, in contrast, abolished PC2 currents in both the homomeric PC2 complexes and the heteromeric PC2/TRPC1 complexes, thus PC2/TRPC1 complexes have distinct functional properties from the homomeric complexes. The topological features of the homomeric PC2-, TRPC1- and heteromeric PC2/TRPC1 channel complexes, assessed by atomic force microscopy, were consistent with structural tetramers. TRPC1 homomeric channels had different average diameter and protruding height when compared with the PC2 homomers. The contribution of individual monomers to the PC2/TRPC1 hetero-complexes was easily distinguishable. The data support tetrameric models of both the PC2 and TRPC1 channels, where the overall conductance of a particular channel will depend on the contribution of the various functional monomers in the complex.
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Affiliation(s)
- Peng Zhang
- Nephrology Division and Electrophysiology Core, Massachusetts General Hospital East, Charlestown, MA 02129, USA
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3B but which 3B and that's just one of the questions: the heterogeneity of human 5-HT3 receptors. Trends Pharmacol Sci 2009; 29:437-44. [PMID: 18597859 DOI: 10.1016/j.tips.2008.06.001] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Revised: 04/14/2008] [Accepted: 06/15/2008] [Indexed: 01/19/2023]
Abstract
The 5-hydroxytryptamine 3 (5-HT3) receptor is expressed widely in the central and peripheral nervous systems, where it mediates or modulates a wide range of physiological processes. The receptor is targeted by drugs administered for nausea and/or emesis and irritable bowel syndrome and has been proposed as a potential drug target in various psychiatric disorders. The 5-HT3 receptor is a pentameric ligand-gated ion channel and belongs to the Cys-loop receptor family. In contrast to the immense heterogeneity characterizing other Cysloop receptors, native 5-HT3 receptors historically have been considered a much more homogenous receptor population. However, the recent discovery of additional 5-HT3 subunits and the dawning realization that central and peripheral 5-HT3 receptor populations might comprise several subtypes characterized by distinct functional properties has emphasized the complexity of human 5-HT3 receptor signaling. In this review potential implications of these findings and of the entirely new layer of interindividual diversity introduced to the 5-HT3 receptor system by genetic variations will be outlined.
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Barnes NM, Hales TG, Lummis SC, Peters JA. The 5-HT3 receptor--the relationship between structure and function. Neuropharmacology 2009; 56:273-84. [PMID: 18761359 PMCID: PMC6485434 DOI: 10.1016/j.neuropharm.2008.08.003] [Citation(s) in RCA: 174] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2008] [Revised: 07/31/2008] [Accepted: 08/01/2008] [Indexed: 12/15/2022]
Abstract
The 5-hydroxytryptamine type-3 (5-HT3) receptor is a cation-selective ion channel of the Cys-loop superfamily. 5-HT3 receptor activation in the central and peripheral nervous systems evokes neuronal excitation and neurotransmitter release. Here, we review the relationship between the structure and the function of the 5-HT3 receptor. 5-HT3A and 5-HT3B subunits are well established components of 5-HT3 receptors but additional HTR3C, HTR3D and HTR3E genes expand the potential for molecular diversity within the family. Studies upon the relationship between subunit structure and the ionic selectivity and single channel conductances of 5-HT3 receptors have identified a novel domain (the intracellular MA-stretch) that contributes to ion permeation and selectivity. Conventional and unnatural amino acid mutagenesis of the extracellular domain of the receptor has revealed residues, within the principle (A-C) and complementary (D-F) loops, which are crucial to ligand binding. An area requiring much further investigation is the subunit composition of 5-HT3 receptors that are endogenous to neurones, and their regional expression within the central nervous system. We conclude by describing recent studies that have identified numerous HTR3A and HTR3B gene polymorphisms that impact upon 5-HT3 receptor function, or expression, and consider their relevance to (patho)physiology.
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Affiliation(s)
- Nicholas M. Barnes
- Cellular and Molecular Neuropharmacology Research Group, Department of Pharmacology, Division of Neuroscience, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Tim G. Hales
- Department of Pharmacology and Physiology, The George Washington University, Washington, DC 20037, USA
| | - Sarah C.R. Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - John A. Peters
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK
- Corresponding author. Tel.: +44 01382 660111x33117; fax: +44 01382 667120. E-mail address: (J.A. Peters)
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Takahashi H, Hizume K, Kumeta M, H Yoshimura S, Takeyasu K. Single-molecule anatomy by atomic force microscopy and recognition imaging. ARCHIVES OF HISTOLOGY AND CYTOLOGY 2009; 72:217-25. [PMID: 21471656 DOI: 10.1679/aohc.72.217] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Atomic force microscopy (AFM) has been a useful technique to visualize cellular and molecular structures at single-molecule resolution. The combination of imaging and force modes has also allowed the characterization of physical properties of biological macromolecules in relation to their structures. Furthermore, recognition imaging, which is obtained under the TREC(TM) (Topography and RECognition) mode of AFM, can map a specific protein of interest within an AFM image. In this study, we first demonstrated structural properties of purified α Actinin-4 by conventional AFM. Since this molecule is an actin binding protein that cross-bridges actin filaments and anchors it to integrin via tailin-vinculin-α actinin adaptor-interaction, we investigated their structural properties using the recognition mode of AFM. For this purpose, we attached an anti-α Actinin-4 monoclonal antibody to the AFM cantilever and performed recognition imaging against α Actinin-4. We finally succeeded in mapping the epitopic region within the α Actinin-4 molecule. Thus, recognition imaging using an antibody coupled AFM cantilever will be useful for single-molecule anatomy of biological macromolecules and structures.
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Affiliation(s)
- Hirohide Takahashi
- Laboratory of Plasma Membrane and Nuclear Signaling, Kyoto University Graduate School of Biostudies, Japan
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Chapter 12 Modulation of the Cys‐Loop Ligand‐Gated Ion Channels by Fatty Acid and Cannabinoids. VITAMINS AND HORMONES 2009; 81:315-35. [DOI: 10.1016/s0083-6729(09)81012-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Characterization of the effects of four HTR3B polymorphisms on human 5-HT3AB receptor expression and signalling. Pharmacogenet Genomics 2008; 18:1027-40. [DOI: 10.1097/fpc.0b013e328310f950] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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66
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Barrera NP, Edwardson JM. The subunit arrangement and assembly of ionotropic receptors. Trends Neurosci 2008; 31:569-76. [PMID: 18774187 DOI: 10.1016/j.tins.2008.08.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 08/05/2008] [Accepted: 08/05/2008] [Indexed: 11/17/2022]
Abstract
Ionotropic receptors mediate rapid communication between neurons. These receptors are oligomers and are usually assembled from multiple subunit types. Receptors built from different subunit combinations have distinct functional properties, such as single-channel conductances, rates of desensitization and sensitivities to activators and inactivators; they can also have different intracellular locations. Methods are now available for determining not only the subunit stoichiometry but also the subunit arrangement within ionotropic receptors. This information will inform experiments designed to understand the molecular basis of receptor assembly and function. It will also permit the modelling of potential ligand-binding sites at the interfaces between the subunits and should lead to a more rational approach to drug development.
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Affiliation(s)
- Nelson P Barrera
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
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Butler AS, Lindesay SA, Dover TJ, Kennedy MD, Patchell VB, Levine BA, Hope AG, Barnes NM. Importance of the C-terminus of the human 5-HT3A receptor subunit. Neuropharmacology 2008; 56:292-302. [PMID: 18786552 DOI: 10.1016/j.neuropharm.2008.08.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2008] [Revised: 07/25/2008] [Accepted: 08/08/2008] [Indexed: 10/25/2022]
Abstract
Amongst the family members of Cys-loop LGICs, the atypical ability of the 5-HT3A subunit to form functional homomeric receptors allowed a direct investigation of the role of the C-terminus. Deletion of the three C-terminal amino acids (DeltaGln453-DeltaTyr454-DeltaAla455) from the h5-HT3A subunit prevented formation of a specific radioligand binding site as well as expression within the cell membrane. Removal of merely the C-terminal residue (DeltaAla455) reduced specific radioligand binding (to 4+/-1% relative to the wild-type; cells grown at 37 degrees C) and also cell membrane expression; these reductions were less evident when the DeltaAla455 expressing cells were grown at 27 degrees C (specific radioligand binding levels 27+/-5% relative to wild-type also grown at 27 degrees C). Mutation of the h5-HT3A C-terminal amino acid, alanine, for either glycine (Ala455Gly), valine (Ala455Val) or leucine (Ala455Leu) reduced specific radioligand binding levels by 24+/-23%, 32+/-12% and 88+/-1%, respectively; the latter mutant also displaying reduced membrane expression. In contrast, mutation to alanine of the two amino acids preceding the C-terminal alanine (Gln453Ala and Tyr454Ala) had no detrimental effects on specific radioligand binding or cell membrane expression levels. The present study demonstrates an important role for the C-terminus in the formation of the functional h5-HT3A receptor. The partial restoration of 5-HT3 receptor binding and cell membrane expression when cells expressing C-terminal mutant 5-HT3A subunits were grown at a lower temperature (27 degrees C) suggests that the C-terminus stabilises the 5-HT3 receptor allowing subunit folding and subsequent maturation.
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Affiliation(s)
- Amy S Butler
- Cellular and Molecular Neuropharmacology Research Group, School of Experimental and Clinical Medicine, The Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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Livesey MR, Cooper MA, Deeb TZ, Carland JE, Kozuska J, Hales TG, Lambert JJ, Peters JA. Structural determinants of Ca2+ permeability and conduction in the human 5-hydroxytryptamine type 3A receptor. J Biol Chem 2008; 283:19301-13. [PMID: 18474595 PMCID: PMC2443672 DOI: 10.1074/jbc.m802406200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Revised: 05/08/2008] [Indexed: 11/17/2022] Open
Abstract
Cation-selective cysteine (Cys)-loop transmitter-gated ion channels provide an important pathway for Ca2+ entry into neurones. We examined the influence on Ca2+ permeation of amino acids located at intra- and extracellular ends of the conduction pathway of the human 5-hydroxytryptamine type 3A (5-HT3A) receptor. Mutation of cytoplasmic arginine residues 432, 436, and 440 to glutamine, aspartate, and alanine (the aligned residues of the human 5-HT3B subunit (yielding 5-HT3A(QDA)) increased PCa/PCs from 1.4 to 3.7. The effect was attributable to the removal of an electrostatic influence of the Arg-436 residue. Despite its relatively high permeability to Ca2+, the single channel conductance of the 5-HT3A(QDA) receptor was depressed in a concentration-dependent and voltage-independent manner by extracellular Ca2+. A conserved aspartate, located toward the extracellular end of the conduction pathway and known to influence ionic selectivity, contributed to the inhibitory effect of Ca2+ on macroscopic currents mediated by 5-HT3A receptors. We introduced a D293A mutation into the 5-HT3A(QDA) receptor (yielding the 5-HT3A(QDA D293A) construct) to determine whether the aspartate is required for the suppression of single channel conductance by Ca2+. The D293A mutation decreased the PCa/PCs ratio to 0.25 and reduced inwardly directed single channel conductance from 41 to 30 pS but did not prevent suppression of single channel conductance by Ca2+. The D293A mutation also reduced PCa/PCs when engineered into the wild-type 5-HT3A receptor. The data helped to identify key residues in the cytoplasmic domain (Arg-436) and extracellular vestibule (Asp-293) that markedly influence PCa/PCs and additionally directly demonstrated a depression of single channel conductance by Ca2+.
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Affiliation(s)
- Matthew R Livesey
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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69
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Noam Y, Wadman WJ, van Hooft JA. On the voltage-dependent Ca2+ block of serotonin 5-HT3 receptors: a critical role of intracellular phosphates. J Physiol 2008; 586:3629-38. [PMID: 18566001 DOI: 10.1113/jphysiol.2008.153486] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Natively expressed serotonin 5-HT(3) receptors typically possess a negative-slope conductance region in their I-V curve, due to a voltage-dependent block by external Ca(2+) ions. However, in almost all studies performed with heterologously expressed 5-HT(3) receptors, this feature was not observed. Here we show that mere addition of ATP to the pipette solution is sufficient to reliably observe a voltage-dependent block in homomeric (h5-HT(3A)) and heteromeric (h5-HT(3AB)) receptors expressed in HEK293 cells. A similar block was observed with a plethora of molecules containing a phosphate moiety, thus excluding a role of phosphorylation. A substitution of three arginines in the intracellular vestibule of 5-HT(3A) with their counterpart residues from the 5-HT(3B) subunit (RRR-QDA) was previously shown to dramatically increase single channel conductance. We find this mutant to have a linear I-V curve that is unaffected by the presence of ATP, with a fractional Ca(2+) current (Pf%) that is reduced (1.8 +/- 0.2%) compared to that of the homomeric receptor (4.1 +/- 0.2%), and similar to that of the heteromeric form (2.0 +/- 0.3%). Moreover, whereas ATP decreased the Pf% of the homomeric receptor, this was not observed with the RRR-QDA mutant. Finally, ATP was found to be critical for voltage-dependent channel block also in hippocampal interneurons that natively express 5-HT(3) receptors. Taken together, our results indicate a novel mechanism by which ATP, and similar molecules, modulate 5-HT(3) receptors via interactions with the intracellular vestibule of the receptor.
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Affiliation(s)
- Yoav Noam
- Swammerdam Institute for Life Sciences, Center for NeuroScience, University of Amsterdam, PO Box 94084, NL-1090 GB Amsterdam, The Netherlands
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70
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Direct visualization of the trimeric structure of the ASIC1a channel, using AFM imaging. Biochem Biophys Res Commun 2008; 372:752-5. [PMID: 18514062 DOI: 10.1016/j.bbrc.2008.05.100] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2008] [Accepted: 05/20/2008] [Indexed: 01/25/2023]
Abstract
There has been confusion about the subunit stoichiometry of the degenerin family of ion channels. Recently, a crystal structure of acid-sensing ion channel (ASIC) 1a revealed that it assembles as a trimer. Here, we used atomic force microscopy (AFM) to image unprocessed ASIC1a bound to mica. We detected a mixture of subunit monomers, dimers and trimers. In some cases, triple-subunit clusters were clearly visible, confirming the trimeric structure of the channel, and indicating that the trimer sometimes disaggregated after adhesion to the mica surface. This AFM-based technique will now enable us to determine the subunit arrangement within heteromeric ASICs.
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71
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Functional characterization of a -100_-102delAAG deletion-insertion polymorphism in the promoter region of the HTR3B gene. Pharmacogenet Genomics 2008; 18:219-30. [PMID: 18300944 DOI: 10.1097/fpc.0b013e3282f51092] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE The HTR3B gene encodes the B-subunit of the type 3 serotonin receptor (5-HT3). A -100_-102delAAG deletion in the promoter region has been associated with poor response to antiemetic medication and susceptibility to bipolar affective disorders. The molecular mechanisms underlying these associations, however, remained unclear. METHODS We performed electrophoretic mobility shift and luciferase reporter gene assays to elucidate the effect of this polymorphism on the HTR3B promoter activity in PC-12 and HEK293 cells. The reporter constructs carried a 2171 bp fragment of the native HTR3B promoter or 30 bp of the polymorphic locus in tandem triplication upstream of the thymidine kinase minimal promoter. RESULTS Deletion mapping indicated that the sequence around the -100_-102delAAG polymorphism had significant promoter activity. Electrophoretic mobility shift assays indicated differential binding of nuclear proteins to the polymorphic DNA region with stronger binding to the insertion than to the deletion allele. The activity of the native promoter carrying the deletion allele was 25% higher in PC-12 (P=0.016) and 40% higher in HEK cells (P=0.016) compared with the respective insertion construct. Constructs carrying the deletion allele in tandem triplicates showed 43% (PC-12 cells, P=0.002) and 28% (HEK293 cells, P=0.015) higher activity than those carrying the insertion allele. The polymorphism was not linked with known amino acid substitutions in HTR3A and HTR3B. CONCLUSIONS The -100_-102delAAG 3 bp deletion increases the HTR3B promoter activity in vitro. The consequences of this for the structure and the function of the resulting 5-HT3 receptors remain to be elucidated.
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72
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Tanaka M, Kobayashi D, Murakami Y, Ozaki N, Suzuki T, Iwata N, Haraguchi K, Ieiri I, Kinukawa N, Hosoi M, Ohtani H, Sawada Y, Mine K. Genetic polymorphisms in the 5-hydroxytryptamine type 3B receptor gene and paroxetine-induced nausea. Int J Neuropsychopharmacol 2008; 11:261-7. [PMID: 17697394 DOI: 10.1017/s1461145707007985] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Selective serotonin reuptake inhibitor (SSRI)-induced nausea can be severe enough to lead to early treatment discontinuation. However, it is currently not possible to predict the occurrence of nausea before the initiation of SSRI treatment. In this study, we investigated the effect of genetic polymorphisms in the 5-hydroxytryptamine type 2A, 3A, and 3B (5-HT3B) receptors, 5-HT transporter, and CYP2D6 genes on the incidence of paroxetine-induced nausea. A consecutive series of 72 Japanese patients with depressive or anxiety disorders were treated with paroxetine. Paroxetine-induced nausea was assessed by a pharmacist and was observed in 29.2% of the patients. A significant (nominal p=0.00286) association was found between the incidence of nausea and the -100_-102AAG insertion/deletion polymorphism of the 5-HT3B receptor gene. No significant associations were observed between the other genetic polymorphisms and the incidence of nausea. The -100_-102AAG deletion variant of the 5-HT3B receptor gene may affect paroxetine-induced nausea.
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Affiliation(s)
- Misuzu Tanaka
- Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan
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73
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Bower KS, Price KL, Sturdee LE, Dayrell M, Dougherty DA, Lummis SC. 5-Fluorotryptamine is a partial agonist at 5-HT3 receptors, and reveals that size and electronegativity at the 5 position of tryptamine are critical for efficient receptor function. Eur J Pharmacol 2008; 580:291-7. [PMID: 18082160 PMCID: PMC2649378 DOI: 10.1016/j.ejphar.2007.11.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Accepted: 11/09/2007] [Indexed: 11/19/2022]
Abstract
Antagonists, but not agonists, of the 5-HT3 receptor are useful therapeutic agents, and it is possible that partial agonists may also be potentially useful in the clinic. Here we show that 5-fluorotryptamine (5-FT) is a partial agonist at both 5-HT3A and 5-HT3AB receptors with an Rmax (Imax/Imax 5-HT) of 0.64 and 0.45 respectively. It is about 10 fold less potent than 5-HT: EC50=16 and 27 microM, and Ki for displacement of [3H]granisetron binding=0.8 and 1.8 microM for 5-HT3A and 5-HT3AB receptors respectively. We have also explored the potencies and efficacies of tryptamine and a range of 5-substituted tryptamine derivatives. At 5-HT3A receptors tryptamine is a weak (Rmax=0.15), low affinity (EC50=113 microM; Ki=4.8 microM) partial agonist, while 5-chlorotryptamine has a similar affinity to 5-FT (EC50=8.1 microM; Ki=2.7 microM) but is a very weak partial agonist (Rmax=0. 0037). These, and data from 5-methyltryptamine and 5-methoxytryptamine, reveal the importance of size and electronegativity at this location for efficient channel opening.
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Affiliation(s)
- Kiowa S. Bower
- California Institute of Technology, Pasadena, California, USA
| | - Kerry L. Price
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | | | - Mariza Dayrell
- Department of Biochemistry, University of Cambridge, Cambridge, UK
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74
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Barrera NP, Ge H, Henderson RM, Fitzgerald WJ, Edwardson JM. Automated analysis of the architecture of receptors, imaged by atomic force microscopy. Micron 2008; 39:101-10. [PMID: 17296302 DOI: 10.1016/j.micron.2006.12.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Accepted: 12/19/2006] [Indexed: 10/23/2022]
Abstract
Fast neurotransmission involves the operation of ionotropic receptors, which are multi-subunit proteins that respond to activation by opening an integral ion channel. Examples of such channels include the GABA(A) receptor, the 5-HT(3) receptor and the P2X receptor for ATP. These receptors contain more than one type of subunit, although the exact subunit stoichiometry and arrangement around the receptor rosette is often unknown. We are using atomic force microscopy (AFM) of purified receptors to address these issues. Measurement of the molecular volume of the receptor permits the determination of the number of subunits that it contains. Furthermore, analysis of the geometry of complexes between receptors and subunit-specific antibodies reveals the subunit arrangement. Our AFM-based approach has so far been dependent on manual data processing, which is both time-consuming and prone to operator bias. In this study, we set out to develop a novel method capable of automatic segmentation and quantitative analysis of both single receptor particles and receptor-antibody complexes. The method was validated using images of wild type and mutant forms of the P2X(6) receptor. We suggest that the automated method will greatly facilitate further progress in the use of AFM for the determination of receptor and multi-protein architecture.
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Affiliation(s)
- Nelson P Barrera
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
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75
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Antiemetics: an update and the MASCC guidelines applied in clinical practice. ACTA ACUST UNITED AC 2008; 5:32-43. [PMID: 18097455 DOI: 10.1038/ncponc1021] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Accepted: 08/22/2007] [Indexed: 12/16/2022]
Abstract
Nausea and vomiting are two of the most severe problems for patients treated with chemotherapy. Until the late 1970s, nausea and vomiting induced by chemotherapy was an almost neglected research area. With the introduction of cisplatin, the cytotoxin with the highest emetic potential, research was stimulated and has now resulted in the development of two new classes of antiemetics, the serotonin and neurokinin antagonists. A large number of trials have fine-tuned antiemetic therapy and made evidence-based recommendations possible for the majority of patients receiving chemotherapy. This Review discusses the pathophysiology of nausea and vomiting, the development of antiemetics, highlights some of the newest antiemetics, and finally summarizes recommendations from the evidence-based guidelines developed by the Multinational Association of Supportive Care in Cancer.
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76
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Hu XQ, Peoples RW. The 5-HT3B subunit confers spontaneous channel opening and altered ligand properties of the 5-HT3 receptor. J Biol Chem 2008; 283:6826-31. [PMID: 18187416 DOI: 10.1074/jbc.m707571200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Current receptor theory suggests that there is an equilibrium between the inactive (R) and active (R*) conformations of ligand-gated ion channels and G protein-coupled receptors. The actions of ligands in both receptor types could be appropriately explained by this two-state model. Ligands such as agonists and antagonists affect receptor function by stabilizing one or both conformations. The 5-HT3 receptor is a member of the Cys-loop ligand-gated ion channel superfamily participating in synaptic transmission. Here we show that co-expression of the 5-HT3A and 5-HT3B receptor subunits in the human embryonic kidney (HEK) 293 cells results in a receptor that displays a low level of constitutive (or agonist-independent) activity. Furthermore, we also demonstrate that the properties of ligands can be modified by receptor composition. Whereas the 5-hydroxytryptamine (5-HT) analog 5-methoxyindole is a partial agonist at the 5-HT3A receptor, it becomes a "protean agonist" (functioning as an agonist and an inverse agonist at the same receptor) at the 5-HT3AB receptor (after the Greek god Proteus, who was able to change his shape and appearance at will). In addition, the 5-HT analog 5-hydroxyindole is a positive allosteric modulator for the liganded active (AR*) conformation of the 5-HT3A and 5-HT3AB receptors and a negative allosteric modulator for the spontaneously active (R*) conformation of the 5-HT3AB receptor, suggesting that the spontaneously active (R*) and liganded active (AR*) conformations are differentially modulated by 5-hydroxyindole. Thus, the incorporation of the 5-HT3B subunit leads to spontaneous channel opening and altered ligand properties.
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Affiliation(s)
- Xiang-Qun Hu
- Department of Biomedical Sciences, College of Health Sciences, Marquette University, Milwaukee, Wisconsin 53201-1881, USA.
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77
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High-frequency HTR3B variant associated with major depression dramatically augments the signaling of the human 5-HT3AB receptor. Proc Natl Acad Sci U S A 2008; 105:722-7. [PMID: 18184810 DOI: 10.1073/pnas.0708454105] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The 5-hydroxytryptamine-3 (5-HT3) receptor mediates the fast excitatory neurotransmission of serotonin and is known to mediate the nausea/emesis induced by radio/chemotherapy and anesthetics. A polymorphism encoding the variation Y129S in the 5-HT3B subunit exists in high frequency in the general population and has been shown to be inversely correlated to the incidence of major depression in women. We show that 5-HT3AB(Y129S) receptors exhibit a substantially increased maximal response to serotonin compared with WT receptors in two fluorescence-based cellular assays. In electrophysiological recordings, the deactivation and desensitization kinetics of the 5-HT3AB(Y129S) receptor are 20- and 10-fold slower, respectively, than those of the WT receptor. Single-channel measurements reveal a 7-fold-increased mean open time of 5-HT3AB(Y129S) receptors compared with WT receptors. The augmented signaling displayed by 5-HT3AB(Y129S) receptors may confer protection against the development of depression. The variant also may influence the development and/or treatment of nausea and other disorders involving 5-HT3 receptors. Thus, the impact of the high-frequency variant 5-HT3B(Y129S) on 5-HT3AB receptor signaling calls for a search for additional phenotypes, and the variant may thus aid in establishing the role of the 5-HT3AB receptor in pathophysiology.
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78
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Shahin V, Barrera NP. Providing Unique Insight into Cell Biology via Atomic Force Microscopy. INTERNATIONAL REVIEW OF CYTOLOGY 2008; 265:227-52. [DOI: 10.1016/s0074-7696(07)65006-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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79
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Maue RA. Understanding ion channel biology using epitope tags: progress, pitfalls, and promise. J Cell Physiol 2007; 213:618-25. [PMID: 17849449 DOI: 10.1002/jcp.21259] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Epitope tags have been increasingly used to understand ion channel subunit assembly and interaction, trafficking, subcellular localization, and function in living cells. In particular, epitope tags have proven extremely useful for analyses of closely related, highly homologous channel subunits in endogenous cell contexts in vitro and in vivo, where multiple channel isoforms may be expressed. However, as the variety of epitope tags that have been used has expanded, and the use of tagged channel subunits has become increasingly sophisticated and widespread, there has also been an increase in the number of examples highlighting the potential problems associated with the use of epitope tags for ion channel studies. Described here are some of the epitope tags that have been used to study ion channel subunits, including the HA, FLAG, myc, His6, and green fluorescent protein (GFP) epitopes, as well as some of the applications and avenues of research in which they have proven advantageous. Potential pitfalls and caveats associated with the use of these epitope tags are also discussed, with an emphasis on the need to include careful characterization of epitope-tagged channel subunits as part of their construction. Finally, potential avenues for future investigation and the development of this approach are considered.
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Affiliation(s)
- Robert A Maue
- Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
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80
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Barrera NP, Betts J, You H, Henderson RM, Martin IL, Dunn SMJ, Edwardson JM. Atomic force microscopy reveals the stoichiometry and subunit arrangement of the alpha4beta3delta GABA(A) receptor. Mol Pharmacol 2007; 73:960-7. [PMID: 18079275 DOI: 10.1124/mol.107.042481] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The GABA(A) receptor is a chloride-selective ligand-gated ion channel of the Cys-loop superfamily. The receptor consists of five subunits arranged pseudosymmetrically around a central pore. The predominant form of the receptor in the brain contains alpha(1)-, beta(2)-, and gamma(2)-subunits in the arrangement alphabetaalphagammabeta, counter-clockwise around the pore. GABA(A) receptors containing delta-instead of gamma-subunits, although a minor component of the total receptor population, have interesting properties, such as an extrasynaptic location, high sensitivity to GABA, and potential association with conditions such as epilepsy. They are therefore attractive targets for drug development. Here we addressed the subunit arrangement within the alpha(4)beta(3)delta form of the receptor. Different epitope tags were engineered onto the three subunits, and complexes between receptors and anti-epitope antibodies were imaged by atomic force microscopy. Determination of the numbers of receptors doubly decorated by each of the three antibodies revealed a subunit stoichiometry of 2alpha:2beta:1delta. The distributions of angles between pairs of antibodies against the alpha- and beta-subunits both had peaks at around 144 degrees , indicating that these pairs of subunits were nonadjacent. Decoration of the receptor with ligands that bind to the extracellular domain (i.e., the lectin concanavalin A and an antibody that recognizes the beta-subunit N-terminal sequence) showed that the receptor preferentially binds to the mica extracellular face down. Given this orientation, the geometry of complexes of receptors with both an antibody against the delta-subunit and Fab fragments against the alpha-subunits indicates a predominant subunit arrangement of alphabetaalphadeltabeta, counter-clockwise around the pore when viewed from the extracellular space.
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Affiliation(s)
- Nelson P Barrera
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
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81
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Determination of the architecture of ionotropic receptors using AFM imaging. Pflugers Arch 2007; 456:199-209. [PMID: 18026748 DOI: 10.1007/s00424-007-0381-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Accepted: 10/26/2007] [Indexed: 10/22/2022]
Abstract
Fast neurotransmission in the nervous system is mediated by ionotropic receptors, all of which contain several subunits surrounding an integral ion channel. There are three major families of ionotropic receptors: the 'Cys-loop' receptors (including the nicotinic receptor for acetylcholine, the 5-HT(3) receptor, the GABA(A) receptor and the glycine receptor), the glutamate receptors (including the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, kainate and N-methyl-D: -aspartic acid receptors) and the P2X receptors for adenosine triphosphate. These receptors are often built from multiple types of subunit, raising the question of the stoichiometry and subunit arrangement within the receptors. This question is of therapeutic significance because in some cases drug-binding sites are located at subunit-subunit interfaces. In this paper, we describe a general method, based on atomic force microscopy imaging, to solve the architecture of multi-subunit proteins, such as the ionotropic receptors. Specific epitope tags are engineered onto each receptor subunit. The subunits are then expressed exogenously in cultured cells, and the receptors are isolated from detergent extracts of membrane fractions by affinity chromatography. The receptors are imaged both alone and in complex with anti-epitope antibodies. The size of the imaged particles provides an estimate of the subunit stoichiometry, whereas the geometry of the receptor-antibody complexes produces more detailed information about the receptor architecture. We use an automated, unbiased system to identify receptors and receptor-antibody complexes and to determine the geometry of the complexes. We are also able to determine the orientation of the receptors on the mica substrate, which will allow us to solve the subunit arrangement within receptors, such as the GABA(A) receptor, which contain three types of subunits.
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82
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You H, Dunn SMJ. Identification of a domain in the delta subunit (S238-V264) of the alpha4beta3delta GABAA receptor that confers high agonist sensitivity. J Neurochem 2007; 103:1092-101. [PMID: 17711419 DOI: 10.1111/j.1471-4159.2007.04817.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have expressed the alpha4beta3delta and alpha4beta3gamma2L subtypes of the rat GABAA receptor in Xenopus oocytes and have investigated their agonist activation properties. GABA was a more potent agonist of the alpha4beta3delta receptor (EC50 approximately 1.4 micromol/L) than of the alpha4beta3gamma2L subtype (EC50 approximately 27.6 micromol/L). Other GABAA receptor agonists (muscimol, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol, imidazole-4-amino acid) displayed similar subtype selectivity. The structural determinants underlying these differences have been investigated by co-expressing chimeric delta/gamma2L subunits with alpha4 and beta3 subunits. A stretch of amino acids in the delta subunit, S238-V264, is shown to play an important role in determining both agonist potency and the efficacies of full or partial agonists. This segment includes transmembrane domain 1 and the short intracellular loop that leads to the second transmembrane domain. The effects of the competitive antagonists, bicuculline and SR95531, and the channel blocker, picrotoxin, were not significantly affected by the incorporation of chimeric subunits. As the delta and gamma2L subunits have not been previously implicated directly in agonist binding, we suggest that the effects are likely to arise from changes in the transduction mechanisms that link agonist binding to channel activation.
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Affiliation(s)
- Haitao You
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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83
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Niesler B, Walstab J, Combrink S, Möller D, Kapeller J, Rietdorf J, Bönisch H, Göthert M, Rappold G, Brüss M. Characterization of the novel human serotonin receptor subunits 5-HT3C,5-HT3D, and 5-HT3E. Mol Pharmacol 2007; 72:8-17. [PMID: 17392525 DOI: 10.1124/mol.106.032144] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Within the family of serotonin receptors, the 5-hydroxytryptamine-3 (5-HT(3)) receptor is the only ligand-gated ion channel. It is composed of five subunits, of which the 5-HT(3A) and 5-HT(3B) subunits are best characterized. Several studies, however, have reported on the functional diversity of native 5-HT(3) receptors, which cannot solely be explained on the basis of the 5-HT(3A) and 5-HT(3B) subunits. After our discovery of further putative 5-HT(3) serotonin receptor-encoding genes, HTR3C, HTR3D, and HTR3E, we investigated whether these novel candidates and the isoform 5-HT(3Ea) are able to form functional 5-HT(3) receptor complexes. Using immunofluorescence and immunoprecipitation studies of heterologously expressed proteins, we found that each of the respective candidates coassembles with 5-HT(3A). To investigate whether the novel subunits modulate 5-HT(3) receptor function, we performed radioligand-binding assays and calcium-influx studies in human embryonic kidney 293 cells. Our experiments revealed that the 5-HT(3C),5-HT(3D), 5-HT(3E), and 5-HT(3Ea) subunits alone cannot form functional receptors. Coexpression with 5-HT(3A), however, results in the formation of functional heteromeric complexes with different serotonin efficacies. Potencies of two agonists and antagonists were nearly identical with respect to homomeric 5-HT(3A) and heteromeric complexes. However, 5-HT showed increased efficacy with respect to 5-HT(3A/D) and 5-HT(3A/E) receptors, which is consistent with the increased surface expression compared with 5-HT(3A) receptors. In contrast, 5-HT(3A/C) and 5-HT(3A/Ea) receptors exhibited decreased 5-HT efficacy. These data show for the first time that the novel 5-HT(3) subunits are able to form heteromeric 5-HT(3) receptors, which exhibit quantitatively different functional properties compared with homomeric 5-HT(3A) receptors.
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Affiliation(s)
- Beate Niesler
- Department of Human Molecular Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany.
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84
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Barrera NP, Shaifta Y, McFadzean I, Ward JPT, Henderson RM, Edwardson JM. AFM imaging reveals the tetrameric structure of the TRPC1 channel. Biochem Biophys Res Commun 2007; 358:1086-90. [PMID: 17517368 DOI: 10.1016/j.bbrc.2007.05.039] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Accepted: 05/08/2007] [Indexed: 11/16/2022]
Abstract
We have determined the subunit stoichiometry of the transient receptor potential C1 (TRPC1) channel by imaging isolated channels using atomic force microscopy (AFM). A frequency distribution of the molecular volumes of individual channel particles had two peaks, at 170 and 720 nm(3), corresponding with the expected sizes of TRPC1 monomers and tetramers, respectively. Complexes were formed between TRPC1 channels and antibodies against a V5 epitope tag present on each subunit. The frequency distribution of angles between pairs of bound antibodies had two peaks, at 88 degrees and 178 degrees. This result again indicates that the channel assembles as a tetramer.
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Affiliation(s)
- Nelson P Barrera
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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85
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Barrera NP, Henderson RM, Murrell-Lagnado RD, Edwardson JM. The stoichiometry of P2X2/6 receptor heteromers depends on relative subunit expression levels. Biophys J 2007; 93:505-12. [PMID: 17449665 PMCID: PMC1896263 DOI: 10.1529/biophysj.106.101048] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Fast synaptic transmission involves the operation of ionotropic receptors, which are often composed of at least two types of subunit. We have developed a method, based on atomic force microscopy imaging to determine the stoichiometry and subunit arrangement within ionotropic receptors. We showed recently that the P2X(2) receptor for ATP is expressed as a trimer but that the P2X(6) subunit is unable to oligomerize. In this study we addressed the subunit stoichiometry of heteromers containing both P2X(2) and P2X(6) subunits. We transfected tsA 201 cells with both P2X(2) and P2X(6) subunits, bearing different epitope tags. We manipulated the transfection conditions so that either P2X(2) or P2X(6) was the predominant subunit expressed. By atomic force microscopy imaging of isolated receptors decorated with antiepitope antibodies, we demonstrate that when expression of the P2X(2) subunit predominates, the receptors contain primarily 2 x P2X(2) subunits and 1 x P2X(6) subunit. In contrast, when the P2X(6) subunit predominates, the subunit stoichiometry of the receptors is reversed. Our results show that the composition of P2X receptor heteromers is plastic and dependent on the relative subunit expression levels. We suggest that this property of receptor assembly might introduce an additional layer of subtlety into P2X receptor signaling.
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Affiliation(s)
- Nelson P Barrera
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
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86
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Faerber L, Drechsler S, Ladenburger S, Gschaidmeier H, Fischer W. The neuronal 5-HT3 receptor network after 20 years of research — Evolving concepts in management of pain and inflammation. Eur J Pharmacol 2007; 560:1-8. [PMID: 17316606 DOI: 10.1016/j.ejphar.2007.01.028] [Citation(s) in RCA: 164] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2006] [Accepted: 01/09/2007] [Indexed: 11/19/2022]
Abstract
The 5-HT3 receptor is a pentameric ligand-gated cation channel which is found in the central and peripheral nervous system and on extraneuronal locations like lymphocytes, monocytes and fetal tissue. Five monomer subtypes, the 5-HT(3A-E) subunits, have been identified which show differences in the amino-terminal and the transmembrane region. The functional relevance of different receptor compositions is not yet clarified. 5-HT3 receptors are located predominantly in CNS regions that are involved in the integration of the vomiting reflex, pain processing, the reward system and anxiety control. The preferential localization on nerve endings is consistent with a physiological role of 5-HT3 receptors in the control of neurotransmitter release such as dopamine, cholecystokinin, glutamate, acetylcholine, GABA, substance P, or serotonin itself. 5-HT3-receptor agonists cause unpleasant effects like nausea and anxiety, and no clinical use has been considered. In contrast, the introduction of 5-HT3-receptor antagonists for chemotherapy-induced vomiting was extremely successful. After development of other gastrointestinal indications like postoperative vomiting and diarrhea-predominant irritable bowel syndrome recent research focuses on rheumatological indications such as fibromyalgia, rheumatoid arthritis and tendinopathies. Positive effects have also been observed for pain syndromes such as chronic neuropathic pain and migraine. These effects seem to be related to substance P-mediated inflammation and hyperalgesia. Furthermore, antiinflammatory and immunomodulatory properties have been observed for 5-HT3-receptor antagonists which might explain promising findings in systemic sclerosis and other immunological conditions. For all of these innovative indications the optimal dosing schedule is a crucial issue, since a bell-shaped dose-response curve has been observed repeatedly for 5-HT3-receptor antagonists, particularly in CNS effects.
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Affiliation(s)
- Lothar Faerber
- Department of Pharmacology, Regensburg Medical School, Universitaetsstr. 31, 93053 Regensburg, Germany.
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87
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Ericksen SS, Boileau AJ. Tandem couture: Cys-loop receptor concatamer insights and caveats. Mol Neurobiol 2007; 35:113-28. [PMID: 17519509 PMCID: PMC2597025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2006] [Revised: 11/30/1999] [Accepted: 09/12/2006] [Indexed: 05/15/2023]
Abstract
Receptor subunits in the Cys-loop superfamily assemble to form channels as homopentamers or heteropentamers, expanding functional diversity through modularity. Expression of two or more compatible subunit types can lead to various receptor assemblies or subtypes. However, what may be good for diversity in vivo may be undesirable for the bench scientist, because we often wish to reduce our analyses to a single receptor subtype. By linking two or more subunits, creating tandems or concatamers, we can control stoichiometry and limit expression to exactly one receptor subtype. In this fashion, receptors with mixed subunit subtypes and heterozygous mutations can be separated from a mixture and can be described in detail. However, several recent studies have shown that this may be more easily conceived than accomplished, because several unforeseen problems have arisen. Concatamers can degrade, linkers can sometimes be clipped after or during translation, and one subunit may "loop out" or even become part of a second (now linked) pentamer with different characteristics. Some strategies have been developed to overcome these drawbacks, and the resultant new information that has begun to emerge has revitalized the study of these receptors in heterologous expression systems.
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Affiliation(s)
| | - Andrew J. Boileau
- Author to whom correspondence and reprint requests should be addressed. E-mail:
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88
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89
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Tzvetkov MV, Meineke C, Oetjen E, Hirsch-Ernst K, Brockmöller J. Tissue-specific alternative promoters of the serotonin receptor gene HTR3B in human brain and intestine. Gene 2006; 386:52-62. [PMID: 17010535 DOI: 10.1016/j.gene.2006.08.002] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Revised: 08/02/2006] [Accepted: 08/05/2006] [Indexed: 11/28/2022]
Abstract
The serotonin receptor type 3 is a pentameric ligand-gated ion channel regulating intestinal motility, nausea, and vomiting in humans. The HTR3B gene codes for the subunit B of this receptor. The HTR3B transcription start site is not unequivocally identified. In the present study we used transcription start site analyses, transcript-specific RT-PCR, and functional promoter analyses to identify the 5' structure of the HTR3B gene. According to these experiments, two alternative promoters control the expression of different HTR3B transcripts in the peripheral and central nervous system. The transcription start sites observed in the intestine corresponded to the current human genome annotation (NCBI Build 36.1, March 2006). The transcription start sites in the brain, however, were localized in a region about 4000 bp downstream. The brain transcripts lacked the coding first exon of the HTR3B structure published earlier but had an upstream-extended exon 2 containing a new potential translational start site. Reporter gene analyses showed significant promoter activity of the genomic region located 1560 bp upstream to 93 bp downstream of the brain-specific transcription start sites. This data suggests a different transcriptional regulation of the HTR3B gene in the peripheral and the central nervous system that leads to the expression of transcripts with variations in the 5' coding sequence. Further studies on the expression, structure and function of therefore expected tissue-specific 5-HT(3B) isoforms are required.
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Affiliation(s)
- Mladen Vassilev Tzvetkov
- Department of Clinical Pharmacology University Hospital Göttingen 4E1-323 Robert-Koch-Str. 40 37075 Göttingen Germany.
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90
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Egan TM, Samways DSK, Li Z. Biophysics of P2X receptors. Pflugers Arch 2006; 452:501-12. [PMID: 16708237 DOI: 10.1007/s00424-006-0078-1] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2006] [Accepted: 03/16/2006] [Indexed: 10/24/2022]
Abstract
The P2X receptor is the baby brother of the ligand-gated ion channel super-family. An understanding of its role in human physiology is still developing, and no one truly knows how it works to transport ions across the membrane. In this study, we review some aspects of P2X channel biophysics, concentrating on ion permeation and gating. P2X channels transport both small and large cations and anions across cell membranes in a manner that depends on both the subunit composition of the receptor and the experimental conditions. We describe the pore properties of wild-type receptors and use the altered phenotypes of mutant receptors to point the way towards a structural model of the pore.
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Affiliation(s)
- Terrance M Egan
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 S. Grand Boulevard, St. Louis, MO 63104, USA.
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91
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Metz AV, Chynoweth J, Allan AM. Influence of genetic background on alcohol drinking and behavioral phenotypes of 5-HT3 receptor over-expressing mice. Pharmacol Biochem Behav 2006; 84:120-7. [PMID: 16765427 DOI: 10.1016/j.pbb.2006.04.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Revised: 04/13/2006] [Accepted: 04/25/2006] [Indexed: 10/24/2022]
Abstract
Behavioral effects of genetic manipulations are influenced by the background genetics of mouse strains used for the creation of transgenic mice. One strategy to address whether background genes may compromise interpretation of phenotype is the production of congenics. 5-HT3 receptor over-expressing mice have been behaviorally characterized on a B6SJL/F2 background (B6SJL/F2-OE mice), and were found to consume less ethanol failed to develop conditioned place preference to moderate doses of cocaine and demonstrate improved hippocampal-dependent learning. To assess the contribution of parental strain genetics to these behaviors, we bred the transgene onto two well-defined backgrounds that differ in ethanol consumption and contextual fear conditioning, C57Bl/6J (B6) and DBA/2J (D2) strains. The behavioral phenotype of B6SJL/F2-OE was recapitulated in C57Bl/6J-OE mice. However, the effect of transgene over-expression on behavior was only apparent for one aspect of the novelty test using DBA/2J-OE mice. Results underscore the need to consider the genetic environment conferred by strain selection on the effects of genetic manipulation in mice.
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Affiliation(s)
- Amber V Metz
- University of New Mexico, School of Medicine, Department of Neurosciences, Albuquerque NM 87131, USA
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92
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Reeves DC, Lummis SCR. Detection of human and rodent 5-HT3B receptor subunits by anti-peptide polyclonal antibodies. BMC Neurosci 2006; 7:27. [PMID: 16571125 PMCID: PMC1481617 DOI: 10.1186/1471-2202-7-27] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2005] [Accepted: 03/29/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The 5-HT3 receptor is a member of a neurotransmitter-gated ion channel family which includes nicotinic acetylcholine, GABAA, and glycine receptors. While antibodies specific for the 5-HT3A receptor subunit are plentiful, and have revealed a wealth of structural and functional information, few antisera exist for the detection of 5-HT3B receptor subunits. Here we describe the generation and characterisation of a rabbit polyclonal antiserum that specifically recognises 5-HT3B receptor subunits RESULTS Immunization of a rabbit with a 20-mer peptide, corresponding to the N-terminus of the human 5-HT3B receptor subunit, generated serum with polyclonal antibodies from which an IgG fraction was purified, yielding pAb77. The antibodies were shown to label 5-HT3B receptor subunits in transfected human embryonic kidney cells and rodent tissues using Western blots. Immunocytochemistry using pAb77 on these cells showed that 5-HT3B receptor subunits do not reach the plasma membrane in the absence of 5-HT3A receptor subunits. Immunohistochemical analysis of rat brain sections showed pAb77 immunoreactivity in distinct populations of cells in the hippocampus. CONCLUSION We have demonstrated that pAb77 antibodies specifically label native and recombinant 5-HT3B receptor subunits with high affinity and specificity. The antibody was shown to be useful for the determination of both receptor trafficking and also mapping 5-HT3B receptor subunit expression in the CNS.
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Affiliation(s)
- David C Reeves
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY, 10461, USA
| | - Sarah CR Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
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93
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Alexander SPH, Mathie A, Peters JA. 5-Hydroxytryptamine3. Br J Pharmacol 2006. [DOI: 10.1038/sj.bjp.0706576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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94
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Ludwig Y, Schafer C, Kramer A, Albermann L, Oberleithner H, Shahin V. Hot Spot Formation in the Nuclear Envelope of Oocytes in Response to Steroids. Cell Physiol Biochem 2006; 17:181-92. [PMID: 16790994 DOI: 10.1159/000094123] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
A Glucocorticoid-sensitive cell rapidly responds to hormone stimulation with bidirectional exchange of specific macromolecules between cytosol and nucleus. Glucocorticoid-initiated macromolecules (GIMs) must overcome the nuclear envelope (NE) to enter or leave the nucleus. GIM translocation occurs through nuclear pore complexes (NPCs) that span the NE. We investigated the question whether transport of GIMs through NPCs occurs random or involves selected groups of NPCs (hot spots). Glucocorticoid receptors were expressed in Xenopus laevis oocytes and GIM transport was activated by triamcinolone acetonide, a potent synthetic glucocorticoid analogon. Glucocorticoid receptors associated with the NE and the chromatin were identified using western blot analysis and, at single molecule level, atomic force microscopy. Fluorescence-labeled dextran was used to describe passive NE permeability. We observed that after hormone injection (i) small GIMs, most likely GRs, localize within seconds on both sides of the NE. (ii) large GIMs, most likely ribonucleoproteins, localize within minutes on NPCs at the nucleoplasmic side (iii) both small and large GIMs accumulate on selected NPC clusters (iv) NE permeability transiently decreases when GIMs attach to NPCs. We conclude that GIM transport across the nuclear barrier does not randomly take place but is carried out by a selected population of NPCs.
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Affiliation(s)
- Yvonne Ludwig
- Institute of Physiology II, University of Muenster, Germany.
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95
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White MM. Pretty subunits all in a row: using concatenated subunit constructs to force the expression of receptors with defined subunit stoichiometry and spatial arrangement. Mol Pharmacol 2005; 69:407-10. [PMID: 16293710 DOI: 10.1124/mol.105.020727] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The members of the Cys-loop ligand-gated ion channel (LGIC) gene family play a major role in fast synaptic transmission, and these receptors represent an important class of targets for therapeutic agents. Each member of this gene family is a pentameric complex containing one or more different subunits, and a large number of subunits for each member have been identified. This large number of subunits could give rise to a bewildering array of possible subunit compositions and spatial arrangements within a single complex, not all of which may occur in vivo. Heterologous expression systems have been used to create specific combinations of individual subunits to mimic naturally occurring receptors. However, this approach is not without its problems. In this issue of Molecular Pharmacology, Groot-Kormelink et al. (page 559) describe a method for constructing "concatameric" receptors, in which five individual subunits are arranged in a predetermined order connected by a flexible linker. Expression of this construct results in the formation of receptors with a unique, predefined subunit stoichiometry and subunit arrangement within the receptor complex. Receptors formed from this construct are fully functional and have properties essentially identical to those formed from individual subunits. The application of this very general approach to other members of the LGIC family should markedly enhance our ability to understand how subunit composition influences receptor function, as well as provide a means for the expression of receptors of predefined subunit composition and arrangement as tools for the development of novel selective pharmacological and therapeutic agents.
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Affiliation(s)
- Michael M White
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
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96
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Peters JA, Hales TG, Lambert JJ. Molecular determinants of single-channel conductance and ion selectivity in the Cys-loop family: insights from the 5-HT3 receptor. Trends Pharmacol Sci 2005; 26:587-94. [PMID: 16194573 DOI: 10.1016/j.tips.2005.09.011] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 08/19/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
The molecular determinants of the ionic selectivity and single-channel conductance of the Cys-loop family of transmitter-gated ion channels are beginning to be understood with increasing precision, in part, as a result of the recent availability of refined ultrastructural information for the archetype of the family, the nicotinic acetylcholine receptor (nAChR). Studies of another member of this family, the 5-HT(3) receptor, have now provided insight into the structure of its channel pore, the location of its gate and mechanisms of ion selectivity and translocation. The anomaly of the extremely low single-channel conductance of the homo-oligomeric 5-HT(3A) receptor has recently been solved, revealing that an intracellular domain of the protein is an important determinant of single-channel conductance. Such data are interpreted, in this article, in light of the most recent developments in structural characterization of the nAChR.
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MESH Headings
- Amino Acid Sequence
- Animals
- Cysteine/chemistry
- Humans
- Ion Channel Gating
- Ion Channels/chemistry
- Ion Channels/genetics
- Ion Channels/metabolism
- Ions
- Models, Molecular
- Molecular Sequence Data
- Mutation
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Receptors, Nicotinic/chemistry
- Receptors, Nicotinic/genetics
- Receptors, Nicotinic/metabolism
- Receptors, Serotonin, 5-HT3/chemistry
- Receptors, Serotonin, 5-HT3/genetics
- Receptors, Serotonin, 5-HT3/metabolism
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Affiliation(s)
- John A Peters
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, The University of Dundee, Dundee DD1 9SY, UK.
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