1
|
Doktorova M, Khelashvili G, Brown MF. Efficient calculation of orientation-dependent lipid dynamics from membrane simulations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.05.23.542012. [PMID: 37292992 PMCID: PMC10245828 DOI: 10.1101/2023.05.23.542012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Molecular dynamics simulations of lipid membranes have become increasingly impactful in biophysics because they offer atomistic resolution of structural fluctuations in relation to their functional outputs. Yet quantitative characterization of multiscale processes is a formidable challenge due to the distribution of motions that evade analysis of discrete simulation data. Here we investigate the efficient calculation of CH bond relaxation rates from membrane simulations. Widely used computational approaches offer numerical simplicity but fall short of capturing crucial aspects of the orientation dependence of the dynamics. To circumvent this problem, we introduced a robust framework based on liquid crystal theory which considers explicitly the CH bond motions with respect to the director axis (bilayer normal). Analysis of the orientation dependence of the dynamics shows excellent agreement with experiment, illustrating how the ordering potential affects the calculated relaxation rates. Furthermore, a fit-based resampling of the autocorrelation function of the bond fluctuations validates the new approach for low-temporal resolution data. The recovered relaxation rates indicate that at short timescales, both with and without cholesterol, the local motions of CH bonds describe the bilayer microviscosity and resemble liquid hydrocarbons. Our results establish the critical role of the orientational anisotropy in analysis of membrane simulations, explain fundamental aspects of lipid dynamics, and provide guidelines for extracting information that can be compared to experimental data.
Collapse
Affiliation(s)
- Milka Doktorova
- Department of Molecular Physiology & Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, NY, USA
- Institute of Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, NY, USA
| | - Michael F. Brown
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA
- Department of Physics, University of Arizona, Tucson, AZ, USA
- Program in Applied Mathematics, University of Arizona, Tucson, AZ, USA
| |
Collapse
|
2
|
Dziura D, Dziura M, Marquardt D. Studying lipid flip-flop in asymmetric liposomes using 1H NMR and TR-SANS. Methods Enzymol 2024; 700:295-328. [PMID: 38971604 DOI: 10.1016/bs.mie.2024.02.012] [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: 07/08/2024]
Abstract
The specific spatial and temporal distribution of lipids in membranes play a crucial role in determining the biochemical and biophysical properties of the system. In nature, the asymmetric distribution of lipids is a dynamic process with ATP-dependent lipid transporters maintaining asymmetry, and passive transbilayer diffusion, that is, flip-flop, counteracting it. In this chapter, two probe-free techniques, 1H NMR and time-resolved small angle neutron scattering, are described in detail as methods of investigating lipid flip-flop rates in synthetic liposomes that have been generated with an asymmetric bilayer composition.
Collapse
Affiliation(s)
- Dominik Dziura
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Maksymilian Dziura
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada; Department of Physics, University of Windsor, Windsor, ON, Canada.
| |
Collapse
|
3
|
Doktorova M, Levental I, Heberle FA. Seeing the Membrane from Both Sides Now: Lipid Asymmetry and Its Strange Consequences. Cold Spring Harb Perspect Biol 2023; 15:a041393. [PMID: 37604588 PMCID: PMC10691478 DOI: 10.1101/cshperspect.a041393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2023]
Abstract
Almost all biomembranes are constructed as lipid bilayers and, in almost all of these, the two opposing monolayers (leaflets) have distinct lipid compositions. This lipid asymmetry arises through the concerted action of a suite of energy-dependent enzymes that maintain living bilayers in a far-from-equilibrium steady-state. Recent discoveries reveal that lipid compositional asymmetry imparts biophysical asymmetries and that this dualistic organization may have major consequences for cellular physiology. Importantly, while transbilayer asymmetry appears to be an essential, near-ubiquitous characteristic of biological membranes, it has been challenging to reproduce in reconstituted or synthetic systems. Although recent methodological developments have overcome some critical challenges, it remains difficult to extrapolate results from available models to biological systems. Concurrently, there are few experimental approaches for targeted, controlled manipulation of lipid asymmetry in living cells. Thus, the biophysical and functional consequences of membrane asymmetry remain almost wholly unexplored. This perspective summarizes the current state of knowledge and highlights emerging themes that are beginning to make inroads into the fundamental question of why life tends toward asymmetry in its bilayers.
Collapse
Affiliation(s)
- Milka Doktorova
- Department of Molecular Physiology and Pharmacology, University of Virginia, Center for Membrane and Cell Physiology, Charlottesville, Virginia 22908, USA
| | - Ilya Levental
- Department of Molecular Physiology and Pharmacology, University of Virginia, Center for Membrane and Cell Physiology, Charlottesville, Virginia 22908, USA
| | - Frederick A Heberle
- Department of Chemistry, University of Tennessee Knoxville, Knoxville, Tennessee 37996, USA
| |
Collapse
|
4
|
Spinozzi F, Barbosa LRS, Corucci G, Mariani P, Itri R. Small-angle scattering from flat bilayers containing correlated scattering length density inhomogeneities. J Appl Crystallogr 2023; 56:1348-1360. [PMID: 37791360 PMCID: PMC10543680 DOI: 10.1107/s1600576723006143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Accepted: 07/12/2023] [Indexed: 10/05/2023] Open
Abstract
Model lipid bilayers have been widely employed as a minimal system to investigate the structural properties of biological membranes by small-angle X-ray (SAXS) and neutron scattering (SANS) techniques. These have nanometre resolution and can give information regarding membrane thickness and scattering length densities (SLDs) of polar and apolar regions. However, biological membranes are complex systems containing different lipids and protein species, in which lipid domains can be dynamically assembled and disassembled. Therefore, SLD variations can occur within the biomembrane. In this work, a novel method has been developed to simulate SAXS and SANS profiles obtained from large unilamellar vesicles containing SLD inhomogeneities that are spatially correlated over the membrane surface. Such inhomogeneities are represented by cylindrical entities with equivalent SLDs. Stacking of bilayers is also included in the model, with no correlation between horizontal and vertical order. The model is applied to a lipid bilayer containing SLD inhomogeneities representing pores, lipid domains, and transmembrane, partially immersed and anchored proteins. It is demonstrated that all the structural information from the host lipid bilayer and from the SLD inhomogeneity can be consistently retrieved by a combined analysis of experimental SAXS and SANS data through the methodology proposed here.
Collapse
Affiliation(s)
- Francesco Spinozzi
- Department of Life and Environmental Sciences, Marche Polytechnic University, Ancona, Italy
| | - Leandro R. S. Barbosa
- Institute of Physics, University of São Paulo, São Paulo, Brazil
- Brazilian Synchrotron Light Laboratory (LNLS), Campinas, São Paulo, Brazil
| | - Giacomo Corucci
- Institut Laue–Langevin, Grenoble, France
- École Doctorale de Physique, Université Grenoble Alpes, Saint-Martin-d’Héres, France
| | - Paolo Mariani
- Department of Life and Environmental Sciences, Marche Polytechnic University, Ancona, Italy
| | - Rosangela Itri
- Institute of Physics, University of São Paulo, São Paulo, Brazil
| |
Collapse
|
5
|
Carrer M, Nielsen JE, Cezar HM, Lund R, Cascella M, Soares TA. Accelerating Lipid Flip-Flop at Low Concentrations: A General Mechanism for Membrane Binding Peptides. J Phys Chem Lett 2023; 14:7014-7019. [PMID: 37523748 PMCID: PMC10424232 DOI: 10.1021/acs.jpclett.3c01284] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Accepted: 07/27/2023] [Indexed: 08/02/2023]
Abstract
We report a physicochemical investigation of the lipid transport properties of model lipid membranes in the presence of the antimicrobial peptide indolicidin through comparisons of experimental SANS/SAXS scattering techniques to fully atomistic molecular dynamics simulations. In agreement with the experiment, we show that upon peripheral binding of the peptides, even at low concentrations, lipid flip-flop dynamics is greatly accelerated. Computer modeling elucidates the interplay between structural changes and lipid dynamics induced by peptides and proposes a mechanism for the mode of action of antimicrobial peptides, assessing the major role of entropy for the catalysis of the flipping events. The mechanism introduced here is universal for all peptides with preferential peripheral binding to the membrane as it does not depend on the specific amino acid sequence.
Collapse
Affiliation(s)
- Manuel Carrer
- Department
of Chemistry, University of Oslo, Postboks 1033 Blindern, 0315 Oslo, Norway
- Hylleraas
Centre for Quantum Molecular Sciences, University
of Oslo, 0315 Oslo, Norway
| | | | - Henrique Musseli Cezar
- Department
of Chemistry, University of Oslo, Postboks 1033 Blindern, 0315 Oslo, Norway
- Hylleraas
Centre for Quantum Molecular Sciences, University
of Oslo, 0315 Oslo, Norway
| | - Reidar Lund
- Department
of Chemistry, University of Oslo, Postboks 1033 Blindern, 0315 Oslo, Norway
- Hylleraas
Centre for Quantum Molecular Sciences, University
of Oslo, 0315 Oslo, Norway
| | - Michele Cascella
- Department
of Chemistry, University of Oslo, Postboks 1033 Blindern, 0315 Oslo, Norway
- Hylleraas
Centre for Quantum Molecular Sciences, University
of Oslo, 0315 Oslo, Norway
| | - Thereza A. Soares
- Department
of Chemistry, University of Oslo, Postboks 1033 Blindern, 0315 Oslo, Norway
- Department
of Chemistry, University of São Paulo, 055508−090 Ribeirão Preto, Brazil
- Hylleraas
Centre for Quantum Molecular Sciences, University
of Oslo, 0315 Oslo, Norway
| |
Collapse
|
6
|
Chaisson EH, Heberle FA, Doktorova M. Building Asymmetric Lipid Bilayers for Molecular Dynamics Simulations: What Methods Exist and How to Choose One? MEMBRANES 2023; 13:629. [PMID: 37504995 PMCID: PMC10384462 DOI: 10.3390/membranes13070629] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 06/20/2023] [Accepted: 06/25/2023] [Indexed: 07/29/2023]
Abstract
The compositional asymmetry of biological membranes has attracted significant attention over the last decade. Harboring more differences from symmetric membranes than previously appreciated, asymmetric bilayers have proven quite challenging to study with familiar concepts and techniques, leaving many unanswered questions about the reach of the asymmetry effects. One particular area of active research is the computational investigation of composition- and number-asymmetric lipid bilayers with molecular dynamics (MD) simulations. Offering a high level of detail into the organization and properties of the simulated systems, MD has emerged as an indispensable tool in the study of membrane asymmetry. However, the realization that results depend heavily on the protocol used for constructing the asymmetric bilayer models has sparked an ongoing debate about how to choose the most appropriate approach. Here we discuss the underlying source of the discrepant results and review the existing methods for creating asymmetric bilayers for MD simulations. Considering the available data, we argue that each method is well suited for specific applications and hence there is no single best approach. Instead, the choice of a construction protocol-and consequently, its perceived accuracy-must be based primarily on the scientific question that the simulations are designed to address.
Collapse
Affiliation(s)
- Emily H. Chaisson
- Department of Chemistry, University of Tennessee Knoxville, Knoxville, TN 37916, USA
| | - Frederick A. Heberle
- Department of Chemistry, University of Tennessee Knoxville, Knoxville, TN 37916, USA
| | - Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22903, USA
| |
Collapse
|
7
|
Doktorova M, Khelashvili G, Ashkar R, Brown MF. Molecular simulations and NMR reveal how lipid fluctuations affect membrane mechanics. Biophys J 2023; 122:984-1002. [PMID: 36474442 PMCID: PMC10111610 DOI: 10.1016/j.bpj.2022.12.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2022] [Revised: 11/21/2022] [Accepted: 12/02/2022] [Indexed: 12/07/2022] Open
Abstract
Lipid bilayers form the main matrix of functional cell membranes, and their dynamics underlie a host of physical and biological processes. Here we show that elastic membrane properties and collective molecular dynamics (MD) are related by the mean-square amplitudes (order parameters) and relaxation rates (correlation times) of lipid acyl chain motions. We performed all-atom MD simulations of liquid-crystalline bilayers that allow direct comparison with carbon-hydrogen (CH) bond relaxations measured with NMR spectroscopy. Previous computational and theoretical approaches have assumed isotropic relaxation, which yields inaccurate description of lipid chain dynamics and incorrect data interpretation. Instead, the new framework includes a fixed bilayer normal (director axis) and restricted anisotropic motion of the CH bonds in accord with their segmental order parameters, enabling robust validation of lipid force fields. Simulated spectral densities of thermally excited CH bond fluctuations exhibited well-defined spin-lattice (Zeeman) relaxations analogous to those in NMR measurements. Their frequency signature could be fit to a simple power-law function, indicative of nematic-like collective dynamics. Moreover, calculated relaxation rates scaled as the squared order parameters yielding an apparent κC modulus for bilayer bending. Our results show a strong correlation with κC values obtained from solid-state NMR studies of bilayers without and with cholesterol as validated by neutron spin-echo measurements of membrane elasticity. The simulations uncover a critical role of interleaflet coupling in membrane mechanics and thus provide important insights into molecular sites of emerging elastic properties within lipid bilayers.
Collapse
Affiliation(s)
- Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia.
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York; Institute of Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York
| | - Rana Ashkar
- Department of Physics, Virginia Tech, Blacksburg, Virginia; Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, Virginia
| | - Michael F Brown
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona; Department of Physics, University of Arizona, Tucson, Arizona; Program in Applied Mathematics, University of Arizona, Tucson, Arizona.
| |
Collapse
|
8
|
Krompers M, Heerklotz H. A Guide to Your Desired Lipid-Asymmetric Vesicles. MEMBRANES 2023; 13:267. [PMID: 36984654 PMCID: PMC10054703 DOI: 10.3390/membranes13030267] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 02/14/2023] [Accepted: 02/18/2023] [Indexed: 06/18/2023]
Abstract
Liposomes are prevalent model systems for studies on biological membranes. Recently, increasing attention has been paid to models also representing the lipid asymmetry of biological membranes. Here, we review in-vitro methods that have been established to prepare free-floating vesicles containing different compositions of the classic two-chain glycero- or sphingolipids in their outer and inner leaflet. In total, 72 reports are listed and assigned to four general strategies that are (A) enzymatic conversion of outer leaflet lipids, (B) re-sorting of lipids between leaflets, (C) assembly from different monolayers and (D) exchange of outer leaflet lipids. To guide the reader through this broad field of available techniques, we attempt to draw a road map that leads to the lipid-asymmetric vesicles that suit a given purpose. Of each method, we discuss advantages and limitations. In addition, various verification strategies of asymmetry as well as the role of cholesterol are briefly discussed. The ability to specifically induce lipid asymmetry in model membranes offers insights into the biological functions of asymmetry and may also benefit the technical applications of liposomes.
Collapse
Affiliation(s)
- Mona Krompers
- Department of Pharmaceutical Technology and Biopharmacy, Institute for Pharmaceutical Sciences, University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Heiko Heerklotz
- Department of Pharmaceutical Technology and Biopharmacy, Institute for Pharmaceutical Sciences, University of Freiburg, 79104 Freiburg im Breisgau, Germany
- Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, ON M5S 3M2, Canada
- Signalling Research Centers BIOSS and CIBSS, University of Freiburg, 79085 Freiburg im Breisgau, Germany
| |
Collapse
|
9
|
Al Badri YN, Chaw CS, Elkordy AA. Insights into Asymmetric Liposomes as a Potential Intervention for Drug Delivery Including Pulmonary Nanotherapeutics. Pharmaceutics 2023; 15:pharmaceutics15010294. [PMID: 36678922 PMCID: PMC9867527 DOI: 10.3390/pharmaceutics15010294] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 12/22/2022] [Accepted: 01/11/2023] [Indexed: 01/18/2023] Open
Abstract
Liposome-based drug delivery systems are nanosized spherical lipid bilayer carriers that can encapsulate a broad range of small drug molecules (hydrophilic and hydrophobic drugs) and large drug molecules (peptides, proteins, and nucleic acids). They have unique characteristics, such as a self-assembling bilayer vesicular structure. There are several FDA-approved liposomal-based medicines for treatment of cancer, bacterial, and viral infections. Most of the FDA-approved liposomal-based therapies are in the form of conventional "symmetric" liposomes and they are administered mainly by injection. Arikace® is the first and only FDA-approved liposomal-based inhalable therapy (amikacin liposome inhalation suspension) to treat only adults with difficult-to-treat Mycobacterium avium complex (MAC) lung disease as a combinational antibacterial treatment. To date, no "asymmetric liposomes" are yet to be approved, although asymmetric liposomes have many advantages due to the asymmetric distribution of lipids through the liposome's membrane (which is similar to the biological membranes). There are many challenges for the formulation and stability of asymmetric liposomes. This review will focus on asymmetric liposomes in contrast to conventional liposomes as a potential clinical intervention drug delivery system as well as the formulation techniques available for symmetric and asymmetric liposomes. The review aims to renew the research in liposomal nanovesicle delivery systems with particular emphasis on asymmetric liposomes as future potential carriers for enhancing drug delivery including pulmonary nanotherapeutics.
Collapse
Affiliation(s)
| | | | - Amal Ali Elkordy
- Correspondence: ; Tel.: +44-(0)-1915152576; Fax: +44-(0)-1915153405
| |
Collapse
|
10
|
London E. Ordered Domain (Raft) Formation in Asymmetric Vesicles and Its Induction upon Loss of Lipid Asymmetry in Artificial and Natural Membranes. MEMBRANES 2022; 12:870. [PMID: 36135889 PMCID: PMC9503047 DOI: 10.3390/membranes12090870] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 09/01/2022] [Accepted: 09/03/2022] [Indexed: 06/16/2023]
Abstract
Lipid asymmetry, the difference in the lipid composition in the inner and outer lipid monolayers (leaflets) of a membrane, is an important feature of eukaryotic plasma membranes. Investigation of the biophysical consequences of lipid asymmetry has been aided by advances in the ability to prepare artificial asymmetric membranes, especially by use of cyclodextrin-catalyzed lipid exchange. This review summarizes recent studies with artificial asymmetric membranes which have identified conditions in which asymmetry can induce or suppress the ability of membranes to form ordered domains (rafts). A consequence of the latter effect is that, under some conditions, a loss of asymmetry can induce ordered domain formation. An analogous study in plasma membrane vesicles has demonstrated that asymmetry can also suppress domain formation in natural membranes. Thus, it is possible that a loss of asymmetry can induce domain formation in vivo.
Collapse
Affiliation(s)
- Erwin London
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
| |
Collapse
|
11
|
Grava M, Helmy S, Gimona M, Parisse P, Casalis L, Brocca P, Rondelli V. Calorimetry of extracellular vesicles fusion to single phospholipid membrane. Biomol Concepts 2022; 13:148-155. [PMID: 35312244 DOI: 10.1515/bmc-2022-0011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 03/01/2022] [Indexed: 12/12/2022] Open
Abstract
Extracellular vesicles (EVs)-mediated communication relies not only on the delivery of complex molecular cargoes as lipids, proteins, genetic material, and metabolites to their target cells but also on the modification of the cell surface local properties induced by the eventual fusion of EVs' membranes with the cells' plasma membrane. Here we applied scanning calorimetry to study the phase transition of single phospholipid (DMPC) monolamellar vesicles, investigating the thermodynamical effects caused by the fusion of doping amounts of mesenchymal stem cells-derived EVs. Specifically, we studied EVs-induced consequences on the lipids distributed in the differently curved membrane leaflets, having different density and order. The effect of EV components was found to be not homogeneous in the two leaflets, the inner (more disordered one) being mainly affected. Fusion resulted in phospholipid membrane flattening associated with lipid ordering, while the transition cooperativity, linked to membrane domains' coexistence during the transition process, was decreased. Our results open new horizons for the investigation of the peculiar effects of EVs of different origins on target cell membrane properties and functionality.
Collapse
Affiliation(s)
- Miriam Grava
- Institute for Condensed Matter Physics, Department of Physics, Technische Universität Darmstadt, Darmstadt, Germany
| | - Sally Helmy
- Department of Medical Biotechnology and Translational Medicine, Università Degli Studi di Milano, Milano, Italy.,Biophysics Group, Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt
| | - Mario Gimona
- GMP Unit, Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University (PMU), Salzburg, Austria.,Research Program "Nanovesicular Therapies", Paracelsus Medical University, Salzburg, Austria
| | - Pietro Parisse
- Istituto Officina dei Materiali, Department of Physical sciences and technologies of matter, Italian National Research Council, Trieste, Italy
| | | | - Paola Brocca
- Department of Medical Biotechnology and Translational Medicine, Università Degli Studi di Milano, Milano, Italy
| | - Valeria Rondelli
- Department of Medical Biotechnology and Translational Medicine, Università Degli Studi di Milano, Milano, Italy
| |
Collapse
|
12
|
Nguyen MHL, DiPasquale M, Castillo SR, Marquardt D. Time-Resolved SANS to Measure Monomer Inter-Bilayer Exchange and Intra-Bilayer Translocation. Methods Mol Biol 2022; 2402:151-161. [PMID: 34854043 DOI: 10.1007/978-1-0716-1843-1_13] [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: 06/13/2023]
Abstract
The monomeric exchange kinetics of sub-micron particles provide insight into their stability and dynamism. Traditional techniques used to measure the intra- and inter-particle exchange often require monitoring the transfer of bulky and perturbing fluorescent labels. Time-resolved small angle neutron scattering (TR-SANS) overcomes these flaws by isotope labeling, allowing for the monomeric exchange rate determination of unperturbed, stress-free particles. Here, we describe TR-SANS in detail and novel applications of the technique.
Collapse
Affiliation(s)
- Michael H L Nguyen
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Mitchell DiPasquale
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Stuart R Castillo
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Drew Marquardt
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada.
| |
Collapse
|
13
|
Arribas Perez M, Beales PA. Biomimetic Curvature and Tension-Driven Membrane Fusion Induced by Silica Nanoparticles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:13917-13931. [PMID: 34788054 DOI: 10.1021/acs.langmuir.1c02492] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Fusion events in living cells are intricate phenomena that require the coordinate action of multicomponent protein complexes. However, simpler synthetic tools to control membrane fusion in artificial cells are highly desirable. Native membrane fusion machinery mediates fusion, driving a delicate balance of membrane curvature and tension between two closely apposed membranes. Here, we show that silica nanoparticles (SiO2 NPs) at a size close to the cross-over between tension-driven and curvature-driven interaction regimes initiate efficient fusion of biomimetic model membranes. Fusion efficiency and mechanisms are studied by Förster resonance energy transfer and confocal fluorescence microscopy. SiO2 NPs induce a slight increase in lipid packing likely to increase the lateral tension of the membrane. We observe a connection between membrane tension and fusion efficiency. Finally, real-time confocal fluorescence microscopy reveals three distinct mechanistic pathways for membrane fusion. SiO2 NPs show significant potential for inclusion in the synthetic biology toolkit for membrane remodeling and fusion in artificial cells.
Collapse
Affiliation(s)
- Marcos Arribas Perez
- Astbury Centre for Structural Molecular Biology and School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - Paul A Beales
- Astbury Centre for Structural Molecular Biology and School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
- Bragg Centre for Materials Research, University of Leeds, Leeds LS2 9JT, U.K
| |
Collapse
|
14
|
Lewis-Laurent A, Doktorova M, Heberle FA, Marquardt D. Vesicle Viewer: Online visualization and analysis of small-angle scattering from lipid vesicles. Biophys J 2021; 120:4639-4648. [PMID: 34571013 DOI: 10.1016/j.bpj.2021.09.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/26/2021] [Accepted: 09/09/2021] [Indexed: 10/20/2022] Open
Abstract
Small-angle X-ray and neutron scattering are among the most powerful experimental techniques for investigating the structure of biological membranes. Much of the critical information contained in small-angle scattering (SAS) data is not easily accessible to researchers who have limited time to analyze results by hand or to nonexperts who may lack the necessary scientific background to process such data. Easy-to-use data visualization software can allow them to take full advantage of their SAS data and maximize the use of limited resources. To this end, we developed an internet-based application called Vesicle Viewer to visualize and analyze SAS data from unilamellar lipid bilayer vesicles. Vesicle Viewer utilizes a modified scattering density profile (SDP) analysis called EZ-SDP in which key bilayer structural parameters, such as area per lipid and bilayer thickness, are easily and robustly determined. Notably, we introduce a bilayer model that is able to describe an asymmetric bilayer, whether it be chemically or isotopically asymmetric. The application primarily uses Django, a Python package specialized for the development of robust web applications. In addition, several other libraries are used to support the more technical aspects of the project; notable examples are Matplotlib (for graphs) and NumPy (for calculations). By eliminating the barrier of downloading and installing software, this web-based application will allow scientists to analyze their own vesicle scattering data using their preferred operating system. The web-based application can be found at https://vesicleviewer.dmarquardt.ca/.
Collapse
Affiliation(s)
- Aislyn Lewis-Laurent
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, Ontario, Canada
| | - Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia
| | | | - Drew Marquardt
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, Ontario, Canada; Department of Physics, University of Windsor, Windsor, Ontario, Canada.
| |
Collapse
|
15
|
Observing the structural variations on binary complex vesicle surfaces and the influence on molecular transportation. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2021.111250] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
16
|
Abstract
Cell membranes - primarily composed of lipids, sterols, and proteins - form a dynamic interface between living cells and their environment. They act as a mechanical barrier around the cell while selectively facilitating material transport, signal transduction, and various other functions necessary for the cell viability. The complex functionality of cell membranes and the hierarchical motions and responses they exhibit demand a thorough understanding of the origin of different membrane dynamics and how they are influenced by molecular additives and environmental cues. These dynamic modes include single-molecule diffusion, thermal fluctuations, and large-scale membrane deformations, to name a few. This review highlights advances in investigating structure-driven dynamics associated with model cell membranes, with a particular focus on insights gained from neutron scattering and spectroscopy experiments. We discuss the uniqueness of neutron contrast variation and its remarkable potential in probing selective membrane structure and dynamics on spatial and temporal scales over which key biological functions occur. We also present a summary of current and future opportunities in synergistic combinations of neutron scattering with molecular dynamics (MD) simulations to gain further understanding of the molecular mechanisms underlying complex membrane functions.
Collapse
Affiliation(s)
- Sudipta Gupta
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA. and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 24061, USA
| | - Rana Ashkar
- Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA. and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 24061, USA
| |
Collapse
|
17
|
Scott HL, Kennison KB, Enoki TA, Doktorova M, Kinnun JJ, Heberle FA, Katsaras J. Model Membrane Systems Used to Study Plasma Membrane Lipid Asymmetry. Symmetry (Basel) 2021; 13. [PMID: 35498375 PMCID: PMC9053528 DOI: 10.3390/sym13081356] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
It is well known that the lipid distribution in the bilayer leaflets of mammalian plasma membranes (PMs) is not symmetric. Despite this, model membrane studies have largely relied on chemically symmetric model membranes for the study of lipid–lipid and lipid–protein interactions. This is primarily due to the difficulty in preparing stable, asymmetric model membranes that are amenable to biophysical studies. However, in the last 20 years, efforts have been made in producing more biologically faithful model membranes. Here, we review several recently developed experimental and computational techniques for the robust generation of asymmetric model membranes and highlight a new and particularly promising technique to study membrane asymmetry.
Collapse
Affiliation(s)
- Haden L. Scott
- Large Scale Structures Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Shull-Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - Kristen B. Kennison
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - Thais A. Enoki
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14850, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22903, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - Jacob J. Kinnun
- Large Scale Structures Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Shull-Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - Frederick A. Heberle
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| | - John Katsaras
- Shull-Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Sample Environment Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
- Correspondence: (H.L.S.); (K.B.K.); (T.A.E.); (M.D.); (J.J.K.); (F.A.H.); (J.K.)
| |
Collapse
|
18
|
Kelley EG, Butler PD, Nagao M. Collective dynamics in lipid membranes containing transmembrane peptides. SOFT MATTER 2021; 17:5671-5681. [PMID: 33942045 PMCID: PMC10466476 DOI: 10.1039/d1sm00314c] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Biological membranes are composed of complex mixtures of lipids and proteins that influence each other's structure and function. The biological activities of many channel-forming peptides and proteins are known to depend on the material properties of the surrounding lipid bilayer. However, less is known about how membrane-spanning channels affect the lipid bilayer properties, and in particular, their collective fluctuation dynamics. Here we use neutron spin echo spectroscopy (NSE) to measure the collective bending and thickness fluctuation dynamics in dimyristoylphosphatidylcholine (di 14 : 0 PC, DMPC) lipid membranes containing two different antimicrobial peptides, alamethicin (Ala) and gramicidin (gD). Ala and gD are both well-studied antimicrobial peptides that form oligomeric membrane-spanning channels with different structures. At low concentrations, the peptides did not have a measurable effect on the average bilayer structure, yet significantly changed the collective membrane dynamics. Despite both peptides forming transmembrane channels, they had opposite effects on the relaxation time of the collective bending fluctuations and associated effective bending modulus, where gD addition stiffened the membrane while Ala addition softened the membrane. Meanwhile, the lowest gD concentrations enhanced the collective thickness fluctuation dynamics, while the higher gD concentrations and all studied Ala concentrations dampened these dynamics. The results highlight the synergy between lipids and proteins in determining the collective membrane dynamics and that not all peptides can be universally treated as rigid bodies when considering their effects on the lipid bilayer fluctuations.
Collapse
Affiliation(s)
- Elizabeth G Kelley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA.
| | - Paul D Butler
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA. and Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA and Department of Chemistry, The University of Tennessee Knoxville, TN 37996, USA
| | - Michihiro Nagao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA. and Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA and Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
| |
Collapse
|
19
|
Jiang W, Lin YC, Luo YL. Mechanical properties of anionic asymmetric bilayers from atomistic simulations. J Chem Phys 2021; 154:224701. [PMID: 34241213 PMCID: PMC8189722 DOI: 10.1063/5.0048232] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Accepted: 05/12/2021] [Indexed: 11/14/2022] Open
Abstract
Mechanotransduction, the biological response to mechanical stress, is often initiated by activation of mechanosensitive (MS) proteins upon mechanically induced deformations of the cell membrane. A current challenge in fully understanding this process is in predicting how lipid bilayers deform upon the application of mechanical stress. In this context, it is now well established that anionic lipids influence the function of many proteins. Here, we test the hypothesis that anionic lipids could indirectly modulate MS proteins by alteration of the lipid bilayer mechanical properties. Using all-atom molecular dynamics simulations, we computed the bilayer bending rigidity (KC), the area compressibility (KA), and the surface shear viscosity (ηm) of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (PC) lipid bilayers with and without phosphatidylserine (PS) or phosphatidylinositol bisphosphate (PIP2) at physiological concentrations in the lower leaflet. Tensionless leaflets were first checked for each asymmetric bilayer model, and a formula for embedding an asymmetric channel in an asymmetric bilayer is proposed. Results from two different sized bilayers show consistently that the addition of 20% surface charge in the lower leaflet of the PC bilayer with PIP2 has minimal impact on its mechanical properties, while PS reduced the bilayer bending rigidity by 22%. As a comparison, supplementing the PIP2-enriched PC membrane with 30% cholesterol, a known rigidifying steroid lipid, produces a significant increase in all three mechanical constants. Analysis of pairwise splay moduli suggests that the effect of anionic lipids on bilayer bending rigidity largely depends on the number of anionic lipid pairs formed during simulations. The potential implication of bilayer bending rigidity is discussed in the framework of MS piezo channels.
Collapse
Affiliation(s)
- Wenjuan Jiang
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California 91766, USA
| | - Yi-Chun Lin
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California 91766, USA
| | - Yun Lyna Luo
- Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California 91766, USA
| |
Collapse
|
20
|
Kinnun JJ, Scott HL, Ashkar R, Katsaras J. Biomembrane Structure and Material Properties Studied With Neutron Scattering. Front Chem 2021; 9:642851. [PMID: 33987167 PMCID: PMC8110834 DOI: 10.3389/fchem.2021.642851] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 03/16/2021] [Indexed: 12/12/2022] Open
Abstract
Cell membranes and their associated structures are dynamical supramolecular structures where different physiological processes take place. Detailed knowledge of their static and dynamic structures is therefore needed, to better understand membrane biology. The structure–function relationship is a basic tenet in biology and has been pursued using a range of different experimental approaches. In this review, we will discuss one approach, namely the use of neutron scattering techniques as applied, primarily, to model membrane systems composed of lipid bilayers. An advantage of neutron scattering, compared to other scattering techniques, is the differential sensitivity of neutrons to isotopes of hydrogen and, as a result, the relative ease of altering sample contrast by substituting protium for deuterium. This property makes neutrons an ideal probe for the study of hydrogen-rich materials, such as biomembranes. In this review article, we describe isotopic labeling studies of model and viable membranes, and discuss novel applications of neutron contrast variation in order to gain unique insights into the structure, dynamics, and molecular interactions of biological membranes. We specifically focus on how small-angle neutron scattering data is modeled using different contrast data and molecular dynamics simulations. We also briefly discuss neutron reflectometry and present a few recent advances that have taken place in neutron spin echo spectroscopy studies and the unique membrane mechanical data that can be derived from them, primarily due to new models used to fit the data.
Collapse
Affiliation(s)
- Jacob J Kinnun
- Large Scale Structures Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Oak Ridge National Laboratory, Shull-Wollan Center, Oak Ridge, TN, United States
| | - Haden L Scott
- Large Scale Structures Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Oak Ridge National Laboratory, Shull-Wollan Center, Oak Ridge, TN, United States
| | - Rana Ashkar
- Department of Physics, Virginia Tech, Blacksburg, VA, United States.,Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA, United States
| | - John Katsaras
- Oak Ridge National Laboratory, Shull-Wollan Center, Oak Ridge, TN, United States.,Sample Environment Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, United States
| |
Collapse
|
21
|
Shukla S, Baumgart T. Enzymatic trans-bilayer lipid transport: Mechanisms, efficiencies, slippage, and membrane curvature. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2021; 1863:183534. [PMID: 33340491 PMCID: PMC8351443 DOI: 10.1016/j.bbamem.2020.183534] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 12/03/2020] [Accepted: 12/07/2020] [Indexed: 12/12/2022]
Abstract
The eukaryotic plasma membrane's lipid composition is found to be ubiquitously asymmetric comparing inner and outer leaflets. This membrane lipid asymmetry plays a crucial role in diverse cellular processes critical for cell survival. A specialized set of transmembrane proteins called translocases, or flippases, have evolved to maintain this membrane lipid asymmetry in an energy-dependent manner. One potential consequence of local variations in membrane lipid asymmetry is membrane remodeling, which is essential for cellular processes such as intracellular trafficking. Recently, there has been a surge in the identification and characterization of flippases, which has significantly advanced the understanding of their functional mechanisms. Furthermore, there are intriguing possibilities for a coupling between membrane curvature and flippase activity. In this review we highlight studies that link membrane shape and remodeling to differential stresses generated by the activity of lipid flippases with an emphasis on data obtained through model membrane systems. We review the common mechanistic models of flippase-mediated lipid flipping and discuss common techniques used to test lipid flippase activity. We then compare the existing data on lipid translocation rates by flippases and conclude with potential future directions for this field.
Collapse
Affiliation(s)
- Sankalp Shukla
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, United States
| | - Tobias Baumgart
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, United States.
| |
Collapse
|
22
|
Nguyen MHL, DiPasquale M, Rickeard BW, Yip CG, Greco KN, Kelley EG, Marquardt D. Time-resolved SANS reveals pore-forming peptides cause rapid lipid reorganization. NEW J CHEM 2021. [DOI: 10.1039/d0nj04717a] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Time-resolved SANS showed alamethicin and melittin promote DMPC lipid vesicle mixing and perturb DMPC kinetics in similar ways.
Collapse
Affiliation(s)
| | | | - Brett W. Rickeard
- Department of Chemistry and Biochemistry
- University of Windsor
- Windsor
- Canada
| | - Caesar G. Yip
- Department of Chemistry and Biochemistry
- University of Windsor
- Windsor
- Canada
| | - Kaity N. Greco
- Department of Chemistry and Biochemistry
- University of Windsor
- Windsor
- Canada
| | - Elizabeth G. Kelley
- NIST Center for Neutron Research
- National Institute of Standards and Technology
- Gaithersburg
- USA
| | - Drew Marquardt
- Department of Chemistry and Biochemistry
- University of Windsor
- Windsor
- Canada
- Department of Physics
| |
Collapse
|
23
|
Nielsen JE, Prévost SF, Jenssen H, Lund R. Impact of antimicrobial peptides on E. coli-mimicking lipid model membranes: correlating structural and dynamic effects using scattering methods. Faraday Discuss 2021; 232:203-217. [DOI: 10.1039/d0fd00046a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using X-rays and neutrons we address the effect of AMPs on structure and dynamics of lipids in bacterial model membranes.
Collapse
Affiliation(s)
| | | | - Håvard Jenssen
- Department of Science and Environment, Roskilde University, 4000 Roskilde, Denmark
| | - Reidar Lund
- Department of Chemistry, University of Oslo, 0315 Oslo, Norway
| |
Collapse
|
24
|
Kelley EG, Butler PD, Ashkar R, Bradbury R, Nagao M. Scaling relationships for the elastic moduli and viscosity of mixed lipid membranes. Proc Natl Acad Sci U S A 2020; 117:23365-23373. [PMID: 32883879 PMCID: PMC7519290 DOI: 10.1073/pnas.2008789117] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The elastic and viscous properties of biological membranes play a vital role in controlling cell functions that require local reorganization of the membrane components as well as dramatic shape changes such as endocytosis, vesicular trafficking, and cell division. These properties are widely acknowledged to depend on the unique composition of lipids within the membrane, yet the effects of lipid mixing on the membrane biophysical properties remain poorly understood. Here, we present a comprehensive characterization of the structural, elastic, and viscous properties of fluid membranes composed of binary mixtures of lipids with different tail lengths. We show that the mixed lipid membrane properties are not simply additive quantities of the single-component analogs. Instead, the mixed membranes are more dynamic than either of their constituents, quantified as a decrease in their bending modulus, area compressibility modulus, and viscosity. While the enhanced dynamics are seemingly unexpected, we show that the measured moduli and viscosity for both the mixed and single-component bilayers all scale with the area per lipid and collapse onto respective master curves. This scaling links the increase in dynamics to mixing-induced changes in the lipid packing and membrane structure. More importantly, the results show that the membrane properties can be manipulated through lipid composition the same way bimodal blends of surfactants, liquid crystals, and polymers are used to engineer the mechanical properties of soft materials, with broad implications for understanding how lipid diversity relates to biomembrane function.
Collapse
Affiliation(s)
- Elizabeth G Kelley
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899;
| | - Paul D Butler
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716
- Department of Chemistry, The University of Tennessee, Knoxville, TN 37996
| | - Rana Ashkar
- Physics Department, Virginia Tech, Blacksburg, VA 20461
- Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 20461
| | - Robert Bradbury
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN 47408
| | - Michihiro Nagao
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
- Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN 47408
- Department of Physics and Astronomy, University of Delaware, Newark, DE 19716
| |
Collapse
|
25
|
DiPasquale M, Gbadamosi O, Nguyen MHL, Castillo SR, Rickeard BW, Kelley EG, Nagao M, Marquardt D. A Mechanical Mechanism for Vitamin E Acetate in E-cigarette/Vaping-Associated Lung Injury. Chem Res Toxicol 2020; 33:2432-2440. [PMID: 32842741 DOI: 10.1021/acs.chemrestox.0c00212] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The outbreak of electronic-cigarette/vaping-associated lung injury (EVALI) has made thousands ill. This lung injury has been attributed to a physical interaction between toxicants from the vaping solution and the pulmonary surfactant. In particular, studies have implicated vitamin E acetate as a potential instigator of EVALI. Pulmonary surfactant is vital to proper respiration through the mechanical processes of adsorption and interface stability to achieve and maintain low surface tension at the air-liquid interface. Using neutron spin echo spectroscopy, we investigate the impact of vitamin E acetate on the mechanical properties of two lipid-only pulmonary surfactant mimics: pure 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and a more comprehensive lipid mixture. It was found that increasing vitamin E acetate concentration nonlinearly increased membrane fluidity and area compressibility to a plateau. Softer membranes would promote adsorption to the air-liquid interface during inspiration as well as collapse from the interface during expiration. These findings indicate the potential for the failure of the pulmonary surfactant upon expiration, attributed to monolayer collapse. This collapse could contribute to the observed EVALI signs and symptoms, including shortness of breath and pneumonitis.
Collapse
Affiliation(s)
| | | | | | | | | | - Elizabeth G Kelley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Michihiro Nagao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.,Center for Exploration of Energy and Matter, Department of Physics, Indiana University, Bloomington, Indiana 47408, United States.,Department of Physics and AstronomyUniversity of DelawareNewarkDelaware19716United States
| | | |
Collapse
|
26
|
Dietel L, Kalie L, Heerklotz H. Lipid Scrambling Induced by Membrane-Active Substances. Biophys J 2020; 119:767-779. [PMID: 32738218 DOI: 10.1016/j.bpj.2020.07.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 07/03/2020] [Accepted: 07/07/2020] [Indexed: 11/26/2022] Open
Abstract
The functional roles of the lipid asymmetry of biomembranes are attracting increasing attention. This study characterizes the activity of surfactants to induce transmembrane flip-flop of lipids and thus "scramble" this asymmetry. Detergent-induced lipid scrambling of liposomes mimicking the charge asymmetry of bacterial membranes with 20 mol % of 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-glycerol in the outer leaflet only was quantified by ζ-potential measurements for octaethylene glycol dodecyl ether (C12EO8), octyl glucoside (OG), and dodecyl maltoside. Membrane leakage was separately measured by the fluorescence lifetime-based calcein leakage assay and the onset of the membrane-to-micelle transition by isothermal titration calorimetry. Partition coefficients and partial molar areas were obtained as well. For the quickly membrane-permeant C12EO8 and OG, leakage proceeds at a rather sharp threshold content in the membrane, which is well below the onset of solubilization and little dependent on incubation time; it is accompanied by fast lipid scrambling. However, unlike leakage, flip-flop is a relaxation process that speeds up gradually from taking weeks in the detergent-free membrane to minutes or less in the leaking membrane. Hence, after 24 h of incubation, 10 mol % of C12EO8 or 50 mol % of OG in the membrane suffice for virtually complete lipid scrambling, whereas leakage remains below 10% for up to 14 mol % of C12EO8 and 88 mol % of OG. There is thus a concentration window in which lipid scrambling proceeds without leakage. This implies that lipid scrambling must be considered a possible mode of action of antimicrobial peptides and other membrane-active drugs or biomolecules. A related, detergent-based protocol for scrambling the lipid asymmetry of liposomes and maybe cells without compromising their overall integrity would be a very valuable tool to study functions of lipid asymmetry.
Collapse
Affiliation(s)
- Lisa Dietel
- Institute of Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany.
| | - Louma Kalie
- Institute of Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany
| | - Heiko Heerklotz
- Institute of Pharmaceutical Sciences, University of Freiburg, Freiburg, Germany; Signaling Research Centers BIOSS and CIBSS, University of Freiburg, Freiburg, Germany; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada.
| |
Collapse
|
27
|
Sun S, Liu C, Rodriguez Melendez D, Yang T, Cremer PS. Immobilization of Phosphatidylinositides Revealed by Bilayer Leaflet Decoupling. J Am Chem Soc 2020; 142:13003-13010. [DOI: 10.1021/jacs.0c03800] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Simou Sun
- Department of Chemistry, Penn State University, University Park, Pennsylvania 16802, United States
| | - Chang Liu
- Department of Chemistry, Penn State University, University Park, Pennsylvania 16802, United States
| | - Danixa Rodriguez Melendez
- Department of Chemistry, University of Puerto Rico at Cayey, Cayey, Puerto Rico 00737, United States
| | - Tinglu Yang
- Department of Chemistry, Penn State University, University Park, Pennsylvania 16802, United States
| | - Paul S. Cremer
- Department of Chemistry, Penn State University, University Park, Pennsylvania 16802, United States
- Department of Biochemistry and Molecular Biology, Penn State University, University Park, Pennsylvania 16802, United States
| |
Collapse
|
28
|
Lorent JH, Levental KR, Ganesan L, Rivera-Longsworth G, Sezgin E, Doktorova M, Lyman E, Levental I. Plasma membranes are asymmetric in lipid unsaturation, packing and protein shape. Nat Chem Biol 2020; 16:644-652. [PMID: 32367017 DOI: 10.1101/698837] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 03/27/2020] [Indexed: 05/26/2023]
Abstract
A fundamental feature of cellular plasma membranes (PMs) is an asymmetric lipid distribution between the bilayer leaflets. However, neither the detailed, comprehensive compositions of individual PM leaflets nor how these contribute to structural membrane asymmetries have been defined. We report the distinct lipidomes and biophysical properties of both monolayers in living mammalian PMs. Phospholipid unsaturation is dramatically asymmetric, with the cytoplasmic leaflet being approximately twofold more unsaturated than the exoplasmic leaflet. Atomistic simulations and spectroscopy of leaflet-selective fluorescent probes reveal that the outer PM leaflet is more packed and less diffusive than the inner leaflet, with this biophysical asymmetry maintained in the endocytic system. The structural asymmetry of the PM is reflected in the asymmetric structures of protein transmembrane domains. These structural asymmetries are conserved throughout Eukaryota, suggesting fundamental cellular design principles.
Collapse
Affiliation(s)
- J H Lorent
- McGovern Medical School, Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX, USA
| | - K R Levental
- McGovern Medical School, Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX, USA
| | - L Ganesan
- McGovern Medical School, Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX, USA
| | | | - E Sezgin
- John Radcliffe Hospital, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
- SciLifeLab, Karolinska Institute, Stockholm, Sweden
| | - M Doktorova
- McGovern Medical School, Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX, USA
| | - E Lyman
- Department of Physics and Astronomy and Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA
| | - I Levental
- McGovern Medical School, Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX, USA.
| |
Collapse
|
29
|
Plasma membranes are asymmetric in lipid unsaturation, packing and protein shape. Nat Chem Biol 2020; 16:644-652. [PMID: 32367017 PMCID: PMC7246138 DOI: 10.1038/s41589-020-0529-6] [Citation(s) in RCA: 355] [Impact Index Per Article: 88.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 03/27/2020] [Indexed: 12/27/2022]
Abstract
A fundamental feature of cellular plasma membranes (PM) is asymmetric lipid distribution between the bilayer leaflets. However, neither the detailed, comprehensive compositions of individual PM leaflets, nor how these contribute to structural membrane asymmetries have been defined. We report the distinct lipidomes and biophysical properties of both monolayers in living mammalian PMs. Phospholipid unsaturation is dramatically asymmetric, with the cytoplasmic leaflet being ~2-fold more unsaturated than the exoplasmic. Atomistic simulations and spectroscopy of leaflet-selective fluorescent probes reveal that the outer PM leaflet is more packed and less diffusive than the inner leaflet, with this biophysical asymmetry maintained in the endocytic system. The structural asymmetry of the PM is reflected in asymmetric structures of protein transmembrane domains (TMD). These structural asymmetries are conserved throughout Eukaryota, suggesting fundamental cellular design principles.
Collapse
|
30
|
Khelashvili G, Cheng X, Falzone ME, Doktorova M, Accardi A, Weinstein H. Membrane lipids are both the substrates and a mechanistically responsive environment of TMEM16 scramblase proteins. J Comput Chem 2020; 41:538-551. [PMID: 31750558 PMCID: PMC7261202 DOI: 10.1002/jcc.26105] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 09/04/2019] [Accepted: 10/17/2019] [Indexed: 12/21/2022]
Abstract
Recent discoveries about functional mechanisms of proteins in the TMEM16 family of phospholipid scramblases have illuminated the dual role of the membrane as both the substrate and a mechanistically responsive environment in the wide range of physiological processes and genetic disorders in which they are implicated. This is highlighted in the review of recent findings from our collaborative investigations of molecular mechanisms of TMEM16 scramblases that emerged from iterative functional, structural, and computational experimentation. In the context of this review, we present new MD simulations and trajectory analyses motivated by the fact that new structural information about the TMEM16 scramblases is emerging from cryo-EM determinations in lipid nanodiscs. Because the functional environment of these proteins in in vivo and in in vitro is closer to flat membranes, we studied comparatively the responses of the membrane to the TMEM16 proteins in flat membranes and nanodiscs. We find that bilayer shapes in the nanodiscs are very different from those observed in the flat membrane systems, but the function-related slanting of the membrane observed at the nhTMEM16 boundary with the protein is similar in the nanodiscs and in the flat bilayers. This changes, however, in the bilayer composed of longer-tail lipids, which is thicker near the phospholipid translocation pathway, which may reflect an enhanced tendency of the long tails to penetrate the pathway and create, as shown previously, a nonconductive environment. These findings support the correspondence between the mechanistic involvement of the lipid environment in the flat membranes, and the nanodiscs. © 2019 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York, 10065
- Institute for Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York, 10065
| | - Xiaolu Cheng
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York, 10065
| | - Maria E Falzone
- Department of Biochemistry, Weill Cornell Medical College of Cornell University, New York, New York, 10065
| | - Milka Doktorova
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas, 77030
| | - Alessio Accardi
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York, 10065
- Department of Biochemistry, Weill Cornell Medical College of Cornell University, New York, New York, 10065
- Department of Anesthesiology, Weill Cornell Medical College of Cornell University, New York, New York, 10065
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, New York, 10065
- Institute for Computational Biomedicine, Weill Cornell Medical College of Cornell University, New York, New York, 10065
| |
Collapse
|
31
|
Rickeard BW, Nguyen MHL, DiPasquale M, Yip CG, Baker H, Heberle FA, Zuo X, Kelley EG, Nagao M, Marquardt D. Transverse lipid organization dictates bending fluctuations in model plasma membranes. NANOSCALE 2020; 12:1438-1447. [PMID: 31746906 DOI: 10.1039/c9nr07977g] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Membrane undulations play a vital role in many biological processes, including the regulation of membrane protein activity. The asymmetric lipid composition of most biological membranes complicates theoretical description of these bending fluctuations, yet experimental data that would inform any such a theory is scarce. Here, we used neutron spin-echo (NSE) spectroscopy to measure the bending fluctuations of large unilamellar vesicles (LUV) having an asymmetric transbilayer distribution of high- and low-melting lipids. The asymmetric vesicles were prepared using cyclodextrin-mediated lipid exchange, and were composed of an outer leaflet enriched in egg sphingomyelin (ESM) and an inner leaflet enriched in 1-palmitoyl-2-oleoyl-phosphoethanolamine (POPE), which have main transition temperatures of 37 °C and 25 °C, respectively. The overall membrane bending rigidity was measured at three temperatures: 15 °C, where both lipids are in a gel state; 45 °C, where both lipids are in a fluid state; and 30 °C, where there is gel-fluid co-existence. Remarkably, the dynamics for the fluid asymmetric LUVs (aLUVs) at 30 °C and 45 °C do not follow trends predicted by their symmetric counterparts. At 30 °C, compositional asymmetry suppressed the bending fluctuations, with the asymmetric bilayer exhibiting a larger bending modulus than that of symmetric bilayers corresponding to either the outer or inner leaflet. We conclude that the compositional asymmetry and leaflet coupling influence the internal dissipation within the bilayer and result in membrane properties that cannot be directly predicted from corresponding symmetric bilayers.
Collapse
Affiliation(s)
- Brett W Rickeard
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Markones M, Fippel A, Kaiser M, Drechsler C, Hunte C, Heerklotz H. Stairway to Asymmetry: Five Steps to Lipid-Asymmetric Proteoliposomes. Biophys J 2020; 118:294-302. [PMID: 31843262 PMCID: PMC6976795 DOI: 10.1016/j.bpj.2019.10.043] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Revised: 10/09/2019] [Accepted: 10/28/2019] [Indexed: 12/15/2022] Open
Abstract
Membrane proteins are embedded in a complex lipid environment that influences their structure and function. One key feature of nearly all biological membranes is a distinct lipid asymmetry. However, the influence of membrane asymmetry on proteins is poorly understood, and novel asymmetric proteoliposome systems are beneficial. To our knowledge, we present the first study on a multispanning protein incorporated in large unilamellar liposomes showing a stable lipid asymmetry. These asymmetric proteoliposomes contain the Na+/H+ antiporter NhaA from Salmonella Typhimurium. Asymmetry was introduced by partial, outside-only exchange of anionic phosphatidylglycerol (PG), mimicking this key asymmetry of bacterial membranes. Outer-leaflet and total fractions of PG were determined via ζ-potential (ζ) measurements after lipid exchange and after scrambling of asymmetry. ζ-Values were in good agreement with exclusive outside localization of PG. The electrogenic Na+/H+ antiporter was active in asymmetric liposomes, and it can be concluded that reconstitution and generation of asymmetry were successful. Lipid asymmetry was stable for more than 7 days at 23°C and thus enabled characterization of the Na+/H+ antiporter in an asymmetric lipid environment. We present and validate a simple five-step protocol that addresses key steps to be taken and pitfalls to be avoided for the preparation of asymmetric proteoliposomes: 1) optimization of desired lipid composition, 2) detergent-mediated protein reconstitution with subsequent detergent removal, 3) generation of lipid asymmetry by partial exchange of outer-leaflet lipid, 4) verification of lipid asymmetry and stability, and 5) determination of protein activity in the asymmetric lipid environment. This work offers guidance in designing asymmetric proteoliposomes that will enable researchers to compare functional and structural properties of membrane proteins in symmetric and asymmetric lipid environments.
Collapse
Affiliation(s)
- Marie Markones
- Institute for Pharmaceutical Sciences, University of Freiburg, Breisgau, Germany; Signaling Research Centers BIOSS and CIBSS, University of Freiburg, Breisgau, Germany; HSGS Hermann Staudinger Graduate School, University of Freiburg, Breisgau, Germany.
| | - Anika Fippel
- Institute for Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Breisgau, Germany; HSGS Hermann Staudinger Graduate School, University of Freiburg, Breisgau, Germany
| | - Michael Kaiser
- Institute for Pharmaceutical Sciences, University of Freiburg, Breisgau, Germany; HSGS Hermann Staudinger Graduate School, University of Freiburg, Breisgau, Germany
| | - Carina Drechsler
- Institute for Pharmaceutical Sciences, University of Freiburg, Breisgau, Germany; Signaling Research Centers BIOSS and CIBSS, University of Freiburg, Breisgau, Germany
| | - Carola Hunte
- Signaling Research Centers BIOSS and CIBSS, University of Freiburg, Breisgau, Germany; Institute for Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Breisgau, Germany
| | - Heiko Heerklotz
- Institute for Pharmaceutical Sciences, University of Freiburg, Breisgau, Germany; Signaling Research Centers BIOSS and CIBSS, University of Freiburg, Breisgau, Germany; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
33
|
Boufroura H, Plais R, Poyer S, Gaucher A, Marrot J, Clavier G, Legrand FX, Huin C, Guégan P, Prim D, Salpin JY. Helically shaped cation receptor: design, synthesis, characterisation and first application to ion transport. RSC Adv 2020; 10:31670-31679. [PMID: 35520653 PMCID: PMC9056421 DOI: 10.1039/d0ra05519k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 07/30/2020] [Indexed: 12/22/2022] Open
Abstract
An helicene-like receptor is able to transport K+ across lipid membrane.
Collapse
Affiliation(s)
- Hamza Boufroura
- Université Paris-Saclay
- UVSQ
- CNRS
- UMR 8180
- Institut Lavoisier de Versailles
| | - Romain Plais
- Université Paris-Saclay
- UVSQ
- CNRS
- UMR 8180
- Institut Lavoisier de Versailles
| | | | - Anne Gaucher
- Université Paris-Saclay
- UVSQ
- CNRS
- UMR 8180
- Institut Lavoisier de Versailles
| | - Jérome Marrot
- Université Paris-Saclay
- UVSQ
- CNRS
- UMR 8180
- Institut Lavoisier de Versailles
| | | | | | - Cécile Huin
- Sorbonne Université
- CNRS
- Institut Parisien de Chimie Moléculaire
- Equipe Chimie des Polymères
- 75005 Paris
| | - Philippe Guégan
- Sorbonne Université
- CNRS
- Institut Parisien de Chimie Moléculaire
- Equipe Chimie des Polymères
- 75005 Paris
| | - Damien Prim
- Université Paris-Saclay
- UVSQ
- CNRS
- UMR 8180
- Institut Lavoisier de Versailles
| | | |
Collapse
|
34
|
Doktorova M. On the Long and Winding Road to a Perfect Membrane Model. Biophys J 2019; 118:273-275. [PMID: 31968235 DOI: 10.1016/j.bpj.2019.11.3386] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 11/08/2019] [Indexed: 01/04/2023] Open
Affiliation(s)
- Milka Doktorova
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas.
| |
Collapse
|
35
|
Scott HL, Skinkle A, Kelley EG, Waxham MN, Levental I, Heberle FA. On the Mechanism of Bilayer Separation by Extrusion, or Why Your LUVs Are Not Really Unilamellar. Biophys J 2019; 117:1381-1386. [PMID: 31586522 DOI: 10.1016/j.bpj.2019.09.006] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 08/18/2019] [Accepted: 09/10/2019] [Indexed: 11/18/2022] Open
Abstract
Extrusion through porous filters is a widely used method for preparing biomimetic model membranes. Of primary importance in this approach is the efficient production of single bilayer (unilamellar) vesicles that eliminate the influence of interlamellar interactions and strictly define the bilayer surface area available to external reagents such as proteins. Submicroscopic vesicles produced using extrusion are widely assumed to be unilamellar, and large deviations from this assumption would impact interpretations from many model membrane experiments. Using three probe-free methods-small angle X-ray and neutron scattering and cryogenic electron microscopy-we report unambiguous evidence of extensive multilamellarity in extruded vesicles composed of neutral phosphatidylcholine lipids, including for the common case of neutral lipids dispersed in physiological buffer and extruded through 100-nm diameter pores. In such preparations, only ∼35% of lipids are externally accessible and this fraction is highly dependent on preparation conditions. Charged lipids promote unilamellarity as does decreasing solvent ionic strength, indicating the importance of electrostatic interactions in determining the lamellarity of extruded vesicles. Smaller extrusion pore sizes also robustly increase the fraction of unilamellar vesicles, suggesting a role for membrane bending. Taken together, these observations suggest a mechanistic model for extrusion, wherein the formation of unilamellar vesicles involves competition between bilayer bending and adhesion energies. The findings presented here have wide-ranging implications for the design and interpretation of model membrane studies, especially ensemble-averaged observations relying on the assumption of unilamellarity.
Collapse
Affiliation(s)
- Haden L Scott
- Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Allison Skinkle
- Department of Biosciences, Rice University, Houston, Texas; Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
| | - Elizabeth G Kelley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland
| | - M Neal Waxham
- Department of Neurobiology and Anatomy, University of Texas Health Science Center, Houston, Texas
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas.
| | - Frederick A Heberle
- Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee; Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas.
| |
Collapse
|
36
|
Nguyen MHL, DiPasquale M, Rickeard BW, Doktorova M, Heberle FA, Scott HL, Barrera FN, Taylor G, Collier CP, Stanley CB, Katsaras J, Marquardt D. Peptide-Induced Lipid Flip-Flop in Asymmetric Liposomes Measured by Small Angle Neutron Scattering. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11735-11744. [PMID: 31408345 PMCID: PMC7393738 DOI: 10.1021/acs.langmuir.9b01625] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Despite the prevalence of lipid transbilayer asymmetry in natural plasma membranes, most biomimetic model membranes studied are symmetric. Recent advances have helped to overcome the difficulties in preparing asymmetric liposomes in vitro, allowing for the examination of a larger set of relevant biophysical questions. Here, we investigate the stability of asymmetric bilayers by measuring lipid flip-flop with time-resolved small-angle neutron scattering (SANS). Asymmetric large unilamellar vesicles with inner bilayer leaflets containing predominantly 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and outer leaflets composed mainly of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) displayed slow spontaneous flip-flop at 37 ◦C (half-time, t1/2 = 140 h). However, inclusion of peptides, namely, gramicidin, alamethicin, melittin, or pHLIP (i.e., pH-low insertion peptide), accelerated lipid flip-flop. For three of these peptides (i.e., pHLIP, alamethicin, and melittin), each of which was added externally to preformed asymmetric vesicles, we observed a completely scrambled bilayer in less than 2 h. Gramicidin, on the other hand, was preincorporated during the formation of the asymmetric liposomes and showed a time resolvable 8-fold increase in the rate of lipid asymmetry loss. These results point to a membrane surface-related (e.g., adsorption/insertion) event as the primary driver of lipid scrambling in the asymmetric model membranes of this study. We discuss the implications of membrane peptide binding, conformation, and insertion on lipid asymmetry.
Collapse
Affiliation(s)
- Michael H. L. Nguyen
- Department of Chemistry and Biochemistry, University
of Windsor, Windsor, N9B 3P4 ON Canada
| | - Mitchell DiPasquale
- Department of Chemistry and Biochemistry, University
of Windsor, Windsor, N9B 3P4 ON Canada
| | - Brett W. Rickeard
- Department of Chemistry and Biochemistry, University
of Windsor, Windsor, N9B 3P4 ON Canada
| | - Milka Doktorova
- Department of Integrative Biology and Pharmacology,
University of Texas Health Science Center at Houston, Houston, Texas 77225, United
States
| | - Frederick A. Heberle
- Department of Integrative Biology and Pharmacology,
University of Texas Health Science Center at Houston, Houston, Texas 77225, United
States
- Center for Environmental Biotechnology, University
of Tennessee, Knoxville, Tennessee 37996, United States
| | - Haden L. Scott
- Center for Environmental Biotechnology, University
of Tennessee, Knoxville, Tennessee 37996, United States
- Department of Biochemistry & Cellular and
Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United
States
| | - Francisco N. Barrera
- Department of Biochemistry & Cellular and
Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996, United
States
| | - Graham Taylor
- The Bredesen Center, University of Tennessee,
Knoxville, Tennessee 37996, United States
| | - Charles P. Collier
- The Bredesen Center, University of Tennessee,
Knoxville, Tennessee 37996, United States
- Center for Nanophase Materials Sciences, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Christopher B. Stanley
- Neutron Scattering Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
| | - John Katsaras
- Large Scale Structures Group, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
- Shull Wollan Center, a Joint Institute for Neutron
Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United
States
- Department of Physics and Astronomy, University of
Tennessee, Knoxville, Tennessee 37996, United States
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University
of Windsor, Windsor, N9B 3P4 ON Canada
- Department of Physics, University of Windsor, Windsor, N9B
3P4 ON Canada
- Corresponding Author:
| |
Collapse
|
37
|
Abstract
The lipid bilayer, together with embedded proteins, is the central structure in biomembranes. While artificial lipid bilayers are useful to model natural membranes, they are generally symmetric, with the same membrane lipid composition in each lipid monolayer (leaflet). In contrast, natural membranes are often asymmetric, with different lipids in each leaflet. To prepare asymmetric lipid vesicles, we developed cyclodextrin-catalyzed phospholipid exchange procedures. The basic method is that an excess of vesicles with one set of lipids (the donor vesicles) is mixed with a second set of vesicles (acceptor vesicles) with a different set of lipids. Cyclodextrin is introduced into the external aqueous solution, so that lipids in the outer leaflet of the vesicles bind to it and are shuttled between the vesicles. At equilibrium, the lipids in the outer leaflet of the acceptor vesicles are replaced by those from the donor vesicles. The exchanged acceptor vesicles are then isolated. Asymmetric vesicles are versatile in terms of vesicle sizes and lipid compositions that can be prepared. Measuring asymmetry is often difficult. A variety of assays can be used to measure the extent of asymmetry, but most are specific for one particular membrane lipid type or class, and there are none that can be used in all situations. Studies using asymmetric vesicles have begun to explore how asymmetry influences lipid movement across the bilayer, the formation of ordered lipid domains, coupling between the physical properties in each leaflet, and membrane protein conformation. Lipid domain formation stands out as one of the most important properties in which asymmetry is likely to be crucial. Lipid bilayers can exist in both liquidlike and solid/ordered-like states depending on lipid structure, and in lipid vesicles with a mixture of lipids highly ordered and disordered domains can coexist. However, until very recently, such studies only had been carried out in symmetric artificial membranes. Whether ordered domains (often called lipid rafts) and disordered lipid domains coexist in asymmetric cell membranes remains controversial partly because lipids favoring the formation of an ordered state are largely restricted to the leaflet facing the external environment. Studies using asymmetric vesicles have recently shown that each leaflet can influence the physical behavior of the other, i.e., that the domain forming properties in each leaflet tend to be coupled, with consequences highly dependent upon the details of lipid structure. Future studies investigating the dependence of coupling and properties upon the details of lipid composition should clarify the potential of natural membranes to form lipid domains. In addition, we recently extended the exchange method to living mammalian cells, using exchange to efficiently replace virtually the entire phospholipid and sphingolipid population of the plasma membrane outer leaflet with exogenous lipids without harming cells. This should allow detailed studies of the functional impact of lipid structure, asymmetry, domain organization, and interactions with membrane proteins in living cells.
Collapse
Affiliation(s)
- Erwin London
- Department of Biochemistry and Cell Biology and Department of Chemistry Stony Brook University, Stony Brook, New York 11794, United States
| |
Collapse
|