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Bondarenko V, Wells M, Xu Y, Tang P. Solution NMR Studies of Anesthetic Interactions with Ion Channels. Methods Enzymol 2018; 603:49-66. [PMID: 29673534 DOI: 10.1016/bs.mie.2018.01.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
NMR spectroscopy is one of the major tools to provide atomic resolution protein structural information. It has been used to elucidate the molecular details of interactions between anesthetics and ion channels, to identify anesthetic binding sites, and to characterize channel dynamics and changes introduced by anesthetics. In this chapter, we present solution NMR methods essential for investigating interactions between ion channels and general anesthetics, including both volatile and intravenous anesthetics. Case studies are provided with a focus on pentameric ligand-gated ion channels and the voltage-gated sodium channel NaChBac.
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Affiliation(s)
- Vasyl Bondarenko
- University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Marta Wells
- University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Yan Xu
- University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
| | - Pei Tang
- University of Pittsburgh School of Medicine, Pittsburgh, PA, United States.
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2
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Davis BM, Brenton J, Davis S, Shamsher E, Sisa C, Grgic L, Cordeiro MF. Assessing anesthetic activity through modulation of the membrane dipole potential. J Lipid Res 2017; 58:1962-1976. [PMID: 28818873 PMCID: PMC5625120 DOI: 10.1194/jlr.m073932] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 08/09/2017] [Indexed: 12/21/2022] Open
Abstract
There is great individual variation in response to general anesthetics (GAs) leading to difficulties in optimal dosing and sometimes even accidental awareness during general anesthesia (AAGA). AAGA is a rare, but potentially devastating, complication affecting between 0.1% and 2% of patients undergoing surgery. The development of novel personalized screening techniques to accurately predict a patient’s response to GAs and the risk of AAGA remains an unmet clinical need. In the present study, we demonstrate the principle of using a fluorescent reporter of the membrane dipole potential, di-8-ANEPPs, as a novel method to monitor anesthetic activity using a well-described inducer/noninducer pair. The membrane dipole potential has previously been suggested to contribute a novel mechanism of anesthetic action. We show that the fluorescence ratio of di-8-ANEPPs changed in response to physiological concentrations of the anesthetic, 1-chloro-1,2,2-trifluorocyclobutane (F3), but not the structurally similar noninducer, 1,2-dichlorohexafluorocyclobutane (F6), to artificial membranes and in vitro retinal cell systems. Modulation of the membrane dipole provides an explanation to overcome the limitations associated with the alternative membrane-mediated mechanisms of GA action. Furthermore, by combining this technique with noninvasive retinal imaging technologies, we propose that this technique could provide a novel and noninvasive technique to monitor GA susceptibility and identify patients at risk of AAGA.
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Affiliation(s)
| | - Jonathan Brenton
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | - Sterenn Davis
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | - Ehtesham Shamsher
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | - Claudia Sisa
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | - Ljuban Grgic
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom
| | - M Francesca Cordeiro
- University College London Institute of Ophthalmology, London EC1V 9EL, United Kingdom .,Western Eye Hospital, Imperial College Healthcare National Health Service Trust, and Imperial College Ophthalmic Research Group, Imperial College London, London NW1 5QH, United Kingdom
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3
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Joyce RE, Williams TL, Serpell LC, Day IJ. Monitoring changes of paramagnetically-shifted 31P signals in phospholipid vesicles. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2016.02.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Mowrey DD, Kinde MN, Xu Y, Tang P. Atomistic insights into human Cys-loop receptors by solution NMR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:307-14. [PMID: 24680782 DOI: 10.1016/j.bbamem.2014.03.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 03/12/2014] [Accepted: 03/20/2014] [Indexed: 12/13/2022]
Abstract
Cys-loop receptors are pentameric ligand-gated ion channels (pLGICs) mediating fast neurotransmission in the central and peripheral nervous systems. They are important targets for many currently used clinical drugs, such as general anesthetics, and for allosteric modulators with potential therapeutic applications. Here, we provide an overview of advances in the use of solution NMR in structural and dynamic characterization of ion channels, particularly human Cys-loop receptors. We present challenges to overcome and realistic solutions for achieving high-resolution structural information for this family of receptors. We discuss how subtle structural differences among homologous channels define unique channel pharmacological properties and advocate the necessity to determine high-resolution structures for individual receptor subtypes. Finally, we describe drug binding to the TMDs of Cys-loop receptors identified by solution NMR and the associated dynamics changes relevant to channel functions.
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Affiliation(s)
- David D Mowrey
- Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, USA
| | - Monica N Kinde
- Department of Anesthesiology, University of Pittsburgh School of Medicine, USA
| | - Yan Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Structural Biology, University of Pittsburgh School of Medicine, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, USA.
| | - Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, USA.
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Wang HJ, Kleinhammes A, Tang P, Xu Y, Wu Y. Critical role of water in the binding of volatile anesthetics to proteins. J Phys Chem B 2013; 117:12007-12. [PMID: 24050264 DOI: 10.1021/jp407115j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Numerous small molecules exhibit drug-like properties by low-affinity binding to proteins. Such binding is known to be influenced by water, the detailed picture of which, however, remains unclear. One particular example is the controversial role of water in the binding of general anesthetics to proteins as an essential step in general anesthesia. Here we demonstrate that a critical amount of hydration water is a prerequisite for anesthetic-protein binding. Using nuclear magnetic resonance, the concurrent adsorption of hydration water and bound anesthetics on model proteins are simultaneously measured. Halothane binding on proteins can only take place after protein hydration reaches a threshold hydration level of ∼0.31 g of water/g of proteins at the relative water vapor pressure of ∼0.95. Similar dependence on hydration is also observed for several other anesthetics. The ratio of anesthetic partial pressures at which two different anesthetics reach the same fractional load is correlated with the anesthetic potency. The binding of nonimmobilizers, which are structurally similar to known anesthetics but unable to produce anesthesia, does not occur even after the proteins are fully hydrated. Our results provide the first unambiguous experimental evidence that water is absolutely required to enable anesthetic-protein interactions, shedding new light on the general mechanism of molecular recognition and binding.
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Affiliation(s)
- Hai-Jing Wang
- Department of Physics and Astronomy, University of North Carolina , Chapel Hill, North Carolina 27599-3255, United States
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Mowrey DD, Cui T, Jia Y, Ma D, Makhov AM, Zhang P, Tang P, Xu Y. Open-channel structures of the human glycine receptor α1 full-length transmembrane domain. Structure 2013; 21:1897-904. [PMID: 23994010 DOI: 10.1016/j.str.2013.07.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Revised: 06/19/2013] [Accepted: 07/22/2013] [Indexed: 11/29/2022]
Abstract
Glycine receptors play a major role in mediating fast inhibitory neurotransmission in the spinal cord and brain stem, yet their high-resolution structures remain unsolved. We determined open-channel structures of the full-length transmembrane domain (TMD) of the human glycine receptor α1-subunit (hGlyR-α1) using nuclear magnetic resonance (NMR) spectroscopy and electron micrographs. hGlyR-α1 TMD spontaneously forms pentameric Cl(-)-conducting channels, with structures sharing overall topology observed in crystal structures of homologous bacterial and nematode pentameric ligand-gated ion channels (pLGICs). However, the mammalian hGlyR-α1 structures present several distinctive features, including a shorter, pore-lining TM2 helix with helical unwinding near the C-terminal end, a TM3 helical kink at A288 that partially overlaps with the homologous ivermectin-binding site in GluCl, and a highly dynamic segment between S267(15') of TM2 and A288 that likely affects allosteric modulations of channel function. Our structures provide additional templates for identifying potential drug targets in GlyRs and other mammalian pLGICs.
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Affiliation(s)
- David D Mowrey
- Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
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NMR resolved multiple anesthetic binding sites in the TM domains of the α4β2 nAChR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:398-404. [PMID: 23000369 DOI: 10.1016/j.bbamem.2012.09.014] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 09/09/2012] [Accepted: 09/14/2012] [Indexed: 12/12/2022]
Abstract
The α4β2 nicotinic acetylcholine receptor (nAChR) has significant roles in nervous system function and disease. It is also a molecular target of general anesthetics. Anesthetics inhibit the α4β2 nAChR at clinically relevant concentrations, but their binding sites in α4β2 remain unclear. The recently determined NMR structures of the α4β2 nAChR transmembrane (TM) domains provide valuable frameworks for identifying the binding sites. In this study, we performed solution NMR experiments on the α4β2 TM domains in the absence and presence of halothane and ketamine. Both anesthetics were found in an intra-subunit cavity near the extracellular end of the β2 transmembrane helices, homologous to a common anesthetic binding site observed in X-ray structures of anesthetic-bound GLIC (Nury et al., [32]). Halothane, but not ketamine, was also found in cavities adjacent to the common anesthetic site at the interface of α4 and β2. In addition, both anesthetics bound to cavities near the ion selectivity filter at the intracellular end of the TM domains. Anesthetic binding induced profound changes in protein conformational exchanges. A number of residues, close to or remote from the binding sites, showed resonance signal splitting from single to double peaks, signifying that anesthetics decreased conformation exchange rates. It was also evident that anesthetics shifted population of two conformations. Altogether, the study comprehensively resolved anesthetic binding sites in the α4β2 nAChR. Furthermore, the study provided compelling experimental evidence of anesthetic-induced changes in protein dynamics, especially near regions of the hydrophobic gate and ion selectivity filter that directly regulate channel functions.
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Holder JW. Physical and physicochemical factors effecting transport of chlorohydrocarbon gases from lung alveolar air to blood as measured by the causation of narcosis. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. PART C, ENVIRONMENTAL CARCINOGENESIS & ECOTOXICOLOGY REVIEWS 2012; 30:42-80. [PMID: 22458856 DOI: 10.1080/10590501.2012.653888] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
This systematic investigation examines gas transport in the lung for two sets of chlorohydrocarbons (CHCs): the chloromethanes (C1) and chloroethanes (C2). The C1 series includes chloromethane, methylene chloride, chloroform, and carbon tetrachloride, and the C2 series includes chloroethane, 1,2-dichloroethane, 1, 1, 2-trichloroethane, and 1, 1, 2, 2-tetrachloroethane. Most CHC gases cause narcosis. The comprehensive narcosis work of Lehmann and colleagues on CHCs was used as a basis for the narcosis endpoint in the present examination. The sites for narcosis are located in the brain (midline cortex and posterior parietal area), the spine, and at many peripheral nerve sites. Central nervous system (CNS) exposure executes a multisite, neural transmission set of inhibitions that promotes rapid loss of consciousness, sensory feeling, and current and stored memory while providing temporary amnesia. Absorption into the system requires dissolution into many lipid membranes and binding to lipoproteins. Lipophilicity is a CHC property shared with many anesthetics according to the Meyer-Overton Rule. Many structurally different lipid chemicals produce the narcosis response when the lipid concentration exceeds -67 mM. This suggests narcotic or anesthetic dissolution into CNS membranes until the lipid organization is disrupted or perturbed. This perturbation includes loading of Na(+)- and K(+)-channel transmembrane lipoprotein complexes and disrupting their respective channel functional organizations. The channel functions become attenuated or abrogated until the CHC exposure ceases and CHC loading reverses. This investigation demonstrates how the CHC physical and chemical properties influence the absorption of these CHCs via the lung and the alveolar system on route to the blood. Narcosis in test animals was used here as an objective biological endpoint to study the effects of the physical factors Bp, Vp, Kd (oil: gas) partition, Henry's constant (HK), and water solubility (S%) on gas transport. Narcosis is immediate after gas exposure and requires no chemical activation only absorption into the blood and circulation to CNS narcotic sites. The three physical factors Bp, K(d) (oil: air), and S% vary directly with unitary narcosis (UN) whereas Vp and HK vary inversely with UN in linear log-log relationships for the C2 series but not for the C1 series. Physicochemical properties of C1 series gases indicate why they depart from what is usually assumed to be an Ideal Gas. An essential discriminating process in the distal lung is the limiting alveolar film layer (AFL) and the membrane layer of the alveolar acini. The AFL step influences gas uptake by physically limiting the absorption process. Interaction with and dissolution into aqueous solvent of the AFL is required for transport and narcotic activity. Narcotics or anesthetics must engage the aqueous AFL with sufficient strength to allow transport and absorption for downstream CNS binding. CHCs that do not engage well with the AFL are not narcotic. Lipophilicity and amphipathicity are also essential solvency properties driving narcotics' transport through the alveolar layer, delivery to the blood fats and lipoproteins, and into critical CNS lipids, lipoproteins, and receptor sites that actuate narcosis. AFL disruption is thought to be strongly related to a number of serious pulmonary diseases such acute respiratory distress syndrome, infant respiratory distress syndrome, emphysema, chronic obstructive pulmonary disease, asthma, chronic bronchitis, pneumonia, pulmonary infections, and idiopathic pulmonary fibrosis. The physical factors (Bp, Vp, Kd [oil: gas] partition, Henry's constant, and water solubility [S%]) combine to affect a specific transport through the AFL if lung C > C(0) (threshold concentration for narcosis). The degree of blood CHC absorption depends on dose, lipophilicity, and lung residence time. AFL passage can be manipulated by physical factors of increased pressure (kPa) or increased gas exposure (moles). Molecular lipophilicity facilitates narcosis but lipophilicity alone does not explain narcosis. Vapor pressure is also required for narcosis. Narcotic activity apparently requires stereospecific processing in the AFL and/or down-stream inhibition at stereospecific lipoproteins at CNS inhibitory sites. It is proposed that CHCs likely cannot proceed through the AFL without perturbation or disruption of the integrity of the AFL at the alveoli. CHC physicochemical properties are not expected to allow their transport through the AFL as physiological CO(2) and O(2) naturally do in respiration. This work considers CHC inspiration and systemic absorption into the blood with special emphasis on the CHC potential perturbation effects on the lipid, protein liquid layer supra to the alveolar membrane (AFL). A heuristic gas transport model for the CHCs is presented as guidance for this examination. The gas transport model can be used to study absorption for other gas delivery endpoints of environmental concern such as carcinogens.
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Chen Q, Cheng MH, Xu Y, Tang P. Anesthetic binding in a pentameric ligand-gated ion channel: GLIC. Biophys J 2010; 99:1801-9. [PMID: 20858424 PMCID: PMC2941008 DOI: 10.1016/j.bpj.2010.07.023] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 07/15/2010] [Accepted: 07/15/2010] [Indexed: 10/19/2022] Open
Abstract
Cys-loop receptors are molecular targets of general anesthetics, but the knowledge of anesthetic binding to these proteins remains limited. Here we investigate anesthetic binding to the bacterial Gloeobacter violaceus pentameric ligand-gated ion channel (GLIC), a structural homolog of cys-loop receptors, using an experimental and computational hybrid approach. Tryptophan fluorescence quenching experiments showed halothane and thiopental binding at three tryptophan-associated sites in the extracellular (EC) domain, transmembrane (TM) domain, and EC-TM interface of GLIC. An additional binding site at the EC-TM interface was predicted by docking analysis and validated by quenching experiments on the N200W GLIC mutant. The binding affinities (K(D)) of 2.3 ± 0.1 mM and 0.10 ± 0.01 mM were derived from the fluorescence quenching data of halothane and thiopental, respectively. Docking these anesthetics to the original GLIC crystal structure and the structures relaxed by molecular dynamics simulations revealed intrasubunit sites for most halothane binding and intersubunit sites for thiopental binding. Tryptophans were within reach of both intra- and intersubunit binding sites. Multiple molecular dynamics simulations on GLIC in the presence of halothane at different sites suggested that anesthetic binding at the EC-TM interface disrupted the critical interactions for channel gating, altered motion of the TM23 linker, and destabilized the open-channel conformation that can lead to inhibition of GLIC channel current. The study has not only provided insights into anesthetic binding in GLIC, but also demonstrated a successful fusion of experiments and computations for understanding anesthetic actions in complex proteins.
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Affiliation(s)
- Qiang Chen
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Mary Hongying Cheng
- Department of Chemistry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Yan Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
- Department of Computational Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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Mowrey D, Haddadian EJ, Liu LT, Willenbring D, Xu Y, Tang P. Unresponsive correlated motion in alpha7 nAChR to halothane binding explains its functional insensitivity to volatile anesthetics. J Phys Chem B 2010; 114:7649-55. [PMID: 20465243 DOI: 10.1021/jp1009675] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) have been implicated as targets for general anesthetics, but the functional responses to anesthetic modulation vary considerably among different subtypes of nAChRs. Inhaled general anesthetics, such as halothane, could effectively inhibit the channel activity of the alpha4beta2 nAChR but not the homologous alpha7 nAChR. To understand why alpha7 is insensitive to inhaled general anesthetics, we performed multiple sets of 20 ns molecular dynamics (MD) simulations on the closed- and open-channel alpha7 in the absence and presence of halothane and critically compared the results with those from our studies on the alpha4beta2 nAChR (Liu et al. J. Phys. Chem. B 2009, 113, 12581 and Liu et al. J. Phys. Chem. B 2010, 114, 626). Several halothane binding sites with fairly high binding affinities were identified in both closed- and open-channel alpha7, suggesting that a lack of sensitive functional responses of the alpha7 nAChR to halothane in the previous experiments was unlikely due to a lack of halothane interaction with alpha7. The binding affinities of halothane in alpha7 seemed to be protein conformation-dependent. Overall, halothane affinity was higher in the closed-channel alpha7. Halothane binding to alpha7 did not induce profound changes in alpha7 structure and dynamics that could be related to the channel function. In contrast, correlated motion of the open-channel alpha4beta2 was reduced substantially in the presence of halothane, primarily due to the more susceptible nature of beta2 to anesthetic modulation. The amphiphilic extracellular and transmembrane domain interface of the beta2 subunit is attractive to halothane and is susceptible to halothane perturbation, which may be why alpha4beta2 is functionally more sensitive to halothane than alpha7.
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Affiliation(s)
- David Mowrey
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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Cui T, Canlas CG, Xu Y, Tang P. Anesthetic effects on the structure and dynamics of the second transmembrane domains of nAChR alpha4beta2. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1798:161-6. [PMID: 19715664 DOI: 10.1016/j.bbamem.2009.08.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Revised: 07/31/2009] [Accepted: 08/12/2009] [Indexed: 01/03/2023]
Abstract
Channel functions of the neuronal alpha4beta2 nicotinic acetylcholine receptor (nAChR), one of the most widely expressed subtypes in the brain, can be inhibited by volatile anesthetics. Our Na(+) flux experiments confirmed that the second transmembrane domains (TM2) of alpha4 and beta2 in 2:3 stoichiometry, (alpha4)(2)(beta2)(3), could form pentameric channels, whereas the alpha4 TM2 alone could not. The structure, topology, and dynamics of the alpha4 TM2 and (alpha4)(2)(beta2)(3) TM2 in magnetically aligned phospholipid bicelles were investigated using solid-state NMR spectroscopy in the absence and presence of halothane and isoflurane, two clinically used volatile anesthetics. (2)H NMR demonstrated that anesthetics increased lipid conformational heterogeneity. Such anesthetic effects on lipids became more profound in the presence of transmembrane proteins. PISEMA experiments on the selectively (15)N-labeled alpha4 TM2 showed that the TM2 formed transmembrane helices with tilt angles of 12 degrees +/-1 degrees and 16 degrees +/-1 degrees relative to the bicelle normal for the alpha4 and (alpha4)(2)(beta2)(3) samples, respectively. Anesthetics changed the tilt angle of the alpha4 TM2 from 12 degrees +/-1 degrees to 14 degrees +/-1 degrees , but had only a subtle effect on the tilt angle of the (alpha4)(2)(beta2)(3) TM2. A small degree of wobbling motion of the helix axis occurred in the (alpha4)(2)(beta2)(3) TM2. In addition, a subset of the (alpha4)(2)(beta2)(3) TM2 exhibited counterclockwise rotational motion around the helix axis on a time scale slower than 10(-4) s in the presence of anesthetics. Both helical tilting and rotational motions have been identified computationally as critical elements for ion channel functions. This study suggested that anesthetics could alter these motions to modulate channel functions.
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Affiliation(s)
- Tanxing Cui
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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Takeuchi H, Ishida H, Hikichi S, Kurahashi T. Mechanism of olfactory masking in the sensory cilia. J Gen Physiol 2009; 133:583-601. [PMID: 19433623 PMCID: PMC2713142 DOI: 10.1085/jgp.200810085] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 04/22/2009] [Indexed: 12/02/2022] Open
Abstract
Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.
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Affiliation(s)
- Hiroko Takeuchi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
| | - Hirohiko Ishida
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Satoshi Hikichi
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Takashi Kurahashi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
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Seto T, Isogai H, Ozaki M, Nosaka S. Noble Gas Binding to Human Serum Albumin Using Docking Simulation: Nonimmobilizers and Anesthetics Bind to Different Sites. Anesth Analg 2008; 107:1223-8. [DOI: 10.1213/ane.0b013e31817f1317] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Canlas CG, Cui T, Li L, Xu Y, Tang P. Anesthetic modulation of protein dynamics: insight from an NMR study. J Phys Chem B 2008; 112:14312-8. [PMID: 18821786 DOI: 10.1021/jp805952w] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Mistic (membrane integrating sequence for translation of integral membrane protein constructs) comprises the four-alpha-helix bundle scaffold found in the transmembrane domains of the Cys-loop receptors that are plausible targets for general anesthetics. Nuclear magnetic resonance (NMR) studies of anesthetic halothane interaction with Mistic in dodecyl phosphocholine (DPC) micelles provide an experimental basis for understanding molecular mechanisms of general anesthesia. Halothane was found to interact directly with Mistic, mostly in the interfacial loop regions. Although the presence of halothane had little effect on Mistic structure, (15)N NMR relaxation dispersion measurements revealed that halothane affected Mistic's motion on the microsecond-millisecond time scale. Halothane shifted the equilibrium of chemical exchange in some residues and made the exchange faster or slower in comparison to the original state in the absence of halothane. The motion on the microsecond-millisecond time scale in several residues disappeared in response to the addition of halothane. Most of the residues experiencing halothane-induced dynamics changes also exhibited profound halothane-induced changes in chemical shift, suggesting that dynamics modification of these residues might result from their direct interaction with halothane molecules. Allosteric modulation by halothane also contributed to dynamics changes, as reflected in residues I52 and Y82 where halothane introduction brought about dynamics changes but not chemical shift changes. The study suggests that inhaled general anesthetics could act on proteins via altering protein motion on the microsecond-millisecond time scale, especially motion in the flexible loops that link different alpha helices. The validation of anesthetic effect on protein dynamics that are potentially correlated with protein functions is a critical step in unraveling the mechanisms of anesthetic action on proteins.
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Affiliation(s)
- Christian G Canlas
- Department of Anesthesiology, Pharmacology and Chemical Biology, and Computational Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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Four-alpha-helix bundle with designed anesthetic binding pockets. Part I: structural and dynamical analyses. Biophys J 2008; 94:4454-63. [PMID: 18310240 DOI: 10.1529/biophysj.107.117838] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The four-alpha-helix bundle mimics the transmembrane domain of the Cys-loop receptor family believed to be the protein target for general anesthetics. Using high resolution NMR, we solved the structure (Protein Data Bank ID: 2I7U) of a prototypical dimeric four-alpha-helix bundle, (Aalpha(2)-L1M/L38M)(2,) with designed specific binding pockets for volatile anesthetics. Two monomers of the helix-turn-helix motif form an antiparallel dimer as originally designed, but the high-resolution structure exhibits an asymmetric quaternary arrangement of the four helices. The two helices from the N-terminus to the linker (helices 1 and 1') are associated with each other in the dimer by the side-chain ring stacking of F12 and W15 along the long hydrophobic core and by a nearly perfect stretch of hydrophobic interactions between the complementary pairs of L4, L11, L18, and L25, all of which are located at the heptad e position along the helix-helix dimer interface. In comparison, the axes of the two helices from the linker to the C-terminus (helices 2 and 2') are wider apart from each other, creating a lateral access pathway around K47 from the aqueous phase to the center of the designed hydrophobic core. The site of the L38M mutation, which was previously shown to increase the halothane binding affinity by approximately 3.5-fold, is not part of the hydrophobic core presumably involved in the anesthetic binding but shows an elevated transverse relaxation (R(2)) rate. Qualitative analysis of the protein dynamics by reduced spectral density mapping revealed exchange contributions to the relaxation at many residues in the helices. This observation was confirmed by the quantitative analysis using the Modelfree approach and by the NMR relaxation dispersion measurements. The NMR structures and Autodock analysis suggest that the pocket with the most favorable amphipathic property for anesthetic binding is located between the W15 side chains at the center of the dimeric hydrophobic core, with the possibility of two additional minor binding sites between the F12 and F52 ring stacks of each monomer. The high-resolution structure of the designed anesthetic-binding protein offers unprecedented atomistic details about possible sites for anesthetic-protein interactions that are essential to the understanding of molecular mechanisms of general anesthesia.
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Abstract
The molecular basis of anesthetic interaction with membrane proteins has been explored via determination of anesthetic effects on the structure and dynamics of the extended second transmembrane domain (TM2e) of the human neuronal nicotinic acetylcholine receptor (nAChR) beta(2) subunit in dodecylphosphocholine (DPC) micelles by (1)H and (15)N solution-state NMR. Both 1-chloro-1,2,2-trifluorocyclobutane (F3) and isoflurane, two volatile general anesthetics, induced nonuniform changes in chemical shifts among residues in TM2e. Saturation transfer difference NMR experiments further confirmed the direct anesthetic interaction with TM2e. A significant and more specific anesthetic interaction was observed on three leucine residues at the helix C-terminus. Although the TM2e helical structure remained after addition of anesthetics, plausible shortening and lengthening of helix hydrogen bonds were evidenced by periodic changes in backbone amide chemical shifts. The TM2e backbone dynamics were determined on the basis of the (15)N relaxation rate constants, R(1) and R(2), and the (15)N-[(1)H] NOE using the model-free approach. The global tumbling time (11.7 ns) of TM2e in micelles slightly increased ( approximately 12.3-12.5 ns) in the presence of anesthetics. The order parameter, S(2), exceeded 0.9 for all (15)N-labeled residues, showing a restricted internal motion. Anesthetics appear to have minor effect on the TM2e's internal motion. This study provided the basis for subsequent more comprehensive studies of anesthetic effects on the transmembrane domain complex of neuronal nAChR.
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Carnini A, Nguyen TT, Cramb DT. Fluorescence quenching of gramicidin D in model membranes by halothane. CAN J CHEM 2007. [DOI: 10.1139/v07-064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Inhaled anesthetics were introduced in surgery over a century ago. To this day, the molecular mechanism of anesthetic action remains largely unknown. However, ion-channels of neuronal membranes are believed to be the most- likely molecular targets of inhaled anesthetics. In the study presented here, we investigated the interaction of a simplified ion-channel system, gramicidin, with halothane, a small haloalkane inhaled anesthetic in various environments. Fluorescence-quenching experiments of gramicidin D in dioleoylphosphatidylcholine (DOPC) large unilamellar vesicles (LUVS) have shown that halothane can directly interact with the ion channel (KSV = 66 M–1). Halothane quenched the fluorescence from tryptophan residues located at the lipid bilayer – aqueous interfaces as well as those tryptophans located deeper in the bilayer. Quenching data from gramicidin D in sodium dodecyl sulfide (SDS) micelles revealed that the tryptophan residues located at the micelle–solvent interface were preferentially quenched by halothane (KSV = 22 M–1). In 1-octanol, fluorescence quenching was observed, but with a lower KSV value (KSV = 6 M–1) than in DOPC LUVS and SDS micelles. Taken together, these results indicate that halothane interactions with gramicidin, mediated by a lipid bilayer, are the strongest, and that the mechanism of anesthetic action may also be lipid-mediated.
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Liu Z, Xu Y, Tang P. Steered Molecular Dynamics Simulations of Na+ Permeation across the Gramicidin A Channel. J Phys Chem B 2006; 110:12789-95. [PMID: 16800614 DOI: 10.1021/jp060688n] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The potential of mean forces (PMF) governing Na+ permeation through gramicidin A (gA) channels with explicit water and membrane was characterized using steered molecular dynamics (SMD) simulations. Constant-force SMD with a steering force parallel to the channel axis revealed at least seven energy wells in each monomer of the channel dimer. Except at the channel dimer interface, each energy well is associated with at least three and at most four backbone carbonyl oxygens and two water oxygens in a pseudo-hexahedral or pseudo-octahedral coordination with the Na+ ion. Repeated constant-velocity SMD by dragging a Na+ ion from each energy well in opposite directions parallel to the channel axis allowed the computation of the PMF across the gA channel, revealing a global minimum corresponding to Na+ binding sites near the entrance of gA at +/-9.3 A from the geometric center of the channel. The effect of volatile anesthetics on the PMF was also analyzed in the presence of halothane molecules. Although the accuracy of the current PMF calculation from SMD simulations is not yet sufficient to quantify the PMF difference with and without anesthetics, the comparison of the overall PMF profiles nevertheless confirms that the anesthetics cause insignificant changes to the structural makeup of the free energy wells along the channel and the overall permeation barrier. On average, the PMF appears less rugged in the outer part of the channel in the presence of anesthetics, consistent with our earlier finding that halothane interaction with anchoring residues makes the gA channel more dynamic. A causal relationship was observed between the reorientation of the coordinating backbone carbonyl oxygen and Na+ transit from one energy well to another, suggesting the possibility that even minute changes in the conformation of pore-lining residues due to dynamic motion could be sufficient to trigger the ion permeation. Because some of the carbonyl oxygens contribute to Na+ coordination in two adjacent energy wells, our SMD results reveal that the atomic picture of ion "hopping" through a gA channel actually involves a Na+ ion being carried in a relay by the coordinating oxygens from one energy well to the next. Steered molecular dynamics complements other computational approaches as an attractive means for the atomistic interpretation of experimental permeation studies.
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Affiliation(s)
- Zhanwu Liu
- Department of Anesthesiology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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Liu Z, Xu Y, Tang P. Molecular dynamics simulations of C2F6 effects on gramicidin A: implications of the mechanisms of general anesthesia. Biophys J 2005; 88:3784-91. [PMID: 15764669 PMCID: PMC1305613 DOI: 10.1529/biophysj.104.055566] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It was recently postulated that the effects of general anesthetics on protein global dynamics might underlie a unitary molecular mechanism of general anesthesia. To verify that the specific dynamics effects caused by general anesthetics were not shared by nonanesthetic molecules, two parallel 8-ns all-atom molecular dynamics simulations were performed on a gramicidin A (gA) channel in a fully hydrated dimyristoylphosphatidylcholine membrane in the presence and absence of hexafluoroethane (HFE), which structurally resembles the potent anesthetic molecule halothane but produces no anesthesia. Similar to halothane, HFE had no measurable effects on the gA channel structure. In contrast to halothane, HFE produced no significant changes in the gA channel dynamics. The difference between halothane and HFE on channel dynamics can be attributed to their distinctly different distributions within the lipid bilayer and consequently to the different interactions of the anesthetic and the nonanesthetic molecules with the channel-anchoring tryptophan residues. The study further supports the notion that anesthetic-induced changes in protein global dynamics may play an important role in mediating anesthetic actions on proteins.
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Affiliation(s)
- Zhanwu Liu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA
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21
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Saladino AC, Tang P. Optimization of Structures and LJ Parameters of 1-Chloro-1,2,2-trifluorocyclobutane and 1,2-Dichlorohexafluorocyclobutane. J Phys Chem A 2004. [DOI: 10.1021/jp046662i] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alexander C. Saladino
- Department of Anesthesiology and Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Pei Tang
- Department of Anesthesiology and Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
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Streiff JH, Juranic NO, Macura SI, Warner DO, Jones KA, Perkins WJ. Saturation Transfer Difference Nuclear Magnetic Resonance Spectroscopy As a Method for Screening Proteins for Anesthetic Binding. Mol Pharmacol 2004. [DOI: 10.1124/mol.66.4.929] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Tang P, Xu Y. Large-scale molecular dynamics simulations of general anesthetic effects on the ion channel in the fully hydrated membrane: the implication of molecular mechanisms of general anesthesia. Proc Natl Acad Sci U S A 2002; 99:16035-40. [PMID: 12438684 PMCID: PMC138560 DOI: 10.1073/pnas.252522299] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Interactions of volatile anesthetics with the central nervous system are characterized by low yet specific binding affinities. Although neurotransmitter-gated ion channels are considered the primary anesthetic targets, the mechanism of action at the molecular level remains elusive. We consider here the theoretical implications of channel dynamics on anesthetic action in a simplified membrane-channel system. Large-scale 2.2-ns all-atom molecular dynamics simulations were performed to study the effects of halothane, a clinical anesthetic, on a gramicidin A (gA) channel in a fully hydrated dimyristoyl phosphatidylcholine membrane. In agreement with experimental results, anesthetics preferentially target the anchoring residues at the channel-lipid-water interface. Although the anesthetic effect on channel structure is minimal, the presence of halothane profoundly affects channel dynamics. For 2.2-ns simulation, the rms fluctuation of gA backbone in the lipid core increases from approximately equal 1 A in the absence of anesthetics to approximately equal 1.5 A in the presence of halothane. Autocorrelation analysis reveals that halothane (i) has no effect on the subpicosecond librational motion, (ii) prolongs the backbone autocorrelation time in the 10- to 100-ps time scale, and (iii) significantly decreases the asymptotic values of generalized order parameter and correlation time of nanosecond motions for the inner but not the outer residues. The simulation results discount the viewpoint of a structure-function paradigm that overrates the importance of structural fitting between general anesthetics and yet-unidentified hydrophobic protein pockets. Instead, the results underscore the global, as opposed to local, effects of anesthetics on protein dynamics as the underlying mechanisms for the action of general anesthetics and possibly of other low-affinity drugs.
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Affiliation(s)
- Pei Tang
- Departments of Anesthesiology and Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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24
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Abstract
Volatile anesthetic agent, 1-chloro-1,2,2-trifluorocyclobutane (F3), was found to alter gramicidin A channel function by enhancing Na(+) transport (. Biophys. J. 77:739-746). Whether this functional change is associated with structural alternation is evaluated by circular dichroism and nuclear magnetic resonance spectroscopy. The circular dichroism and nuclear magnetic resonance results indicate that at low millimolar concentrations, 1-chloro-1,2,2-trifluorocyclobutane causes minimal changes in gramicidin A channel structure in sodium dodecyl sulfate micelles. All hydrogen bonds between channel backbones are well maintained in the presence of 1-chloro-1,2,2-trifluorocyclobutane, and the channel structure is stable. The finding supports the notion that low affinity drugs such as volatile anesthetics and alcohols can cause significant changes in protein function without necessarily producing associated changes in protein structure. To understand the molecular mechanism of general anesthesia, it is important to recognize that in addition to structural changes, other protein properties, including dynamic characteristics of channel motions, may also be of functional significance.
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Affiliation(s)
- Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261 USA.
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Tang P, Mandal PK, Xu Y. NMR structures of the second transmembrane domain of the human glycine receptor alpha(1) subunit: model of pore architecture and channel gating. Biophys J 2002; 83:252-62. [PMID: 12080117 PMCID: PMC1302144 DOI: 10.1016/s0006-3495(02)75166-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Glycine receptors (GlyR) are the primary inhibitory receptors in the spinal cord and belong to a superfamily of ligand-gated ion channels (LGICs) that are extremely sensitive to low-affinity neurological agents such as general anesthetics and alcohols. The high-resolution pore architecture and the gating mechanism of this superfamily, however, remain unclear. The pore-lining second transmembrane (TM2) segments of the GlyR alpha(1) subunit are unique in that they form functional homopentameric channels with conductance characteristics nearly identical to those of an authentic receptor (Opella, S. J., J. Gesell, A. R. Valente, F. M. Marassi, M. Oblatt-Montal, W. Sun, A. F. Montiel, and M. Montal. 1997. Chemtracts Biochem. Mol. Biol. 10:153-174). Using NMR and circular dichroism (CD), we determined the high-resolution structures of the TM2 segment of human alpha(1) GlyR and an anesthetic-insensitive mutant (S267Y) in dodecyl phosphocholine (DPC) and sodium dodecyl sulfate (SDS) micelles. The NMR structures showed right-handed alpha-helices without kinks. A well-defined hydrophilic path, composed of side chains of G2', T6', T10', Q14', and S18', runs along the helical surfaces at an angle approximately 10-20 degrees relative to the long axis of the helices. The side-chain arrangement of the NMR-derived structures and the energy minimization of a homopentameric TM2 channel in a fully hydrated DMPC membrane using large-scale computation suggest a model of pore architecture in which simultaneous tilting movements of entire TM2 helices by a mere 10 degrees may be sufficient to account for the channel gating. The model also suggests that additional residues accessible from within the pore include L3', T7', T13', and G17'. A similar pore architecture and gating mechanism may apply to other channels in the same superfamily, including GABA(A), nACh, and 5-HT(3) receptors.
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Affiliation(s)
- Pei Tang
- Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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26
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Trudell JR, Bertaccini E. Molecular modelling of specific and non-specific anaesthetic interactions. Br J Anaesth 2002; 89:32-40. [PMID: 12173239 DOI: 10.1093/bja/aef157] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
There has been rapid progress in molecular modelling in recent years. The convergence of improved software for molecular mechanics and dynamics, techniques for chimeric substitution and site-directed mutations, and the first x-ray structures of transmembrane ion channels have made it possible to build and test models of anaesthetic binding sites. These models have served as guides for site-directed mutagenesis and as starting points for understanding the molecular dynamics of anaesthetic-site interactions. Ligand-gated ion channels are targets for inhaled anaesthetics and alcohols in the central nervous system. The inhibitory strychnine-sensitive glycine and gamma-aminobutyric acid type A receptors are positively modulated by anaesthetics and alcohols; site-directed mutagenesis techniques have identified amino acid residues important for the action of volatile anaesthetics and alcohols in these receptors. Key questions are whether these amino acid mutations form part of alcohol- or anaesthetic-binding sites or if they alter protein stability in a way that allows anaesthetic molecules to act remotely by non-specific mechanisms. It is likely that molecular modelling will play a major role in answering these questions.
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Affiliation(s)
- J R Trudell
- Department of Anaesthesia, Beckman Program for Molecular and Genetic Medicine, Stanford University, Stanford, CA 94305-5117, USA
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Koubi L, Tarek M, Bandyopadhyay S, Klein ML, Scharf D. Membrane structural perturbations caused by anesthetics and nonimmobilizers: a molecular dynamics investigation. Biophys J 2001; 81:3339-45. [PMID: 11720997 PMCID: PMC1301791 DOI: 10.1016/s0006-3495(01)75967-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The structural perturbations of the fully hydrated dimyristoyl-phosphatidylcholine bilayer induced by the presence of hexafluoroethane C(2F6), a "nonimmobilizer," have been examined by molecular dynamics simulations and compared with the effects produced by halothane CF3CHBrCl, an "anesthetic," on a similar bilayer (DPPC) (Koubi et al., Biophys. J. 2000. 78:800). We find that the overall structure of the lipid bilayer and the zwitterionic head-group dipole orientation undergo only a slight modification compared with the pure lipid bilayer, with virtually no change in the potential across the interface. This is in contrast to the anesthetic case in which the presence of the molecule led to a large perturbation of the electrostatic potential across to the membrane interface. Similarly, the analysis of the structural and dynamical properties of the lipid core are unchanged in the presence of the nonimmobilizer although there is a substantial increase in the microscopic viscosity for the system containing the anesthetic. These contrasting perturbations of the lipid membrane caused by those quite similarly sized molecules may explain the difference in their physiological effects as anesthetics and nonimmobilizers, respectively.
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Affiliation(s)
- L Koubi
- Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
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Tang P, Zubryzcki I, Xu Y. Ab Initio Calculation of structures and properties of halogenated general anesthetics: halothane and sevoflurane. J Comput Chem 2001. [DOI: 10.1002/1096-987x(200103)22:4<436::aid-jcc1014>3.0.co;2-u] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
There is a distinct possibility that general anesthetics exert their action on the postsynaptic receptor channels. The structural requirements for anesthetic binding in transmembrane channels, however, are largely unknown. High-resolution (1)H nuclear magnetic resonance and direct photoaffinity labeling were used in this study to characterize the volatile anesthetic binding sites in gramicidin A (gA) incorporated into sodium dodecyl sulfate (SDS) micelles and into dimyristoylphosphatidylcholine (DMPC) bilayers, respectively. To confirm that the structural arrangement of the peptide side chains can affect anesthetic binding, gA in nonchannel forms in methanol was also analyzed. The addition of volatile anesthetic halothane to gA in SDS with a channel conformation caused a concentration-dependent change in resonant frequencies of the indole amide protons of W9, W11, W13, and W15, with the most profound changes in W9. These frequency changes were observed only for gA carefully prepared to ensure a channel conformation and were absent for gA in methanol. For gA in DMPC bilayers, direct [(14)C]halothane photolabeling and microsequencing demonstrated dominant labeling of W9, less labeling of W11 and W13, and no significant labeling of W15. In methanol, gA showed much less labeling of any residues. Inspection of the 3-D structure of gA suggests that the spatial arrangements of the tryptophan residues in the channel form of gA, combined with the amphiphilic regions of lipid, create a favorable anesthetic binding motif.
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Affiliation(s)
- P Tang
- Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh, PA 15261, USA.
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Xu Y, Seto T, Tang P, Firestone L. NMR study of volatile anesthetic binding to nicotinic acetylcholine receptors. Biophys J 2000; 78:746-51. [PMID: 10653787 PMCID: PMC1300677 DOI: 10.1016/s0006-3495(00)76632-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
New lines of evidence suggest that volatile anesthetics interact specifically with proteins. Direct binding analysis, however, has been largely limited to soluble proteins. In this study, specific interaction was investigated between isoflurane, a clinically important volatile anesthetic, and membrane-bound nicotinic acetylcholine receptors (nAChRs) from Torpedo electroplax, using (19)F nuclear magnetic resonance spectroscopy and gas chromatography. The receptors were reconstituted into 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles. After correcting for nonspecific partitioning into the lipid, the equilibrium dissociation constant, K(d), of isoflurane binding to nAChR at 15 degrees C was found to be 0.36 +/- 0.03 mM. This value is within the clinically relevant concentration range of the agent. Based on the receptor concentrations in the vesicle suspension assayed by the bicinchoninic acid method and the fraction of bound isoflurane, X(b), determined by gas chromatography, an estimate of an average of 9-10 specifically bound isoflurane molecules can be made for each receptor, or two for each subunit. Upon binding, the transverse relaxation time constant (T(2)) of (19)F resonance of isoflurane is decreased by nearly three orders of magnitude, indicating a dramatic reduction in the mobility of specifically bound isoflurane. Kinetic analysis reveals that the off rate of binding, k(-1), is 1.7 x 10(4) s(-1). The on rate, k(+1), can thus be calculated to be approximately 4.8 x 10(7) M(-1) s(-1), suggesting a nearly diffusion-limited association. This is in contrast to anesthetic binding to a soluble protein, bovine serum albumin (BSA), where k(+1) and k(-1) are at least an order of magnitude slower. It is concluded that the presence of lipids may be critical for the correct evaluation of binding kinetics between volatile anesthetics and neuronal receptors.
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Affiliation(s)
- Y Xu
- Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh, Pennsylvania 15261, USA.
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