1
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Kundu A, Yamaguchi S, Tahara T. Local pH at Nonionic and Zwitterionic Lipid/Water Interfaces Revealed by Heterodyne-Detected Electronic Sum-Frequency Generation: A Unified View to Predict Interfacial pH of Biomembranes. J Phys Chem B 2023; 127:5445-5452. [PMID: 37308160 PMCID: PMC10292198 DOI: 10.1021/acs.jpcb.3c02002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 05/20/2023] [Indexed: 06/14/2023]
Abstract
For biomembranes, which are composed of neutral as well as charged lipids, the local pH at lipid/water interfaces is extremely important in their structural formation and functional activity. In our previous study of the charged lipid/water interfaces, we found that the local pH at the interface is governed by the positive or negative sign of the charge of the lipid: i.e., the local pH is dictated by the repulsive or attractive electrostatic interaction between the charged lipid headgroup and the proton. Because of the lack of net charge in the headgroup of the neutral lipid, the factor determining the local pH at neutral lipid/water interfaces is less straightforward, and therefore it is more challenging to predict the local pH. Here we apply heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopy to nonionic and zwitterionic lipids to investigate the local pH at the neutral lipid/water interfaces. The obtained results indicate that the local pH at the nonionic lipid/water interface is higher than in bulk water by 0.8 whereas the local pH at the zwitterionic lipid/water interface is lower by 0.6, although the latter is subject to significant uncertainty. The present HD-ESFG study on neutral lipids, combined with the previous study on charged lipids, presents a unified view to consider the local pH at biomembranes based on the balance between the electrostatic interaction and the hydrophobicity provided by the lipid.
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Affiliation(s)
- Achintya Kundu
- Molecular
Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
| | - Shoichi Yamaguchi
- Molecular
Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
- Department
of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
| | - Tahei Tahara
- Molecular
Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
- Ultrafast
Spectroscopy Research Team, RIKEN Center
for Advanced Photonics (RAP), Wako, Saitama 351-0198, Japan
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2
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Ion permeation across the membrane: A comprehensive comparison analysis on passive permeations of differently charged ions. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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3
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Explicit-pH Coarse-Grained Molecular Dynamics Simulations Enable Insights into Restructuring of Intestinal Colloidal Aggregates with Permeation Enhancers. Processes (Basel) 2021. [DOI: 10.3390/pr10010029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Permeation enhancers (PEs) can increase the bioavailability of drugs. The mechanisms of action of these PEs are complex, but, typically, when used for oral administration, they can transiently induce the alteration of trans- and paracellular pathways, including increased solubilization and membrane fluidity, or the opening of the tight junctions. To elucidate these mechanistic details, it is important to understand the aggregation behavior of not only the PEs themselves but also other molecules already present in the intestine. Aggregation processes depend critically on, among other factors, the charge state of ionizable chemical groups, which is affected by the pH of the system. In this study, we used explicit-pH coarse-grained molecular dynamics simulations to investigate the aggregation behavior and pH dependence of two commonly used PEs—caprate and SNAC—together with other components of fasted- and fed-state simulated intestinal fluids. We also present and validate a coarse-grained molecular topology for the bile salt taurocholate suitable for the Martini3 force-field. Our results indicate an increase in the number of free molecules as a function of the system pH and for each combination of FaSSIF/FeSSIF and PEs. In addition, there are differences between caprate and SNAC, which are rationalized based on their different molecular structures and critical micelle concentrations.
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4
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Kell DB. A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation. Adv Microb Physiol 2021; 78:1-177. [PMID: 34147184 DOI: 10.1016/bs.ampbs.2021.01.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.
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Affiliation(s)
- Douglas B Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative, Biology, University of Liverpool, Liverpool, United Kingdom; The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby, Denmark.
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5
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Hossain Saad MZ, Xiang L, Liao YS, Reznikov LR, Du J. The Underlying Mechanism of Modulation of Transient Receptor Potential Melastatin 3 by protons. Front Pharmacol 2021; 12:632711. [PMID: 33603674 PMCID: PMC7884864 DOI: 10.3389/fphar.2021.632711] [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: 11/23/2020] [Accepted: 01/04/2021] [Indexed: 12/03/2022] Open
Abstract
Transient receptor potential melastatin 3 channel (TRPM3) is a calcium-permeable nonselective cation channel that plays an important role in modulating glucose homeostasis in the pancreatic beta cells. However, how TRPM3 is regulated under physiological and pathological conditions is poorly understood. In this study, we found that both intracellular and extracellular protons block TRPM3 through its binding sites in the pore region. We demonstrated that external protons block TRPM3 with an inhibitory pH50 of 5.5. whereas internal protons inhibit TRPM3 with an inhibitory pH50 of 6.9. We identified three titratable residues, D1059, D1062, and D1073, at the vestibule of the channel pore that contributes to pH sensitivity. The mutation of D1073Q reduced TRPM3 current by low external pH 5.5 from 62 ± 3% in wildtype to 25 ± 6.0% in D1073Q mutant. These results indicate that D1073 is essential for pH sensitivity. In addition, we found that a single mutation of D1059 or D1062 enhanced pH sensitivity. In summary, our findings identify molecular determinants respionsible for the pH regulation of TRPM3. The inhibition of TRPM3 by protons may indicate an endogenous mechanism governing TRPM3 gating and its physiological/pathological functions.
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Affiliation(s)
- Md Zubayer Hossain Saad
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, United States.,Department of Biological Sciences, University of Toledo, Toledo, OH, United States
| | - Liuruimin Xiang
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, United States.,Department of Biological Sciences, University of Toledo, Toledo, OH, United States.,Program of Neuroscience, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Yan-Shin Liao
- Department of Physiological Sciences, University of Florida, Gainesville, FL, United States
| | - Leah R Reznikov
- Department of Physiological Sciences, University of Florida, Gainesville, FL, United States
| | - Jianyang Du
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, United States.,Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, United States
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6
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Grünewald F, Souza PCT, Abdizadeh H, Barnoud J, de Vries AH, Marrink SJ. Titratable Martini model for constant pH simulations. J Chem Phys 2020; 153:024118. [PMID: 32668918 DOI: 10.1063/5.0014258] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In this work, we deliver a proof of concept for a fast method that introduces pH effects into classical coarse-grained (CG) molecular dynamics simulations. Our approach is based upon the latest version of the popular Martini CG model to which explicit proton mimicking particles are added. We verify our approach against experimental data involving several different molecules and different environmental conditions. In particular, we compute titration curves, pH dependent free energies of transfer, and lipid bilayer membrane affinities as a function of pH. Using oleic acid as an example compound, we further illustrate that our method can be used to study passive translocation in lipid bilayers via protonation. Finally, our model reproduces qualitatively the expansion of the macromolecule dendrimer poly(propylene imine) as well as the associated pKa shift of its different generations. This example demonstrates that our model is able to pick up collective interactions between titratable sites in large molecules comprising many titratable functional groups.
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Affiliation(s)
- Fabian Grünewald
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Paulo C T Souza
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Haleh Abdizadeh
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Jonathan Barnoud
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Alex H de Vries
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
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7
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Stoppelman JP, McDaniel JG. Proton Transport in [BMIM+][BF4–]/Water Mixtures Near the Percolation Threshold. J Phys Chem B 2020; 124:5957-5970. [DOI: 10.1021/acs.jpcb.0c02487] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- John P. Stoppelman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia30332-0400, United States
| | - Jesse G. McDaniel
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia30332-0400, United States
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8
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Morelli AM, Ravera S, Calzia D, Panfoli I. An update of the chemiosmotic theory as suggested by possible proton currents inside the coupling membrane. Open Biol 2020; 9:180221. [PMID: 30966998 PMCID: PMC6501646 DOI: 10.1098/rsob.180221] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Understanding how biological systems convert and store energy is a primary purpose of basic research. However, despite Mitchell's chemiosmotic theory, we are far from the complete description of basic processes such as oxidative phosphorylation (OXPHOS) and photosynthesis. After more than half a century, the chemiosmotic theory may need updating, thanks to the latest structural data on respiratory chain complexes. In particular, up-to date technologies, such as those using fluorescence indicators following proton displacements, have shown that proton translocation is lateral rather than transversal with respect to the coupling membrane. Furthermore, the definition of the physical species involved in the transfer (proton, hydroxonium ion or proton currents) is still an unresolved issue, even though the latest acquisitions support the idea that protonic currents, difficult to measure, are involved. Moreover, FoF1-ATP synthase ubiquitous motor enzyme has the peculiarity (unlike most enzymes) of affecting the thermodynamic equilibrium of ATP synthesis. It seems that the concept of diffusion of the proton charge expressed more than two centuries ago by Theodor von Grotthuss is to be taken into consideration to resolve these issues. All these uncertainties remind us that also in biology it is necessary to consider the Heisenberg indeterminacy principle, which sets limits to analytical questions.
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Affiliation(s)
- Alessandro Maria Morelli
- 1 Pharmacy Department, Biochemistry Lab, University of Genova , Viale Benedetto XV 3, 16132 Genova , Italy
| | - Silvia Ravera
- 2 Experimental Medicine Department, University of Genova , Via De Toni 14, 16132 Genova , Italy
| | - Daniela Calzia
- 1 Pharmacy Department, Biochemistry Lab, University of Genova , Viale Benedetto XV 3, 16132 Genova , Italy
| | - Isabella Panfoli
- 2 Experimental Medicine Department, University of Genova , Via De Toni 14, 16132 Genova , Italy
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9
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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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10
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Proton leakage across lipid bilayers: Oxygen atoms of phospholipid ester linkers align water molecules into transmembrane water wires. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:439-451. [PMID: 30904457 DOI: 10.1016/j.bbabio.2019.03.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 02/20/2019] [Accepted: 03/10/2019] [Indexed: 12/31/2022]
Abstract
Up to half of the cellular energy gets lost owing to membrane proton leakage. The permeability of lipid bilayers to protons is by several orders of magnitude higher than to other cations, which implies efficient proton-specific passages. The nature of these passages remains obscure. By combining experimental measurements of proton flow across phosphatidylcholine vesicles, steered molecular dynamics (MD) simulations of phosphatidylcholine bilayers and kinetic modelling, we have analyzed whether protons could pass between opposite phospholipid molecules when they sporadically converge. The MD simulations showed that each time, when the phosphorus atoms of the two phosphatidylcholine molecules got closer than 1.6 nm, the eight oxygen atoms of their ester linkages could form a transmembrane 'oxygen passage' along which several water molecules aligned into a water wire. Proton permeability along such water wires would be limited by rearrangement of oxygen atoms, which could explain the experimentally shown independence of the proton permeability of pH, H2O/D2O substitution, and membrane dipole potential. We suggest that protons can cross lipid bilayers by moving along short, self-sustaining water wires supported by oxygen atoms of lipid ester linkages.
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11
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Yandrapalli N, Robinson T. Ultra-high capacity microfluidic trapping of giant vesicles for high-throughput membrane studies. LAB ON A CHIP 2019; 19:626-633. [PMID: 30632596 DOI: 10.1039/c8lc01275j] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Biomimetic systems such as model lipid membranes are vital to many research fields including synthetic biology, drug discovery and membrane biophysics. One of the most commonly used are giant unilamellar vesicles (GUVs) due to their size similarity with biological cells and their ease of production. Typical methods for handling such delicate objects are low-throughput and do not allow solution exchange or long-term observations, all of which limits the experimental options. Herein, we present a new device designed to confine large assemblies of GUVs in microfluidic traps but is still able to perform precise and fast solution exchanges. An optimised design allows efficient filling with as many as 114 GUVs per trap and over 23 000 GUVs per device. This allows high-throughput dataset acquisitions which we demonstrate with two proof-of-concept experiments: (i) end-point measurements of vesicle interior pH and (ii) membrane transport kinetics. Moreover, we show that the design is able to selectively trap sub-populations of specific vesicle sizes and assemble them in different layers. The device can easily be applied to other high-throughput membrane studies and will pave the way for future applications using vesicle assemblies to model cellular tissues or even prototissues.
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Affiliation(s)
- Naresh Yandrapalli
- Department of Theory & Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
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12
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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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13
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14
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Moss FR, Shuken SR, Mercer JAM, Cohen CM, Weiss TM, Boxer SG, Burns NZ. Ladderane phospholipids form a densely packed membrane with normal hydrazine and anomalously low proton/hydroxide permeability. Proc Natl Acad Sci U S A 2018; 115:9098-9103. [PMID: 30150407 PMCID: PMC6140541 DOI: 10.1073/pnas.1810706115] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Ladderane lipids are unique to anaerobic ammonium-oxidizing (anammox) bacteria and are enriched in the membrane of the anammoxosome, an organelle thought to compartmentalize the anammox process, which involves the toxic intermediate hydrazine (N2H4). Due to the slow growth rate of anammox bacteria and difficulty of isolating pure ladderane lipids, experimental evidence of the biological function of ladderanes is lacking. We have synthesized two natural and one unnatural ladderane phosphatidylcholine lipids and compared their thermotropic properties in self-assembled bilayers to distinguish between [3]- and [5]-ladderane function. We developed a hydrazine transmembrane diffusion assay using a water-soluble derivative of a hydrazine sensor and determined that ladderane membranes are as permeable to hydrazine as straight-chain lipid bilayers. However, pH equilibration across ladderane membranes occurs 5-10 times more slowly than across straight-chain lipid membranes. Langmuir monolayer analysis and the rates of fluorescence recovery after photobleaching suggest that dense ladderane packing may preclude formation of proton/hydroxide-conducting water wires. These data support the hypothesis that ladderanes prevent the breakdown of the proton motive force rather than blocking hydrazine transmembrane diffusion in anammox bacteria.
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Affiliation(s)
- Frank R Moss
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Steven R Shuken
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Jaron A M Mercer
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Carolyn M Cohen
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Thomas M Weiss
- Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, Menlo Park, CA 94025
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, CA 94305;
| | - Noah Z Burns
- Department of Chemistry, Stanford University, Stanford, CA 94305;
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15
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Srivastava A, Debnath A. Hydration dynamics of a lipid membrane: Hydrogen bond networks and lipid-lipid associations. J Chem Phys 2018. [DOI: 10.1063/1.5011803] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Affiliation(s)
- Abhinav Srivastava
- Department of Chemistry, Indian Institute of Technology Jodhpur, Karwad, Rajasthan, India
| | - Ananya Debnath
- Department of Chemistry, Indian Institute of Technology Jodhpur, Karwad, Rajasthan, India
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16
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Deplazes E, Poger D, Cornell B, Cranfield CG. The effect of hydronium ions on the structure of phospholipid membranes. Phys Chem Chem Phys 2018; 20:357-366. [DOI: 10.1039/c7cp06776c] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
This work studies the mechanisms by which hydronium ions modulate the structure of phospholipid bilayers.
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Affiliation(s)
- Evelyne Deplazes
- School of Biomedical Sciences
- Curtin Health Innovation Research Institute and Curtin Institute for Computation
- Curtin University
- Perth
- Australia
| | - David Poger
- School of Chemistry and Molecular Biosciences
- The University of Queensland
- Brisbane
- Australia
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17
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Affiliation(s)
- Jesse G. McDaniel
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Arun Yethiraj
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, United States
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18
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Gonzalez MA, Barriga HMG, Richens JL, Law RV, O'Shea P, Bresme F. How does ytterbium chloride interact with DMPC bilayers? A computational and experimental study. Phys Chem Chem Phys 2017; 19:9199-9209. [DOI: 10.1039/c7cp01400g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Lanthanide salts have been studied for many years, primarily in Nuclear Magnetic Resonance (NMR) experiments of mixed lipid–protein systems and more recently to study lipid flip-flop in model membrane systems.
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Affiliation(s)
| | | | | | - Robert V. Law
- Department of Chemistry
- Imperial College London
- London
- UK
| | - Paul O'Shea
- Department of Chemistry
- Imperial College London
- London
- UK
- School of Life Sciences
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19
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Strbak O, Kanuchova Z, Krafcik A. Proton Gradients as a Key Physical Factor in the Evolution of the Forced Transport Mechanism Across the Lipid Membrane. ORIGINS LIFE EVOL B 2016; 46:523-531. [PMID: 27038470 DOI: 10.1007/s11084-016-9496-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Accepted: 12/15/2015] [Indexed: 12/29/2022]
Abstract
A critical phase in the transition from prebiotic chemistry to biological evolution was apparently an asymmetric ion flow across the lipid membrane. Due to imbalance in the ion flow, the early lipid vesicles could selectively take the necessary molecules from the environment, and release the side-products from the vesicle. Natural proton gradients played a definitively crucial role in this process, since they remain the basis of energy transfer in the present-day cells. On the basis of this supposition, and the premise of the early vesicle membrane's impermeability to protons, we have shown that the emergence of the proton gradient in the lipid vesicle could be a key physical factor in the evolution of the forced transport mechanism (pore formation and active transport) across the lipid bilayer. This driven flow of protons across the membrane is the result of the electrochemical proton gradient and osmotic pressures on the integrity of the lipid vesicle. At a critical number of new lipid molecules incorporated into the vesicle, the energies associated with the creation of the proton gradient exceed the bending stiffness of the lipid membrane, and overlap the free energy of the lipid bilayer pore formation.
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Affiliation(s)
- Oliver Strbak
- Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Dubravska cesta 9, 841 04, Bratislava, Slovakia.
| | - Zuzana Kanuchova
- Astronomical Institute, Slovak Academy of Sciences, 059 60, Tatranska Lomnica, Slovakia
| | - Andrej Krafcik
- Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Dubravska cesta 9, 841 04, Bratislava, Slovakia
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20
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Zhang HY, Xu Q, Wang YK, Zhao TZ, Hu D, Wei DQ. Passive Transmembrane Permeation Mechanisms of Monovalent Ions Explored by Molecular Dynamics Simulations. J Chem Theory Comput 2016; 12:4959-4969. [PMID: 27599103 DOI: 10.1021/acs.jctc.6b00695] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Passive or unassisted ion permeation through lipid bilayers involves a type of rare events by which cells regulate their salt concentrations and pH. It is important to understand its mechanism in order to develop technologies of, for example, delivering or maintaining small drug-like molecules inside cells. In earlier simulations of passive ion permeations, the commonly used sampling methods usually define the positions of ions relative to the membrane as a measure of permeation, i.e., the collective variable, ignoring the active participations of other particles. Newly defined collective variables involving the movements of ions, lipids, and water molecules allow us to identify the transition paths on the free energy landscape using the 2D umbrella sampling techniques. In this work, this technique was used to study the permeation processes of some well-known ions, sodium, potassium, and chloride. It is found permeations of sodium and potassium are assisted by important lipid bilayer deformations and massive water solvation, while chloride may not. Chloride may have two different possible pathways, in which the energetic favorable one is similar to the solubility-diffusion model. The free energy barriers for the permeation of these ions are in semiquantitative agreement with experiments. Further analyses on the distributions of oxygens and interaction energies suggest the electrostatic interactions between ions and polar headgroups of lipids may greatly influence membrane deformation as well as the water wire and furthermore the free energy barriers of waterwire mediated pathways. For chloride, the nonwaterwire pathway may be energetically favorable.
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Affiliation(s)
- Hui-Yuan Zhang
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
| | - Qin Xu
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
| | - Yu-Kun Wang
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
| | - Tang-Zhen Zhao
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
| | - Dan Hu
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
| | - Dong-Qing Wei
- State Key Laboratory of Microbial Metabolism and School of Life Science and Biotechnology and ‡Department of Mathematics, Institute of Natural Science, and MOE-LEC, Shanghai Jiao Tong University , Shanghai 200240, China
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21
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Awasthi N, Hub JS. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects. J Chem Theory Comput 2016; 12:3261-9. [DOI: 10.1021/acs.jctc.6b00369] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Neha Awasthi
- Institute for Microbiology
and Genetics, Georg-August-Universität, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
| | - Jochen S. Hub
- Institute for Microbiology
and Genetics, Georg-August-Universität, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
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22
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Permeability across lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2254-2265. [PMID: 27085977 DOI: 10.1016/j.bbamem.2016.03.032] [Citation(s) in RCA: 182] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2016] [Revised: 03/28/2016] [Accepted: 03/29/2016] [Indexed: 11/22/2022]
Abstract
Molecular permeation through lipid membranes is a fundamental biological process that is important for small neutral molecules and drug molecules. Precise characterization of free energy surface and diffusion coefficients along the permeation pathway is required in order to predict molecular permeability and elucidate the molecular mechanisms of permeation. Several recent technical developments, including improved molecular models and efficient sampling schemes, are illustrated in this review. For larger penetrants, explicit consideration of multiple collective variables, including orientational, conformational degrees of freedom, are required to be considered in addition to the distance from the membrane center along the membrane normal. Although computationally demanding, this method can provide significant insights into the molecular mechanisms of permeation for molecules of medical and pharmaceutical importance. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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23
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McDaniel JG, Yethiraj A. Importance of hydrophobic traps for proton diffusion in lyotropic liquid crystals. J Chem Phys 2016; 144:094705. [DOI: 10.1063/1.4943131] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jesse G. McDaniel
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Arun Yethiraj
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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24
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Abstract
Water is crucial to the structure and function of biological membranes. In fact, the membrane's basic structural unit, i.e. the lipid bilayer, is self-assembled and stabilized by the so-called hydrophobic effect, whereby lipid molecules unable to hydrogen bond with water aggregate in order to prevent their hydrophobic portions from being exposed to water. However, this is just the beginning of the lipid-bilayer-water relationship. This mutual interaction defines vesicle stability in solution, controls small molecule permeation, and defines the spacing between lamella in multi-lamellar systems, to name a few examples. This chapter will describe the structural and dynamical properties central to these, and other water- lipid bilayer interactions.
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Affiliation(s)
- Jonathan D Nickels
- Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
| | - John Katsaras
- Biology & Soft Matter and Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
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25
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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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26
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Song B, Yuan H, Pham SV, Jameson CJ, Murad S. Nanoparticle permeation induces water penetration, ion transport, and lipid flip-flop. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:16989-17000. [PMID: 23171434 DOI: 10.1021/la302879r] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Nanoparticles are generally considered excellent candidates for targeted drug delivery. However, ion leakage and cytotoxicity induced by nanoparticle permeation is a potential problem in such drug delivery schemes because of the toxic effect of many ions. In this study, we have carried out a series of coarse-grained molecular dynamics simulations to investigate the water penetration, ion transport, and lipid molecule flip-flop in a protein-free phospholipid bilayer membrane during nanoparticle permeation. The effect of ion concentration gradient, pressure differential across the membrane, nanoparticle size, and permeation velocity have been examined in this work. Some conclusions from our studies include (1) The number of water molecules in the interior of the membrane during the nanoparticle permeation increases with the nanoparticle size and the pressure differential across the membrane but is unaffected by the nanoparticle permeation velocity or the ion concentration gradient. (2) Ion transport is sensitive to the size of nanoparticle as well as the ion concentration gradient between two sides of the membrane; no anion/cation selectivity is observed for small nanoparticle permeation, while anions are preferentially translocated through the membrane when the size of nanoparticle is large enough. (3) Incidences of lipid molecule flip-flop increases with the size of nanoparticle and ion concentration gradient and decreases with the pressure differential and the nanoparticle permeation velocity.
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Affiliation(s)
- Bo Song
- Department of Chemical Engineering, University of Illinois at Chicago, 810 South Clinton Street, Chicago, Illinois 60607, USA
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27
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Yamashita T, Peng Y, Knight C, Voth GA. Computationally Efficient Multiconfigurational Reactive Molecular Dynamics. J Chem Theory Comput 2012; 8:4863-4875. [PMID: 25100924 DOI: 10.1021/ct3006437] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
It is a computationally demanding task to explicitly simulate the electronic degrees of freedom in a system to observe the chemical transformations of interest, while at the same time sampling the time and length scales required to converge statistical properties and thus reduce artifacts due to initial conditions, finite-size effects, and limited sampling. One solution that significantly reduces the computational expense consists of molecular models in which effective interactions between particles govern the dynamics of the system. If the interaction potentials in these models are developed to reproduce calculated properties from electronic structure calculations and/or ab initio molecular dynamics simulations, then one can calculate accurate properties at a fraction of the computational cost. Multiconfigurational algorithms model the system as a linear combination of several chemical bonding topologies to simulate chemical reactions, also sometimes referred to as "multistate". These algorithms typically utilize energy and force calculations already found in popular molecular dynamics software packages, thus facilitating their implementation without significant changes to the structure of the code. However, the evaluation of energies and forces for several bonding topologies per simulation step can lead to poor computational efficiency if redundancy is not efficiently removed, particularly with respect to the calculation of long-ranged Coulombic interactions. This paper presents accurate approximations (effective long-range interaction and resulting hybrid methods) and multiple-program parallelization strategies for the efficient calculation of electrostatic interactions in reactive molecular simulations.
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Affiliation(s)
- Takefumi Yamashita
- Laboratory for Systems Biology and Medicine, Research Center for Advanced Science and Technology, the University of Tokyo, 4-6-1 Komaba, Tokyo, Japan
| | - Yuxing Peng
- Department of Chemistry, James Franck Institute, and Computation Institute, University of Chicago, Chicago, IL 6063
| | - Chris Knight
- Computing, Environment, and Life Sciences, Argonne National Laboratory, Argonne, IL 60439
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Computation Institute, University of Chicago, Chicago, IL 6063 ; Computing, Environment, and Life Sciences, Argonne National Laboratory, Argonne, IL 60439
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28
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Yamashita T, Voth GA. Insights into the mechanism of proton transport in cytochrome c oxidase. J Am Chem Soc 2012; 134:1147-52. [PMID: 22191804 DOI: 10.1021/ja209176e] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cytochrome c oxidase (CcO), known as complex IV of the electron transport chain, plays several important roles in aerobic cellular respiration. Electrons transferred from cytochrome c to CcO's catalytic site reduce molecular oxygen and produce a water molecule. These electron transfers also drive active proton pumping from the matrix (N-side) to intermembrane region (P-side) in mitochondria; the resultant proton gradient activates ATP synthase to produce ATP from ADP. Although the existence of the coupling between the electron transfer and the proton transport (PT) is established experimentally, its mechanism is not yet fully understood at the molecular level. In this work, it is shown why the reduction of heme a is essential for proton pumping. This is demonstrated via novel reactive molecular dynamics (MD) simulations that can describe the Grotthuss shuttling associated with the PT as well as the dynamic delocalization of the excess proton electronic charge defect. Moreover, the "valve" role of the Glu242 residue (bovine CcO notation) and the gate role of d-propionate of heme a(3) (PRDa3) in the explicit PT are explicitly demonstrated for the first time. These results provide conclusive evidence for the CcO proton transporting mechanism inferred from experiments, while deepening the molecular level understanding of the CcO proton switch.
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Affiliation(s)
- Takefumi Yamashita
- Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago, 5735 S. Ellis Ave., Chicago, Illinois 60637, USA
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29
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Agostini F, Vuilleumier R, Ciccotti G. Infrared spectroscopy of small protonated water clusters at room temperature: An effective modes analysis. J Chem Phys 2011; 134:084302. [DOI: 10.1063/1.3533229] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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30
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Agostini F, Vuilleumier R, Ciccotti G. Infrared spectroscopy and effective modes analysis of the protonated water dimer H+(H2O)2 at room temperature under H/D substitution. J Chem Phys 2011; 134:084303. [DOI: 10.1063/1.3521273] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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31
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Kausik R, Han S. Dynamics and state of lipid bilayer-internal water unraveled with solution state 1H dynamic nuclear polarization. Phys Chem Chem Phys 2011; 13:7732-46. [DOI: 10.1039/c0cp02512g] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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32
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A view of hydrogen/hydroxide flux across lipid membranes. J Membr Biol 2010; 237:21-30. [PMID: 20871986 DOI: 10.1007/s00232-010-9303-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 08/27/2010] [Indexed: 10/19/2022]
Abstract
A topic emerging roughly 30 years ago and engendering an incompletely resolved controversy is reviewed in this article: the relatively high permeability and pH independence associated with H(+)/OH(-) passive movements across lipid membranes. We summarize the expected characteristics of simple H(+)/OH(-) diffusion and those of a reaction between H(+) and OH(-) being attracted from opposite surfaces and condensing in an interfacial zone of the membrane. An interfacial H(+)/OH(-) reaction mechanism gives the experimentally observed behavior of an H(+)/OH(-) flux that is independent of the pH measurement range. This mechanism assumes that H(+) and OH(-) within the interfacial zone become electrostatically aligned on opposite sides of the hydrophobic membrane core. Electrostatic attraction and charge delocalization among a small cluster of water molecules surrounding the ions reduce the Born energy for H(+)/OH(-) insertion into lipid. This transmembrane condensation model predicts the magnitude of the experimentally determined H(+)/OH(-) flux, which is significantly greater than that of other monovalent ions. The consequences of an elevated H(+)/OH(-) permeability compared to other ions and the relative pH independence of this flux have consequences for understanding the chemical evolution of life.
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33
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Gurtovenko AA, Anwar J, Vattulainen I. Defect-Mediated Trafficking across Cell Membranes: Insights from in Silico Modeling. Chem Rev 2010; 110:6077-103. [DOI: 10.1021/cr1000783] [Citation(s) in RCA: 158] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Andrey A. Gurtovenko
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | - Jamshed Anwar
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | - Ilpo Vattulainen
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
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34
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Yamashita T, Voth GA. Properties of hydrated excess protons near phospholipid bilayers. J Phys Chem B 2010; 114:592-603. [PMID: 19924872 DOI: 10.1021/jp908768c] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The behavior of the hydrated excess proton near different lipid membranes is studied with the third generation of the multistate empirical valence bond (MS-EVB3) model [Wu, Y. J.; Chen, H. N.; Wang, F.; Paesani, F.; Voth, G. A. J. Phys. Chem. B 2008, 112, 467]. Dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylethanolamine (DOPE), and dioleoylphosphatidylglycerol (DOPG) are selected as example lipids. In spite of the differences of the head groups, the molecular dynamics simulations show that all the lipid membranes have a proton-collecting antenna effect with no free energy barrier between the bulk water and interface regions. By comparison with classical hydronium model simulations, it is found that an appropriate description of proton Grotthuss shuttling and associated charge defect delocalization are necessary to obtain the correct free energy profile for the hydrated excess proton. In addition, nanosecond time scale sampling is essential to evaluate the free energy profiles, because certain slow motions are needed to stabilize the excess proton in the deep membrane interface region. It is also found that the lateral diffusion coefficients are 1 order of magnitude smaller in the interface region than in bulk water for all the lipids. These coefficients are almost the same as those of the lipid head groups. Finally, since the lipid phosphates may possibly be protonated due to the proton antenna effect of the membrane, phosphate group protonation is investigated and discussed within the MS-EVB framework.
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Affiliation(s)
- Takefumi Yamashita
- Center of Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850, USA
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35
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Apajalahti T, Niemelä P, Govindan PN, Miettinen MS, Salonen E, Marrink SJ, Vattulainen I. Concerted diffusion of lipids in raft-like membranes. Faraday Discuss 2010; 144:411-30; discussion 445-81. [DOI: 10.1039/b901487j] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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36
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Khavrutskii IV, Gorfe AA, Lu B, McCammon JA. Free energy for the permeation of Na(+) and Cl(-) ions and their ion-pair through a zwitterionic dimyristoyl phosphatidylcholine lipid bilayer by umbrella integration with harmonic fourier beads. J Am Chem Soc 2009; 131:1706-16. [PMID: 19146415 PMCID: PMC2651636 DOI: 10.1021/ja8081704] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Understanding the mechanism of ion permeation across lipid bilayers is key to controlling osmotic pressure and developing new ways of delivering charged, drug-like molecules inside cells. Recent reports suggest ion-pairing as the mechanism to lower the free energy barrier for the ion permeation in disagreement with predictions from the simple electrostatic models. In this paper we quantify the effect of ion-pairing or charge quenching on the permeation of Na(+) and Cl(-) ions across DMPC lipid bilayer by computing the corresponding potentials of mean force (PMFs) using fully atomistic molecular dynamics simulations. We find that the free energy barrier to permeation reduces in the order Na(+)-Cl(-) ion-pair (27.6 kcal/mol) > Cl(-) (23.6 kcal/mol) > Na(+) (21.9 kcal/mol). Furthermore, with the help of these PMFs we derive the change in the binding free energy between the Na(+) and Cl(-) with respect to that in water as a function of the bilayer permeation depth. Despite the fact that the bilayer boosts the Na(+)-Cl(-) ion binding free energy by as high as 17.9 kcal/mol near its center, ion-pairing between such hydrophilic ions as Na(+) and Cl(-) does not assist their permeation. However, based on a simple thermodynamic cycle, we suggest that ion-pairing between ions of opposite charge and solvent philicity could enhance ion permeation. Comparison of the computed permeation barriers for Na(+) and Cl(-) ions with available experimental data supports this notion. This work establishes general computational methodology to address ion-pairing in fluid anisotropic media and details the ion permeation mechanism on atomic level.
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Affiliation(s)
- Ilja V Khavrutskii
- Howard Hughes Medical Institute, University of CaliforniaSan Diego, La Jolla, California 92093-0365, USA.
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37
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Marrink SJ, de Vries AH, Tieleman DP. Lipids on the move: simulations of membrane pores, domains, stalks and curves. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1788:149-68. [PMID: 19013128 DOI: 10.1016/j.bbamem.2008.10.006] [Citation(s) in RCA: 369] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2008] [Revised: 10/13/2008] [Accepted: 10/14/2008] [Indexed: 11/16/2022]
Abstract
In this review we describe the state-of-the-art of computer simulation studies of lipid membranes. We focus on collective lipid-lipid and lipid-protein interactions that trigger deformations of the natural lamellar membrane state, showing that many important biological processes including self-aggregation of membrane components into domains, the formation of non-lamellar phases, and membrane poration and curving, are now amenable to detailed simulation studies.
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Affiliation(s)
- Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
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38
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Iuchi S, Chen H, Paesani F, Voth GA. Hydrated Excess Proton at Water−Hydrophobic Interfaces. J Phys Chem B 2008; 113:4017-30. [DOI: 10.1021/jp805304j] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Satoru Iuchi
- Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850
| | - Hanning Chen
- Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850
| | - Francesco Paesani
- Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850
| | - Gregory A. Voth
- Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850
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39
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Simulations of skin barrier function: free energies of hydrophobic and hydrophilic transmembrane pores in ceramide bilayers. Biophys J 2008; 95:4763-71. [PMID: 18708461 DOI: 10.1529/biophysj.108.138545] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Transmembrane pore formation is central to many biological processes such as ion transport, cell fusion, and viral infection. Furthermore, pore formation in the ceramide bilayers of the stratum corneum may be an important mechanism by which penetration enhancers such as dimethylsulfoxide (DMSO) weaken the barrier function of the skin. We have used the potential of mean constraint force (PMCF) method to calculate the free energy of pore formation in ceramide bilayers in both the innate gel phase and in the DMSO-induced fluidized state. Our simulations show that the fluid phase bilayers form archetypal water-filled hydrophilic pores similar to those observed in phospholipid bilayers. In contrast, the rigid gel-phase bilayers develop hydrophobic pores. At the relatively small pore diameters studied here, the hydrophobic pores are empty rather than filled with bulk water, suggesting that they do not compromise the barrier function of ceramide membranes. A phenomenological analysis suggests that these vapor pores are stable, below a critical radius, because the penalty of creating water-vapor and tail-vapor interfaces is lower than that of directly exposing the strongly hydrophobic tails to water. The PMCF free energy profile of the vapor pore supports this analysis. The simulations indicate that high DMSO concentrations drastically impair the barrier function of the skin by strongly reducing the free energy required for pore opening.
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40
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Köfinger J, Dellago C. Biasing the Center of Charge in Molecular Dynamics Simulations with Empirical Valence Bond Models: Free Energetics of an Excess Proton in a Water Droplet. J Phys Chem B 2008. [DOI: 10.1021/jp8048422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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41
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Protein exchange dynamics at chemoreceptor clusters in Escherichia coli. Proc Natl Acad Sci U S A 2008; 105:6403-8. [PMID: 18427119 DOI: 10.1073/pnas.0710611105] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Signal processing in bacterial chemotaxis relies on large sensory complexes consisting of thousands of protein molecules. These clusters create a scaffold that increases the efficiency of pathway reactions and amplifies and integrates chemotactic signals. The cluster core in Escherichia coli comprises a ternary complex composed of receptors, kinase CheA, and adaptor protein CheW. All other chemotaxis proteins localize to clusters by binding either directly to receptors or to CheA. Here, we used fluorescence recovery after photobleaching (FRAP) to investigate the turnover of chemotaxis proteins at the cluster and their mobility in the cytoplasm. We found that cluster exchange kinetics were protein-specific and took place on several characteristic time scales that correspond to excitation, adaptation, and cell division, respectively. We further applied analytical and numerical data fitting to analyze intracellular protein diffusion and to estimate the rate constants of cluster equilibration in vivo. Our results indicate that the rates of protein turnover at the cluster have evolved to ensure optimal performance of the chemotaxis pathway.
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42
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Wu Y, Chen H, Wang F, Paesani F, Voth GA. An improved multistate empirical valence bond model for aqueous proton solvation and transport. J Phys Chem B 2007; 112:467-82. [PMID: 17999484 DOI: 10.1021/jp076658h] [Citation(s) in RCA: 208] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
A new multistate empirical valence bond model (MS-EVB3) is developed for proton solvation and transport in aqueous solutions. The new model and its quantum version (qMS-EVB3) are based on the MS-EVB2 model [Day et al., J. Chem. Phys. 2002, 117, 5839] and recently developed flexible water models-the SPC/Fw model [Wu et al. J. Chem. Phys. 2006, 124, 24503] and the qSPC/Fw model [Paesani et al. J. Chem. Phys. 2006, 125, 184507]-for classical and quantum simulations, respectively. Using ab initio data as benchmarks, the binding energies and optimized geometries calculated with the new model for protonated water clusters, as well as the potential energy surface for proton shuttling between water molecules in a cluster environment, are improved in comparison to the MS-EVB2 model. For aqueous solutions, classical and quantum molecular dynamics simulations with the MS-EVB3 model yield a more accurate description of the solvation structure and diffusive dynamics of the excess proton. New insight is also provided into the proton solvation and hopping dynamics in water, as well as the "amphiphilic" nature of the hydrated proton that has been predicted to give rise to its enhanced concentration at aqueous interfaces and an effectively lower pH of the air-water interface [Petersen et al. J. Phys. Chem. B 2004, 108, 14804].
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Affiliation(s)
- Yujie Wu
- Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850, USA
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Qin Z, Tepper HL, Voth GA. Effect of Membrane Environment on Proton Permeation through Gramicidin A Channels. J Phys Chem B 2007; 111:9931-9. [PMID: 17672487 DOI: 10.1021/jp0708998] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Multistate empirical valence bond simulations were employed to study proton transport through gramicidin A channels embedded in two different lipid bilayers, glycerol 1-monooleate (GMO) and diphytanolphosphatidylcholine (DiPhPC). Free energy barriers to proton permeation were derived using a new internal reaction coordinate describing the proton permeation process. The large quantitative and qualitative differences between the two systems are discussed in terms of local bilayer structures, ordering of interfacial water, and channel flexibility in the two environments.
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Affiliation(s)
- Zhen Qin
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA
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Leontiadou H, Mark AE, Marrink SJ. Ion transport across transmembrane pores. Biophys J 2007; 92:4209-15. [PMID: 17384063 PMCID: PMC1877794 DOI: 10.1529/biophysj.106.101295] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2006] [Accepted: 02/07/2007] [Indexed: 11/18/2022] Open
Abstract
To study the pore-mediated transport of ionic species across a lipid membrane, a series of molecular dynamics simulations have been performed of a dipalmitoyl-phosphatidyl-choline bilayer containing a preformed water pore in the presence of sodium and chloride ions. It is found that the stability of the transient water pores is greatly reduced in the presence of the ions. Specifically, the binding of sodium cations at the lipid/water interface increases the pore line tension, resulting in a destabilization of the pore. However, the application of mechanical stress opposes this effect. The flux of ions through these mechanically stabilized pores has been analyzed. Simulations indicate that the transport of the ions through the pores depends strongly on the size of the water channel. In the presence of small pores (radius <1.5 nm) permeation is slow, with both sodium and chloride permeating at similar rates. In the case in which the pores are larger (radius >1.5 nm), a crossover is observed to a regime where the anion flux is greatly enhanced. Based on these observations, a mechanism for the basal membrane permeability of ions is discussed.
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Affiliation(s)
- Hari Leontiadou
- Groningen Biomolecular Sciences and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4 9747 AG, Groningen, The Netherlands
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Swanson JMJ, Maupin CM, Chen H, Petersen MK, Xu J, Wu Y, Voth GA. Proton solvation and transport in aqueous and biomolecular systems: insights from computer simulations. J Phys Chem B 2007; 111:4300-14. [PMID: 17429993 PMCID: PMC2548316 DOI: 10.1021/jp070104x] [Citation(s) in RCA: 239] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The excess proton in aqueous media plays a pivotal role in many fundamental chemical (e.g., acid-base chemistry) and biological (e.g., bioenergetics and enzyme catalysis) processes. Understanding the hydrated proton is, therefore, crucial for chemistry, biology, and materials sciences. Although well studied for over 200 years, excess proton solvation and transport remains to this day mysterious, surprising, and perhaps even misunderstood. In this feature article, various efforts to address this problem through computer modeling and simulation will be described. Applications of computer simulations to a number of important and interesting systems will be presented, highlighting the roles of charge delocalization and Grotthuss shuttling, a phenomenon unique in many ways to the excess proton in water.
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Affiliation(s)
- Jessica M J Swanson
- Center for Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850, USA
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Tepper HL, Voth GA. Mechanisms of passive ion permeation through lipid bilayers: insights from simulations. J Phys Chem B 2006; 110:21327-37. [PMID: 17048962 PMCID: PMC4129643 DOI: 10.1021/jp064192h] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Multistate empirical valence bond and classical molecular dynamics simulations were used to explore mechanisms for passive ion leakage through a dimyristoyl phosphatidylcholine lipid bilayer. In accordance with a previous study on proton leakage (Biophys. J. 2005, 88, 3095), it was found that the permeation mechanism must be a highly concerted one, in which ion, solvent, and membrane coordinates are coupled. The presence of the ion itself significantly alters the response of those coordinates, suggesting that simulations of transmembrane water structures without explicit inclusion of the ionic solute are insufficient for elucidating transition mechanisms. The properties of H(+), Na(+), OH(-), and bare water molecules in the membrane interior were compared, both by biased sampling techniques and by constructing complete and unbiased transition paths. It was found that the anomalous difference in leakage rates between protons and other cations can be largely explained by charge delocalization effects rather than the usual kinetic picture (Grotthuss hopping of the proton). Permeability differences between anions and cations through phosphatidylcholine bilayers are correlated with suppression of favorable membrane breathing modes by cations.
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Affiliation(s)
- Harald L Tepper
- FOM Institute for Atomic and Molecular Physics, AMOLF, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
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Chen H, Ilan B, Wu Y, Zhu F, Schulten K, Voth GA. Charge delocalization in proton channels, I: the aquaporin channels and proton blockage. Biophys J 2006; 92:46-60. [PMID: 17056733 PMCID: PMC1697834 DOI: 10.1529/biophysj.106.091934] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The explicit contribution to the free energy barrier and proton conductance from the delocalized nature of the excess proton is examined in aquaporin channels using an accurate all-atom molecular dynamics computer simulation model. In particular, the channel permeation free energy profiles are calculated and compared for both a delocalized (fully Grotthuss shuttling) proton and a classical (nonshuttling) hydronium ion along two aquaporin channels, Aqp1 and GlpF. To elucidate the effects of the bipolar field thought to arise from two alpha-helical macrodipoles on proton blockage, free energy profiles were also calculated for computational mutants of the two channels where the bipolar field was eliminated by artificially discharging the backbone atoms. Comparison of the free energy profiles between the proton and hydronium cases indicates that the magnitude of the free energy barrier and position of the barrier peak for the fully delocalized and shuttling proton are somewhat different from the case of the (localized) classical hydronium. The proton conductance through the two aquaporin channels is also estimated using Poisson-Nernst-Planck theory for both the Grotthuss shuttling excess proton and the classical hydronium cation.
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Affiliation(s)
- Hanning Chen
- Center for Biophysical Modeling and Simulation, Department of Chemistry, University of Utah, Salt Lake City, Utah, USA
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Gensure R, Zeidel M, Hill W. Lipid raft components cholesterol and sphingomyelin increase H+/OH- permeability of phosphatidylcholine membranes. Biochem J 2006; 398:485-95. [PMID: 16706750 PMCID: PMC1559473 DOI: 10.1042/bj20051620] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
H+/OH- permeation through lipid bilayers occurs at anomalously high rates and the determinants of proton flux through membranes are poorly understood. Since all life depends on proton gradients, it is important to develop a greater understanding of proton leak phenomena. We have used stopped-flow fluorimetry to probe the influence of two lipid raft components, chol (cholesterol) and SM (sphingomyelin), on H+/OH- and water permeability. Increasing the concentrations of both lipids in POPC (palmitoyl-2-oleoyl phosphatidylcholine) liposomes decreased water permeability in a concentration-dependent manner, an effect that correlated with increased lipid order. Surprisingly, proton flux was increased by increasing the concentration of chol and SM. The chol effect was complex with molar concentrations of 17.9, 33 and 45.7% giving 2.8-fold (P<0.01), 2.2-fold (P<0.001) and 5.1-fold (P<0.001) increases in H+/OH- permeability from a baseline of 2.4x10(-2) cm/s. SM at 10 mole% effected a 2.8-fold increase (P<0.01), whereas 20 and 30 mole% enhanced permeability by 3.6-fold (P<0.05) and 4.1-fold respectively (P<0.05). Supplementing membranes containing chol with SM did not enhance H+/OH- permeability. Of interest was the finding that chol addition to soya-bean lipids decreased H+/OH- permeability, consistent with an earlier report [Ira and Krishnamoorthy (2001) J. Phys. Chem. B 105, 1484-1488]. We speculate that the presence of proton carriers in crude lipid extracts might contribute to this result. We conclude that (i) chol and SM specifically and independently increase rates of proton permeation in POPC bilayers, (ii) domains enriched in these lipids or domain interfaces may represent regions with high H+/OH- conductivity, (iii) H+/OH- fluxes are not governed by lipid order and (iv) chol can inhibit or promote H+/OH- permeability depending on the total lipid environment. Theories of proton permeation are discussed in the light of these results.
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Affiliation(s)
- Rebekah H. Gensure
- Laboratory of Epithelial Cell Biology, Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A
| | - Mark L. Zeidel
- Laboratory of Epithelial Cell Biology, Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A
| | - Warren G. Hill
- Laboratory of Epithelial Cell Biology, Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, U.S.A
- To whom correspondence should be addressed, at the present address: Beth Israel Deaconess Medical Center, 840 Memorial Drive, Cambridge, MA 02139, U.S.A. (email )
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Summons RE, Bradley AS, Jahnke LL, Waldbauer JR. Steroids, triterpenoids and molecular oxygen. Philos Trans R Soc Lond B Biol Sci 2006; 361:951-68. [PMID: 16754609 PMCID: PMC1578733 DOI: 10.1098/rstb.2006.1837] [Citation(s) in RCA: 165] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
There is a close connection between modern-day biosynthesis of particular triterpenoid biomarkers and presence of molecular oxygen in the environment. Thus, the detection of steroid and triterpenoid hydrocarbons far back in Earth history has been used to infer the antiquity of oxygenic photosynthesis. This prompts the question: were these compounds produced similarly in the past? In this paper, we address this question with a review of the current state of knowledge surrounding the oxygen requirement for steroid biosynthesis and phylogenetic patterns in the distribution of steroid and triterpenoid biosynthetic pathways. The hopanoid and steroid biosynthetic pathways are very highly conserved within the bacterial and eukaryotic domains, respectively. Bacteriohopanepolyols are produced by a wide range of bacteria, and are methylated in significant abundance at the C2 position by oxygen-producing cyanobacteria. On the other hand, sterol biosynthesis is sparsely distributed in distantly related bacterial taxa and the pathways do not produce the wide range of products that characterize eukaryotes. In particular, evidence for sterol biosynthesis by cyanobacteria appears flawed. Our experiments show that cyanobacterial cultures are easily contaminated by sterol-producing rust fungi, which can be eliminated by treatment with cycloheximide affording sterol-free samples. Sterols are ubiquitous features of eukaryotic membranes, and it appears likely that the initial steps in sterol biosynthesis were present in their modern form in the last common ancestor of eukaryotes. Eleven molecules of O2 are required by four enzymes to produce one molecule of cholesterol. Thermodynamic arguments, optimization of function and parsimony all indicate that an ancestral anaerobic pathway is highly unlikely. The known geological record of molecular fossils, especially steranes and triterpanes, is notable for the limited number of structural motifs that have been observed. With a few exceptions, the carbon skeletons are the same as those found in the lipids of extant organisms and no demonstrably extinct structures have been reported. Furthermore, their patterns of occurrence over billion year time-scales correlate strongly with environments of deposition. Accordingly, biomarkers are excellent indicators of environmental conditions even though the taxonomic affinities of all biomarkers cannot be precisely specified. Biomarkers are ultimately tied to biochemicals with very specific functional properties, and interpretations of the biomarker record will benefit from increased understanding of the biological roles of geologically durable molecules.
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Affiliation(s)
- Roger E Summons
- Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, 77 Massachusetts Avenue E34-246, Cambridge, MA 02139-4307, USA.
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Abstract
Two new studies demonstrate that transmembrane voltage-sensing domains can act without an obvious pore-forming domain to sense membrane potential changes and make a proton-selective pore.
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