1
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Trpevski D, Khodadadi Z, Carannante I, Hellgren Kotaleski J. Glutamate spillover drives robust all-or-none dendritic plateau potentials-an in silico investigation using models of striatal projection neurons. Front Cell Neurosci 2023; 17:1196182. [PMID: 37469606 PMCID: PMC10352111 DOI: 10.3389/fncel.2023.1196182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 05/31/2023] [Indexed: 07/21/2023] Open
Abstract
Plateau potentials are a critical feature of neuronal excitability, but their all-or-none behavior is not easily captured in modeling. In this study, we investigated models of plateau potentials in multi-compartment neuron models and found that including glutamate spillover provides robust all-or-none behavior. This result arises due to the prolonged duration of extrasynaptic glutamate. When glutamate spillover is not included, the all-or-none behavior is very sensitive to the steepness of the Mg2+ block. These results suggest a potentially significant role of glutamate spillover in plateau potential generation, providing a mechanism for robust all-or-none behavior across a wide range of slopes of the Mg2+ block curve. We also illustrate the importance of the all-or-none plateau potential behavior for nonlinear computation with regard to the nonlinear feature binding problem.
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Affiliation(s)
- Daniel Trpevski
- Science for Life Laboratory, Department of Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Zahra Khodadadi
- Science for Life Laboratory, Department of Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Ilaria Carannante
- Science for Life Laboratory, Department of Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Jeanette Hellgren Kotaleski
- Science for Life Laboratory, Department of Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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2
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Li XJ, Xie L, Pan FS, Wang Y, Liu H, Tang YR, Hutnik CM. A feasibility study of using biodegradable magnesium alloy in glaucoma drainage device. Int J Ophthalmol 2018; 11:135-142. [PMID: 29376002 DOI: 10.18240/ijo.2018.01.21] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2017] [Accepted: 08/31/2017] [Indexed: 12/13/2022] Open
Abstract
Technological advances in glaucoma have challenged the traditional treatment paradigm. Historically incisional surgery has been used in cases of advanced disease and/or uncontrolled intraocular pressures resistant to medical or laser interventions. More recently, perhaps due to advancements in imaging, surgery has been suggested to be beneficial earlier in the treatment paradigm. Despite these trends, surgical manipulation of the tissues and unpredictability of wound healing continue to result in surgical failure. Magnesium is an essential element for human body and plays a critically important role in maintaining the functional and structural integrity of several tissues, including the eye. Due to several of its advantageous properties such as non-toxicity, biodegradability, and high biological compatibility, magnesium alloy has attracted great attention as a novel biomaterial. Biodegradable cardiovascular stents made of magnesium alloy have already been introduced into clinical practice. The purpose of this review is to determine if bioabsorbable magnesium alloys can be utilized as a promising candidate for the development of a new generation of glaucoma surgical assistive devices.
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Affiliation(s)
- Xiang-Ji Li
- Department of Ophthalmology, University of Western Ontario, Ivey Eye Institute, St. Joseph's Hospital, 268 Grosvenor Street, London, ON N6A 4V2, Canada.,Department of Ophthalmology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing 400042, China
| | - Lin Xie
- Department of Ophthalmology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing 400042, China
| | - Fu-Sheng Pan
- Collage of Material Science & Engineering, Chongqing University, Chongqing 400045, China.,National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400045, China
| | - Yong Wang
- Collage of Material Science & Engineering, Chongqing University, Chongqing 400045, China.,National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400045, China
| | - Hong Liu
- Department of Ophthalmology, University of Western Ontario, Ivey Eye Institute, St. Joseph's Hospital, 268 Grosvenor Street, London, ON N6A 4V2, Canada
| | - Yu-Rong Tang
- Department of Ophthalmology, People's Hospital Zhongshan Branch, Chongqing 400013, China
| | - Cindy Ml Hutnik
- Department of Ophthalmology, University of Western Ontario, Ivey Eye Institute, St. Joseph's Hospital, 268 Grosvenor Street, London, ON N6A 4V2, Canada
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3
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Tian M, Ye S. Allosteric regulation in NMDA receptors revealed by the genetically encoded photo-cross-linkers. Sci Rep 2016; 6:34751. [PMID: 27713495 PMCID: PMC5054432 DOI: 10.1038/srep34751] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 09/16/2016] [Indexed: 11/09/2022] Open
Abstract
Allostery is essential to neuronal receptor function, but its transient nature poses a challenge for characterization. The N-terminal domains (NTDs) distinct from ligand binding domains are a major locus for allosteric regulation of NMDA receptors (NMDARs), where different modulatory binding sites have been observed. The inhibitor ifenprodil, and related phenylethanoamine compounds specifically targeting GluN1/GluN2B NMDARs have neuroprotective activity. However, whether they use differential structural pathways than the endogenous inhibitor Zn2+ for regulation is unknown. We applied genetically encoded unnatural amino acids (Uaas) and monitored the functional changes in living cells with photo-cross-linkers specifically incorporated at the ifenprodil binding interface between GluN1 and GluN2B subunits. We report constraining the NTD domain movement, by a light induced crosslinking bond that introduces minimal perturbation to the ligand binding, specifically impedes the transduction of ifenprodil but not Zn2+ inhibition. Subtle distance changes reveal interfacial flexibility and NTD rearrangements in the presence of modulators. Our results present a much richer dynamic picture of allostery than conventional approaches targeting the same interface, and highlight key residues that determine functional and subtype specificity of NMDARs. The light-sensitive mutant neuronal receptors provide complementary tools to the photo-switchable ligands for opto-neuropharmacology.
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Affiliation(s)
- Meilin Tian
- Shanghai Key Laboratory of Brain Functional Genomics, East China Normal University, Shanghai, China.,Ecole Normale Supérieure, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Paris, France.,Institut National de la Santé et de la Recherche Médicale, U1024, Paris, France.,Centre National de la Recherche Scientifique, UMR 8197, Paris, France
| | - Shixin Ye
- Ecole Normale Supérieure, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Paris, France.,Institut National de la Santé et de la Recherche Médicale, U1024, Paris, France.,Centre National de la Recherche Scientifique, UMR 8197, Paris, France
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4
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Dougherty DA, Van Arnam EB. In vivo incorporation of non-canonical amino acids by using the chemical aminoacylation strategy: a broadly applicable mechanistic tool. Chembiochem 2014; 15:1710-20. [PMID: 24990307 DOI: 10.1002/cbic.201402080] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Indexed: 01/05/2023]
Abstract
We describe a strategy for incorporating non-canonical amino acids site-specifically into proteins expressed in living cells, involving organic synthesis to chemically aminoacylate a suppressor tRNA, protein expression in Xenopus oocytes, and monitoring protein function, primarily by electrophysiology. With this protocol, a very wide range of non-canonical amino acids can be employed, allowing both systematic structure-function studies and the incorporation of reactive functionalities. Here, we present an overview of the methodology and examples meant to illustrate the versatility and power of the method as a tool for investigating protein structure and function.
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Affiliation(s)
- Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (USA).
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5
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Abstract
Glutamate receptors are ligand-gated ion channels that mediate fast excitatory synaptic transmission throughout the central nervous system. Functional receptors are homo- or heteromeric tetramers with each subunit contributing a re-entrant pore loop that dips into the membrane from the cytoplasmic side. The pore loops form a narrow constriction near their apex with a wide vestibule toward the cytoplasm and an aqueous central cavity facing the extracellular solution. This article focuses on the pore region, reviewing how structural differences among glutamate receptor subtypes determine their distinct functional properties.
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Affiliation(s)
- James E Huettner
- Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO, 63110, USA
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6
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Serefko A, Szopa A, Wlaź P, Nowak G, Radziwoń-Zaleska M, Skalski M, Poleszak E. Magnesium in depression. Pharmacol Rep 2014; 65:547-54. [PMID: 23950577 DOI: 10.1016/s1734-1140(13)71032-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2012] [Revised: 01/08/2013] [Indexed: 12/15/2022]
Abstract
Magnesium is one of the most essential mineral in the human body, connected with brain biochemistry and the fluidity of neuronal membrane. A variety of neuromuscular and psychiatric symptoms, including different types of depression, was observed in magnesium deficiency. Plasma/serum magnesium levels do not seem to be the appropriate indicators of depressive disorders, since ambiguous outcomes, depending on the study, were obtained. The emergence of a new approach to magnesium compounds in medical practice has been seen. Apart from being administered as components of dietary supplements, they are also perceived as the effective agents in treatment of migraine, alcoholism, asthma, heart diseases, arrhythmias, renal calcium stones, premenstrual tension syndrome etc. Magnesium preparations have an essential place in homeopathy as a remedy for a range of mental health problems. Mechanisms of antidepressant action of magnesium are not fully understood yet. Most probably, magnesium influences several systems associated with development of depression. The first information on the beneficial effect of magnesium sulfate given hypodermically to patients with agitated depression was published almost 100 years ago. Numerous pre-clinical and clinical studies confirmed the initial observations as well as demonstrated the beneficial safety profile of magnesium supplementation. Thus, magnesium preparations seem to be a valuable addition to the pharmacological armamentarium for management of depression.
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Affiliation(s)
- Anna Serefko
- Chair and Department of Applied Pharmacy, Medical University of Lublin, Lublin, Poland
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7
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Agarwal R, Iezhitsa L, Agarwal P. Pathogenetic role of magnesium deficiency in ophthalmic diseases. Biometals 2013; 27:5-18. [PMID: 24233809 DOI: 10.1007/s10534-013-9684-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Accepted: 11/01/2013] [Indexed: 12/25/2022]
Abstract
Magnesium is one of the most important regulatory cation involved in several biological processes. It is important for maintaining the structural and functional integrity of several vital ocular tissues such as cornea, lens and retina. The magnesium content of lens, especially in its peripheral part, is higher than that in aqueous and vitreous humor. Magnesium has also been shown to play critically important role in retinal functions. Magnesium plays significant role as a cofactor for more than 350 enzymes in the body and regulates neuroexcitability and several ion channels. Membrane associated ATPase functions that are crucial in regulating the intracellular ionic environment, are magnesium-dependent. Moreover, the enzymes involved in ATP production and hydrolysis are also magnesium-dependent. Magnesium deficiency by interfering with ATPase functions causes increased intracellular calcium and sodium and decreases intracellular potassium concentration. Such ionic imbalances in turn alter the other cellular enzymatic reactions and form the basis of the association of magnesium deficiency with ophthalmic diseases such as cataract. In presence of magnesium deficiency, an imbalance between mediators of vasoconstriction and vasorelaxation may underlie the vasospasm, which is one of the pathogenic factors in primary open angle glaucoma. Furthermore, magnesium deficiency is also a contributing factor in increased oxidative stress and inducible NOS stimulation that can further contribute in the initiation and progression of ocular pathologies such as cataract, glaucoma and diabetic retinopathy. In this paper we review the association of disturbances of magnesium homeostasis with several ophthalmic diseases.
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Affiliation(s)
- Renu Agarwal
- Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh Campus, Jalan Hospital, 47000, Sungai Buloh, Selangor Darul Ehsan, Malaysia
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8
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Ye S, Riou M, Carvalho S, Paoletti P. Expanding the genetic code in Xenopus laevis oocytes. Chembiochem 2013; 14:230-5. [PMID: 23292655 DOI: 10.1002/cbic.201200515] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Indexed: 01/12/2023]
Abstract
Heterologous expression of ligand-gated ion channels (LGICs) in Xenopus laevis oocytes combined with site-directed mutagenesis has been demonstrated to be a powerful approach to study structure-function relationships. In particular, introducing unnatural amino acids (UAAs) has enabled modifications that are not found in natural proteins. However, the current strategy relies on the technically demanding in vitro synthesis of aminoacylated suppressor tRNA. We report here a general method that circumvents this limitation by utilizing orthogonal aminoacyl-tRNA synthetase (aaRS)/suppressor tRNA(CUA) pairs to genetically encode UAAs in Xenopus oocytes. We show that UAAs inserted in the N-terminal domain of N-methyl-D-aspartate receptors (NMDARs) serve as photo-crosslinkers that lock the receptor in a discrete conformational state in response to UV photo treatment. Our method should be generally applicable to studies of other LGICs in Xenopus oocytes.
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Affiliation(s)
- Shixin Ye
- Ecole Normale Supérieure, Institut de Biologie de l'ENS, IBENS, 46 rue d'Ulm, Paris 75005, France.
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9
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Mahadevi AS, Sastry GN. Cation-π interaction: its role and relevance in chemistry, biology, and material science. Chem Rev 2012; 113:2100-38. [PMID: 23145968 DOI: 10.1021/cr300222d] [Citation(s) in RCA: 728] [Impact Index Per Article: 60.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- A Subha Mahadevi
- Molecular Modeling Group, CSIR-Indian Institute of Chemical Technology Tarnaka, Hyderabad 500 607, Andhra Pradesh, India
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10
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Eby GA, Eby KL. Magnesium for treatment-resistant depression: A review and hypothesis. Med Hypotheses 2010; 74:649-60. [DOI: 10.1016/j.mehy.2009.10.051] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Accepted: 10/31/2009] [Indexed: 12/15/2022]
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11
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Limapichat W, Lester HA, Dougherty DA. Chemical scale studies of the Phe-Pro conserved motif in the cys loop of Cys loop receptors. J Biol Chem 2010; 285:8976-84. [PMID: 20068044 DOI: 10.1074/jbc.m109.060939] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The functions of two conserved residues, Phe(135) and Pro(136), located at the apex of the Cys loop of the nicotinic acetylcholine receptor are investigated. Both residues were substituted with natural and unnatural amino acids, focusing on the role of aromaticity at Phe(135), backbone conformation at Pro(136), side chain polarity and volume, and the specific interaction between the aromatic side chain and the proline. NMR spectroscopy studies of model peptides containing proline and unnatural proline analogues following a Phe show a consistent increase in the population of the cis conformer relative to peptides lacking the Phe. In the receptor, a strong interaction between the Phe and Pro residues is evident, as is a strong preference for aromaticity and hydrophobicity at the Phe site. A similar influence of hydrophobicity is observed at the proline site. In addition, across a simple homologous series of proline analogues, the results reveal a correlation between receptor function and cis bias at the proline backbone. This could suggest a significant role for the cis proline conformer at this site in receptor function.
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Affiliation(s)
- Walrati Limapichat
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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12
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Abstract
K(+) channels are revered for their universal action of suppressing electrical activity in nerve and muscle, as well as regulating salt and water transport in epithelial tissues involved in metabolism and digestion. These multisubunit membrane-embedded proteins carry out their physiological chore, selectively allowing the passage of potassium across the membrane, in response to changes in membrane voltage and ligand concentration. Elucidating the diverse gating properties of K(+) channels is of great biological interest since their molecular motions provide insight into how these structurally similar proteins function in a wide variety of tissues. Armed with patch clamps, chart recorders, and now high-resolution structures, electrophysiologists have been dipping into the top tray of the chemist's tool box: synthesizing cysteine-modifying agents and organic cations and grinding up insects, spiders, and other vermin to isolate natural products to poke, probe, and prod K(+) channels. Recently, there has been further cross-fertilization between chemists and K(+) channelologists, resulting in greater accessibility to more elaborate synthetic methodologies and screening approaches. In this review, we catalogue the evolution of chemical tools and approaches that have been utilized to elucidate the mechanistic underpinnings of K(+) channel biology.
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Affiliation(s)
- Christopher A Ahern
- Department of Anesthesiology, University of British Columbia, 2350 Health Science Mall, Vancouver, BC V6T 1Z3, Canada.
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13
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Abstract
Voltage-clamp techniques are typically used to study the plasma membrane proteins, such as ion channels and transporters that control bioelectrical signals. Many of these proteins have been cloned and can now be studied as potential targets for drug development. The two approaches most commonly used for heterologous expression of cloned ion channels and transporters involve either transfection of the genes into small cells grown in tissue culture or the injection of the genetic material into larger cells. The standard large cells used for the expression of cloned cDNA or synthetic RNA are the egg progenitor cells (oocytes) of the African frog, Xenopus laevis. Until recently, cellular electrophysiology was performed manually by a single operator, one cell at a time. However, methods of high throughput electrophysiology have been developed which are automated and permit data acquisition and analysis from multiple cells in parallel. These methods are breaking a bottleneck in drug discovery, useful in some cases for primary screening as well as for thorough characterization of new drugs. Increasing throughput of high-quality functional data greatly augments the efficiency of academic research and pharmaceutical drug development. Some examples of studies that benefit most from high throughput electrophysiology include pharmaceutical screening of targeted compound libraries, secondary screening of identified compounds for subtype selectivity, screening mutants of ligand-gated channels for changes in receptor function, scanning mutagenesis of protein segments, and mutant-cycle analysis. We describe here the main features and potential applications of OpusXpress, an efficient commercially available system for automated recording from Xenopus oocytes. We show some types of data that have been gathered by this system and review realized and potential applications.
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Affiliation(s)
- Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida, USA.
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14
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Huang LY, Umanah G, Hauser M, Son C, Arshava B, Naider F, Becker JM. Unnatural Amino Acid Replacement in a Yeast G Protein-Coupled Receptor in Its Native Environment. Biochemistry 2008; 47:5638-48. [DOI: 10.1021/bi701866e] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Li-Yin Huang
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - George Umanah
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Melinda Hauser
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Cagdas Son
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Boris Arshava
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Fred Naider
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Jeffrey M. Becker
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
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15
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Abstract
The challenges to obtaining chemical-scale information on the molecules of neuroscience are considerable. Most targets are complex integral membrane proteins that are not amenable to direct structural characterization. However, by combining the tools of organic synthesis, molecular biology, and electrophysiology, rational and systematic structure-function studies can be performed in what we have termed physical organic chemistry on the brain. Using these tools, we have probed hydrophobic effects, hydrogen bonding, cation-pi interactions, and conformational changes associated with channel gating. The insights gained provide important guidance for drug discovery efforts targeting ion channels and neuroreceptors and mechanistic insights for the complex proteins of neuroscience.
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Affiliation(s)
- Dennis A Dougherty
- Division of Chemistry and Chemical Engineering California Institute of Technology, Pasadena, CA 91125, USA.
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16
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Santarelli VP, Eastwood AL, Dougherty DA, Ahern CA, Horn R. Calcium block of single sodium channels: role of a pore-lining aromatic residue. Biophys J 2007; 93:2341-9. [PMID: 17545248 PMCID: PMC1965434 DOI: 10.1529/biophysj.107.106856] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 05/22/2007] [Indexed: 11/18/2022] Open
Abstract
Extracellular Ca(2+) ions cause a rapid block of voltage-gated sodium channels, manifest as an apparent reduction of the amplitude of single-channel currents. We examined the influence of residue Tyr-401 in the isoform rNa(V)1.4 on both single-channel conductance and Ca(2+) block. An aromatic residue at this position in the outer mouth of the pore plays a critical role in high-affinity block by the guanidinium toxin tetrodotoxin, primarily due to an electrostatic attraction between the cationic blocker and the system of pi electrons on the aromatic face. We tested whether a similar attraction between small metal cations (Na(+) and Ca(2+)) and this residue would enhance single-channel conductance or pore block, using a series of fluorinated derivatives of phenylalanine at this position. Our results show a monotonic decrease in Ca(2+) block as the aromatic ring is increasingly fluorinated, a result in accord with a cation-pi interaction between Ca(2+) and the aromatic ring. This occurred without a change of single-channel conductance, consistent with a greater electrostatic effect of the pi system on divalent than on monovalent cations. High-level quantum mechanical calculations show that Ca(2+) ions likely do not bind directly to the aromatic ring because of the substantial energetic penalty of dehydrating a Ca(2+) ion. However, the complex of a Ca(2+) ion with its inner hydration shell, Ca(2+)(H(2)O)(6), interacts electrostatically with the aromatic ring in a way that affects the local concentration of Ca(2+) ions in the extracellular vestibule.
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Affiliation(s)
- Vincent P Santarelli
- Department of Molecular Physiology and Biophysics, Institute of Hyperexcitability, Jefferson Medical College, Philadelphia, Pennsylvania, USA
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17
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Wang J, Lester HA, Dougherty DA. Establishing an ion pair interaction in the homomeric rho1 gamma-aminobutyric acid type A receptor that contributes to the gating pathway. J Biol Chem 2007; 282:26210-6. [PMID: 17606618 DOI: 10.1074/jbc.m702314200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
gamma-Aminobutyric acid type A (GABA(A)) receptors are members of the Cys-loop superfamily of ligand-gated ion channels. Upon agonist binding, the receptor undergoes a structural transition from the closed to the open state, but the mechanism of gating is not well understood. Here we utilized a combination of conventional mutagenesis and the high precision methodology of unnatural amino acid incorporation to study the gating interface of the human homopentameric rho1 GABA(A) receptor. We have identified an ion pair interaction between two conserved charged residues, Glu(92) in loop 2 of the extracellular domain and Arg(258) in the pre-M1 region. We hypothesize that the salt bridge exists in the closed state by kinetic measurements and free energy analysis. Several other charged residues at the gating interface are not critical to receptor function, supporting previous conclusions that it is the global charge pattern of the gating interface that controls receptor function in the Cys-loop superfamily.
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Affiliation(s)
- Jinti Wang
- Division of Chemistry and Chemical Engineering and Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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18
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Ahern CA, Eastwood AL, Lester HA, Dougherty DA, Horn R. A cation-pi interaction between extracellular TEA and an aromatic residue in potassium channels. ACTA ACUST UNITED AC 2007; 128:649-57. [PMID: 17130518 PMCID: PMC2151593 DOI: 10.1085/jgp.200609654] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Open-channel blockers such as tetraethylammonium (TEA) have a long history as probes of the permeation pathway of ion channels. High affinity blockade by extracellular TEA requires the presence of an aromatic amino acid at a position that sits at the external entrance of the permeation pathway (residue 449 in the eukaryotic voltage-gated potassium channel Shaker). We investigated whether a cation–π interaction between TEA and such an aromatic residue contributes to TEA block using the in vivo nonsense suppression method to incorporate a series of increasingly fluorinated Phe side chains at position 449. Fluorination, which is known to decrease the cation–π binding ability of an aromatic ring, progressively increased the inhibitory constant Ki for the TEA block of Shaker. A larger increase in Ki was observed when the benzene ring of Phe449 was substituted by nonaromatic cyclohexane. These results support a strong cation–π component to the TEA block. The data provide an empirical basis for choosing between Shaker models that are based on two classes of reported crystal structures for the bacterial channel KcsA, showing residue Tyr82 in orientations either compatible or incompatible with a cation–π mechanism. We propose that the aromatic residue at this position in Shaker is favorably oriented for a cation–π interaction with the permeation pathway. This choice is supported by high level ab initio calculations of the predicted effects of Phe modifications on TEA binding energy.
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Affiliation(s)
- Christopher A Ahern
- Department of Molecular Physiology and Biophysics, Jefferson Medical College, Philadelphia, PA 19107, USA
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19
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Santarelli VP, Eastwood AL, Dougherty DA, Horn R, Ahern CA. A cation-pi interaction discriminates among sodium channels that are either sensitive or resistant to tetrodotoxin block. J Biol Chem 2007; 282:8044-51. [PMID: 17237232 DOI: 10.1074/jbc.m611334200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated sodium channels control the upstroke of the action potential in excitable cells of nerve and muscle tissue, making them ideal targets for exogenous toxins that aim to squelch electrical excitability. One such toxin, tetrodotoxin (TTX), blocks sodium channels with nanomolar affinity only when an aromatic Phe or Tyr residue is present at a specific location in the external vestibule of the ion-conducting pore. To test whether TTX is attracted to Tyr401 of NaV1.4 through a cation-pi interaction, this aromatic residue was replaced with fluorinated derivatives of Phe using in vivo nonsense suppression. Consistent with a cation-pi interaction, increased fluorination of Phe401, which reduces the negative electrostatic potential on the aromatic face, caused a monotonic increase in the inhibitory constant for block. Trifluorination of the aromatic ring decreased TTX affinity by approximately 50-fold, a reduction similar to that caused by replacement with the comparably hydrophobic residue Leu. Furthermore, we show that an energetically equivalent cation-pi interaction underlies both use-dependent and tonic block by TTX. Our results are supported by high level ab initio quantum mechanical calculations applied to a model of TTX binding to benzene. Our analysis suggests that the aromatic side chain faces the permeation pathway where it orients TTX optimally and interacts with permeant ions. These results are the first of their kind to show the incorporation of unnatural amino acids into a voltage-gated sodium channel and demonstrate that a cation-pi interaction is responsible for the obligate nature of an aromatic at this position in TTX-sensitive sodium channels.
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Affiliation(s)
- Vincent P Santarelli
- Department of Molecular Physiology and Biophysics, Institute of Hyperexcitability, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA
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Maloney DJ, Ghanem N, Zhou J, Hecht SM. Positional assignment of differentially substituted bisaminoacylated pdCpAs. Org Biomol Chem 2007; 5:3135-8. [PMID: 17878972 DOI: 10.1039/b708786a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The synthesis and NMR analysis of a 2'-O-alanyl, 3'-O-[1-(13)C]valyl-pdCpA derivative has permitted the definitive assignment of the positions of acylation of tandemly activated pdCpAs, and the bisaminoacylated transfer RNAs derived therefrom.
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Affiliation(s)
- David J Maloney
- Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA
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Sredojević D, Bogdanović GA, Tomić ZD, Zarić SD. Stacking vs. CH–π interactions between chelate and aryl rings in crystal structures of square-planar transition metal complexes. CrystEngComm 2007. [DOI: 10.1039/b704302c] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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