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Fathizadeh A, Kogan M, Anderson CM, Webb LJ, Elber R. Defect-Assisted Permeation Through a Phospholipid Membrane: Experimental and Computational Study of the Peptide WKW. J Phys Chem B 2019; 123:6792-6798. [PMID: 31304755 PMCID: PMC6687544 DOI: 10.1021/acs.jpcb.9b05414] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We investigate membrane permeation by the peptide WKW that is amidated at its C-terminus and therefore carries a positive charge of +2. To facilitate an efficient calculation, we introduce a novel set of simple coarse variables that measure permeation depth and membrane distortion. The phospholipid head groups shift toward the center of the membrane, following the permeating peptide, and create a defect that assists permeation. The Milestoning algorithm was used in the new coarse space to compute the free-energy profile and the mean first passage time. The barrier was lower than expected from a simple continuum estimate. This behavior is consistent with the known behavior of positively charged cell-penetrating peptides, and is explained by a detailed mechanism of defect formation and propagation revealed by the simulations.
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Affiliation(s)
- Arman Fathizadeh
- Oden Institute for Computational Engineering and Sciences, University of Texas at Austin, Austin. TX, 78712
| | - Molly Kogan
- Department of Chemistry, University of Texas at Austin, Austin TX, 78712
| | - Cari M. Anderson
- Department of Chemistry, University of Texas at Austin, Austin TX, 78712
| | - Lauren J. Webb
- Department of Chemistry, University of Texas at Austin, Austin TX, 78712
| | - Ron Elber
- Oden Institute for Computational Engineering and Sciences, University of Texas at Austin, Austin. TX, 78712
- Department of Chemistry, University of Texas at Austin, Austin TX, 78712
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2
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Cardenas AE, Anderson CM, Elber R, Webb LJ. Partition of Positively and Negatively Charged Tryptophan Ions in Membranes with Inverted Phospholipid Heads: Simulations and Experiments. J Phys Chem B 2019; 123:3272-3281. [PMID: 30912653 DOI: 10.1021/acs.jpcb.9b00754] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A joint experimental and computational study illustrates that the partitioning of positively and negatively charged tryptophan in a phospholipid bilayer is significantly altered by a reversal in the head group dipole arrangement. Experiments were conducted using tryptophan as a fluorescent reporter of its local environment. Based on the experimental design in a recent publication ( Anderson , C. M. ; Cardenas , A. ; Elber , R. ; Webb , L. J. J. Phys. Chem. B 2018 , 123 , 170 - 179 ), we were able to determine that the arrangement of the head group dipole altered the degree of partitioning of charged tryptophan in the lipid bilayer. In parallel, atomically detailed simulations were performed for the two membrane systems. The simulation results are in accord with the experimental findings and support a simple molecular partition mechanism of electrostatic interactions with the head groups, glycerol linkers, and interfacial water dipoles.
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3
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Fathizadeh A, Elber R. Ion Permeation through a Phospholipid Membrane: Transition State, Path Splitting, and Calculation of Permeability. J Chem Theory Comput 2019; 15:720-730. [PMID: 30474968 PMCID: PMC6467798 DOI: 10.1021/acs.jctc.8b00882] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigate the thermodynamics and kinetics of the permeation of a potassium ion through a phospholipid membrane. We illustrate that the conventional reaction coordinate (the position of the ion along the normal to the membrane plane) is insufficient to capture essential elements of the process. It is necessary to add coarse variables that measure membrane distortion. New coarse variables are suggested, and a two-dimensional coarse-space is proposed to describe the permeation. We illustrate path splitting and two transition states of comparable barrier heights. The alternative pathways differ by the extent of water solvation of the ion-phosphate pairs. The permeation process cannot be described by a local one-dimensional reaction coordinate, and a network formulation is more appropriate. We use Milestoning with Voronoi tessellation in two dimensions to quantify the equilibrium and rate of the permeation of the positively charged ion. The permeation coefficient is computed and compared favorably to experiment.
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Affiliation(s)
- Arman Fathizadeh
- Institute for Computational Engineering and Sciences , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Ron Elber
- Institute for Computational Engineering and Sciences , University of Texas at Austin , Austin , Texas 78712 , United States
- Department of Chemistry , University of Texas at Austin , Austin , Texas 78712 , United States
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4
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Uchida Y, Nakamura S, Kouyama JI, Naiki K, Motoya D, Sugawara K, Inao M, Imai Y, Nakayama N, Tomiya T, Hedskog C, Brainard D, Mo H, Mochida S. Significance of NS5B Substitutions in Genotype 1b Hepatitis C Virus Evaluated by Bioinformatics Analysis. Sci Rep 2018; 8:8818. [PMID: 29892096 PMCID: PMC5995875 DOI: 10.1038/s41598-018-27291-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 05/10/2018] [Indexed: 01/03/2023] Open
Abstract
To evaluate the effects of HCV NS5B amino acid substitutions on treatment outcome in Ledipasvir (LDV)/Sofosbuvir (SOF) for Japanese patients with genotype 1b HCV infection, NS5B sequences were examined in i) seven patients experiencing virologic failure after LDV/SOF in real-world practice, ii) 109 SOF-naïve patients, iii) 165 patients enrolled in Phase-3 LDV/SOF trial. A218S and C316N were detected in all patients with viral relapse; the percentages of these substitutions in SOF-naïve patients were 64.2% and 55.0%, respectively. Genotype 1b HCV strains with NS5B-C316N mutation were located in the leaves different from those in which HCV strains without such substitutions were present on the phylogenetic tree. Structural modeling revealed that amino acid 218 was located on the surface of the NTP tunnel. Free energy analysis based on molecular dynamics simulations demonstrated that the free energy required to pass through the tunnel was larger for triphosphate SOF than for UTP in NS5B polymerase carrying A218S, but not in wild-type. However, no susceptibility change was observed for these substitutions to SOF in replicon assay. Furthermore, the SVR rate was 100% in patients enrolled the Phase-3 trial. In conclusion, NS5B A218S and C316N were detected in all patients who relapsed following LDV/SOF in real-world practice. These substitutions did not impact the overall SVR rate after LDV/SOF, however, further studies are needed to elucidate the impact of these substitutions.
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Affiliation(s)
- Yoshihito Uchida
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Shugo Nakamura
- Faculty of Information Networking for Innovation and Design, Toyo University, Toyo, Japan
| | - Jun-Ichi Kouyama
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Kayoko Naiki
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Daisuke Motoya
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Kayoko Sugawara
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Mie Inao
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Yukinori Imai
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Nobuaki Nakayama
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | - Tomoaki Tomiya
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan
| | | | | | - Hongmei Mo
- Gilead Sciences, Inc., Foster City, California, USA
| | - Satoshi Mochida
- Department of Gastroenterology & Hepatology, Faculty of Medicine, Saitama Medical University, Saitama, Japan.
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5
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Bonhenry D, Dehez F, Tarek M. Effects of hydration on the protonation state of a lysine analog crossing a phospholipid bilayer – insights from molecular dynamics and free-energy calculations. Phys Chem Chem Phys 2018; 20:9101-9107. [DOI: 10.1039/c8cp00312b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Protonation states of amino acids crossing lipid bilayers from multidimensional free energy surfaces.
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Affiliation(s)
| | | | - Mounir Tarek
- Université de Lorraine
- CNRS
- LPCT
- F-54000 Nancy
- France
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6
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Houriez C, Meot-Ner Mautner M, Masella M. Solvation of the Guanidinium Ion in Pure Aqueous Environments: A Theoretical Study from an "Ab Initio"-Based Polarizable Force Field. J Phys Chem B 2017; 121:11219-11228. [PMID: 29182348 DOI: 10.1021/acs.jpcb.7b07874] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We report simulation results regarding the hydration process of the guanidinium cation in water droplets and in bulk liquid water, at a low concentration of 0.03 M, performed using a polarizable approach to model both water/water and ion/water interactions. In line with earlier theoretical studies, our simulations show a preferential orientation of guanidinium at water-vacuum interfaces, i.e., a parallel orientation of the guanidinium plane to the aqueous surface. In an apparent contradiction with earlier simulation studies, we show also that guanidinium has a stronger propensity for the cores of aqueous systems than the ammonium cation. However, our bulk simulation conditions correspond to weaker cation concentrations than in earlier studies, by 2 orders of magnitude, and that the same simulations performed using a standard nonpolarizable force field leads to the same conclusion. From droplet data, we extrapolate the guanidinium single hydration enthalpy value to be -82.9 ± 2.2 kcal mol-1. That is about half as large as the sole experimental estimate reported to date, about -144 kcal mol-1. Our result yields a guanidinium absolute bulk hydration free energy at ambiant conditions to be -78.4 ± 2.6 kcal mol-1, a value smaller by 3 kcal mol-1 compared to ammonium. The relatively large magnitude of our guanidinium hydration free energy estimate suggests the Gdm+ protein denaturing properties to result from a competition between the cation hydration effects and the cation/protein interactions, a competition that can be modulated by weak differences in the protein or in the cation chemical environment.
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Affiliation(s)
- Céline Houriez
- MINES ParisTech, PSL Research University, CTP - Centre Thermodynamique des Procédés , 35 rue Saint-Honoré, 77300 Fontainebleau, France
| | - Michael Meot-Ner Mautner
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.,Department of Chemistry, University of Canterbury , Christchurch 8001, New Zealand
| | - Michel Masella
- Laboratoire de Biologie Structurale et Radiobiologie, Service de Bioénergétique, Biologie Structurale et Mécanismes, Institut Joliot, CEA Saclay , F-91191 Gif sur Yvette Cedex, France
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7
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Chu H, Cao L, Peng X, Li G. Polarizable force field development for lipids and their efficient applications in membrane proteins. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2017. [DOI: 10.1002/wcms.1312] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Affiliation(s)
- Huiying Chu
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics; Dalian Institute of Chemical Physics, Chinese Academy of Science; Dalian China
| | - Liaoran Cao
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics; Dalian Institute of Chemical Physics, Chinese Academy of Science; Dalian China
| | - Xiangda Peng
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics; Dalian Institute of Chemical Physics, Chinese Academy of Science; Dalian China
| | - Guohui Li
- Laboratory of Molecular Modeling and Design, State Key Laboratory of Molecular Reaction Dynamics; Dalian Institute of Chemical Physics, Chinese Academy of Science; Dalian China
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8
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Neale C, Pomès R. Sampling errors in free energy simulations of small molecules in lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2539-2548. [PMID: 26952019 DOI: 10.1016/j.bbamem.2016.03.006] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 03/01/2016] [Accepted: 03/02/2016] [Indexed: 12/14/2022]
Abstract
Free energy simulations are a powerful tool for evaluating the interactions of molecular solutes with lipid bilayers as mimetics of cellular membranes. However, these simulations are frequently hindered by systematic sampling errors. This review highlights recent progress in computing free energy profiles for inserting molecular solutes into lipid bilayers. Particular emphasis is placed on a systematic analysis of the free energy profiles, identifying the sources of sampling errors that reduce computational efficiency, and highlighting methodological advances that may alleviate sampling deficiencies. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Chris Neale
- Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th St, Troy, New York 12180-3590, USA
| | - Régis Pomès
- Molecular Structure and Function, The Hospital for Sick Children, 686 Bay Street, Toronto, Ontario M5G 0A4, Canada; Department of Biochemistry, University of Toronto, 101 College Street, Toronto, Ontario M5G 1L7, Canada.
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9
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Allolio C, Baxova K, Vazdar M, Jungwirth P. Guanidinium Pairing Facilitates Membrane Translocation. J Phys Chem B 2015; 120:143-53. [DOI: 10.1021/acs.jpcb.5b10404] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Christoph Allolio
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic
- Institut
für Physikalische and Theoretische Chemie, Universität Regensburg, 93040 Regensburg, Germany
| | - Katarina Baxova
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic
| | - Mario Vazdar
- Institut
Rudjer
Bošković, Bijenička
cesta 54, 10000 Zagreb, Croatia
| | - Pavel Jungwirth
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, CZ-166 10 Prague 6, Czech Republic
- Department
of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland
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10
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Hu Y, Sinha SK, Patel S. Investigating Hydrophilic Pores in Model Lipid Bilayers Using Molecular Simulations: Correlating Bilayer Properties with Pore-Formation Thermodynamics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6615-31. [PMID: 25614183 PMCID: PMC4934177 DOI: 10.1021/la504049q] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Cell-penetrating and antimicrobial peptides show a remarkable ability to translocate across physiological membranes. Along with factors such as electric-potential-induced perturbations of membrane structure and surface tension effects, experiments invoke porelike membrane configurations during the solute transfer process into vesicles and cells. The initiation and formation of pores are associated with a nontrivial free-energy cost, thus necessitating a consideration of the factors associated with pore formation and the attendant free energies. Because of experimental and modeling challenges related to the long time scales of the translocation process, we use umbrella sampling molecular dynamics simulations with a lipid-density-based order parameter to investigate membrane-pore-formation free energy employing Martini coarse-grained models. We investigate structure and thermodynamic features of the pore in 18 lipids spanning a range of headgroups, charge states, acyl chain lengths, and saturation. We probe the dependence of pore-formation barriers on the area per lipid, lipid bilayer thickness, and membrane bending rigidities in three different lipid classes. The pore-formation free energy in pure bilayers and peptide translocating scenarios are significantly coupled with bilayer thickness. Thicker bilayers require more reversible work to create pores. The pore-formation free energy is higher in peptide-lipid systems than in peptide-free lipid systems due to penalties to maintain the solvation of charged hydrophilic solutes within the membrane environment.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Sudipta Kumar Sinha
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Sandeep Patel
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
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11
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Ou SC, Cui D, Wezowicz M, Taufer M, Patel S. Free energetics of carbon nanotube association in aqueous inorganic NaI salt solutions: Temperature effects using all-atom molecular dynamics simulations. J Comput Chem 2015; 36:1196-212. [PMID: 25868455 PMCID: PMC4445429 DOI: 10.1002/jcc.23906] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Revised: 01/22/2015] [Accepted: 02/21/2015] [Indexed: 11/06/2022]
Abstract
In this study, we examine the temperature dependence of free energetics of nanotube association using graphical processing unit-enabled all-atom molecular dynamics simulations (FEN ZI) with two (10,10) single-walled carbon nanotubes in 3 m NaI aqueous salt solution. Results suggest that the free energy, enthalpy and entropy changes for the association process are all reduced at the high temperature, in agreement with previous investigations using other hydrophobes. Via the decomposition of free energy into individual components, we found that solvent contribution (including water, anion, and cation contributions) is correlated with the spatial distribution of the corresponding species and is influenced distinctly by the temperature. We studied the spatial distribution and the structure of the solvent in different regions: intertube, intratube and the bulk solvent. By calculating the fluctuation of coarse-grained tube-solvent surfaces, we found that tube-water interfacial fluctuation exhibits the strongest temperature dependence. By taking ions to be a solvent-like medium in the absence of water, tube-anion interfacial fluctuation shows similar but weaker dependence on temperature, while tube-cation interfacial fluctuation shows no dependence in general. These characteristics are discussed via the malleability of their corresponding solvation shells relative to the nanotube surface. Hydrogen bonding profiles and tetrahedrality of water arrangement are also computed to compare the structure of solvent in the solvent bulk and intertube region. The hydrophobic confinement induces a relatively lower concentration environment in the intertube region, therefore causing different intertube solvent structures which depend on the tube separation. This study is relevant in the continuing discourse on hydrophobic interactions (as they impact generally a broad class of phenomena in biology, biochemistry, and materials science and soft condensed matter research), and interpretations of hydrophobicity in terms of alternative but parallel signatures such as interfacial fluctuations, dewetting transitions, and enhanced fluctuation probabilities at interfaces.
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Affiliation(s)
- Shu-Ching Ou
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Di Cui
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
| | - Matthew Wezowicz
- Department of Computer and Information Sciences, University of Delaware, Newark, Delaware 19716, USA
| | - Michela Taufer
- Department of Computer and Information Sciences, University of Delaware, Newark, Delaware 19716, USA
| | - Sandeep Patel
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
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12
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Cardenas AE, Shrestha R, Webb LJ, Elber R. Membrane permeation of a peptide: it is better to be positive. J Phys Chem B 2015; 119:6412-20. [PMID: 25941740 DOI: 10.1021/acs.jpcb.5b02122] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A joint experimental and computational study investigates the translocation of a tryptophan molecule through a phospholipid membrane. Time dependent spectroscopy of the tryptophan side chain determines the rate of permeation into 150 nm phospholipid vesicles. Atomically detailed simulations are conducted to calculate the free energy profiles and the permeation coefficient. Different charging conditions of the peptide (positive, negative, or zwitterion) are considered. Both experiment and simulation reproduce the qualitative trend and suggest that the fastest permeation is when the tryptophan is positively charged. The permeation mechanism, which is revealed by molecular dynamics simulations, is of a translocation assisted by a local defect. The influence of long-range electrostatic interactions, such as the membrane dipole potential on the permeation process, is not significant.
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Affiliation(s)
- Alfredo E Cardenas
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Rebika Shrestha
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Lauren J Webb
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Ron Elber
- †Institute for Computational Engineering and Sciences and ‡Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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13
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Vosmeer CR, Kiewisch K, Keijzer K, Visscher L, Geerke DP. A comparison between QM/MM and QM/QM based fitting of condensed-phase atomic polarizabilities. Phys Chem Chem Phys 2015; 16:17857-62. [PMID: 25042275 DOI: 10.1039/c4cp02401j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Recently we reported a combined QM/MM approach to estimate condensed-phase values of atomic polarizabilities for use in (bio)molecular simulation. The setup relies on a MM treatment of the solvent when determining atomic polarizabilities to describe the response of a QM described solute to its external electric field. In this work, we study the effect of using alternative descriptions of the solvent molecules when evaluating atomic polarizabilities of a methanol solute. In a first step, we show that solute polarizabilities are not significantly affected upon substantially increasing the MM dipole moments towards values that are typically reported in literature for water solvent molecules. Subsequently, solute polarization is evaluated in the presence of a QM described solvent (using the frozen-density embedding method). In the latter case, lower oxygen polarizabilities were obtained than when using MM point charges to describe the solvent, due to introduction of Pauli-repulsion effects.
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Affiliation(s)
- C Ruben Vosmeer
- AIMMS Division of Molecular Toxicology, Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, the Netherlands.
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14
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Sun D, Forsman J, Woodward CE. Evaluating Force Fields for the Computational Prediction of Ionized Arginine and Lysine Side-Chains Partitioning into Lipid Bilayers and Octanol. J Chem Theory Comput 2015; 11:1775-91. [PMID: 26574387 DOI: 10.1021/ct501063a] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Abundant peptides and proteins containing arginine (Arg) and lysine (Lys) amino acids can apparently permeate cell membranes with ease. However, the mechanisms by which these peptides and proteins succeed in traversing the free energy barrier imposed by cell membranes remain largely unestablished. Precise thermodynamic studies (both theoretical and experimental) on the interactions of Arg and Lys residues with model lipid bilayers can provide valuable clues to the efficacy of these cationic peptides and proteins. We have carried out molecular dynamics simulations to calculate the interactions of ionized Arg and Lys side-chains with the zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer for 10 widely used lipid/protein force fields: CHARMM36/CHARMM36, SLIPID/AMBER99SB-ILDN, OPLS-AA/OPLS-AA, Berger/OPLS-AA, Berger/GROMOS87, Berger/GROMOS53A6, GROMOS53A6/GROMOS53A6, nonpolarizable MARTINI, polarizable MARTINI, and BMW MARTINI. We performed umbrella sampling simulations to obtain the potential of mean force for Arg and Lys side-chains partitioning from water to the bilayer interior. We found significant differences between the force fields, both for the interactions between side-chains and bilayer surface, as well as the free energy cost for placing the side-chain at the center of the bilayer. These simulation results were compared with the Wimley-White interfacial scale. We also calculated the free energy cost for transferring ionized Arg and Lys side-chains from water to both dry and wet octanol. Our simulations reveal rapid diffusion of water molecules into octanol whereby the equilibrium mole fraction of water in the wet octanol phase was ∼25%. Surprisingly, our free energy calculations found that the high water content in wet octanol lowered the water-to-octanol partitioning free energies for cationic residues by only 0.6 to 0.7 kcal/mol.
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Affiliation(s)
- Delin Sun
- School of Physical, Environmental and Mathematical Sciences, University of New South Wales , Canberra ACT 2600, Australia
| | - Jan Forsman
- Theoretical Chemistry, Chemical Centre, Lund University , P.O. Box 124, S-221 00 Lund, Sweden
| | - Clifford E Woodward
- School of Physical, Environmental and Mathematical Sciences, University of New South Wales , Canberra ACT 2600, Australia
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15
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Baker CM. Polarizable force fields for molecular dynamics simulations of biomolecules. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2015. [DOI: 10.1002/wcms.1215] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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16
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Hu Y, Sinha SK, Patel S. Reconciling structural and thermodynamic predictions using all-atom and coarse-grain force fields: the case of charged oligo-arginine translocation into DMPC bilayers. J Phys Chem B 2014; 118:11973-92. [PMID: 25290376 PMCID: PMC4199542 DOI: 10.1021/jp504853t] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Using the translocation of short, charged cationic oligo-arginine peptides (mono-, di-, and triarginine) from bulk aqueous solution into model DMPC bilayers, we explore the question of the similarity of thermodynamic and structural predictions obtained from molecular dynamics simulations using all-atom and Martini coarse-grain force fields. Specifically, we estimate potentials of mean force associated with translocation using standard all-atom (CHARMM36 lipid) and polarizable and nonpolarizable Martini force fields, as well as a series of modified Martini-based parameter sets. We find that we are able to reproduce qualitative features of potentials of mean force of single amino acid side chain analogues into model bilayers. In particular, modifications of peptide-water and peptide-membrane interactions allow prediction of free energy minima at the bilayer-water interface as obtained with all-atom force fields. In the case of oligo-arginine peptides, the modified parameter sets predict interfacial free energy minima as well as free energy barriers in almost quantitative agreement with all-atom force field based simulations. Interfacial free energy minima predicted by a modified coarse-grained parameter set are -2.51, -4.28, and -5.42 for mono-, di-, and triarginine; corresponding values from all-atom simulations are -0.83, -3.33, and -3.29, respectively, all in units of kcal/mol. We found that a stronger interaction between oligo-arginine and the membrane components and a weaker interaction between oligo-arginine and water are crucial for producing such minima in PMFs using the polarizable CG model. The difference between bulk aqueous and bilayer center states predicted by the modified coarse-grain force field are 11.71, 14.14, and 16.53 kcal/mol, and those by the all-atom model are 6.94, 8.64, and 12.80 kcal/mol; those are of almost the same order of magnitude. Our simulations also demonstrate a remarkable similarity in the structural aspects of the ensemble of configurations generated using the all-atom and coarse-grain force fields. Both resolutions show that oligo-arginine peptides adopt preferential orientations as they translocate into the bilayer. The guiding theme centers on charged groups maintaining coordination with polar and charged bilayer components as well as local water. We also observe similar behaviors related with membrane deformations.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States
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Bennett WFD, Tieleman DP. The importance of membrane defects-lessons from simulations. Acc Chem Res 2014; 47:2244-51. [PMID: 24892900 DOI: 10.1021/ar4002729] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The defects and pores within lipid membranes are scientifically interesting and have a number of biological applications. Although lipid bilayers are extremely thin hydrophobic barriers, just ∼3 nm thick, they include diverse chemistry and have complex structures. Bilayers are soft and dynamic, and as a result, they can bend and deform in response to different stimuli by means of structural changes in their component lipids. Though defects occur within these structures, their transience and small size have made it difficult to characterize them. However, with recent advances in computer power and computational modeling techniques, researchers can now use simulations as a powerful tool to probe the mechanism and energies of defect and pore formation in a number of situations. In this Account, we present results from our detailed molecular dynamics computer simulations of hydrophilic pores and related defects in lipid bilayers at an atomistic level. Electroporation can be used to increase the permeability of cellular membranes, with potential therapeutic applications. Atomistic simulations of electroporation have illustrated the molecular details of this process, including the importance of water dipole interactions at the water-membrane interface. Characterization of the lipid-protein interactions provides an important tool for understanding transmembrane protein structure and thermodynamic stability. Atomistic simulations give a detailed picture of the free energies of model peptides and side chains in lipid membranes; the energetic cost of defect formation strongly influences the energies of interactions between lipids and polar and charged residues. Many antimicrobial peptides form hydrophilic pores in lipid membranes, killing bacteria or cancer cells. On the basis of simulation data, at least some of these peptides form defects and pores near the center of the bilayer, with a common disordered structure where hydrated headgroups form an approximately toroidal shape. The localization and trafficking of lipids supports general membrane structure and a number of important signaling cascades, such as those involving ceramide, diacylglycerol, and cholesterol. Atomistic simulations have determined the rates and free energies of lipid flip-flop. During the flip-flop of most phosphatidylcholine lipids, a hydrophilic pore forms when the headgroup moves near the center of the bilayer. Simulations have provided novel insight into many features of defects and pores in lipid membranes. Simulation data from very different systems and models show how water penetration and defect formation can determine the free energies of many membrane processes. Bilayers can deform and allow transient defects and pores when exposed to a diverse range of stimuli. Future work will explore many aspects of membrane defects with increased resolution and scope, including the study of more complex lipid mixtures, membrane domains, and large-scale membrane remodeling. Such studies will examine processes including vesicle budding and fusion, non-bilayer lipid phases, and interactions between lipid bilayers and other biomolecules. Simulations provide information that complements experimental studies, allowing microscopic insight into experimental observations and suggesting novel hypotheses and experiments. These studies should enable a deeper understanding of the role of lipid bilayers in cellular biology and support the development of future lipid-based biotechnology.
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Affiliation(s)
- W. F. Drew Bennett
- Department of Biological
Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
| | - D. Peter Tieleman
- Department of Biological
Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
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Hu Y, Liu X, Sinha SK, Patel S. Translocation thermodynamics of linear and cyclic nonaarginine into model DPPC bilayer via coarse-grained molecular dynamics simulation: implications of pore formation and nonadditivity. J Phys Chem B 2014; 118:2670-82. [PMID: 24506488 PMCID: PMC3983342 DOI: 10.1021/jp412600e] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
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Structural mechanisms
and underlying thermodynamic determinants
of efficient internalization of charged cationic peptides (cell-penetrating
peptides, CPPs) such as TAT, polyarginine, and their variants, into
cells, cellular constructs, and model membrane/lipid bilayers (large
and giant unilamellar or multilamelar vesicles) continue to garner
significant attention. Two widely held views on the translocation
mechanism center on endocytotic and nonendocytotic (diffusive) processes.
Espousing the view of a purely diffusive internalization process (supported
by recent experimental evidence, [Säälik, P.; et al. J. Controlled Release2011, 153, 117–125]), we consider the underlying free energetics of
the translocation of a nonaarginine peptide (Arg9) into
a model DPPC bilayer. In the case of the Arg9 cationic
peptide, recent experiments indicate a higher internalization efficiency
of the cyclic structure (cyclic Arg9) relative to the linear
conformer. Furthermore, recent all-atom resolution molecular dynamics
simulations of cyclic Arg9 [Huang, K.; et al. Biophys.
J., 2013, 104, 412–420]
suggested a critical stabilizing role of water- and lipid-constituted
pores that form within the bilayer as the charged Arg9 translocates
deep into the bilayer center. Herein, we use umbrella sampling molecular
dynamics simulations with coarse-grained Martini lipids, polarizable
coarse-grained water, and peptide to explore the dependence of translocation
free energetics on peptide structure and conformation via calculation
of potentials of mean force along preselected reaction paths allowing
and preventing membrane deformations that lead to pore formation.
Within the context of the coarse-grained force fields we employ, we
observe significant barriers for Arg9 translocation from
bulk aqueous solution to bilayer center. Moreover, we do not find
free-energy minima in the headgroup–water interfacial region,
as observed in simulations using all-atom force fields. The pore-forming
paths systematically predict lower free-energy barriers (ca. 90 kJ/mol
lower) than the non pore-forming paths, again consistent with all-atom
force field simulations. The current force field suggests no preference
for the more compact or covalently cyclic structures upon entering
the bilayer. Decomposition of the PMF into the system’s components
indicates that the dominant stabilizing contribution along the pore-forming
path originates from the membrane as both layers of it deformed due
to the formation of pore. Furthermore, our analysis revealed that
although there is significant entropic stabilization arising from
the enhanced configurational entropy exposing more states as the peptide
moves through the bilayer, the enthalpic loss (as predicted by the
interactions of this coarse-grained model) far outweighs any former
stabilization, thus leading to significant barrier to translocation.
Finally, we observe reduction in the translocation free-energy barrier
for a second Arg9 entering the bilayer in the presence
of an initial peptide restrained at the center, again, in qualitative
agreement with all-atom force fields.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware , 238 Brown Laboratory, Newark, Delaware 19716, United States
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Ou S, Cui D, Patel S. Liquid-vapor interfacial properties of aqueous solutions of guanidinium and methyl guanidinium chloride: influence of molecular orientation on interface fluctuations. J Phys Chem B 2013; 117:11719-31. [PMID: 23937431 DOI: 10.1021/jp405862p] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The guanidinium cation (C(NH2)3(+)) is a highly stable cation in aqueous solution due to its efficient solvation by water molecules and resonance stabilization of the charge. Its salts increase the solubility of nonpolar molecules ("salting-in") and decrease the ordering of water. It is one of the strongest denaturants used in biophysical studies of protein folding. We investigate the behavior of guanidinium and its derivative, methyl guanidinium (an amino acid analogue) at the air-water surface, using atomistic molecular dynamics (MD) simulations and calculation of potentials of mean force. Methyl guanidinium cation is less excluded from the air-water surface than guanidinium cation, but both cations show orientational dependence of surface affinity. Parallel orientations of the guanidinium ring (relative to the Gibbs dividing surface) show pronounced free energy minima in the interfacial region, while ring orientations perpendicular to the GDS exhibit no discernible surface stability. Calculations of surface fluctuations demonstrate that, near the air-water surface, the parallel-oriented cations generate significantly greater interfacial fluctuations compared to other orientations, which induces more long-ranged perturbations and solvent density redistribution. Our results suggest a strong correlation with induced interfacial fluctuations and ion surface stability. These results have implications for interpreting molecular-level, mechanistic action of this osmolyte's interaction with hydrophobic interfaces as they impact protein denaturation (solubilization).
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Affiliation(s)
- Shuching Ou
- Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States
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Hu Y, Ou S, Patel S. Free energetics of arginine permeation into model DMPC lipid bilayers: coupling of effective counterion concentration and lateral bilayer dimensions. J Phys Chem B 2013; 117:11641-53. [PMID: 23888915 DOI: 10.1021/jp404829y] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Mechanisms and underlying thermodynamic determinants of translocation of charged cationic peptides such as cell-penetrating peptides across the cellular membrane continue to receive much attention. Two widely held views include endocytotic and non-endocytotic (diffusive) processes of permeant transfer across the bilayer. Considering a purely diffusive process, we consider the free energetics of translocation of a monoarginine peptide mimic across a model DMPC bilayer. We compute potentials of mean force for the transfer of a charged monoarginine peptide unit from water to the center of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model lipid bilayer. We use fully atomistic molecular dynamics simulations coupled with the adaptive biasing force (ABF) method for free energy estimation. The estimated potential of mean force difference from bulk to bilayer center is 6.94 ± 0.28 kcal/mol. The order of magnitude of this prediction is consistent with past experimental estimates of arginine partitioning into physiological bilayers in the context of translocon-based experiments, though the correlation between the bench and computer experiments is not unambiguous. Moreover, the present value is roughly one-half of previous estimates based on all-atom molecular dynamics free energy calculations. We trace the differences between the present and earlier calculations to system sizes used in the simulations and the dependence of the contributions to the free energy from various system components (water, lipids, ions, peptide) on overall system size. By varying the bilayer lateral dimensions in simulations using only sufficient numbers of counterions to maintain overall system charge neutrality, we find the possibility of an inherent convergent transfer free energy value.
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Affiliation(s)
- Yuan Hu
- Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States
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Neale C, Madill C, Rauscher S, Pomès R. Accelerating Convergence in Molecular Dynamics Simulations of Solutes in Lipid Membranes by Conducting a Random Walk along the Bilayer Normal. J Chem Theory Comput 2013; 9:3686-703. [DOI: 10.1021/ct301005b] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Chris Neale
- Molecular Structure
and Function,
The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario,
M5G 1X8, Canada
- Department
of Biochemistry,
University of Toronto, 101 College Street, Toronto, Ontario, M5G 1L7,
Canada
| | - Chris Madill
- Molecular Structure
and Function,
The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario,
M5G 1X8, Canada
- Department
of Biochemistry,
University of Toronto, 101 College Street, Toronto, Ontario, M5G 1L7,
Canada
| | - Sarah Rauscher
- Molecular Structure
and Function,
The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario,
M5G 1X8, Canada
- Department
of Biochemistry,
University of Toronto, 101 College Street, Toronto, Ontario, M5G 1L7,
Canada
| | - Régis Pomès
- Molecular Structure
and Function,
The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario,
M5G 1X8, Canada
- Department
of Biochemistry,
University of Toronto, 101 College Street, Toronto, Ontario, M5G 1L7,
Canada
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