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Wazawa T, Nagai T. Joule heating involving ion currents through channel proteins. Biophys Physicobiol 2023; 20:e200030. [PMID: 38124793 PMCID: PMC10728626 DOI: 10.2142/biophysico.bppb-v20.0030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Accepted: 06/26/2023] [Indexed: 12/23/2023] Open
Abstract
Ion currents associated with channel proteins in the presence of membrane potential are ubiquitous in cellular and organelle membranes. When an ion current occurs through a channel protein, Joule heating should occur. However, this Joule heating seems to have been largely overlooked in biology. Here we show theoretical investigation of Joule heating involving channel proteins in biological processes. We used electrochemical potential to derive the Joule's law for an ion current through an ion transport protein in the presence of membrane potential, and we suggest that heat production and absorption can occur. Simulation of temperature distribution around a single channel protein with the Joule heating revealed that the temperature increase was as small as <10-3 K, although an ensemble of channel proteins was suggested to exhibit a noticeable temperature increase. Thereby, we theoretically investigated the Joule heating of systems containing ensembles of channel proteins. Nerve is known to undergo rapid heat production followed by heat absorption during the action potential, and our simulation of Joule heating for a squid giant axon combined with the Hodgkin-Huxley model successfully reproduced the feature of the heat. Furthermore, we extended the theory of Joule heating to uncoupling protein 1 (UCP1), a solute carrier family transporter, which is important to the non-shivering thermogenesis in brown adipose tissue mitochondria (BATM). Our calculations showed that the Joule heat involving UCP1 was comparable to the literature calorimetry data of BATM. Joule heating of ion transport proteins is likely to be one of important mechanisms of cellular thermogenesis.
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Affiliation(s)
| | - Takeharu Nagai
- SANKEN, Osaka University, Ibaraki, Osaka 567-0047, Japan
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2
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Wei C, Pohorille A. Multi-oligomeric states of alamethicin ion channel: Assemblies and conductance. Biophys J 2023; 122:2531-2543. [PMID: 37161094 PMCID: PMC10323028 DOI: 10.1016/j.bpj.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 04/03/2023] [Accepted: 05/04/2023] [Indexed: 05/11/2023] Open
Abstract
Transmembrane assemblies of the peptaibol alamethicin (ALM) are among the most extensively studied ion channels not only because of their antimicrobial activity but also as models for channel structure and aggregation. In this study, several oligomeric states of ALM are investigated with molecular dynamics simulations to establish properties of the channel and obtain free energy profiles for ion transport and the corresponding values of conductance. The hexamer, heptamer, and octamer of ALM in phospholipid membrane are found to be stable but highly dynamic in barrel-stave structures, with calculated conductance equal to 18, 195, and 1270 pS, respectively, in 1 M KCl ion solution. The corresponding free energy profiles, reported for the first time, are reconstructed from simulations at applied voltage of 200 mV with the aid of the electrodiffusion model both with and without the knowledge of diffusivity. The calculated free energy barriers are equal to 2.5, 1.5, and 0.5 kcal/mol for K+ and 4.0, 2.2, and 1.5 kcal/mol for Cl-, for hexamer, heptamer, and octamer, respectively. The calculated conductance and the ratio between conductance in consecutive states are in good agreement with those measured experimentally. This suggests that the hexamer is the lowest conducting state, with measured conductance equal to 19 pS. The selectivity of K+ over Cl- is calculated as 1.5 and 2.3 for the octameric and heptameric channels, close to the selectivity measured for high-conductance states. Selectivity increases to 13 in the hexameric channel in which the narrowest Gln7 site has a pore radius of only ∼1.6 Å, again in accord with experiment. A good agreement found between calculated and measured conductance through a hexamer templated on cyclodextrin lands additional support for the results of our simulations, and the comparison with ALM reveals the dependence of conductance on the nature of phospholipid membrane.
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Affiliation(s)
- Chenyu Wei
- NASA Ames Research Center, Moffett Field, California; SETI Institute, Mountain View, California.
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3
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Wilson MA, Pohorille A. Structure and Computational Electrophysiology of Ac-LS3, a Synthetic Ion Channel. J Phys Chem B 2022; 126:8985-8999. [PMID: 36306164 DOI: 10.1021/acs.jpcb.2c05965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Computer simulations are reported on Ac-LS3, a synthetic ion channel, containing 21 residues with a Leu-Ser-Ser-Leu-Leu-Ser-Leu heptad repeat, which forms ions channels upon application of voltage. A hexameric, coiled-coil bundle initially positioned perpendicular to the membrane settled into a stable, tilted structure after 1.5 μs, most likely to improve contacts between the non-polar exterior of the channel and the hydrophobic core of the membrane. Once tilted, the bundle remained in this state during subsequent simulations of nearly 10 μs at voltages ranging from 200 to -100 mV. In contrast, attempts to identify a stable pentameric structure failed, thus supporting the hypothesis that the channel is a hexamer. Results at 100 mV were used to reconstruct the free energy profiles for K+ and Cl- in the channel. This was done by way of several methods in which results of molecular dynamics (MD) simulations were combined with the electrodiffusion model. Two of them developed recently do not require knowledge of the diffusivity. Instead, they utilize one-sided density profiles and committor probabilities. The consistency between different methods is very good, supporting the utility of the newly developed methods for reconstructing free energies of ions in channels. The flux of K+, which accounts for most of the current through the channel, calculated directly from MD matches well the total measured current. However, the current of Cl- is somewhat overestimated, possibly due to a slightly unbalanced force field involving chloride. The current-voltage dependence was also reconstructed by way of a recently developed, efficient method that requires simulations only at a single voltage, yielding good agreement with the experiment. Taken together, the results demonstrate that computational electrophysiology has become a reliable tool for studying how channels mediate ion transport through membranes.
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Affiliation(s)
- Michael A Wilson
- Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California94035, United States.,SETI Institute, 189 Bernardo Avenue, Suite 200, Mountain View, California94043, United States
| | - Andrew Pohorille
- Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California94033, United States.,Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California94132, United States
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Wilson MA, Pohorille A. Electrophysiological Properties from Computations at a Single Voltage: Testing Theory with Stochastic Simulations. ENTROPY 2021; 23:e23050571. [PMID: 34066581 PMCID: PMC8148522 DOI: 10.3390/e23050571] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 04/24/2021] [Accepted: 04/28/2021] [Indexed: 12/13/2022]
Abstract
We use stochastic simulations to investigate the performance of two recently developed methods for calculating the free energy profiles of ion channels and their electrophysiological properties, such as current–voltage dependence and reversal potential, from molecular dynamics simulations at a single applied voltage. These methods require neither knowledge of the diffusivity nor simulations at multiple voltages, which greatly reduces the computational effort required to probe the electrophysiological properties of ion channels. They can be used to determine the free energy profiles from either forward or backward one-sided properties of ions in the channel, such as ion fluxes, density profiles, committor probabilities, or from their two-sided combination. By generating large sets of stochastic trajectories, which are individually designed to mimic the molecular dynamics crossing statistics of models of channels of trichotoxin, p7 from hepatitis C and a bacterial homolog of the pentameric ligand-gated ion channel, GLIC, we find that the free energy profiles obtained from stochastic simulations corresponding to molecular dynamics simulations of even a modest length are burdened with statistical errors of only 0.3 kcal/mol. Even with many crossing events, applying two-sided formulas substantially reduces statistical errors compared to one-sided formulas. With a properly chosen reference voltage, the current–voltage curves can be reproduced with good accuracy from simulations at a single voltage in a range extending for over 200 mV. If possible, the reference voltages should be chosen not simply to drive a large current in one direction, but to observe crossing events in both directions.
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Affiliation(s)
- Michael A. Wilson
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, CA 94035, USA;
- SETI Institute, 189 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
| | - Andrew Pohorille
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, CA 94035, USA;
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94132, USA
- Correspondence: ; Tel.: +1-650-604-5759
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Pohorille A, Wilson MA. Computational Electrophysiology from a Single Molecular Dynamics Simulation and the Electrodiffusion Model. J Phys Chem B 2021; 125:3132-3144. [DOI: 10.1021/acs.jpcb.0c10737] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andrew Pohorille
- Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California 94035, United States
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94132, United States
| | - Michael A. Wilson
- Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California 94035, United States
- SETI Institute, 189 Bernardo Avenue, Suite 200, Mountain View, California 94043, United States
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6
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Freire MJ, Bernal-Méndez J, Pérez AT. The Lorentz force on ions in membrane channels of neurons as a mechanism for transcranial static magnetic stimulation. Electromagn Biol Med 2020; 39:310-315. [PMID: 32666841 DOI: 10.1080/15368378.2020.1793172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Transcranial static magnetic stimulation is a novel noninvasive method of reduction of the cortical excitability in certain neurological diseases that makes use of static magnetic fields generated by permanent magnets. By contrast, ordinary transcranial magnetic stimulation makes use of pulsed magnetic fields generated by strong currents. Whereas the physical principle underlying ordinary transcranial magnetic stimulation is well known, that is, the Faraday´s law, the physical mechanism that explains the interaction between neurons and static magnetic fields in transcranial static magnetic stimulation remains unclear. In the present work, it is discussed the possibility that this mechanism might be the Lorentz force exerted on the ions flowing along the membrane channels of neurons. The overall effect of the static magnetic field would be to introduce an additional friction between the ions and the walls of the membrane channels, thus reducing its conductance. Calculations performed by using a Hodgkin-Huxley model demonstrate that even a slight reduction of the conductance of the membrane channels can lead to the suppression of the action potential, thus inhibiting neuronal activity.
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Affiliation(s)
- Manuel J Freire
- Department of Electronics and Electromagnetism, Universidad de Sevilla , Seville, Spain
| | | | - Alberto T Pérez
- Department of Electronics and Electromagnetism, Universidad de Sevilla , Seville, Spain
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Chaudhari MI, Vanegas JM, Pratt LR, Muralidharan A, Rempe SB. Hydration Mimicry by Membrane Ion Channels. Annu Rev Phys Chem 2020; 71:461-484. [PMID: 32155383 DOI: 10.1146/annurev-physchem-012320-015457] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Ions transiting biomembranes might pass readily from water through ion-specific membrane proteins if these protein channels provide environments similar to the aqueous solution hydration environment. Indeed, bulk aqueous solution is an important reference condition for the ion permeation process. Assessment of this hydration mimicry concept depends on understanding the hydration structure and free energies of metal ions in water in order to provide a comparison for the membrane channel environment. To refine these considerations, we review local hydration structures of ions in bulk water and the molecular quasi-chemical theory that provides hydration free energies. In doing so, we note some current views of ion binding to membrane channels and suggest new physical chemical calculations and experiments that might further clarify the hydration mimicry concept.
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Affiliation(s)
- Mangesh I Chaudhari
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA;
| | - Juan M Vanegas
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA; .,Current affiliation: Department of Physics, University of Vermont, Burlington, Vermont 05405, USA
| | - L R Pratt
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA
| | - Ajay Muralidharan
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, USA.,Current affiliation: Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Susan B Rempe
- Department of Computational Biology and Biophysics, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA;
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8
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Marik T, Tyagi C, Balázs D, Urbán P, Szepesi Á, Bakacsy L, Endre G, Rakk D, Szekeres A, Andersson MA, Salonen H, Druzhinina IS, Vágvölgyi C, Kredics L. Structural Diversity and Bioactivities of Peptaibol Compounds From the Longibrachiatum Clade of the Filamentous Fungal Genus Trichoderma. Front Microbiol 2019; 10:1434. [PMID: 31293557 PMCID: PMC6606783 DOI: 10.3389/fmicb.2019.01434] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 06/06/2019] [Indexed: 01/18/2023] Open
Abstract
This study examined the structural diversity and bioactivity of peptaibol compounds produced by species from the phylogenetically separated Longibrachiatum Clade of the filamentous fungal genus Trichoderma, which contains several biotechnologically, agriculturally and clinically important species. HPLC-ESI-MS investigations of crude extracts from 17 species of the Longibrachiatum Clade (T. aethiopicum, T. andinense, T. capillare, T. citrinoviride, T. effusum, T. flagellatum, T. ghanense, T. konilangbra, T. longibrachiatum, T. novae-zelandiae, T. pinnatum, T. parareesei, T. pseudokoningii, T. reesei, T. saturnisporum, T. sinensis, and T. orientale) revealed several new and recurrent 20-residue peptaibols related to trichobrachins, paracelsins, suzukacillins, saturnisporins, trichoaureocins, trichocellins, longibrachins, hyporientalins, trichokonins, trilongins, metanicins, trichosporins, gliodeliquescins, alamethicins and hypophellins, as well as eight 19-residue sequences from a new subfamily of peptaibols named brevicelsins. Non-ribosomal peptide synthetase genes were mined from the available genome sequences of the Longibrachiatum Clade. Their annotation and product prediction were performed in silico and revealed full agreement in 11 out of 20 positions regarding the amino acids predicted based on the signature sequences and the detected amino acids incorporated. Molecular dynamics simulations were performed for structural characterization of four selected peptaibol sequences: paracelsins B, H and their 19-residue counterparts brevicelsins I and IV. Loss of position R6 in brevicelsins resulted in smaller helical structures with higher atomic fluctuation for every residue than the structures formed by paracelsins. We observed the formation of highly bent, almost hairpin-like, helical structures throughout the trajectory, along with linear conformation. Bioactivity tests were performed on the purified peptaibol extract of T. reesei on clinically and phytopathologically important filamentous fungi, mammalian cells, and Arabidopsis thaliana seedlings. Porcine kidney cells and boar spermatozoa proved to be sensitive to the purified peptaibol extract. Peptaibol concentrations ≥0.3 mg ml-1 deterred the growth of A. thaliana. However, negative effects to plants were not detected at concentrations below 0.1 mg ml-1, which could still inhibit plant pathogenic filamentous fungi, suggesting that those peptaibols reported here may have applications for plant protection.
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Affiliation(s)
- Tamás Marik
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Chetna Tyagi
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Dóra Balázs
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Péter Urbán
- Department of General and Environmental Microbiology, Faculty of Sciences, and Szentágothai Research Center, University of Pécs, Pécs, Hungary
| | - Ágnes Szepesi
- Department of Plant Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - László Bakacsy
- Department of Plant Biology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Gábor Endre
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Dávid Rakk
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - András Szekeres
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | | | - Heidi Salonen
- Department of Civil Engineering, Aalto University, Espoo, Finland
| | - Irina S. Druzhinina
- Research Area Biochemical Technology, Institute of Chemical, Environmental and Bioscience Engineering, TU Wien, Vienna, Austria
- Jiangsu Provincial Key Laboratory of Organic Solid Waste Utilization, Nanjing Agricultural University, Nanjing, China
| | - Csaba Vágvölgyi
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - László Kredics
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
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Fragiadaki I, Katogiritis A, Calogeropoulou T, Brückner H, Scoulica E. Synergistic combination of alkylphosphocholines with peptaibols in targeting Leishmania infantum in vitro. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2018; 8:194-202. [PMID: 29631127 PMCID: PMC6039304 DOI: 10.1016/j.ijpddr.2018.03.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 02/20/2018] [Accepted: 03/19/2018] [Indexed: 12/11/2022]
Abstract
Anti-leishmanial treatment increasingly encounters therapeutic limitations due to drug toxicity and development of resistance. The effort for new therapeutic strategies led us to work on combinations of chemically different compounds that could yield enhanced leishmanicidal effect. Peptaibols are a special type of antimicrobial peptides that are able to form ion channels in cell membranes and potentially affect cell viability. We assayed the antileishmanial activity of two well studied helical peptaibols, the 16-residue antiamoebin and the 20-residue alamethicin-analogue suzukacillin, and we evaluated the biological effect of their combination with the alkylphosphocholine miltefosine and its synthetic analogue TC52. The peptaibols tested exhibited only moderate antileishmanial activity, however their combination with miltefosine had a super-additive effect against the intracellular parasite (combination index 0.83 and 0.43 for antiamoebin and suzukacillin respectively). Drug combinations altered the redox stage of promastigotes, rapidly dissipated mitochondrial membrane potential and induced concatenation of mitochondrial network promoting spheroidal morphology. These results evidenced a potent and specific antileishmanial effect of the peptaibols/miltefosine combinations, achieved with significantly lower concentrations of the compounds compared to monotherapy. Furthermore, they revealed the importance of exploring novel classes of bioactive compounds such as peptaibols and demonstrated for the first time that they can act in synergy with currently used antileishmanial drugs to improve the therapeutic outcome.
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Affiliation(s)
- Irene Fragiadaki
- University of Crete, Department of Clinical Microbiology and Microbial Pathogenesis, Faculty of Medicine, P.O. Box 2208, Heraklion, Greece
| | - Anna Katogiritis
- University of Crete, Department of Clinical Microbiology and Microbial Pathogenesis, Faculty of Medicine, P.O. Box 2208, Heraklion, Greece
| | - Theodora Calogeropoulou
- National Hellenic Research Foundation, Institute of Biology Medicinal Chemistry and Biotechnology, 48 Vassileos Constantinou Ave., 116 35, Athens, Greece
| | - Hans Brückner
- Institute of Nutritional Sciences, Interdisciplinary Research Center (IFZ), University of Giessen, 35390, Giessen, Germany
| | - Effie Scoulica
- University of Crete, Department of Clinical Microbiology and Microbial Pathogenesis, Faculty of Medicine, P.O. Box 2208, Heraklion, Greece.
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Sidky H, Colón YJ, Helfferich J, Sikora BJ, Bezik C, Chu W, Giberti F, Guo AZ, Jiang X, Lequieu J, Li J, Moller J, Quevillon MJ, Rahimi M, Ramezani-Dakhel H, Rathee VS, Reid DR, Sevgen E, Thapar V, Webb MA, Whitmer JK, de Pablo JJ. SSAGES: Software Suite for Advanced General Ensemble Simulations. J Chem Phys 2018; 148:044104. [DOI: 10.1063/1.5008853] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Affiliation(s)
- Hythem Sidky
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Yamil J. Colón
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Institute for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Julian Helfferich
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Steinbuch Center for Computing, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Benjamin J. Sikora
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Cody Bezik
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Weiwei Chu
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Federico Giberti
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Ashley Z. Guo
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Xikai Jiang
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Joshua Lequieu
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Jiyuan Li
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Joshua Moller
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Michael J. Quevillon
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Mohammad Rahimi
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Hadi Ramezani-Dakhel
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA
| | - Vikramjit S. Rathee
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Daniel R. Reid
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Emre Sevgen
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Vikram Thapar
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
| | - Michael A. Webb
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Institute for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Jonathan K. Whitmer
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Juan J. de Pablo
- Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA
- Institute for Molecular Engineering and Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
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11
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Castro TG, Micaêlo NM, Melle-Franco M. Modeling the secondary structures of the peptaibols antiamoebin I and zervamicin II modified with D-amino acids and proline analogues. J Mol Model 2017; 23:313. [DOI: 10.1007/s00894-017-3479-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 09/19/2017] [Indexed: 11/29/2022]
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12
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Pohorille A, Wilson MA, Shannon G. Flexible Proteins at the Origin of Life. Life (Basel) 2017; 7:E23. [PMID: 28587235 PMCID: PMC5492145 DOI: 10.3390/life7020023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Revised: 05/10/2017] [Accepted: 05/24/2017] [Indexed: 11/17/2022] Open
Abstract
Almost all modern proteins possess well-defined, relatively rigid scaffolds that provide structural preorganization for desired functions. Such scaffolds require the sufficient length of a polypeptide chain and extensive evolutionary optimization. How ancestral proteins attained functionality, even though they were most likely markedly smaller than their contemporary descendants, remains a major, unresolved question in the origin of life. On the basis of evidence from experiments and computer simulations, we argue that at least some of the earliest water-soluble and membrane proteins were markedly more flexible than their modern counterparts. As an example, we consider a small, evolved in vitro ligase, based on a novel architecture that may be the archetype of primordial enzymes. The protein does not contain a hydrophobic core or conventional elements of the secondary structure characteristic of modern water-soluble proteins, but instead is built of a flexible, catalytic loop supported by a small hydrophilic core containing zinc atoms. It appears that disorder in the polypeptide chain imparts robustness to mutations in the protein core. Simple ion channels, likely the earliest membrane protein assemblies, could also be quite flexible, but still retain their functionality, again in contrast to their modern descendants. This is demonstrated in the example of antiamoebin, which can serve as a useful model of small peptides forming ancestral ion channels. Common features of the earliest, functional protein architectures discussed here include not only their flexibility, but also a low level of evolutionary optimization and heterogeneity in amino acid composition and, possibly, the type of peptide bonds in the protein backbone.
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Affiliation(s)
- Andrew Pohorille
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, CA 94035, USA.
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94132, USA.
| | - Michael A Wilson
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, CA 94035, USA.
- SETI Institute, 189 N Bernardo Ave #200, Mountain View, CA 94043, USA.
| | - Gareth Shannon
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, CA 94035, USA.
- NASA Postdoctoral Program Fellow, NASA Ames Research Center, Moffett Field, CA 94035, USA.
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Pohorille A, Wilson MA, Wei C. Validity of the Electrodiffusion Model for Calculating Conductance of Simple Ion Channels. J Phys Chem B 2016; 121:3607-3619. [PMID: 27936743 DOI: 10.1021/acs.jpcb.6b09598] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
We examine the validity and utility of the electrodiffusion (ED) equation, i.e., the generalized Nernst-Planck equation, to characterize, in combination with molecular dynamics, the electrophysiological behavior of simple ion channels. As models, we consider three systems-two naturally occurring channels formed by α-helical bundles of peptaibols, trichotoxin, and alamethicin, and a synthetic, hexameric channel, formed by a peptide that contains only leucine and serine. All these channels mediate transport of potassium and chloride ions. Starting with equilibrium properties, such as the potential of mean force experienced by an ion traversing the channel and diffusivity, obtained from molecular dynamics simulations, the ED equation can be used to determine the full current-voltage dependence with modest or no additional effort. The potential of mean force can be obtained not only from equilibrium simulations, but also, with comparable accuracy, from nonequilibrium simulations at a single voltage. The main assumptions underlying the ED equation appear to hold well for the channels and voltages studied here. To expand the utility of the ED equation, we examine what are the necessary and sufficient conditions for Ohmic and nonrectifying behavior and relate deviations from this behavior to the shape of the ionic potential of mean force.
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Affiliation(s)
- Andrew Pohorille
- Exobiology Branch, MS 239-4, NASA Ames Research Center , Moffett Field, California 94035, United States.,Department of Pharmaceutical Chemistry University of California , San Francisco, California 94132, United States
| | - Michael A Wilson
- Exobiology Branch, MS 239-4, NASA Ames Research Center , Moffett Field, California 94035, United States.,SETI Institute , 189 N Bernardo Ave #200, Mountain View, California 94043, United States
| | - Chenyu Wei
- Exobiology Branch, MS 239-4, NASA Ames Research Center , Moffett Field, California 94035, United States.,Department of Pharmaceutical Chemistry University of California , San Francisco, California 94132, United States
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14
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Naranjo D, Moldenhauer H, Pincuntureo M, Díaz-Franulic I. Pore size matters for potassium channel conductance. J Gen Physiol 2016; 148:277-91. [PMID: 27619418 PMCID: PMC5037345 DOI: 10.1085/jgp.201611625] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/10/2016] [Indexed: 01/31/2023] Open
Abstract
Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K+ channels discriminate K+ over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K+ channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K+ channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K+ channels, accounting for their diversity in unitary conductance.
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Affiliation(s)
- David Naranjo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Hans Moldenhauer
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile
| | - Matías Pincuntureo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Programa de Doctorado en Ciencias, mención Biofísica y Biología Computacional, Universidad de Valparaíso, Valparaíso 2360103, Chile
| | - Ignacio Díaz-Franulic
- Centro Interdisciplinario de Neurociencia de Valparaíso, Universidad de Valparaíso, Playa Ancha, Valparaíso 2360103, Chile Center for Bioinformatics and Integrative Biology, Universidad Andrés Bello, Santiago 8370146, Chile Fraunhofer Chile Research, Las Condes 7550296, Chile
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15
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Non-Enveloped Virus Entry: Structural Determinants and Mechanism of Functioning of a Viral Lytic Peptide. J Mol Biol 2016; 428:3540-56. [DOI: 10.1016/j.jmb.2016.06.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 06/08/2016] [Accepted: 06/08/2016] [Indexed: 11/20/2022]
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16
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Pothula KR, Solano CJF, Kleinekathöfer U. Simulations of outer membrane channels and their permeability. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1858:1760-71. [PMID: 26721326 DOI: 10.1016/j.bbamem.2015.12.020] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 12/15/2015] [Accepted: 12/17/2015] [Indexed: 12/25/2022]
Abstract
Channels in the outer membrane of Gram-negative bacteria provide essential pathways for the controlled and unidirectional transport of ions, nutrients and metabolites into the cell. At the same time the outer membrane serves as a physical barrier for the penetration of noxious substances such as antibiotics into the bacteria. Most antibiotics have to pass through these membrane channels to either reach cytoplasmic bound targets or to further cross the hydrophobic inner membrane. Considering the pharmaceutical significance of antibiotics, understanding the functional role and mechanism of these channels is of fundamental importance in developing strategies to design new drugs with enhanced permeation abilities. Due to the biological complexity of membrane channels and experimental limitations, computer simulations have proven to be a powerful tool to investigate the structure, dynamics and interactions of membrane channels. Considerable progress has been made in computer simulations of membrane channels during the last decade. The goal of this review is to provide an overview of the computational techniques and their roles in modeling the transport across outer membrane channels. A special emphasis is put on all-atom molecular dynamics simulations employed to better understand the transport of molecules. Moreover, recent molecular simulations of ion, substrate and antibiotics translocation through membrane pores are briefly summarized. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.
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Affiliation(s)
- Karunakar R Pothula
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
| | - Carlos J F Solano
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
| | - Ulrich Kleinekathöfer
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
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17
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Comer J, Schulten K, Chipot C. Calculation of Lipid-Bilayer Permeabilities Using an Average Force. J Chem Theory Comput 2015; 10:554-64. [PMID: 26580032 DOI: 10.1021/ct400925s] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Calculations of lipid bilayer permeabilities from first principles, using molecular simulations, would be valuable to rapidly assess the bioavailability of drug candidates, as well as to decipher, at the atomic level, the mechanisms that underlie the translocation of permeants. The most common theoretical approach, the solubility-diffusion model, requires determination of the free energy and the diffusivity as functions of the position of the permeant. Quantitative predictions of permeability have, however, been stymied by acute difficulties in calculating the diffusivity, inadequate sampling, and, most insidiously, systematic biases due to imperfections in the force field, simulation parameters, and the inherent limitations of the diffusive model. In the present work, we combine importance-sampling simulations employing an adaptive biasing force with a Bayesian-inference algorithm to determine the free energy and diffusivity with noteworthy precision and spatial resolution. In multimicrosecond simulations, we probe the sensitivity of the permeability estimates to different aspects of the methodology, including the truncation of short-range interactions, the thermostat, the force-field parameters of the permeant, the time scale over which the diffusivity is estimated, and the size of the simulated system. The force-field parameters and time scale dependence of the diffusivities impose the greatest uncertainties on the permeability estimates. Our simulations highlight the importance of membrane distortion due to the presence of the permeant, which may be partially suppressed if the bilayer patch is not large enough. We suggest that improvements to force fields and more robust kinetic models may be needed to reduce systematic errors below a factor of two.
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Affiliation(s)
- Jeffrey Comer
- Laboratoire International Associé, Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign , Unité Mixte de Recherche n°7565, Université de Lorraine , B.P. 70239 54506 Vandœuvre-lès-Nancy cedex, France
| | - Klaus Schulten
- Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801, United States.,Theoretical and Computational Biophysics Group, Beckman Institute for Advanced Science and Engineering, University of Illinois at Urbana-Champaign , 405 North Mathews, Urbana, Illinois 61801, United States
| | - Christophe Chipot
- Laboratoire International Associé, Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign , Unité Mixte de Recherche n°7565, Université de Lorraine , B.P. 70239 54506 Vandœuvre-lès-Nancy cedex, France.,Theoretical and Computational Biophysics Group, Beckman Institute for Advanced Science and Engineering, University of Illinois at Urbana-Champaign , 405 North Mathews, Urbana, Illinois 61801, United States
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18
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19
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Wilson MA, Nguyen TH, Pohorille A. Combining molecular dynamics and an electrodiffusion model to calculate ion channel conductance. J Chem Phys 2014; 141:22D519. [DOI: 10.1063/1.4900879] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Affiliation(s)
- Michael A. Wilson
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, California 94035, USA
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94132, USA
| | - Thuy Hien Nguyen
- Department of Chemistry and Biochemistry, University of the Sciences, Philadelphia, Pennsylvania 19104, USA
| | - Andrew Pohorille
- Exobiology Branch, MS 239-4, NASA Ames Research Center, Moffett Field, California 94035, USA
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94132, USA
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20
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A Wilson M, Wei C, Pohorille A. Towards co-evolution of membrane proteins and metabolism. ORIGINS LIFE EVOL B 2014; 44:357-61. [PMID: 25614291 DOI: 10.1007/s11084-014-9393-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 10/31/2014] [Indexed: 11/25/2022]
Abstract
Primordial metabolism co-evolved with the earliest membrane peptides to produce more environmentally fit progeny. Here, we map a continuous, evolutionary path that connects nascent biochemistry with simple, membrane-bound oligopeptides, ion channels and, further, membrane proteins capable of energy transduction and utilization of energy for active transport.
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Affiliation(s)
- Michael A Wilson
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, USA
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21
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Wei C, Pohorille A. Flip-flop of oleic acid in a phospholipid membrane: rate and mechanism. J Phys Chem B 2014; 118:12919-26. [PMID: 25319959 DOI: 10.1021/jp508163e] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Flip-flop of protonated oleic acid molecules dissolved at two different concentrations in membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine is studied with the aid of molecular dynamics simulations at a time scale of several microseconds. Direct, single-molecule flip-flop events are observed at this time scale, and the flip-flop rate is estimated at 0.2-0.3 μs(-1). As oleic acid molecules move toward the center of the bilayer during flip-flop, they undergo gradual, correlated translational, and rotational motion. Rare, double-flipping events of two hydrogen-bonded oleic acid molecules are also observed. A two-dimensional free energy surface is obtained for the translational and rotational degree of freedom of the oleic acid molecule, and the minimum energy path on this surface is determined. A barrier to flip-flop of ~4.2 kcal/mol is found at the center of the bilayer. A two-dimensional diffusion model is found to provide a good description of the flip-flop process. The fast flip-flop rate lends support to the proposal that fatty acids permeate membranes without assistance of transport proteins. It also suggests that desorption rather than flip-flop is the rate-limiting step in fatty acid transport through membranes. The relation of flip-flop rates to the evolution of ancestral cellular systems is discussed.
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Affiliation(s)
- Chenyu Wei
- NASA Ames Research Center , Mail Stop 229-1, Moffett Field, California 94035, United States
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22
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Comer J, Gumbart JC, Hénin J, Lelièvre T, Pohorille A, Chipot C. The adaptive biasing force method: everything you always wanted to know but were afraid to ask. J Phys Chem B 2014; 119:1129-51. [PMID: 25247823 PMCID: PMC4306294 DOI: 10.1021/jp506633n] [Citation(s) in RCA: 269] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
![]()
In the host of numerical schemes
devised to calculate free energy
differences by way of geometric transformations, the adaptive biasing
force algorithm has emerged as a promising route to map complex free-energy
landscapes. It relies upon the simple concept that as a simulation
progresses, a continuously updated biasing force is added to the equations
of motion, such that in the long-time limit it yields a Hamiltonian
devoid of an average force acting along the transition coordinate
of interest. This means that sampling proceeds uniformly on a flat
free-energy surface, thus providing reliable free-energy estimates.
Much of the appeal of the algorithm to the practitioner is in its
physically intuitive underlying ideas and the absence of any requirements
for prior knowledge about free-energy landscapes. Since its inception
in 2001, the adaptive biasing force scheme has been the subject of
considerable attention, from in-depth mathematical analysis of convergence
properties to novel developments and extensions. The method has also
been successfully applied to many challenging problems in chemistry
and biology. In this contribution, the method is presented in a comprehensive,
self-contained fashion, discussing with a critical eye its properties,
applicability, and inherent limitations, as well as introducing novel
extensions. Through free-energy calculations of prototypical molecular
systems, many methodological aspects are examined, from stratification
strategies to overcoming the so-called hidden barriers in orthogonal
space, relevant not only to the adaptive biasing force algorithm but
also to other importance-sampling schemes. On the basis of the discussions
in this paper, a number of good practices for improving the efficiency
and reliability of the computed free-energy differences are proposed.
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Affiliation(s)
- Jeffrey Comer
- Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Unité Mixte de Recherche CNRS n°7565, Université de Lorraine , B.P. 70239, 54506 Vandoeuvre-lès-Nancy cedex, France
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23
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Ion-dynamics in hepatitis C virus p7 helical transmembrane domains — a molecular dynamics simulation study. Biophys Chem 2014; 192:33-40. [DOI: 10.1016/j.bpc.2014.06.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2014] [Revised: 06/04/2014] [Accepted: 06/06/2014] [Indexed: 12/31/2022]
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24
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Turchenkov DA, Bystrov VS. Conductance simulation of the purinergic P2X2, P2X4, and P2X7 ionic channels using a combined Brownian dynamics and molecular dynamics approach. J Phys Chem B 2014; 118:9119-27. [PMID: 25006754 DOI: 10.1021/jp501177d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper investigates the application of an original combined approach of molecular and Brownian dynamic methods with quantum chemistry calculations for modeling the process of conductance of ion channels using purinergic P2X family receptors P2X2, P2X4, and P2X7 as a case study. A simplified model of the ionic channel in the lipid bilayer has been developed. A high level of conductance (30 pS) of P2X2 ionic channel together with the key role of Asp349 in forming the selectivity filter of P2X2 has been shown by using this approach. Calculated P2X2 permeability to monovalent cations Li(+), Na(+), and K(+) conforms to the free diffusion coefficient of these ions, which shows the low selectivity of P2X2 ionic channel.
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25
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Enhanced Sampling in Molecular Dynamics Using Metadynamics, Replica-Exchange, and Temperature-Acceleration. ENTROPY 2013. [DOI: 10.3390/e16010163] [Citation(s) in RCA: 282] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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26
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Attempts toward the Synthesis of the Peptaibol Antiamoebin by Using the ‘Azirine/Oxazolone Method’. Chem Biodivers 2013; 10:920-41. [DOI: 10.1002/cbdv.201200386] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Indexed: 11/07/2022]
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27
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Shenkarev ZO, Paramonov AS, Lyukmanova EN, Gizatullina AK, Zhuravleva AV, Tagaev AA, Yakimenko ZA, Telezhinskaya IN, Kirpichnikov MP, Ovchinnikova TV, Arseniev AS. Peptaibol Antiamoebin I: Spatial Structure, Backbone Dynamics, Interaction with Bicelles and Lipid-Protein Nanodiscs, and Pore Formation in Context of Barrel-Stave Model. Chem Biodivers 2013; 10:838-63. [DOI: 10.1002/cbdv.201200421] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Indexed: 11/12/2022]
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Maffeo C, Bhattacharya S, Yoo J, Wells D, Aksimentiev A. Modeling and simulation of ion channels. Chem Rev 2012; 112:6250-84. [PMID: 23035940 PMCID: PMC3633640 DOI: 10.1021/cr3002609] [Citation(s) in RCA: 148] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Christopher Maffeo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Swati Bhattacharya
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Jejoong Yoo
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - David Wells
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
| | - Aleksei Aksimentiev
- Department of Physics, University of Illinois, 1110 W. Green St., Urbana, IL
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29
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Gessmann R, Axford D, Evans G, Brückner H, Petratos K. The crystal structure of samarosporin I at atomic resolution. J Pept Sci 2012; 18:678-84. [PMID: 23019149 DOI: 10.1002/psc.2454] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 08/24/2012] [Accepted: 08/27/2012] [Indexed: 01/24/2023]
Abstract
The atomic resolution structures of samarosporin I have been determined at 100 and 293 K. This is the first crystal structure of a natural 15-residue peptaibol. The amino acid sequence in samarosporin I is identical to emerimicin IV and stilbellin I. Samarosporin is a peptide antibiotic produced by the ascomycetous fungus Samarospora rostrup and belongs to peptaibol subfamily 2. The structures at both temperatures are very similar to each other adopting mainly a 3₁₀-helical and a minor fraction of α-helical conformation. The helices are significantly bent and packed in an antiparallel fashion in the centered monoclinic lattice leaving among them an approximately 10-Å channel extending along the crystallographic twofold axis. Only two ordered water molecules per peptide molecule were located in the channel. Comparisons have been carried out with crystal structures of subfamily 2 16-residue peptaibols antiamoebin and cephaibols. The repercussion of the structural analysis of samarosporin on membrane function is discussed.
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30
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Zhu F, Hummer G. Theory and simulation of ion conduction in the pentameric GLIC channel. J Chem Theory Comput 2012; 8:3759-3768. [PMID: 23413364 DOI: 10.1021/ct2009279] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
GLIC is a bacterial member of the large family of pentameric ligand-gated ion channels. To study ion conduction through GLIC and other membrane channels, we combine the one-dimensional potential of mean force for ion passage with a Smoluchowski diffusion model, making it possible to calculate single-channel conductance in the regime of low ion concentrations from all-atom molecular dynamics (MD) simulations. We then perform MD simulations to examine sodium ion conduction through the GLIC transmembrane pore in two systems with different bulk ion concentrations. The ion potentials of mean force, calculated from umbrella sampling simulations with Hamiltonian replica exchange, reveal a major barrier at the hydrophobic constriction of the pore. The relevance of this barrier for ion transport is confirmed by a committor function that rises sharply in the barrier region. From the free evolution of Na(+) ions starting at the barrier top, we estimate the effective diffusion coefficient in the barrier region, and subsequently calculate the conductance of the pore. The resulting diffusivity compares well with the position-dependent ion diffusion coefficient obtained from restrained simulations. The ion conductance obtained from the diffusion model agrees with the value determined via a reactive-flux rate calculation. Our results show that the conformation in the GLIC crystal structure, with an estimated conductance of ~1 picosiemens at 140 mM ion concentration, is consistent with a physiologically open state of the channel.
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Affiliation(s)
- Fangqiang Zhu
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892-0520, USA
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31
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Abstract
In theory and in the analysis of experiments, protein folding is often described as diffusion along a single coordinate. We explore here the application of a one-dimensional diffusion model to interpret simulations of protein folding, where the parameters of a model that "best" describes the simulation trajectories are determined using a Bayesian analysis. We discuss the requirements for such a model to be a good approximation to the global dynamics, and several methods for testing its accuracy. For example, one test considers the effect of an added bias potential on the fitted free energies and diffusion coefficients. Such a bias may also be used to extend our approach to determining parameters for the model to systems that would not normally explore the full coordinate range on accessible time scales. Alternatively, the propagators predicted from the model at different "lag" times may be compared with observations from simulation. We then present some applications of the model to protein folding, including Kramers-like turnover in folding rates of coarse-grained models, the effect of non-native interactions on folding, and the effect of the chosen coordinate on the observed position-dependence of the diffusion coefficients. Lastly, we consider how our results are useful for the interpretation of experiments, and how this type of Bayesian analysis may eventually be applied directly to analyse experimental data.
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Affiliation(s)
- Robert B. Best
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom. Fax: +44-1223-336362; Tel: +44-1223-336470;
| | - Gerhard Hummer
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, U.S.A.
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