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Treptow W. Allosteric Modulation of Membrane Proteins by Small Low-Affinity Ligands. J Chem Inf Model 2023; 63:2047-2057. [PMID: 36933226 DOI: 10.1021/acs.jcim.2c01542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
Abstract
Membrane proteins may respond to a variety of ligands under an applied external stimulus. These ligands include small low-affinity molecules that account for functional effects in the mM range. Understanding the modulation of protein function by low-affinity ligands requires characterizing their atomic-level interactions under dilution, challenging the current resolution of theoretical and experimental routines. Part of the problem derives from the fact that small low-affinity ligands may interact with multiple sites of a membrane protein in a highly degenerate manner to a degree that it is better conceived as a partition phenomenon, hard to track at the molecular interface of the protein. Looking for new developments in the field, we rely on the classic two-state Boltzmann model to devise a novel theoretical description of the allosteric modulation mechanism of membrane proteins in the presence of small low-affinity ligands and external stimuli. Free energy stability of the partition process and its energetic influence on the protein coupling with the external stimulus are quantified. The outcome is a simple formulation that allows the description of the equilibrium shifts of the protein in terms of the grand-canonical partition function of the ligand at dilute concentrations. The model's predictions of the spatial distribution and response probability shift across a variety of ligand concentrations, and thermodynamic conjugates can be directly compared to macroscopic measurements, making it especially useful to interpret experimental data at the atomic level. Illustration and discussion of the theory is shown in the context of general anesthetics and voltage-gated channels for which structural data are available.
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Affiliation(s)
- Werner Treptow
- Laboratório de Biologia Teórica e Computacional (LBTC), Universidade de Brasília, Distrito Federal, Brasília CEP 70904-970, Brasil
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Cantor RS. Kinetic Model of Adsorption of Aqueous Solutes onto Lipid Bilayers: Modulation of the Activity of Membrane Proteins. J Phys Chem B 2023; 127:1598-1606. [PMID: 36763041 DOI: 10.1021/acs.jpcb.2c08714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
It has been argued that membrane proteins that are activated by agonist binding and whose activity depends on conformational transitions are sensitive to membrane adsorption of agonists as well as other solutes such as anesthetics. Ligand-gated ion channels such as GABAAR have been observed electrophysiologically to exhibit remarkable temporal complexity, with multiple time scales of desensitization and deactivation that depend on concentration over a very broad range. Earlier theoretical work was able to predict much of this complexity for GABAAR using a model that incorporates a simple Langmuir approximation of adsorption and desorption of neurotransmitters and solutes such as anesthetics, along with classical modeling of ligand binding and conformational transitions among the three canonical protein states. Here, a simple kinetic model is developed that improves on the Langmuir approach by incorporating the energetics of adsorbate-adsorbate (and adsorbate-bilayer) interactions. Predicted equilibrium isotherms are compared to experimental results, along with the time-course of adsorption/desorption, over a range of values of energetic parameters. Initial predictions of effects of adsorbate energetics on ion current traces involving long and short pulses of agonists show remarkably large effects on the time scale(s) of desensitization and deactivation.
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Affiliation(s)
- Robert S Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
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Robertson J, Jeffs A, Hedges C, Hickey AJR. Cardiac mitochondrial energetics of the Australasian red spiny lobster, Jasus edwardsii, when exposed to isoeugenol within the commercial anaesthetic AQUI-S. J Exp Biol 2022; 225:275578. [PMID: 35647661 DOI: 10.1242/jeb.242771] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 05/24/2022] [Indexed: 11/20/2022]
Abstract
The anaesthetic isoeugenol has been used as metabolic suppressant for commercial transport of live lobsters in order to decrease energy expenditure aand improve survival. Given the central role of mitochondria in metabolism and structural similarities of isoeugenol to the mitochondrial electron carrier coenzyme Q, we explored the influence on mitochondrial function of isoeugenol. Mitochondrial function was measured using high resolution respirometry and saponin permeabilized heart fibres from the Australasian red spiny lobster, Jasus edwardsii. Relative to vehicle (polysorbate), isoeugenol inhibited respiration supported by complex I (CI) and cytochrome c oxidase (CCO). While complex II (CII), which also reduces coenzyme Q was largely unaffected by isoeugenol, respiration supported by CII when uncoupled was depressed. Titration of isoeugenol indicates that respiration through CI has a half inhibition constant (IC50) of 2.4±0.1 µM, and full inhibition constant IC100 of approximately 6.3 µM. These concentrations are consistent with those used for transport and euthanasia of J. edwardsii and indicates that CI is a possible target of isoeugenol like many other anaesthetics with quinone-like structures.
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Affiliation(s)
- James Robertson
- School of Biological Sciences, The University of Auckland, Auckland 1142, New Zealand
| | - Andrew Jeffs
- School of Biological Sciences, The University of Auckland, Auckland 1142, New Zealand
| | - Christopher Hedges
- School of Biological Sciences, The University of Auckland, Auckland 1142, New Zealand
| | - Anthony J R Hickey
- School of Biological Sciences, The University of Auckland, Auckland 1142, New Zealand
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Goodfellow M, Andrzejak RG, Masoller C, Lehnertz K. What Models and Tools can Contribute to a Better Understanding of Brain Activity? FRONTIERS IN NETWORK PHYSIOLOGY 2022; 2:907995. [PMID: 36926061 PMCID: PMC10013030 DOI: 10.3389/fnetp.2022.907995] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Accepted: 06/06/2022] [Indexed: 12/18/2022]
Abstract
Despite impressive scientific advances in understanding the structure and function of the human brain, big challenges remain. A deep understanding of healthy and aberrant brain activity at a wide range of temporal and spatial scales is needed. Here we discuss, from an interdisciplinary network perspective, the advancements in physical and mathematical modeling as well as in data analysis techniques that, in our opinion, have potential to further advance our understanding of brain structure and function.
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Affiliation(s)
- Marc Goodfellow
- Living Systems Institute, University of Exeter, Exeter, United Kingdom
| | - Ralph G Andrzejak
- Department of Information and Communication Technologies, University Pompeu Fabra, Barcelona, Spain
| | - Cristina Masoller
- Department of Physics, Universitat Politecnica de Catalunya, Barcelona, Spain
| | - Klaus Lehnertz
- Department of Epileptology, University of Bonn Medical Centre, Bonn, Germany.,Helmholtz Institute for Radiation and Nuclear Physics, University of Bonn, Bonn, Germany.,Interdisciplinary Center for Complex Systems, University of Bonn, Bonn, Germany
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A Metabolic Mechanism for Anaesthetic Suppression of Cortical Synaptic Function in Mouse Brain Slices-A Pilot Investigation. Int J Mol Sci 2020; 21:ijms21134703. [PMID: 32630300 PMCID: PMC7370287 DOI: 10.3390/ijms21134703] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 06/24/2020] [Accepted: 06/29/2020] [Indexed: 02/07/2023] Open
Abstract
Regulation of synaptically located ionotropic receptors is thought to be the main mechanism by which anaesthetics cause unconsciousness. An alternative explanation, which has received much less attention, is that of primary anaesthetic disruption of brain metabolism via suppression of mitochondrial proteins. In this pilot study in mouse cortical slices, we investigated the effect of disrupting cellular metabolism on tissue oxygen handling and cortical population seizure-like event (SLE) activity, using the mitochondrial complex I inhibitor rotenone, and compared this to the effects of the general anaesthetics sevoflurane, propofol and ketamine. Rotenone caused an increase in tissue oxygen (98 mmHg to 157 mmHg (p < 0.01)) before any measurable change in SLE activity. Thereafter, tissue oxygen continued to increase and was accompanied by a significant and prolonged reduction in SLE root mean square (RMS) activity (baseline RMS of 1.7 to 0.7 µV, p < 0.001) and SLE frequency (baseline 4.2 to 0.4 events/min, p = 0.001). This temporal sequence of effects was replicated by all three anaesthetic drugs. In conclusion, anaesthetics with differing synaptic receptor mechanisms all effect changes in tissue oxygen handling and cortical network activity, consistent with a common inhibitory effect on mitochondrial function. The temporal sequence suggests that the observed synaptic depression—as seen in anaesthesia—may be secondary to a reduction in cellular metabolic capacity.
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Josey BP, Heinrich F, Silin V, Lösche M. Association of Model Neurotransmitters with Lipid Bilayer Membranes. Biophys J 2020; 118:1044-1057. [PMID: 32032504 DOI: 10.1016/j.bpj.2020.01.016] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 01/08/2020] [Accepted: 01/15/2020] [Indexed: 11/15/2022] Open
Abstract
Aimed at reproducing the results of electrophysiological studies of synaptic signal transduction, conventional models of neurotransmission are based on the specific binding of neurotransmitters to ligand-gated receptor ion channels. However, the complex kinetic behavior observed in synaptic transmission cannot be reproduced in a standard kinetic model without the ad hoc postulation of additional conformational channel states. On the other hand, if one invokes unspecific neurotransmitter adsorption to the bilayer-a process not considered in the established models-the electrophysiological data can be rationalized with only the standard set of three conformational receptor states that also depend on this indirect coupling of neurotransmitters via their membrane interaction. Experimental verification has been difficult because binding affinities of neurotransmitters to the lipid bilayer are low. We quantify this interaction with surface plasmon resonance to measure equilibrium dissociation constants in neurotransmitter membrane association. Neutron reflection measurements on artificial membranes, so-called sparsely tethered bilayer lipid membranes, reveal the structural aspects of neurotransmitters' association with zwitterionic and anionic bilayers. We thus establish that serotonin interacts nonspecifically with the membrane at physiologically relevant concentrations, whereas γ-aminobutyric acid does not. Surface plasmon resonance shows that serotonin adsorbs with millimolar affinity, and neutron reflectometry shows that it penetrates the membrane deeply, whereas γ-aminobutyric is excluded from the bilayer.
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Affiliation(s)
- Brian P Josey
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania
| | - Frank Heinrich
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania; National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland
| | - Vitalii Silin
- Institute for Bioscience and Biotechnology Research, Rockville, Maryland
| | - Mathias Lösche
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania; National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland; Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania.
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Understanding Anesthetic Mechanisms: Analysis of the Complex Kinetics of Ligand-Gated Ion Channels. Methods Enzymol 2018. [PMID: 29588043 DOI: 10.1016/bs.mie.2018.02.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Anesthetics modulate the response of ligand-gated ion channels to their neurotransmitter agonists, in a way that is consistent with clinical anesthesia: inhibition of synaptic transmission, by activation of inhibitory receptors and/or inhibition of excitatory receptors. Electrophysiological results for receptors such as GABAAR indicate that this modulation can be remarkably kinetically complex, characterized by concentration-dependent changes in the extent and (multiple) time scales of desensitization and deactivation. The full range of these features cannot be reproduced by a kinetic model in which anesthetic acts only by binding to putative protein sites, without having multiple sites with varying affinities, as well as many additional conformational states beyond the canonical set of three (resting, open, and desensitized). So, we discuss the implementation of a kinetic approach that incorporates only these three states, but accounts for effects of adsorption of anesthetic and agonist to the membrane in which the receptor is embedded, which modulates the conformational free energy landscape of the protein. As a result, the rate constants of conformational transitions become time dependent (non-Markovian), requiring nonstandard methods of kinetic analysis that can readily be implemented using available computational software.
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Cantor RS. Path to the Desensitized State of Ligand-Gated Ion Channels: Why Are Inhibitory and Excitatory Receptors Different? J Phys Chem B 2018; 122:5368-5374. [DOI: 10.1021/acs.jpcb.7b10961] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Robert S. Cantor
- Dept. of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States
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A combined X-ray scattering and simulation study of halothane in membranes at raised pressures. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2016.12.041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Wieteska J, Welche P, Tu KM, ElGamacy M, Csanyi G, Payne M, Chau PL. Isoflurane does not aggregate inside POPC bilayers at high pressure: Implications for pressure reversal of general anaesthesia. Chem Phys Lett 2015. [DOI: 10.1016/j.cplett.2015.07.065] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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Cantor RS. The evolutionary origin of the need to sleep: an inevitable consequence of synaptic neurotransmission? Front Synaptic Neurosci 2015; 7:15. [PMID: 26441631 PMCID: PMC4585021 DOI: 10.3389/fnsyn.2015.00015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 09/03/2015] [Indexed: 11/13/2022] Open
Abstract
It is proposed that the evolutionary origin of the need to sleep is the removal of neurotransmitters (NTs) that escape reuptake and accumulate in brain interstitial fluid (ISF). Recent work suggests that the activity of ionotropic postsynaptic receptors, rapidly initiated by binding of NTs to extracellular sites, is modulated over longer times by adsorption of these NTs to the lipid bilayers in which the receptors are embedded. This bilayer-mediated mechanism is far less molecularly specific than binding, so bilayer adsorption of NTs that have diffused into synapses for other receptors would modulate their activity as well. Although NTs are recycled by membrane protein reuptake, the process is less than 100% efficient; a fraction escapes the region in which these specific reuptake proteins are localized and eventually diffuses throughout the ISF. It is estimated that even if only 0.1% of NTs escape reuptake, they would accumulate and adsorb to bilayers in synapses of other receptors sufficiently to affect receptor activity, the harmful consequences of which are avoided by sleep: a period of efficient convective clearance of solutes together with greatly reduced synaptic activity.
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Affiliation(s)
- Robert S Cantor
- Burke Laboratory, Department of Chemistry, Dartmouth College Hanover, NH, USA ; Memphys Center for Biomembrane Physics, University of Southern Denmark Odense, Denmark
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