1
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Scott HL, Burns-Casamayor V, Dixson AC, Standaert RF, Stanley CB, Stingaciu LR, Carrillo JMY, Sumpter BG, Katsaras J, Qiang W, Heberle FA, Mertz B, Ashkar R, Barrera FN. Neutron spin echo shows pHLIP is capable of retarding membrane thickness fluctuations. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184349. [PMID: 38815687 PMCID: PMC11365786 DOI: 10.1016/j.bbamem.2024.184349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2024] [Revised: 04/03/2024] [Accepted: 05/21/2024] [Indexed: 06/01/2024]
Abstract
Cell membranes are responsible for a range of biological processes that require interactions between lipids and proteins. While the effects of lipids on proteins are becoming better understood, our knowledge of how protein conformational changes influence membrane dynamics remains rudimentary. Here, we performed experiments and computer simulations to study the dynamic response of a lipid membrane to changes in the conformational state of pH-low insertion peptide (pHLIP), which transitions from a surface-associated (SA) state at neutral or basic pH to a transmembrane (TM) α-helix under acidic conditions. Our results show that TM-pHLIP significantly slows down membrane thickness fluctuations due to an increase in effective membrane viscosity. Our findings suggest a possible membrane regulatory mechanism, where the TM helix affects lipid chain conformations, and subsequently alters membrane fluctuations and viscosity.
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Affiliation(s)
- Haden L Scott
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville 37996, United States of America
| | - Violeta Burns-Casamayor
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506, United States of America
| | - Andrew C Dixson
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville 37996, United States of America
| | - Robert F Standaert
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville 37996, United States of America; C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506, United States of America; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Christopher B Stanley
- Shull Wollan Center - a Joint Institute for Neutron Sciences, Oak Ridge, TN 37831, United States of America; Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Laura-Roxana Stingaciu
- Labs and Soft Matter Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America; JCNS1, FZJ outstation at SNS, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - Jan-Michael Y Carrillo
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America; Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, United States of America
| | - Bobby G Sumpter
- Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America; Center for Nanophase Materials Sciences, Oak Ridge, TN 37831, United States of America
| | - John Katsaras
- Shull Wollan Center - a Joint Institute for Neutron Sciences, Oak Ridge, TN 37831, United States of America; Labs and Soft Matter Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America; Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, United States of America
| | - Wei Qiang
- Department of Chemistry, the State University of New York, Binghamton, NY 13902, United States of America
| | - Frederick A Heberle
- Department of Chemistry, University of Tennessee, Knoxville, TN 37920, United States of America
| | - Blake Mertz
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506, United States of America; West Virginia University Cancer Institute, Morgantown, WV 26506, United States of America
| | - Rana Ashkar
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, United States of America; Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 24061, United States of America.
| | - Francisco N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville 37996, United States of America.
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2
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Hossain MZ, Stroberg W. Bilayer tension-induced clustering of the UPR sensor IRE1. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184262. [PMID: 38081494 DOI: 10.1016/j.bbamem.2023.184262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 10/19/2023] [Accepted: 12/07/2023] [Indexed: 12/17/2023]
Abstract
The endoplasmic reticulum acts as a protein quality control center where a range of chaperones and foldases facilitates protein folding. IRE1 is a sensory transmembrane protein that transduces signals of proteotoxic stress by forming clusters and activating a cellular program called the unfolded protein response (UPR). Recently, membrane thickness variation due to membrane compositional changes have been shown to drive IRE1 cluster formation, activating the UPR even in the absence of proteotoxic stress. Here, we demonstrate a direct relationship between bilayer tension and UPR activation based on IRE1 dimer stability. The stability of the IRE1 dimer in a (50%DOPC-50%POPC) membrane at different applied bilayer tensions was analyzed via molecular dynamics simulations. The potential of mean force for IRE1 dimerization predicts a higher concentration of IRE1 dimers for both tensed and compressed ER membranes. This study shows that IRE1 may be a mechanosensitive membrane protein and establishes a direct biophysical relationship between bilayer tension and UPR activation.
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Affiliation(s)
- Md Zobayer Hossain
- Department of Mechanical Engineering, University of Alberta, 9211-116 Street NW, Edmonton, T6G 1H9, Alberta, Canada.
| | - Wylie Stroberg
- Department of Mechanical Engineering, University of Alberta, 9211-116 Street NW, Edmonton, T6G 1H9, Alberta, Canada.
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3
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Ahmed M, Billah MM, Tamba Y, Yamazaki M. Estimation of negative membrane tension in lipid bilayers and its effect on antimicrobial peptide magainin 2-induced pore formation. J Chem Phys 2024; 160:011101. [PMID: 38165103 DOI: 10.1063/5.0174288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 12/10/2023] [Indexed: 01/03/2024] Open
Abstract
Positive membrane tension in the stretched plasma membrane of cells and in the stretched lipid bilayer of vesicles has been well analyzed quantitatively, whereas there is limited quantitative information on negative membrane tension in compressed plasma membranes and lipid bilayers. Here, we examined negative membrane tension quantitatively. First, we developed a theory to describe negative membrane tension by analyzing the free energy of lipid bilayers to obtain a theoretical equation for negative membrane tension. This allowed us to obtain an equation describing the negative membrane tension (σosm) for giant unilamellar vesicles (GUVs) in hypertonic solutions due to negative osmotic pressure (Π). Then, we experimentally estimated the negative membrane tension for GUVs in hypertonic solutions by measuring the rate constant (kr) of rupture of the GUVs induced by the constant tension (σex) due to an external force as a function of σex. We found that larger σex values were required to induce the rupture of GUVs under negative Π compared with GUVs in isotonic solution and quantitatively determined the negative membrane tension induced by Π (σosm) by the difference between these σex values. At small negative Π, the experimental values of negative σosm agree with their theoretical values within experimental error, but as negative Π increases, the deviation increases. Negative tension increased the stability of GUVs because higher tensions were required for GUV rupture, and the rate constant of antimicrobial peptide magainin 2-induced pore formation decreased.
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Affiliation(s)
- Marzuk Ahmed
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
| | - Md Masum Billah
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
| | - Yukihiro Tamba
- General Education, National Institute of Technology, Suzuka College, Suzuka 510-0294, Japan
| | - Masahito Yamazaki
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
- Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, Shizuoka 422-8529, Japan
- Department of Physics, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan
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4
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Huang W, Sakuma S, Tottori N, Sugano SS, Yamanishi Y. Viscosity-aided electromechanical poration of cells for transfecting molecules. LAB ON A CHIP 2022; 22:4276-4291. [PMID: 36263697 DOI: 10.1039/d2lc00628f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Cell poration technologies offer opportunities not only to understand the activities of biological molecules but also to investigate genetic manipulation possibilities. Unfortunately, transferring large molecules that can carry huge genomic information is challenging. Here, we demonstrate electromechanical poration using a core-shell-structured microbubble generator, consisting of a fine microelectrode covered with a dielectric material. By introducing a microcavity at its tip, we could concentrate the electrical field with the application of electric pulses and generate microbubbles for electromechanical stimulation of cells. Specifically, the technology enables transfection with molecules that are thousands of kDa even into osteoblasts and Chlamydomonas, which are generally considered to be difficult to inject. Notably, we found that the transfection efficiency can be enhanced by adjusting the viscosity of the cell suspension, which was presumably achieved by remodeling of the membrane cytoskeleton. The applicability of the approach to a variety of cell types opens up numerous emerging gene engineering applications.
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Affiliation(s)
- Wenjing Huang
- Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan.
| | - Shinya Sakuma
- Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan.
| | - Naotomo Tottori
- Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan.
| | - Shigeo S Sugano
- Bioproduction Research Institute, The National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki 305-8566, Japan.
| | - Yoko Yamanishi
- Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan.
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5
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Rajagopal V, Arumugam S, Hunter PJ, Khadangi A, Chung J, Pan M. The Cell Physiome: What Do We Need in a Computational Physiology Framework for Predicting Single-Cell Biology? Annu Rev Biomed Data Sci 2022; 5:341-366. [PMID: 35576556 DOI: 10.1146/annurev-biodatasci-072018-021246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Modern biology and biomedicine are undergoing a big data explosion, needing advanced computational algorithms to extract mechanistic insights on the physiological state of living cells. We present the motivation for the Cell Physiome project: a framework and approach for creating, sharing, and using biophysics-based computational models of single-cell physiology. Using examples in calcium signaling, bioenergetics, and endosomal trafficking, we highlight the need for spatially detailed, biophysics-based computational models to uncover new mechanisms underlying cell biology. We review progress and challenges to date toward creating cell physiome models. We then introduce bond graphs as an efficient way to create cell physiome models that integrate chemical, mechanical, electromagnetic, and thermal processes while maintaining mass and energy balance. Bond graphs enhance modularization and reusability of computational models of cells at scale. We conclude with a look forward at steps that will help fully realize this exciting new field of mechanistic biomedical data science. Expected final online publication date for the Annual Review of Biomedical Data Science, Volume 5 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Vijay Rajagopal
- Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia;
| | - Senthil Arumugam
- Cellular Physiology Lab, Monash Biomedicine Discovery Institute, Faculty of Medicine, Nursing and Health Sciences; European Molecular Biological Laboratory (EMBL) Australia; and Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton/Melbourne, Victoria, Australia
| | - Peter J Hunter
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Afshin Khadangi
- Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia;
| | - Joshua Chung
- Department of Biomedical Engineering, University of Melbourne, Melbourne, Victoria, Australia;
| | - Michael Pan
- School of Mathematics and Statistics, University of Melbourne, Melbourne, Victoria, Australia
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6
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Assessing hypoxic damage to placental trophoblasts by measuring membrane viscosity of extracellular vesicles. Placenta 2022; 121:14-22. [PMID: 35245720 PMCID: PMC9010367 DOI: 10.1016/j.placenta.2022.02.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 02/06/2022] [Accepted: 02/22/2022] [Indexed: 11/22/2022]
Abstract
INTRODUCTION As highly sophisticated intercellular communication vehicles in biological systems, extracellular vesicles (EVs) have been investigated as both promising liquid biopsy-based disease biomarkers and drug delivery carriers. Despite tremendous progress in understanding their biological and physiological functions, mechanical characterization of these nanoscale entities remains challenging due to the limited availability of proper techniques. Especially, whether damage to parental cells can be reflected by the mechanical properties of their EVs remains unknown. METHODS In this study, we characterized membrane viscosities of different types of EVs collected from primary human trophoblasts (PHTs), including apoptotic bodies, microvesicles and small extracellular vesicles, using fluorescence lifetime imaging microscopy (FLIM). The biochemical origin of EV membrane viscosity was examined by analyzing their phospholipid composition, using mass spectrometry. RESULTS We found that different EV types derived from the same cell type exhibit different membrane viscosities. The measured membrane viscosity values are well supported by the lipidomic analysis of the phospholipid compositions. We further demonstrate that the membrane viscosity of microvesicles can faithfully reveal hypoxic injury of the human trophoblasts. More specifically, the membrane of PHT microvesicles released under hypoxic condition is less viscous than its counterpart under standard culture condition, which is supported by the reduction in the phosphatidylethanolamine-to-phosphatidylcholine ratio in PHT microvesicles. DISCUSSION Our study suggests that biophysical properties of released trophoblastic microvesicles can reflect cell health. Characterizing EV's membrane viscosity may pave the way for the development of new EV-based clinical applications.
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7
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Abstract
The cell membrane serves as a barrier that restricts the rate of exchange of diffusible molecules. Tension in the membrane regulates many crucial cell functions involving shape changes and motility, cell signaling, endocytosis, and mechanosensation. Tension reflects the forces contributed by the lipid bilayer, the cytoskeleton, and the extracellular matrix. With a fluid-like bilayer model, membrane tension is presumed uniform and hence propagated instantaneously. In this review, we discuss techniques to measure the mean membrane tension and how to resolve the stresses in different components and consider the role of bilayer heterogeneity.
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Affiliation(s)
- Pei-Chuan Chao
- Department of Civil, Structural and Environmental Engineering, University at Buffalo, The State University of New York, Buffalo, NY, United States
| | - Frederick Sachs
- Department of Physiology and Biophysics, University at Buffalo, The State University of New York, Buffalo, NY, United States.
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8
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Yee SM, Gillams RJ, McLain SE, Lorenz CD. Effects of lipid heterogeneity on model human brain lipid membranes. SOFT MATTER 2021; 17:126-135. [PMID: 33155582 DOI: 10.1039/d0sm01766c] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Cell membranes naturally contain a heterogeneous lipid distribution. However, homogeneous bilayers are commonly preferred and utilised in computer simulations due to their relative simplicity, and the availability of lipid force field parameters. Recently, experimental lipidomics data for the human brain cell membranes under healthy and Alzheimer's disease (AD) conditions were investigated, since disruption to the lipid composition has been implicated in neurodegenerative disorders, including AD [R. B. Chan et al., J. Biol. Chem., 2012, 287, 2678-2688]. In order to observe the effects of lipid complexity on the various bilayer properties, molecular dynamics simulations were used to study four membranes with increasing heterogeneity: a pure POPC membrane, a POPC and cholesterol membrane in a 1 : 1 ratio (POPC-CHOL), and to our knowledge, the first realistic models of a healthy brain membrane and an Alzheimer's diseased brain membrane. Numerous structural, interfacial, and dynamical properties, including the area per lipid, interdigitation, dipole potential, and lateral diffusion of the two simple models, POPC and POPC-CHOL, were analysed and compared to those of the complex brain models consisting of 27 lipid components. As the membranes gain heterogeneity, a number of alterations were found in the structural and dynamical properties, and more significant differences were observed in the lateral diffusion. Additionally, we observed snorkeling behaviour of the lipid tails that may play a role in the permeation of small molecules across biological membranes. In this work, atomistic description of realistic brain membrane models is provided, which can add insight towards the permeability and transport pathways of small molecules across these membrane barriers.
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Affiliation(s)
- Sze May Yee
- Department of Physics, King's College London, London WC2R 2LS, UK.
| | - Richard J Gillams
- School of Electronics and Computer Science, and Institute for Life Sciences, University of Southampton, Southampton SO17 1BJ, UK
| | - Sylvia E McLain
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9RH, UK
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9
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Filipe HAL, Moreno MJ, Loura LMS. The Secret Lives of Fluorescent Membrane Probes as Revealed by Molecular Dynamics Simulations. Molecules 2020; 25:E3424. [PMID: 32731549 PMCID: PMC7435664 DOI: 10.3390/molecules25153424] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/23/2020] [Accepted: 07/25/2020] [Indexed: 12/15/2022] Open
Abstract
Fluorescent probes have been employed for more than half a century to study the structure and dynamics of model and biological membranes, using spectroscopic and/or microscopic experimental approaches. While their utilization has led to tremendous progress in our knowledge of membrane biophysics and physiology, in some respects the behavior of bilayer-inserted membrane probes has long remained inscrutable. The location, orientation and interaction of fluorophores with lipid and/or water molecules are often not well known, and they are crucial for understanding what the probe is actually reporting. Moreover, because the probe is an extraneous inclusion, it may perturb the properties of the host membrane system, altering the very properties it is supposed to measure. For these reasons, the need for independent methodologies to assess the behavior of bilayer-inserted fluorescence probes has been recognized for a long time. Because of recent improvements in computational tools, molecular dynamics (MD) simulations have become a popular means of obtaining this important information. The present review addresses MD studies of all major classes of fluorescent membrane probes, focusing in the period between 2011 and 2020, during which such work has undergone a dramatic surge in both the number of studies and the variety of probes and properties accessed.
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Affiliation(s)
- Hugo A. L. Filipe
- Chemistry Department, Coimbra Chemistry Center, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal;
| | - Maria João Moreno
- Coimbra Chemistry Center and CNC—Center for Neuroscience and Cell Biology, Chemistry Department, Faculty of Sciences and Technology, University of Coimbra, 3004-535 Coimbra, Portugal;
| | - Luís M. S. Loura
- Coimbra Chemistry Center and CNC—Center for Neuroscience and Cell Biology, Faculty of Pharmacy, University of Coimbra, 3000-548 Coimbra, Portugal
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10
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Zaki AM, Carbone P. Amphiphilic copolymers change the nature of the ordered-to-disordered phase transition of lipid membranes from discontinuous to continuous. Phys Chem Chem Phys 2019; 21:13746-13757. [PMID: 31209450 DOI: 10.1039/c9cp01293a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The phase behaviour as a function of temperature is explored for pure phospholipid (DPPC) and hybrid lipid-polymer (DPPC/Pluronic L64) bilayers with the aid of atomistic MD simulations. The range of the fixed-temperature simulations includes temperatures below and above the known melting temperature (Tm) for DPPC membranes. For the pure lipid bilayer, the main phase transition is discontinuous, as verified by the abrupt changes observed in the membrane structure, elasticity and the lipid diffusivity near the critical temperature Tm, which lies in the region 298.15-303.15 K. A pre-transition step is detected at 298.15 K which has been identified as the ripple phase (Pβ'), where ordered and disordered lipids coexist, causing thickness fluctuations. In the ordered gel phase, the positional ordering as assessed by the lipid radial distribution functions is long-range and some degree of hexagonal packing is measured. The hybrid bilayers on the other hand, transform from a more ordered to a disordered phase in a continuous manner, without finite jumps in their properties. No signs of the ripple phase are identified and the ordered phase exhibits very limited hexagonal packing and some positional ordering that decays fast. The effect of the inserted polymers in the two phases is reversed; at low temperatures, they render the membrane thinner, less cohesive and less ordered compared to the pure one, with the lipids assuming faster diffusion rates, whereas at high temperatures, the polymer interaction with the lipids acts reducing their diffusivity, but also increasing the lipid tail ordering and the membrane stiffness. The ability of the amphiphilic L64 copolymers to change the nature of the main phase transition of lipid membranes and their properties both in the ordered and the disordered phase is of vital importance for the prediction of both the efficacy of hybrid lipid/polymer nanoparticles as drug delivery vehicles as well as their potential adverse implications during interactions with healthy cell membranes.
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Affiliation(s)
- Afroditi Maria Zaki
- School of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester M13 9PL, UK.
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11
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Giliberti V, Polito R, Ritter E, Broser M, Hegemann P, Puskar L, Schade U, Zanetti-Polzi L, Daidone I, Corni S, Rusconi F, Biagioni P, Baldassarre L, Ortolani M. Tip-Enhanced Infrared Difference-Nanospectroscopy of the Proton Pump Activity of Bacteriorhodopsin in Single Purple Membrane Patches. NANO LETTERS 2019; 19:3104-3114. [PMID: 30950626 PMCID: PMC6745627 DOI: 10.1021/acs.nanolett.9b00512] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 04/02/2019] [Indexed: 05/21/2023]
Abstract
Photosensitive proteins embedded in the cell membrane (about 5 nm thickness) act as photoactivated proton pumps, ion gates, enzymes, or more generally, as initiators of stimuli for the cell activity. They are composed of a protein backbone and a covalently bound cofactor (e.g. the retinal chromophore in bacteriorhodopsin (BR), channelrhodopsin, and other opsins). The light-induced conformational changes of both the cofactor and the protein are at the basis of the physiological functions of photosensitive proteins. Despite the dramatic development of microscopy techniques, investigating conformational changes of proteins at the membrane monolayer level is still a big challenge. Techniques based on atomic force microscopy (AFM) can detect electric currents through protein monolayers and even molecular binding forces in single-protein molecules but not the conformational changes. For the latter, Fourier-transform infrared spectroscopy (FTIR) using difference-spectroscopy mode is typically employed, but it is performed on macroscopic liquid suspensions or thick films containing large amounts of purified photosensitive proteins. In this work, we develop AFM-assisted, tip-enhanced infrared difference-nanospectroscopy to investigate light-induced conformational changes of the bacteriorhodopsin mutant D96N in single submicrometric native purple membrane patches. We obtain a significant improvement compared with the signal-to-noise ratio of standard IR nanospectroscopy techniques by exploiting the field enhancement in the plasmonic nanogap that forms between a gold-coated AFM probe tip and an ultraflat gold surface, as further supported by electromagnetic and thermal simulations. IR difference-spectra in the 1450-1800 cm-1 range are recorded from individual patches as thin as 10 nm, with a diameter of less than 500 nm, well beyond the diffraction limit for FTIR microspectroscopy. We find clear spectroscopic evidence of a branching of the photocycle for BR molecules in direct contact with the gold surfaces, with equal amounts of proteins either following the standard proton-pump photocycle or being trapped in an intermediate state not directly contributing to light-induced proton transport. Our results are particularly relevant for BR-based optoelectronic and energy-harvesting devices, where BR molecular monolayers are put in contact with metal surfaces, and, more generally, for AFM-based IR spectroscopy studies of conformational changes of proteins embedded in intrinsically heterogeneous native cell membranes.
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Affiliation(s)
- Valeria Giliberti
- Istituto
Italiano di Tecnologia, Center for Life NanoScience, Viale Regina Elena 291, I-00161 Roma, Italy
- E-mail:
| | - Raffaella Polito
- Department
of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, I-00185 Roma, Italy
| | - Eglof Ritter
- Humboldt-Universität
zu Berlin, Institut für
Biologie, Invalidenstraße
42, D-10115 Berlin, Germany
| | - Matthias Broser
- Humboldt-Universität
zu Berlin, Institut für
Biologie, Invalidenstraße
42, D-10115 Berlin, Germany
| | - Peter Hegemann
- Humboldt-Universität
zu Berlin, Institut für
Biologie, Invalidenstraße
42, D-10115 Berlin, Germany
| | - Ljiljana Puskar
- Helmholtz-Zentrum
Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany
| | - Ulrich Schade
- Helmholtz-Zentrum
Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany
| | - Laura Zanetti-Polzi
- Department
of Physical and Chemical Sciences, University
of L’Aquila, Via Vetoio, I-67010 L’Aquila, Italy
| | - Isabella Daidone
- Department
of Physical and Chemical Sciences, University
of L’Aquila, Via Vetoio, I-67010 L’Aquila, Italy
| | - Stefano Corni
- Department
of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova, Italy
- CNR
Institute
of Nanoscience, Via Campi
213/A, I-41125 Modena, Italy
| | - Francesco Rusconi
- Dipartimento
di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
| | - Paolo Biagioni
- Dipartimento
di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
| | - Leonetta Baldassarre
- Department
of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, I-00185 Roma, Italy
| | - Michele Ortolani
- Istituto
Italiano di Tecnologia, Center for Life NanoScience, Viale Regina Elena 291, I-00161 Roma, Italy
- Department
of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, I-00185 Roma, Italy
- E-mail:
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12
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Liu J, Chen C, Lu C, Li W. Different mechanisms on the stabilization of POPC membrane by trehalose upon varied mechanical stress. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2018.10.094] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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13
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Zhang J, Wang Y, Zheng Z, Sun X, Chen T, Li C, Zhang X, Guo J. Intracellular ion and protein nanoparticle-induced osmotic pressure modify astrocyte swelling and brain edema in response to glutamate stimuli. Redox Biol 2019; 21:101112. [PMID: 30685709 PMCID: PMC6351271 DOI: 10.1016/j.redox.2019.101112] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 01/02/2019] [Accepted: 01/14/2019] [Indexed: 12/28/2022] Open
Abstract
Intracellular tension activity plays a crucial role in cytotoxic brain edema and astrocyte swelling. Here, a few genetically encoded FRET-based tension probes were designed to detect cytoskeletal structural tension optically, including their magnitude and vectors. The astrocyte swelling resulted in GFAP tension increment, which is associated with the antagonistic effect of inward microfilaments (MFs) and microtubules (MTs) forces. In glutamate-induced astrocyte swelling, GFAP tension rise resulted from outward ion and protein nanoparticle-induced osmotic pressure (PN-OP) increases, where PN-OP could be elicited by MF and MT depolymerization, protein nanoparticle production, and activation of cofilin and stathmin-1. Attenuation of both ion osmotic pressure and PN-OP by drug combinations, together with free-radical scavenger, relieved cerebral edema in vivo. The study suggests that intracellular osmotic pressure (especially PN-OP) has a pivotal role in glutamate-induced astrocyte swelling and brain edema. Recovery of cytoplasmic potential is a promising target to develop new drugs and cure brain edema.
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Affiliation(s)
- JiaRui Zhang
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - YuXuan Wang
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - ZiHui Zheng
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - XiaoHe Sun
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - TingTing Chen
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - Chen Li
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - XiaoLong Zhang
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China
| | - Jun Guo
- State Key Laboratory Cultivation Base For TCM Quality and Efficacy, School of Medicine and Life Science, Nanjing University of Chinese Medicine, Nanjing 210023, PR China; Key Laboratory of Drug Target and Drug for Degenerative Disease, Nanjing University of Chinese Medicine, Nanjing, PR China; Jiangsu Key Laboratory of Pediatric Respiratory Disease, Institute of Pediatrics, Nanjing University of Chinese Medicine, Nanjing, PR China.
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14
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Oroskar PA, Jameson CJ, Murad S. Molecular-Level "Observations" of the Behavior of Gold Nanoparticles in Aqueous Solution and Interacting with a Lipid Bilayer Membrane. Methods Mol Biol 2019; 2000:303-359. [PMID: 31148024 DOI: 10.1007/978-1-4939-9516-5_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We use coarse-grained molecular dynamics simulations to "observe" details of interactions between ligand-covered gold nanoparticles and a lipid bilayer model membrane. In molecular dynamics simulations, one puts the individual atoms and groups of atoms of the physical system to be "observed" into a simulation box, specifies the forms of the potential energies of interactions between them (ultimately quantum based), and lets them individually move classically according to Newton's equations of motion, based on the forces arising from the assumed potential energy forms. The atoms that are chemically bonded to each other stay chemically bonded, following known potentials (force fields) that permit internal degrees of freedom (internal rotation, torsion, vibrations), and the interactions between nonbonded atoms are simplified to Lennard-Jones forms (in our case) and coulombic (where electrical charges are present) in which the parameters are previously optimized to reproduce thermodynamic properties or are based on quantum electronic calculations. The system is started out at a reasonable set of coordinates for all atoms or groups of atoms, and then permitted to develop according to the equations of motion, one small step (usually 10 fs time step) at a time, for millions of steps until the system is at a quasi-equilibrium (usually reached after hundreds of nanoseconds). We then let the system play out its motions further for many nanoseconds to observe the behavior, periodically taking snapshots (saving all positions and energies), and post-processing the snapshots to obtain various average descriptions of the system. Alkanethiols of various lengths serve as examples of hydrophobic ligands and methyl-terminated PEG with various numbers of monomer units serve as examples of hydrophilic ligands. Spherical gold particles of various diameters as well as gold nanorods form the core to which ligands are attached. The nanoparticles are characterized at the molecular level, especially the distributions of ligand configurations and their dependence on ligand length, and surface coverage. Self-assembly of the bilayer from an isotropic solution and observation of membrane properties that correspond well to experimental values validate the simulations. The mechanism of permeation of a gold NP coated with either a hydrophobic or a hydrophilic ligand, and its dependence on surface coverage, ligand length, core diameter, and core shape, is investigated. Lipid response such as lipid flip-flops, lipid extraction, and changes in order parameter of the lipid tails are examined in detail. The mechanism of permeation of a PEGylated nanorod is shown to occur by tilting, lying down, rotating, and straightening up. The nature of the information provided by molecular dynamics simulations permits understanding of the detailed behavior of gold nanoparticles interacting with lipid membranes which in turn helps to understand why some known systems work better than others and aids the design of new particles and improvement of methods for preparing existing ones.
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Affiliation(s)
- Priyanka A Oroskar
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL, USA
| | - Cynthia J Jameson
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL, USA
| | - Sohail Murad
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL, USA.
- Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL, USA.
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15
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Abstract
Vascular endothelial cells (ECs) maintain circulatory system homeostasis by changing their functions in response to changes in hemodynamic forces, including shear stress and stretching. However, it is unclear how ECs sense changes in shear stress and stretching and transduce these changes into intracellular biochemical signals. The plasma membranes of ECs have recently been shown to respond to shear stress and stretching differently by rapidly changing their lipid order, fluidity, and cholesterol content. Such changes in the membranes' physical properties trigger the activation of membrane receptors and cell responses specific to each type of force. Artificial lipid-bilayer membranes show similar changes in lipid order in response to shear stress and stretching, indicating that they are physical phenomena rather than biological reactions. These findings suggest that the plasma membranes of ECs act as mechanosensors; in response to mechanical forces, they first alter their physical properties, modifying the conformation and function of membrane proteins, which then activates downstream signaling pathways. This new appreciation of plasma membranes as mechanosensors could help to explain the distinctive features of mechanotransduction in ECs involving shear stress and stretching, which activate a variety of membrane proteins and multiple signal transduction pathways almost simultaneously.
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Affiliation(s)
- Kimiko Yamamoto
- Laboratory of System Physiology, Department of Biomedical Engineering, Graduate School of Medicine, The University of Tokyo
| | - Joji Ando
- Laboratory of Biomedical Engineering, School of Medicine, Dokkyo Medical University
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16
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Distribution of mechanical stress in the Escherichia coli cell envelope. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2566-2575. [PMID: 30278180 DOI: 10.1016/j.bbamem.2018.09.020] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Revised: 09/14/2018] [Accepted: 09/26/2018] [Indexed: 01/05/2023]
Abstract
The cell envelope in Gram-negative bacteria comprises two distinct membranes with a cell wall between them. There has been a growing interest in understanding the mechanical adaptation of this cell envelope to the osmotic pressure (or turgor pressure), which is generated by the difference in the concentration of solutes between the cytoplasm and the external environment. However, it remains unexplored how the cell wall, the inner membrane (IM), and the outer membrane (OM) effectively protect the cell from this pressure by bearing the resulting surface tension, thus preventing the formation of inner membrane bulges, abnormal cell morphology, spheroplasts and cell lysis. In this study, we have used molecular dynamics (MD) simulations combined with experiments to resolve how and to what extent models of the IM, OM, and cell wall respond to changes in surface tension. We calculated the area compressibility modulus of all three components in simulations from tension-area isotherms. Experiments on monolayers mimicking individual leaflets of the IM and OM were also used to characterize their compressibility. While the membranes become softer as they expand, the cell wall exhibits significant strain stiffening at moderate to high tensions. We integrate these results into a model of the cell envelope in which the OM and cell wall share the tension at low turgor pressure (0.3 atm) but the tension in the cell wall dominates at high values (>1 atm).
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17
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Accurate In Silico Modeling of Asymmetric Bilayers Based on Biophysical Principles. Biophys J 2018; 115:1638-1643. [PMID: 30297133 DOI: 10.1016/j.bpj.2018.09.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 08/20/2018] [Accepted: 09/07/2018] [Indexed: 12/24/2022] Open
Abstract
Technological advances in the last decade have enabled the study of ever more complex and physiologically relevant model membranes to help dispel the mystery surrounding the role of plasma membrane asymmetry in various cellular processes. The slowly accumulating body of experimental data is fueling renewed interest in and the need for computational methods to support interpretations and address a wide range of problems that are still not amenable to direct experimental study. The specific appeal of molecular dynamics simulations for this purpose lies in their ability to access information at atomic resolution, which is useful for the formulation of testable mechanistic hypotheses. But, the range of questions that can be addressed reliably with such simulations is determined by the appropriate construction and simulation of asymmetric bilayer models. One essential way to achieve this goal is to follow rigorous biophysical criteria and principles. In this context, we show that the requirement for a robust comparison between the properties of simulated asymmetric and symmetric model membranes is for the tension in each bilayer leaflet to be zero. Commonly used methods for constructing asymmetric bilayers, including matching the average areas of the leaflets from the corresponding symmetric systems, do not ensure zero leaflet tension, thus precluding physically realistic changes in the areas of the two leaflets. We present, to our knowledge, a new method for identifying the ideal lipid packing in bilayers with different leaflet compositions that achieves the zero-tension goal, and discuss the basic principles underlying the biophysically correct computational study of asymmetric membranes.
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18
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Qian Z, Zou Y, Zhang Q, Chen P, Ma B, Wei G, Nussinov R. Atomistic-level study of the interactions between hIAPP protofibrils and membranes: Influence of pH and lipid composition. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2018; 1860:1818-1825. [PMID: 29428499 PMCID: PMC6408309 DOI: 10.1016/j.bbamem.2018.02.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2017] [Revised: 02/01/2018] [Accepted: 02/03/2018] [Indexed: 01/25/2023]
Abstract
The pathology of type 2 diabetes mellitus is associated with the aggregation of human islet amyloid polypeptide (hIAPP) and aggregation-mediated membrane disruption. The interactions of hIAPP aggregates with lipid membrane, as well as the effects of pH and lipid composition at the atomic level, remain elusive. Herein, using molecular dynamics simulations, we investigate the interactions of hIAPP protofibrillar oligomers with lipids, and the membrane perturbation that they induce, when they are partially inserted in an anionic dipalmitoyl-phosphatidylglycerol (DPPG) membrane or a mixed dipalmitoyl-phosphatidylcholine (DPPC)/DPPG (7:3) lipid bilayer under acidic/neutral pH conditions. We observed that the tilt angles and insertion depths of the hIAPP protofibril are strongly correlated with the pH and lipid composition. At neutral pH, the tilt angle and insertion depth of hIAPP protofibrils at a DPPG bilayer reach ~52° and ~1.62 nm with respect to the membrane surface, while they become ~77° and ~1.75 nm at a mixed DPPC/DPPG membrane. The calculated tilt angle of hIAPP at DPPG membrane is consistent with a recent chiral sum frequency generation spectroscopic study. The acidic pH induces a smaller tilt angle of ~40° and a shallower insertion depth (~1.24 nm) of hIAPP at the DPPG membrane surface, mainly due to protonation of His18 near the turn region. These differences mainly result from a combination of distinct electrostatic, van der Waals, hydrogen bonding and salt-bridge interactions between hIAPP and lipid bilayers. The hIAPP-membrane interaction energy analysis reveals that besides charged residues K1, R11 and H18, aromatic residues Phe15 and Phe23 also exhibit strong interactions with lipid bilayers, revealing the crucial role of aromatic residues in stabilizing the membrane-bound hIAPP protofibrils. hIAPP-membrane interactions disturb the lipid ordering and the local bilayer thickness around the peptides. Our results provide atomic-level information of membrane interaction of hIAPP protofibrils, revealing pH-dependent and membrane-modulated hIAPP aggregation at the early stage.
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Affiliation(s)
- Zhenyu Qian
- Key Laboratory of Exercise and Health Sciences (Ministry of Education) and School of Kinesiology, Shanghai University of Sport, Shanghai 200438, China; Department of Physics, State Key Laboratory of Surface physics, Key Laboratory for Computational Physical Science (Ministry of Education), and Collaborative Innovation Center of Advanced Microstructures (Nanjing), Fudan University, Shanghai 200433, China
| | - Yu Zou
- College of Physical Education and Training, Shanghai University of Sport, Shanghai 200438, China
| | - Qingwen Zhang
- College of Physical Education and Training, Shanghai University of Sport, Shanghai 200438, China
| | - Peijie Chen
- Key Laboratory of Exercise and Health Sciences (Ministry of Education) and School of Kinesiology, Shanghai University of Sport, Shanghai 200438, China
| | - Buyong Ma
- Basic Science Program, Leidos Biomedical Research, Inc., Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, United States
| | - Guanghong Wei
- Department of Physics, State Key Laboratory of Surface physics, Key Laboratory for Computational Physical Science (Ministry of Education), and Collaborative Innovation Center of Advanced Microstructures (Nanjing), Fudan University, Shanghai 200433, China.
| | - Ruth Nussinov
- Basic Science Program, Leidos Biomedical Research, Inc., Cancer and Inflammation Program, National Cancer Institute, Frederick, MD 21702, United States; Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Sackler Institute of Molecular Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
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19
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Knippenberg S, Fabre G, Osella S, Di Meo F, Paloncýová M, Ameloot M, Trouillas P. Atomistic Picture of Fluorescent Probes with Hydrocarbon Tails in Lipid Bilayer Membranes: An Investigation of Selective Affinities and Fluorescent Anisotropies in Different Environmental Phases. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:9072-9084. [PMID: 29983063 DOI: 10.1021/acs.langmuir.8b01164] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
By reverting to spectroscopy, changes in the biological environment of a fluorescent probe can be monitored and the presence of various phases of the surrounding lipid bilayer membranes can be detected. However, it is currently not always clear in which phase the probe resides. The well-known orange 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbo-cyanine perchlorate (DiI-C18(5)) fluorophore, for instance, and the new, blue BODIPY (4,4-difluoro-4-bora-3 a,4 a-diaza- s-indacene) derivative were experimentally seen to target and highlight identical parts of giant unilamellar vesicles of various compositions, comprising mixtures of dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), and cholesterol (Chol). However, it was not clear which of the coexisting membrane phases were visualized (Bacalum et al., Langmuir. 2016, 32, 3495). The present study addresses this issue by utilizing large-scale molecular dynamics simulations and the z-constraint method, which allows evaluating Gibbs free-energy profiles. The current calculations give an indication why, at room temperature, both BODIPY and DiI-C18(5) probes prefer the gel (So) phase in DOPC/DPPC (2:3 molar ratio) and the liquid-ordered (Lo) phase in DOPC/SM/Chol (1:2:1 molar ratio) mixtures. This study highlights the important differences in orientation and location and therefore in efficiency between the probes when they are used in fluorescence microscopy to screen various lipid bilayer membrane phases. Dependent on the lipid composition, the angle between the transition-state dipole moments of both probes and the normal to the membrane is found to deviate clearly from 90°. It is seen that the DiI-C18(5) probe is located in the headgroup region of the SM/Chol mixture, in close contact with water molecules. A fluorescence anisotropy study also indicates that DiI-C18(5) gives rise to a distinctive behavior in the SM/Chol membrane compared to the other considered membranes. The latter behavior has not been seen for the studied BODIPY probe, which is located deeper in the membrane.
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Affiliation(s)
- S Knippenberg
- Department of Theoretical Chemistry and Biology , KTH Royal Institute of Technology , Roslagstullsbacken 15 , S-106 91 Stockholm , Sweden
- Biomedical Research Institute , Hasselt University , Agoralaan Building C , 3590 Diepenbeek , Belgium
| | - G Fabre
- LCSN-EA1069, Faculty of Pharmacy , Limoges University , 2 rue du Dr. Marcland , 87025 Limoges Cedex , France
| | - S Osella
- Centre of New Technologies , University of Warsaw , Banacha 2C , 02-097 Warsaw , Poland
| | - F Di Meo
- Faculty of Pharmacy , INSERM UMR 1248, Limoges University , 2 rue du Docteur Marcland , 87025 Limoges Cedex , France
| | - M Paloncýová
- Department of Theoretical Chemistry and Biology , KTH Royal Institute of Technology , Roslagstullsbacken 15 , S-106 91 Stockholm , Sweden
| | - M Ameloot
- Biomedical Research Institute , Hasselt University , Agoralaan Building C , 3590 Diepenbeek , Belgium
| | - P Trouillas
- Faculty of Pharmacy , INSERM UMR 1248, Limoges University , 2 rue du Docteur Marcland , 87025 Limoges Cedex , France
- Centre of Advanced Technologies and Materials, Faculty of Science , Palacký University , tř. 17 listopadu 12 , 771 46 Olomouc , Czech Republic
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20
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Hasan M, Saha SK, Yamazaki M. Effect of membrane tension on transbilayer movement of lipids. J Chem Phys 2018; 148:245101. [DOI: 10.1063/1.5035148] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Affiliation(s)
- Moynul Hasan
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
| | - Samiron Kumar Saha
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
| | - Masahito Yamazaki
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka 422-8529, Japan
- Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan
- Department of Physics, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan
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21
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Abstract
The PhoQ/PhoP two-component system plays an essential role in the response of enterobacteria to the environment of their mammalian hosts. It is known to sense several stimuli that are potentially associated with the host, including extracellular magnesium limitation, low pH, and the presence of cationic antimicrobial peptides. Here, we show that the PhoQ/PhoP two-component systems of Escherichia coli and Salmonella can also perceive an osmotic upshift, another key stimulus to which bacteria become exposed within the host. In contrast to most previously established stimuli of PhoQ, the detection of osmotic upshift does not require its periplasmic sensor domain. Instead, we show that the activity of PhoQ is affected by the length of the transmembrane (TM) helix as well as by membrane lateral pressure. We therefore propose that osmosensing relies on a conformational change within the TM domain of PhoQ induced by a perturbation in cell membrane thickness and lateral pressure under hyperosmotic conditions. Furthermore, the response mediated by the PhoQ/PhoP two-component system was found to improve bacterial growth recovery under hyperosmotic stress, partly through stabilization of the sigma factor RpoS. Our findings directly link the PhoQ/PhoP two-component system to bacterial osmosensing, suggesting that this system can mediate a concerted response to most of the established host-related cues.
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22
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Zaki AM, Carbone P. How the Incorporation of Pluronic Block Copolymers Modulates the Response of Lipid Membranes to Mechanical Stress. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:13284-13294. [PMID: 29084428 DOI: 10.1021/acs.langmuir.7b02244] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We employ atomistic molecular dynamics simulations to investigate the effect that the incorporation of the nonionic amphiphilic copolymer known as Pluronic L64 has on the mechanical stability of a DPPC membrane. The simulations reveal that the incorporation of the polymer chains leads to membranes that can sustain increasing mechanical stresses. Analysis of mechanical, structural, and dynamic properties of the membrane shows that the polymer chains interact strongly with the lipids in the vicinity, restraining their mobility and imparting better mechanical stability to the membrane. The hybrid membranes under tension remain thicker, more ordered, and stiffer in comparison to their lipid analogues. Trans-bilayer lipid movements (flip-flop) are observed and appear to be triggered by the presence of the polymer chains. A careful analysis of the pore formation under high tensions reveals two distinctive mechanisms that depend on the distribution of the hydrophilic polymer blocks in the bilayer. Finally, the rate of growth of the formed membrane defects is slowed down in the presence of polymers. These findings show that Pluronic block copolymers could be exploited for the formation of optimized hybrid nanodevices with controlled elastic and dynamic properties.
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Affiliation(s)
- Afroditi Maria Zaki
- School of Chemical Engineering and Analytical Science, The University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
| | - Paola Carbone
- School of Chemical Engineering and Analytical Science, The University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom
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23
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Thoms VL, Hormel TT, Reyer MA, Parthasarathy R. Tension Independence of Lipid Diffusion and Membrane Viscosity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:12510-12515. [PMID: 28984459 DOI: 10.1021/acs.langmuir.7b02917] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The diffusion of biomolecules at lipid membranes is governed by the viscosity of the underlying two-dimensionally fluid lipid bilayer. For common three-dimensional fluids, viscosity can be modulated by hydrostatic pressure, and pressure-viscosity data have been measured for decades. Remarkably, the two-dimensional analogue of this relationship, the dependence of molecular mobility on tension, has to the best of our knowledge never been measured for lipid bilayers, limiting our understanding of cellular mechanotransduction as well as the fundamental fluid mechanics of membranes. Here we report both molecular-scale and mesoscopic measures of fluidity in giant lipid vesicles as a function of mechanical tension applied using micropipette aspiration. Both molecular-scale data, from fluorescence recovery after photobleaching, and micron-scale data, from tracking the diffusion of phase-separated domains, show a surprisingly weak dependence of viscosity on tension, in contrast to predictions of recent molecular dynamics simulations, highlighting fundamental gaps in our understanding of membrane fluidity.
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Affiliation(s)
- Vincent L Thoms
- Department of Physics and Materials Science Institute, The University of Oregon , Eugene, Oregon 97403-1274, United States
| | - Tristan T Hormel
- Department of Physics and Materials Science Institute, The University of Oregon , Eugene, Oregon 97403-1274, United States
| | - Matthew A Reyer
- Department of Physics and Materials Science Institute, The University of Oregon , Eugene, Oregon 97403-1274, United States
| | - Raghuveer Parthasarathy
- Department of Physics and Materials Science Institute, The University of Oregon , Eugene, Oregon 97403-1274, United States
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24
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Alam Shibly SU, Ghatak C, Sayem Karal MA, Moniruzzaman M, Yamazaki M. Experimental Estimation of Membrane Tension Induced by Osmotic Pressure. Biophys J 2017; 111:2190-2201. [PMID: 27851942 DOI: 10.1016/j.bpj.2016.09.043] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 09/22/2016] [Accepted: 09/23/2016] [Indexed: 01/08/2023] Open
Abstract
Osmotic pressure (Π) induces the stretching of plasma membranes of cells or lipid membranes of vesicles, which plays various roles in physiological functions. However, there have been no experimental estimations of the membrane tension of vesicles upon exposure to Π. In this report, we estimated experimentally the lateral tension of the membranes of giant unilamellar vesicles (GUVs) when they were transferred into a hypotonic solution. First, we investigated the effect of Π on the rate constant, kp, of constant-tension (σex)-induced rupture of dioleoylphosphatidylcholine (DOPC)-GUVs using the method developed by us recently. We obtained the σex dependence of kp in GUVs under Π and by comparing this result with that in the absence of Π, we estimated the tension of the membrane due to Π at the swelling equilibrium, σosmeq. Next, we measured the volume change of DOPC-GUVs under small Π. The experimentally obtained values of σosmeq and the volume change agreed with their theoretical values within the limits of the experimental errors. Finally, we investigated the characteristics of the Π-induced pore formation in GUVs. The σosmeq corresponding to the threshold Π at which pore formation is induced is similar to the threshold tension of the σex-induced rupture. The time course of the radius change of GUVs in the Π-induced pore formation depends on the total membrane tension, σt; for small σt, the radius increased with time to an equilibrium one, which remained constant for a long time until pore formation, but for large σt, the radius increased with time and pore formation occurred before the swelling equilibrium was reached. Based on these results, we discussed the σosmeq and the Π-induced pore formation in lipid membranes.
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Affiliation(s)
- Sayed Ul Alam Shibly
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan
| | - Chiranjib Ghatak
- Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, Shizuoka, Japan
| | - Mohammad Abu Sayem Karal
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan
| | - Md Moniruzzaman
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan
| | - Masahito Yamazaki
- Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan; Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University, Shizuoka, Japan; Department of Physics, Faculty of Science, Shizuoka University, Shizuoka, Japan.
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25
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Gnanasambandam R, Ghatak C, Yasmann A, Nishizawa K, Sachs F, Ladokhin AS, Sukharev SI, Suchyna TM. GsMTx4: Mechanism of Inhibiting Mechanosensitive Ion Channels. Biophys J 2017; 112:31-45. [PMID: 28076814 PMCID: PMC5231890 DOI: 10.1016/j.bpj.2016.11.013] [Citation(s) in RCA: 136] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 10/12/2016] [Accepted: 11/03/2016] [Indexed: 12/21/2022] Open
Abstract
GsMTx4 is a spider venom peptide that inhibits cationic mechanosensitive channels (MSCs). It has six lysine residues that have been proposed to affect membrane binding. We synthesized six analogs with single lysine-to-glutamate substitutions and tested them against Piezo1 channels in outside-out patches and independently measured lipid binding. Four analogs had ∼20% lower efficacy than the wild-type (WT) peptide. The equilibrium constants calculated from the rates of inhibition and washout did not correlate with the changes in inhibition. The lipid association strength of the WT GsMTx4 and the analogs was determined by tryptophan autofluorescence quenching and isothermal calorimetry with membrane vesicles and showed no significant differences in binding energy. Tryptophan fluorescence-quenching assays showed that both WT and analog peptides bound superficially near the lipid-water interface, although analogs penetrated deeper. Peptide-lipid association, as a function of lipid surface pressure, was investigated in Langmuir monolayers. The peptides occupied a large fraction of the expanded monolayer area, but that fraction was reduced by peptide expulsion as the pressure approached the monolayer-bilayer equivalence pressure. Analogs with compromised efficacy had pressure-area isotherms with steeper slopes in this region, suggesting tighter peptide association. The pressure-dependent redistribution of peptide between "deep" and "shallow" binding modes was supported by molecular dynamics (MD) simulations of the peptide-monolayer system under different area constraints. These data suggest a model placing GsMTx4 at the membrane surface, where it is stabilized by the lysines, and occupying a small fraction of the surface area in unstressed membranes. When applied tension reduces lateral pressure in the lipids, the peptides penetrate deeper acting as "area reservoirs" leading to partial relaxation of the outer monolayer, thereby reducing the effective magnitude of stimulus acting on the MSC gate.
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Affiliation(s)
| | - Chiranjib Ghatak
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas
| | - Anthony Yasmann
- Department of Biology, University of Maryland, College Park, Maryland
| | - Kazuhisa Nishizawa
- Clinical Laboratory Science, Teikyo University School of Medical Technology, Tokyo, Japan
| | - Frederick Sachs
- Department of Physiology and Biophysics, State University of New York, Buffalo, New York
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas
| | - Sergei I Sukharev
- Department of Biology, University of Maryland, College Park, Maryland
| | - Thomas M Suchyna
- Department of Physiology and Biophysics, State University of New York, Buffalo, New York.
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26
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Ahmadi S, Heidelberg T. Modelling and molecular dynamics simulation studies on a hexagonal glycolipid assembly. JOURNAL OF THE IRANIAN CHEMICAL SOCIETY 2016. [DOI: 10.1007/s13738-016-0958-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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27
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Poger D, Caron B, Mark AE. Validating lipid force fields against experimental data: Progress, challenges and perspectives. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1556-65. [DOI: 10.1016/j.bbamem.2016.01.029] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 01/07/2016] [Accepted: 01/27/2016] [Indexed: 01/16/2023]
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28
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Kepczynski M, Róg T. Functionalized lipids and surfactants for specific applications. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2362-2379. [PMID: 26946243 DOI: 10.1016/j.bbamem.2016.02.038] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 02/23/2016] [Accepted: 02/25/2016] [Indexed: 12/17/2022]
Abstract
Synthetic lipids and surfactants that do not exist in biological systems have been used for the last few decades in both basic and applied science. The most notable applications for synthetic lipids and surfactants are drug delivery, gene transfection, as reporting molecules, and as support for structural lipid biology. In this review, we describe the potential of the synergistic combination of computational and experimental methodologies to study the behavior of synthetic lipids and surfactants embedded in lipid membranes and liposomes. We focused on select cases in which molecular dynamics simulations were used to complement experimental studies aiming to understand the structure and properties of new compounds at the atomistic level. We also describe cases in which molecular dynamics simulations were used to design new synthetic lipids and surfactants, as well as emerging fields for the application of these compounds. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Mariusz Kepczynski
- Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
| | - Tomasz Róg
- Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101, Tampere, Finland; Department of Physics, Helsinki University, P.O. Box 64, FI 00014 Helsinki, Finland.
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29
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30
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Abstract
This review article focuses on the physiochemical mechanisms underlying nanoparticle uptake into cells. When nanoparticles are in close vicinity to a cell, the interactions between the nanoparticles and the cell membrane generate forces from different origins. This leads to the membrane wrapping of the nanoparticles followed by cellular uptake. This article discusses how the kinetics, energetics, and forces are related to these interactions and dependent on the size, shape, and stiffness of nanoparticles, the biomechanical properties of the cell membrane, as well as the local environment of the cells. The discussed fundamental principles of the physiochemical causes for nanoparticle-cell interaction may guide new studies of nanoparticle endocytosis and lead to better strategies to design nanoparticle-based approaches for biomedical applications.
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Affiliation(s)
- Sulin Zhang
- Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Biomedical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Address correspondence to , ,
| | - Huajian Gao
- School of Engineering, Brown University, Providence, Rhode Island 02912, United States
- Address correspondence to , ,
| | - Gang Bao
- Department of Bioengineering, Rice University, Houston, Texas 77005, United States
- Address correspondence to , ,
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31
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Chmyrov V, Spielmann T, Hevekerl H, Widengren J. Trans–Cis Isomerization of Lipophilic Dyes Probing Membrane Microviscosity in Biological Membranes and in Live Cells. Anal Chem 2015; 87:5690-7. [DOI: 10.1021/acs.analchem.5b00863] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Volodymyr Chmyrov
- Experimental
Biomolecular
Physics, Department of Applied Physics, Royal Institute of Technology, Stockholm 106 91, Sweden
| | - Thiemo Spielmann
- Experimental
Biomolecular
Physics, Department of Applied Physics, Royal Institute of Technology, Stockholm 106 91, Sweden
| | - Heike Hevekerl
- Experimental
Biomolecular
Physics, Department of Applied Physics, Royal Institute of Technology, Stockholm 106 91, Sweden
| | - Jerker Widengren
- Experimental
Biomolecular
Physics, Department of Applied Physics, Royal Institute of Technology, Stockholm 106 91, Sweden
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32
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Huang C, Ozdemir T, Xu LC, Butler PJ, Siedlecki CA, Brown JL, Zhang S. The role of substrate topography on the cellular uptake of nanoparticles. J Biomed Mater Res B Appl Biomater 2015; 104:488-95. [PMID: 25939598 DOI: 10.1002/jbm.b.33397] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Revised: 01/15/2015] [Accepted: 02/08/2015] [Indexed: 12/12/2022]
Abstract
Improving targeting efficacy has been a central focus of the studies on nanoparticle (NP)-based drug delivery nanocarriers over the past decades. As cells actively sense and respond to the local physical environments, not only the NP design (e.g., size, shape, ligand density, etc.) but also the cell mechanics (e.g., stiffness, spreading, expressed receptors, etc.) affect the cellular uptake efficiency. While much work has been done to elucidate the roles of NP design for cells seeded on a flat tissue culture surface, how the local physical environments of cells mediate uptake of NPs remains unexplored, despite the widely known effect of local physical environments on cellular responses in vitro and disease states in vivo. Here, we report the active responses of human osteosarcoma cells to fibrous substrate topographies and the subsequent changes in the cellular uptake of NPs. Our experiments demonstrate that surface topography modulates cellular uptake efficacy by mediating cell spreading and membrane mechanics. The findings provide a concrete example of the regulative role of the physical environments of cells on cellular uptake of NPs, therefore advancing the rational design of NPs for enhanced drug delivery in targeted cancer therapy.
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Affiliation(s)
- Changjin Huang
- Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, 16802
| | - Tugba Ozdemir
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
| | - Li-Chong Xu
- Department of Surgery, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, 17033
| | - Peter J Butler
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
| | - Christopher A Siedlecki
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, 16802.,Department of Surgery, The Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, 17033
| | - Justin L Brown
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
| | - Sulin Zhang
- Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, 16802.,Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
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33
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Lee IH, Saha S, Polley A, Huang H, Mayor S, Rao M, Groves JT. Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures. J Phys Chem B 2015; 119:4450-9. [PMID: 25747462 DOI: 10.1021/jp512839q] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14-37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.
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Affiliation(s)
- Il-Hyung Lee
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States
| | - Suvrajit Saha
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India
| | - Anirban Polley
- ∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India
| | - Hector Huang
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States
| | - Satyajit Mayor
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India
| | - Madan Rao
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India.,∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India
| | - Jay T Groves
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States.,‡Materials Sciences Division, Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
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34
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Atomistic simulation studies of the α/β-glucoside and galactoside in anhydrous bilayers: effect of the anomeric and epimeric configurations. J Mol Model 2014; 20:2165. [DOI: 10.1007/s00894-014-2165-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 01/31/2014] [Indexed: 10/25/2022]
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35
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Molecular dynamics simulations of lipid membranes with lateral force: Rupture and dynamic properties. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:994-1002. [DOI: 10.1016/j.bbamem.2013.12.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Revised: 12/15/2013] [Accepted: 12/18/2013] [Indexed: 01/06/2023]
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36
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Mori T, Jung J, Sugita Y. Surface-Tension Replica-Exchange Molecular Dynamics Method for Enhanced Sampling of Biological Membrane Systems. J Chem Theory Comput 2013; 9:5629-40. [PMID: 26592297 DOI: 10.1021/ct400445k] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Conformational sampling is fundamentally important for simulating complex biomolecular systems. The generalized-ensemble algorithm, especially the temperature replica-exchange molecular dynamics method (T-REMD), is one of the most powerful methods to explore structures of biomolecules such as proteins, nucleic acids, carbohydrates, and also of lipid membranes. T-REMD simulations have focused on soluble proteins rather than membrane proteins or lipid bilayers, because explicit membranes do not keep their structural integrity at high temperature. Here, we propose a new generalized-ensemble algorithm for membrane systems, which we call the surface-tension REMD method. Each replica is simulated in the NPγT ensemble, and surface tensions in a pair of replicas are exchanged at certain intervals to enhance conformational sampling of the target membrane system. We test the method on two biological membrane systems: a fully hydrated DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine) lipid bilayer and a WALP23-POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) membrane system. During these simulations, a random walk in surface tension space is realized. Large-scale lateral deformation (shrinking and stretching) of the membranes takes place in all of the replicas without collapse of the lipid bilayer structure. There is accelerated lateral diffusion of DPPC lipid molecules compared with conventional MD simulation, and a much wider range of tilt angle of the WALP23 peptide is sampled due to large deformation of the POPC lipid bilayer and through peptide-lipid interactions. Our method could be applicable to a wide variety of biological membrane systems.
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Affiliation(s)
- Takaharu Mori
- RIKEN Quantitative Biology Center, 7-1-26 minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan.,RIKEN Theoretical Molecular Science Laboratory, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Jaewoon Jung
- RIKEN Advanced Institute for Computational Science, 7-1-26 minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Yuji Sugita
- RIKEN Quantitative Biology Center, 7-1-26 minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan.,RIKEN Theoretical Molecular Science Laboratory, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.,RIKEN Advanced Institute for Computational Science, 7-1-26 minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
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37
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Robalo JR, Ramalho JPP, Loura LMS. NBD-Labeled Cholesterol Analogues in Phospholipid Bilayers: Insights from Molecular Dynamics. J Phys Chem B 2013; 117:13731-42. [DOI: 10.1021/jp406135a] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- João R. Robalo
- Departamento
de Química, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal
- Centro
de Química de Évora, Universidade de Évora, Rua
Romão Ramalho, 59, 7000-671 Évora, Portugal
| | - J. P. Prates Ramalho
- Departamento
de Química, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal
- Centro
de Química de Évora, Universidade de Évora, Rua
Romão Ramalho, 59, 7000-671 Évora, Portugal
| | - Luís M. S. Loura
- Faculdade
de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal
- Centro
de Química de Coimbra, Largo D. Dinis, Rua Larga, 3004-535 Coimbra, Portugal
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38
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Khoshnood A, Jalali MA. Anomalous diffusion of proteins in sheared lipid membranes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:032705. [PMID: 24125292 DOI: 10.1103/physreve.88.032705] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2012] [Revised: 08/08/2013] [Indexed: 06/02/2023]
Abstract
We use coarse grained molecular dynamics simulations to investigate diffusion properties of sheared lipid membranes with embedded transmembrane proteins. In membranes without proteins, we find normal in-plane diffusion of lipids in all flow conditions. Protein embedded membranes behave quite differently: by imposing a simple shear flow and sliding the monolayers of the membrane over each other, the motion of protein clusters becomes strongly superdiffusive in the shear direction. In such a circumstance, the subdiffusion regime is predominant perpendicular to the flow. We show that superdiffusion is a result of accelerated chaotic motions of protein-lipid complexes within the membrane voids, which are generated by hydrophobic mismatch or the transport of lipids by proteins.
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Affiliation(s)
- Atefeh Khoshnood
- Computational Mechanics Laboratory, Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran and Center of Excellence in Design, Robotics and Automation, Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran
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39
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Coimbra JT, Sousa SF, Fernandes PA, Rangel M, Ramos MJ. Biomembrane simulations of 12 lipid types using the general amber force field in a tensionless ensemble. J Biomol Struct Dyn 2013; 32:88-103. [DOI: 10.1080/07391102.2012.750250] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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40
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Ackerman DG, Heberle FA, Feigenson GW. Limited perturbation of a DPPC bilayer by fluorescent lipid probes: a molecular dynamics study. J Phys Chem B 2013; 117:4844-52. [PMID: 23548205 DOI: 10.1021/jp400289d] [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 properties of lipid bilayer nanometer-scale domains could be crucial for understanding cell membranes. Fluorescent probes are often used to study bilayers, yet their effects on host lipids are not well understood. We used molecular dynamics simulations to investigate perturbations in a fluid DPPC bilayer upon incorporation of three indocarbocyanine probes: DiI-C18:0, DiI-C18:2, or DiI-C12:0. We find a 10-12% decrease in chain order for DPPC in the solvation shell nearest the probe but smaller effects in subsequent shells, indicating that the probes significantly alter only their local environment. We also observe order perturbations of lipids directly across from the probe in the opposite leaflet. Additionally, the DPPC headgroup phosphorus-to-nitrogen vector of lipids nearest the probe exhibits preferential orientation pointing away from the DiI. We show that, while DiI probes perturb their local environment, they do not strongly influence the average properties of "nanoscopic" domains containing a few hundred lipids.
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Affiliation(s)
- David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
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41
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Huang C, Butler PJ, Tong S, Muddana HS, Bao G, Zhang S. Substrate stiffness regulates cellular uptake of nanoparticles. NANO LETTERS 2013; 13:1611-1615. [PMID: 23484640 DOI: 10.1021/nl400033h] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Nanoparticle (NP)-bioconjugates hold great promise for more sensitive disease diagnosis and more effective anticancer drug delivery compared with existing approaches. A critical aspect in both applications is cellular internalization of NPs, which is influenced by NP properties and cell surface mechanics. Despite considerable progress in optimization of the NP-bioconjugates for improved targeting, the role of substrate stiffness on cellular uptake has not been investigated. Using polyacrylamide (PA) hydrogels as model substrates with tunable stiffness, we quantified the relationship between substrate stiffness and cellular uptake of fluorescent NPs by bovine aortic endothelial cells (BAECs). We found that a stiffer substrate results in a higher total cellular uptake on a per cell basis, but a lower uptake per unit membrane area. To obtain a mechanistic understanding of the cellular uptake behavior, we developed a thermodynamic model that predicts that membrane spreading area and cell membrane tension are two key factors controlling cellular uptake of NPs, both of which are modulated by substrate stiffness. Our experimental and modeling results not only open up new avenues for engineering NP-based cancer cell targets for more effective in vivo delivery but also contribute an example of how the physical environment dictates cellular behavior and function.
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Affiliation(s)
- Changjin Huang
- Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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42
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Lai K, Wang B, Zhang Y, Zheng Y. Computer simulation study of nanoparticle interaction with a lipid membrane under mechanical stress. Phys Chem Chem Phys 2012; 15:270-8. [PMID: 23165312 DOI: 10.1039/c2cp42027a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Pore formation of lipid bilayers under mechanical stress is critical to biological processes. A series of coarse grained molecular dynamics simulations of lipid bilayers with carbon nanoparticles different in size have been performed. Surface tension was applied to study the disruption of lipid bilayers by nanoparticles and the formation of pores inside the bilayers. The presence of small nanoparticles enhances the probability of water penetration thus decreasing the membrane rupture tension, while big nanoparticles have the opposite effect. Nanoparticle volume affects bilayer strength indirectly, and particle surface density can complicate the interaction. The structural, dynamic, elastic properties and lateral densities of lipid bilayers with nanoparticles under mechanical stress were analyzed. The results demonstrate the ability of nanoparticles to adjust the structural and dynamic properties of a lipid membrane, and to efficiently regulate the pore formation behavior and hydrophobicity of membranes.
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Affiliation(s)
- Kan Lai
- School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, China
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43
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Poger D, Mark AE. Lipid Bilayers: The Effect of Force Field on Ordering and Dynamics. J Chem Theory Comput 2012; 8:4807-17. [PMID: 26605633 DOI: 10.1021/ct300675z] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The sensitivity of the structure and dynamics of a fully hydrated pure bilayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in molecular dynamics simulations to changes in force-field and simulation parameters has been assessed. Three related force fields (the Gromos 54A7 force field, a Gromos 53A6-derived parameter set and a variant of the Berger parameters) in combination with either particle-mesh Ewald (PME) or a reaction field (RF) were compared. Structural properties such as the area per lipid, carbon-deuterium order parameters, electron density profile and bilayer thicknesses, are reproduced by all the parameter sets within the uncertainty of the available experimental data. However, there are clear differences in the ordering of the glycerol backbone and choline headgroup, and the orientation of the headgroup dipole. In some cases, the degree of ordering was reminiscent of a liquid-ordered phase. It is also shown that, although the lateral diffusion of the lipids in the plane of the bilayer is often used to validate lipid force fields, because of the uncertainty in the experimental measurements and the fact that the lateral diffusion is dependent on the choice of the simulation conditions, it should not be employed as a measure of quality. Finally, the simulations show that the effect of small changes in force-field parameters on the structure and dynamics of a bilayer is more significant than the treatment of the long-range electrostatic interactions using RF or PME. Overall, the Gromos 54A7 best reproduced the range of experimental data examined.
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Affiliation(s)
- David Poger
- The University of Queensland, School of Chemistry and Molecular Biosciences, Brisbane QLD 4072, Australia
| | - Alan E Mark
- The University of Queensland, School of Chemistry and Molecular Biosciences, Brisbane QLD 4072, Australia.,The University of Queensland, Institute for Molecular Bioscience, Brisbane QLD 4072, Australia
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44
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Balleza D. Mechanical properties of lipid bilayers and regulation of mechanosensitive function: from biological to biomimetic channels. Channels (Austin) 2012; 6:220-33. [PMID: 22790280 DOI: 10.4161/chan.21085] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Material properties of lipid bilayers, including thickness, intrinsic curvature and compressibility regulate the function of mechanosensitive (MS) channels. This regulation is dependent on phospholipid composition, lateral packing and organization within the membrane. Therefore, a more complete framework to understand the functioning of MS channels requires insights into bilayer structure, thermodynamics and phospholipid structure, as well as lipid-protein interactions. Phospholipids and MS channels interact with each other mainly through electrostatic forces and hydrophobic matching, which are also crucial for antimicrobial peptides. They are excellent models for studying the formation and stabilization of membrane pores. Importantly, they perform equivalent responses as MS channels: (1) tilting in response to tension and (2) dissipation of osmotic gradients. Lessons learned from pore forming peptides could enrich our knowledge of mechanisms of action and evolution of these channels. Here, the current state of the art is presented and general principles of membrane regulation of mechanosensitive function are discussed.
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Affiliation(s)
- Daniel Balleza
- Unidad de Biofísica, CSIC, UPV/EHU, Universidad del País Vasco, Leioa, Spain.
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45
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Reddy AS, Warshaviak DT, Chachisvilis M. Effect of membrane tension on the physical properties of DOPC lipid bilayer membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2271-81. [PMID: 22588133 DOI: 10.1016/j.bbamem.2012.05.006] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 05/03/2012] [Accepted: 05/07/2012] [Indexed: 01/15/2023]
Abstract
Molecular dynamics simulations of a dioleoylphosphocholine (DOPC) lipid bilayer were performed to explore its mechanosensitivity. Variations in the bilayer properties, such as area per lipid, volume, thickness, hydration depth (HD), hydration thickness (HT), lateral diffusion coefficient, and changes in lipid structural order were computed in the membrane tension range 0 to 15dyn/cm. We determined that an increase in membrane tension results in a decrease in the bilayer thickness and HD of ~5% and ~5.7% respectively, whereas area per lipid, volume, and HT/HD increased by 6.8%, 2.4%, and 5% respectively. The changes in lipid conformation and orientation were characterized using orientational (S(2)) and deuterium (S(CD)) order parameters. Upon increase of membrane tension both order parameters indicated an increase in lipid disorder by 10-20%, mostly in the tail end region of the hydrophobic chains. The effect of membrane tension on lipid lateral diffusion in the DOPC bilayer was analyzed on three different time scales corresponding to inertial motion, anomalous diffusion and normal diffusion. The results showed that lateral diffusion of lipid molecules is anomalous in nature due to the non-exponential distribution of waiting times. The anomalous and normal diffusion coefficients increased by 20% and 52% when the membrane tension changed from 0 to 15dyn/cm, respectively. In conclusion, our studies showed that membrane tension causes relatively significant changes in the area per lipid, volume, polarity, membrane thickness, and fluidity of the membrane suggesting multiple mechanisms by which mechanical perturbation of the membrane could trigger mechanosensitive response in cells.
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46
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Lesoine JF, Lee JY, Krogmeier JR, Kang H, Clarke ML, Chang R, Sackett DL, Nossal R, Hwang J. Quantitative scheme for full-field polarization rotating fluorescence microscopy using a liquid crystal variable retarder. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:053705. [PMID: 22667623 PMCID: PMC3365914 DOI: 10.1063/1.4717682] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We present a quantitative scheme for full-field polarization rotating fluorescence microscopy. A quarter-wave plate, in combination with a liquid crystal variable retarder, provides a tunable method to rotate polarization states of light prior to its being coupled into a fluorescence microscope. A calibration of the polarization properties of the incident light is performed in order to correct for elliptical polarization states. This calibration allows the response of the sample to linear polarization states of light to be recovered. Three known polarization states of light can be used to determine the average fluorescent dipole orientations in the presence of a spatially varying dc offset or background polarization-invariant fluorescence signal. To demonstrate the capabilities of this device, we measured a series of full-field fluorescence polarization images from fluorescent analogs incorporated in the lipid membrane of Burkitts lymphoma CA46 cells. The fluorescent lipid-like analogs used in this study are molecules that are labeled by either a DiI (1,1(')-Dioctadecyl 3,3,3('),3(')-Tetramethylindocarbocyanine) fluorophore in its head group or a Bodipy (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) molecule in its acyl chain. A spatially varying contrast in the normalized amplitude was observed on the cell surface, where the orientation of the DiI molecules is tangential to the cell membrane. The internally labeled cellular structures showed zero response to changes in linear polarization, and the net linear polarization amplitude for these regions was zero. This instrument provides a low cost calibrated method that may be coupled to existing fluorescence microscopes to perform investigations of cellular processes that involve a change in molecular orientations.
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Affiliation(s)
- John F Lesoine
- Radiation and Biomolecular Physics Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA
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Muddana HS, Chiang HH, Butler PJ. Tuning membrane phase separation using nonlipid amphiphiles. Biophys J 2012; 102:489-97. [PMID: 22325271 DOI: 10.1016/j.bpj.2011.12.033] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 12/14/2011] [Accepted: 12/19/2011] [Indexed: 01/25/2023] Open
Abstract
Lipid phase separation may be a mechanism by which lipids participate in sorting membrane proteins and facilitate membrane-mediated biochemical signaling in cells. To provide new tools for membrane lipid phase manipulation that avoid direct effects on protein activity and lipid composition, we studied phase separation in binary and ternary lipid mixtures under the influence of three nonlipid amphiphiles, vitamin E (VE), Triton-X (TX)-100, and benzyl alcohol (BA). Mechanisms of additive-induced phase separation were elucidated using coarse-grained molecular dynamics simulations of these additives in a liquid bilayer made from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine [corrected]. From simulations, the additive's partitioning preference, changes in membrane thickness, and alterations in lipid order were quantified. Simulations showed that VE favored the DPPC phase but partitioned predominantly to the domain boundaries and lowered the tendency for domain formation, and therefore acted as a linactant. This simulated behavior was consistent with experimental observations in which VE promoted lipid mixing and dispersed domains in both gel/liquid and liquid-ordered/liquid-disordered systems. From simulation, BA partitioned predominantly to the DUPC phase, decreased lipid order there, and thinned the membrane. These actions explain why, experimentally, BA promoted phase separation in both binary and ternary lipid mixtures. In contrast, TX, a popular detergent used to isolate raft membranes in cells, exhibited equal preference for both phases, as demonstrated by simulations, but nonetheless, was a strong domain promoter in all lipid mixtures. Further analysis showed that TX increased membrane thickness of the DPPC phase to a greater extent than the DUPC phase and thus increased hydrophobic mismatch, which may explain experimental observation of phase separation in the presence of TX. In summary, these nonlipid amphiphiles provide new tools to tune domain formation in model vesicle systems and could provide the means to form or disperse membrane lipid domains in cells, in addition to the well-known methods involving cholesterol enrichment and sequestration.
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Affiliation(s)
- Hari S Muddana
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania, USA
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Lai K, Wang B, Zhang Y, Zhang Y. High pressure effect on phase transition behavior of lipid bilayers. Phys Chem Chem Phys 2012; 14:5744-52. [DOI: 10.1039/c2cp24140d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Loura LMS, Ramalho JPP. Recent developments in molecular dynamics simulations of fluorescent membrane probes. Molecules 2011; 16:5437-52. [PMID: 21709624 PMCID: PMC6264736 DOI: 10.3390/molecules16075437] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 06/21/2011] [Accepted: 06/22/2011] [Indexed: 01/25/2023] Open
Abstract
Due to their sensitivity and versatility, the use of fluorescence techniques in membrane biophysics is widespread. Because membrane lipids are non-fluorescent, extrinsic membrane probes are widely used. However, the behaviour of these probes when inserted in the bilayer is often poorly understood, and it can be hard to distinguish between legitimate membrane properties and perturbation resulting from probe incorporation. Atomistic molecular dynamics simulations present a convenient way to address these issues and have been increasingly used in recent years in this context. This article reviews the application of molecular dynamics to the study of fluorescent membrane probes, focusing on recent work with complex design fluorophores and ordered bilayer systems.
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Affiliation(s)
- Luís M. S. Loura
- Faculdade de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal;
- Centro de Química de Coimbra, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - J. P. Prates Ramalho
- Centro de Química de Évora e Departamento de Química, Escola de Ciências e Tecnologia, Colégio Luís Verney, Rua Romão Ramalho 59, 7002-554 Évora, Portugal
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Warshaviak DT, Muellner MJ, Chachisvilis M. Effect of membrane tension on the electric field and dipole potential of lipid bilayer membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2608-17. [PMID: 21722624 DOI: 10.1016/j.bbamem.2011.06.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 06/08/2011] [Accepted: 06/14/2011] [Indexed: 12/15/2022]
Abstract
The dipole potential of lipid bilayer membrane controls the difference in permeability of the membrane to oppositely charged ions. We have combined molecular dynamics (MD) simulations and experimental studies to determine changes in electric field and electrostatic potential of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid bilayer in response to applied membrane tension. MD simulations based on CHARMM36 force field showed that electrostatic potential of DOPC bilayer decreases by ~45mV in the physiologically relevant range of membrane tension values (0 to 15dyn/cm). The electrostatic field exhibits a peak (~0.8×10(9)V/m) near the water/lipid interface which shifts by 0.9Å towards the bilayer center at 15dyn/cm. Maximum membrane tension of 15dyn/cm caused 6.4% increase in area per lipid, 4.7% decrease in bilayer thickness and 1.4% increase in the volume of the bilayer. Dipole-potential sensitive fluorescent probes were used to detect membrane tension induced changes in DOPC vesicles exposed to osmotic stress. Experiments confirmed that dipole potential of DOPC bilayer decreases at higher membrane tensions. These results are suggestive of a potentially new mechanosensing mechanism by which mechanically induced structural changes in the lipid bilayer membrane could modulate the function of membrane proteins by altering electrostatic interactions and energetics of protein conformational states.
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