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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Nicolella Z, Okamoto Y, Watanabe NM, Thompson GL, Umakoshi H. Significance of in situ quantitative membrane property-morphology relation (QmPMR) analysis. SOFT MATTER 2024; 20:4935-4949. [PMID: 38873752 DOI: 10.1039/d4sm00253a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2024]
Abstract
Deformation of the cell membrane is well understood from the viewpoint of protein interactions and free energy balance. However, the various dynamic properties of the membrane, such as lipid packing and hydrophobicity, and their relationship with cell membrane deformation are unknown. Therefore, the deformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and oleic acid (OA) giant unilamellar vesicles (GUVs) was induced by heating and cooling cycles, and time-lapse analysis was conducted based on the membrane hydrophobicity and physical parameters of "single-parent" and "daughter" vesicles. Fluorescence ratiometric analysis by simultaneous dual-wavelength detection revealed the variation of different hydrophilic GUVs and enabled inferences of the "daughter" vesicle composition and the "parent" membrane's local composition during deformation; the "daughter" vesicle composition of OA was lower than that of the "parents", and lateral movement of OA was the primary contributor to the formation of the "daughter" vesicles. Thus, our findings and the newly developed methodology, named in situ quantitative membrane property-morphology relation (QmPMR) analysis, would provide new insights into cell deformation and accelerate research on both deformation and its related events, such as budding and birthing.
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Affiliation(s)
- Zachary Nicolella
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
| | - Yukihiro Okamoto
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
| | - Nozomi Morishita Watanabe
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
| | - Gary Lee Thompson
- Rowan University, Rowan Hall, Room 333 70 Sewell St., Ste. E Glassboro, NJ 08028, USA
| | - Hiroshi Umakoshi
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
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3
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Grosfils P, Losada-Pérez P. Kinetic control of liposome size by direct lipid transfer. J Colloid Interface Sci 2023; 652:1381-1393. [PMID: 37659307 DOI: 10.1016/j.jcis.2023.08.059] [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] [Received: 02/14/2023] [Revised: 08/07/2023] [Accepted: 08/09/2023] [Indexed: 09/04/2023]
Abstract
Spontaneous lipid vesiculation and related size distribution are traditionally studied in the framework of equilibrium thermodynamics and continuum mechanics, overlooking the kinetic aspects of the process. In the scenario of liposomes consisting of different lipid molecules dispersed in the same medium - a non-equilibrium situation -, the system evolves driven by lipid monomer transfer among the different liposomes. This process encompasses time-dependent changes in liposome size and size distribution, thus predicting size and composition at a given time would entail the control of the size of liposomes by kinetic means, an asset in the framework of diagnostics and synthetic biology. We introduce a direct transfer model, based on the fact that monomers are highly reactive species and apply it to saturated phospholipid molecules differing in hydrophobic chain length. Considering a well-defined gamma-type liposome size distribution, we demonstrate a clear liposome size-composition correlation and are able to predict liposome size and size distribution at any time in the transfer process. The size-composition correlation opens up new prospects for the control of the self-assembling properties of lipids and thereby the control of the liposome size.
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Affiliation(s)
- Patrick Grosfils
- Center for Nonlinear Phenomena and Complex Systems, Department of Physics, Université Libre de Bruxelles, Boulevard du Triomphe CP231, 1050 Brussels, Belgium.
| | - Patricia Losada-Pérez
- Experimental Soft Matter and Thermal Physics (EST) group, Department of Physics, Université Libre de Bruxelles, Boulevard du Triomphe CP223, 1050 Brussels, Belgium.
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4
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Punia R, Goel G. Free Energy Surface and Molecular Mechanism of Slow Structural Transitions in Lipid Bilayers. J Chem Theory Comput 2023; 19:8245-8257. [PMID: 37947833 DOI: 10.1021/acs.jctc.3c00856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2023]
Abstract
Lipid membrane remodeling, crucial for many cellular processes, is governed by the coupling of membrane structure and shape fluctuations. Given the importance of the ∼ nm length scale, details of the transition intermediates for conformational change are not fully captured by a continuum-mechanical description. Slow dynamics and the lack of knowledge of reaction coordinates (RCs) for biasing methods pose a challenge for all-atom (AA) simulations. Here, we map system dynamics on Langevin dynamics in a normal mode space determined from an elastic network model representation for the lipid-water Hamiltonian. AA molecular dynamics (MD) simulations are used to determine model parameters, and Langevin dynamics predictions for bilayer structural, mechanical, and dynamic properties are validated against MD simulations and experiments. Transferability to describe the dynamics of a larger lipid bilayer and a heterogeneous membrane-protein system is assessed. A set of generic RCs for pore formation in two tensionless bilayers is obtained by coupling Langevin dynamics to the underlying energy landscape for membrane deformations. Structure evolution is carried out by AA MD, wherein the generic RCs are used in a path metadynamics or an umbrella sampling simulation to determine the thermodynamics of pore formation and its molecular determinants, such as the role of distinct bilayer motions, lipid solvation, and lipid packing.
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Affiliation(s)
- Rajat Punia
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Gaurav Goel
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India
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5
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Valdivieso González D, Makowski M, Lillo MP, Cao‐García FJ, Melo MN, Almendro‐Vedia VG, López‐Montero I. Rotation of the c-Ring Promotes the Curvature Sorting of Monomeric ATP Synthases. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2301606. [PMID: 37705095 PMCID: PMC10625105 DOI: 10.1002/advs.202301606] [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: 03/14/2023] [Revised: 07/07/2023] [Indexed: 09/15/2023]
Abstract
ATP synthases are proteins that catalyse the formation of ATP through the rotatory movement of their membrane-spanning subunit. In mitochondria, ATP synthases are found to arrange as dimers at the high-curved edges of cristae. Here, a direct link is explored between the rotatory movement of ATP synthases and their preference for curved membranes. An active curvature sorting of ATP synthases in lipid nanotubes pulled from giant vesicles is found. Coarse-grained simulations confirm the curvature-seeking behaviour of rotating ATP synthases, promoting reversible and frequent protein-protein contacts. The formation of transient protein dimers relies on the membrane-mediated attractive interaction of the order of 1.5 kB T produced by a hydrophobic mismatch upon protein rotation. Transient dimers are sustained by a conic-like arrangement characterized by a wedge angle of θ ≈ 50°, producing a dynamic coupling between protein shape and membrane curvature. The results suggest a new role of the rotational movement of ATP synthases for their dynamic self-assembly in biological membranes.
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Affiliation(s)
- David Valdivieso González
- Departamento Química FísicaUniversidad Complutense de MadridAvda. Complutense s/nMadrid28040Spain
- Instituto de Investigación Biomédica Hospital Doce de Octubre (imas12)Avenida de Córdoba s/nMadrid28041Spain
| | - Marcin Makowski
- Instituto de Medicina MolecularFacultade de MedicinaUniversidade de LisboaLisbon1649‐028Portugal
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da RepúblicaOeiras2780‐157Portugal
| | - M. Pilar Lillo
- Departamento Química Física BiológicaInstituto de Química‐Física “Blas Cabrera” (CSIC)Serrano 119Madrid28006Spain
| | - Francisco J. Cao‐García
- Departamento de Estructura de la MateriaFísica Térmica y ElectrónicaUniversidad Complutense de MadridPlaza de Ciencias 1Madrid28040Spain
- Instituto Madrileño de Estudios Avanzados en NanocienciaIMDEA NanocienciaC/ Faraday 9Madrid28049Spain
| | - Manuel N. Melo
- Instituto de Tecnologia Química e Biológica António XavierUniversidade Nova de LisboaAv. da RepúblicaOeiras2780‐157Portugal
| | - Víctor G. Almendro‐Vedia
- Departamento Química FísicaUniversidad Complutense de MadridAvda. Complutense s/nMadrid28040Spain
- Instituto de Investigación Biomédica Hospital Doce de Octubre (imas12)Avenida de Córdoba s/nMadrid28041Spain
| | - Iván López‐Montero
- Departamento Química FísicaUniversidad Complutense de MadridAvda. Complutense s/nMadrid28040Spain
- Instituto de Investigación Biomédica Hospital Doce de Octubre (imas12)Avenida de Córdoba s/nMadrid28041Spain
- Instituto PluridisciplinarPaseo Juan XXIII 1Madrid28040Spain
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6
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Gupta S, Soni J, Kumar A, Mandal T. Origin of the nonlinear structural and mechanical properties in oppositely curved lipid mixtures. J Chem Phys 2023; 159:165102. [PMID: 37873964 DOI: 10.1063/5.0167144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 10/04/2023] [Indexed: 10/25/2023] Open
Abstract
Structural and mechanical properties of membranes such as thickness, tail order, bending modulus and curvature energetics play crucial role in controlling various cellular functions that depend on the local lipid organization and membrane reshaping. While behavior of these biophysical properties are well understood in single component membranes, very little is known about how do they change in the mixed lipid membranes. Often various properties of the mixed lipid bilayers are assumed to change linearly with the mole fractions of the constituent lipids which, however, is true for "ideal" mixing only. In this study, using molecular dynamics simulations, we show that structural and mechanical properties of binary lipid mixture change nonlinearly with the lipid mole fractions, and the strength of the nonlinearity depends on two factors - spontaneous curvature difference and locally inhomogeneous interactions between the lipid components.
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Affiliation(s)
- Shivam Gupta
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Jatin Soni
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Awneesh Kumar
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Taraknath Mandal
- Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India
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7
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Maliha F, Adnan A. Mechanical Responses of a Single Myelin Layer: A Molecular Simulation Study. Biomolecules 2023; 13:1525. [PMID: 37892207 PMCID: PMC10605433 DOI: 10.3390/biom13101525] [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] [Received: 08/28/2023] [Revised: 10/06/2023] [Accepted: 10/12/2023] [Indexed: 10/29/2023] Open
Abstract
The myelin sheath provides insulation to the brain's neuron cells, which aids in signal transmission and communication with the body. Degenerated myelin hampers the connection between the glial cells, which are the front row responders during traumatic brain injury mitigation. Thus, the structural integrity of the myelin layer is critical for protecting the brain tissue from traumatic injury. At the molecular level, myelin consists of a lipid bilayer, myelin basic proteins (MBP), proteolipid proteins (PLP), water and ions. Structurally, the myelin sheath is formed by repeatedly wrapping forty or more myelin layers around an axon. Here, we have used molecular dynamic simulations to model and capture the tensile response of a single myelin layer. An openly available molecular dynamic solver, LAMMPS, was used to conduct the simulations. The interatomic potentials for the interacting atoms and molecules were defined using CHARMM force fields. Following a standard equilibration process, the molecular model was stretched uniaxially at a deformation rate of 5 Å/ps. We observed that, at around 10% applied strain, the myelin started to cohesively fail via flaw formation inside the bilayers. Further stretching led to a continued expansion of the defect inside the bilayer, both radially and transversely. This study provides the cellular-level mechanisms of myelin damage due to mechanical load.
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Affiliation(s)
| | - Ashfaq Adnan
- Department of Mechanical and Aerospace Engineering, The University of Texas at Arlington, Arlington, TX 76019, USA;
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8
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Dobrynina EA, Zykova VA, Surovtsev NV. In-plane and out-of-plane gigahertz sound velocities of saturated and unsaturated phospholipid bilayers from cryogenic to room temperatures. Chem Phys Lipids 2023; 256:105335. [PMID: 37579988 DOI: 10.1016/j.chemphyslip.2023.105335] [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] [Received: 03/31/2023] [Revised: 06/23/2023] [Accepted: 08/11/2023] [Indexed: 08/16/2023]
Abstract
Here, we examined the gigahertz sound velocities of hydrated multibilayers of saturated (1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC) and unsaturated (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC) phospholipids by Brillouin spectroscopy. Out-of-plane and in-plane (lateral) phonons were studied independently of each other. Similar strong temperature dependences of the sound velocities were found for phonons of both types. The sound velocities in the low-temperature limit were two-fold higher than that at physiological temperatures; a significant part of the changes in sound velocity occurs in the solid-like gel phase. The factors that may be involved in the peculiar behavior of sound velocity include changes in the chain conformational state, relaxation susceptibility, changes in the elastic modulus at infinite frequencies, and lateral packing of molecules.
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Affiliation(s)
- E A Dobrynina
- Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk 630090, Russia
| | - V A Zykova
- Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk 630090, Russia
| | - N V Surovtsev
- Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk 630090, Russia.
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9
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Kumar J, Chng CP, Huang C. Hydrophobic Matching Dictates over the Linear Rule of Mixtures in Binary Lipid Membranes. J Phys Chem B 2023; 127:7946-7954. [PMID: 37674349 DOI: 10.1021/acs.jpcb.3c04502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/08/2023]
Abstract
Biological membranes feature heterogeneous mixtures of lipids with different head and tail characteristics. Their biophysical properties are dictated by the intimate interaction among different constituent lipids. Previous studies suggest that the membrane area-per-lipid (APL) deviates from the linear rule of mixtures (LRM) for binary lipid membranes, but the underlying mechanism remains elusive. Our molecular dynamics (MD) simulations of binary lipid membranes consisting of lipids with different tail characteristics reveal a competitive mechanism whereby lipids tend to deform each other to minimize the hydrophobic mismatch between their tails. Depending on the relative tail lengths and saturation levels, this may result in an either positive or negative deviation of APL from the LRM. As lipid packing plays an essential role in membrane fusion and peptide-membrane binding, our findings may help guide the selection of lipids for the effective rational design of nanoliposomes and membrane-targeting peptides.
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Affiliation(s)
- Jatin Kumar
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore
| | - Choon-Peng Chng
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore
| | - Changjin Huang
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore
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10
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Dommer A, Wauer NA, Angle KJ, Davasam A, Rubio P, Luo M, Morris CK, Prather KA, Grassian VH, Amaro RE. Revealing the Impacts of Chemical Complexity on Submicrometer Sea Spray Aerosol Morphology. ACS CENTRAL SCIENCE 2023; 9:1088-1103. [PMID: 37396863 PMCID: PMC10311664 DOI: 10.1021/acscentsci.3c00184] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Indexed: 07/04/2023]
Abstract
Sea spray aerosol (SSA) ejected through bursting bubbles at the ocean surface is a complex mixture of salts and organic species. Submicrometer SSA particles have long atmospheric lifetimes and play a critical role in the climate system. Composition impacts their ability to form marine clouds, yet their cloud-forming potential is difficult to study due to their small size. Here, we use large-scale molecular dynamics (MD) simulations as a "computational microscope" to provide never-before-seen views of 40 nm model aerosol particles and their molecular morphologies. We investigate how increasing chemical complexity impacts the distribution of organic material throughout individual particles for a range of organic constituents with varying chemical properties. Our simulations show that common organic marine surfactants readily partition between both the surface and interior of the aerosol, indicating that nascent SSA may be more heterogeneous than traditional morphological models suggest. We support our computational observations of SSA surface heterogeneity with Brewster angle microscopy on model interfaces. These observations indicate that increased chemical complexity in submicrometer SSA leads to a reduced surface coverage by marine organics, which may facilitate water uptake in the atmosphere. Our work thus establishes large-scale MD simulations as a novel technique for interrogating aerosols at the single-particle level.
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11
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Nagao M, Seto H. Neutron scattering studies on dynamics of lipid membranes. BIOPHYSICS REVIEWS 2023; 4:021306. [PMID: 38504928 PMCID: PMC10903442 DOI: 10.1063/5.0144544] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 05/01/2023] [Indexed: 03/21/2024]
Abstract
Neutron scattering methods are powerful tools for the study of the structure and dynamics of lipid bilayers in length scales from sub Å to tens to hundreds nm and the time scales from sub ps to μs. These techniques also are nondestructive and, perhaps most importantly, require no additives to label samples. Because the neutron scattering intensities are very different for hydrogen- and deuterium-containing molecules, one can replace the hydrogen atoms in a molecule with deuterium to prepare on demand neutron scattering contrast without significantly altering the physical properties of the samples. Moreover, recent advances in neutron scattering techniques, membrane dynamics theories, analysis tools, and sample preparation technologies allow researchers to study various aspects of lipid bilayer dynamics. In this review, we focus on the dynamics of individual lipids and collective membrane dynamics as well as the dynamics of hydration water.
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Affiliation(s)
| | - Hideki Seto
- Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan
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12
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Yu K, Jiang Y, Chen Y, Hu X, Chang J, Hartland GV, Wang GP. Compressible viscoelasticity of cell membranes determined by gigahertz-frequency acoustic vibrations. PHOTOACOUSTICS 2023; 31:100494. [PMID: 37131996 PMCID: PMC10149280 DOI: 10.1016/j.pacs.2023.100494] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 04/09/2023] [Accepted: 04/11/2023] [Indexed: 05/04/2023]
Abstract
Membrane viscosity is an important property of cell biology, which determines cellular function, development and disease progression. Various experimental and computational methods have been developed to investigate the mechanics of cells. However, there have been no experimental measurements of the membrane viscosity at high-frequencies in live cells. High frequency measurements are important because they can probe viscoelastic effects. Here, we investigate the membrane viscosity at gigahertz-frequencies through the damping of the acoustic vibrations of gold nanoplates. The experiments are modeled using a continuum mechanics theory which reveals that the membranes display viscoelasticity, with an estimated relaxation time of ca. 5.7 + 2.4 / - 2.7 ps. We further demonstrate that membrane viscoelasticity can be used to differentiate a cancerous cell line (the human glioblastoma cells LN-18) from a normal cell line (the mouse brain microvascular endothelial cells bEnd.3). The viscosity of cancerous cells LN-18 is lower than that of healthy cells bEnd.3 by a factor of three. The results indicate promising applications of characterizing membrane viscoelasticity at gigahertz-frequency in cell diagnosis.
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Affiliation(s)
- Kuai Yu
- State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Electronics and Information Engineering, Shenzhen University, Shenzhen 518060, China
| | - Yiqi Jiang
- Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen 518060, China
| | - Yungao Chen
- Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen 518060, China
| | - Xiaoyan Hu
- Institute of Biomedicine and Biotechnology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Junlei Chang
- Institute of Biomedicine and Biotechnology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Gregory V. Hartland
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Guo Ping Wang
- State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Electronics and Information Engineering, Shenzhen University, Shenzhen 518060, China
- Corresponding author.
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13
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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.
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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.
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14
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Fiorin G, Forrest LR, Faraldo-Gómez JD. Membrane free-energy landscapes derived from atomistic dynamics explain nonuniversal cholesterol-induced stiffening. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.02.525347. [PMID: 36778237 PMCID: PMC9915699 DOI: 10.1101/2023.02.02.525347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
All lipid membranes have inherent morphological preferences and resist deformation. Yet adaptations in membrane shape can and do occur at multiple length scales. While this plasticity is crucial for cellular physiology, the factors controlling the morphological energetics of lipid bilayers and the dominant mechanisms of membrane remodeling remain unclear. An ongoing debate regarding the universality of the stiffening effect of cholesterol underscores the challenges facing this field, both experimentally and theoretically, even for simple lipid mixtures. On the computational side, we have argued that enhanced- sampling all-atom molecular dynamics simulations are uniquely suited for quantification of membrane conformational energetics, not only because they minimize a-priori assumptions, but also because they permit analysis of bilayers in deformed states. To showcase this approach, we examine reported inconsistencies between alternative experimental measurements of bending moduli for cholesterol-enriched membranes. Specifically, we analyze lipid bilayers with different chain saturation, and compute free-energy landscapes for curvature deformations distributed over areas from ∼5 to ∼60 nm 2 . These enhanced simulations, totaling over 100 microseconds of sampling time, enable us to directly quantify both bending and tilt moduli, and to dissect the contributing factors and molecular mechanisms of curvature generation at each length scale. Our results show that cholesterol effects are lipid-specific, in agreement with giantvesicle measurements, and explain why experiments probing nanometer scale lipid dynamics diverge. In summary, we demonstrate that quantitative structure-mechanics relationships can now be established for heterogenous membranes, paving the way for addressing open fundamental questions in cell membrane mechanics. Significance Elucidating the energetics and mechanisms of membrane remodeling is an essential step towards understanding cell physiology. This problem is challenging, however, because membrane bending involves both large-scale and atomic-level dynamics, which are difficult to measure simultaneously. A recent controversy regarding the stiffening effect of cholesterol, which is ubiquitous in animal cells, illustrates this challenge. We show how enhanced molecular-dynamics simulations can bridge this length-scale gap and reconcile seemingly incongruent observations. This approach facilitates a conceptual connection between lipid chemistry and membrane mechanics, thereby providing a solid basis for future research on remodeling phenomena, such as in membrane trafficking or viral infection.
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Affiliation(s)
- Giacomo Fiorin
- National Institute for Neurological Disorders and Stroke, Bethesda, MD, USA
- National Heart, Lung and Blood Institute, Bethesda, MD, USA
| | - Lucy R Forrest
- National Institute for Neurological Disorders and Stroke, Bethesda, MD, USA
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15
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Daniel M, Eleršič Filipič K, Filová E, Judl T, Fojt J. Modelling the role of membrane mechanics in cell adhesion on titanium oxide nanotubes. Comput Methods Biomech Biomed Engin 2023; 26:281-290. [PMID: 35380071 DOI: 10.1080/10255842.2022.2058875] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Titanium surface treated with titanium oxide nanotubes was used in many studies to quantify the effect of surface topography on cell fate. However, the predicted optimal diameter of nanotubes considerably differs among studies. We propose a model that explains cell adhesion to a nanostructured surface by considering the deformation energy of cell protrusions into titanium nanotubes and the adhesion to the surface. The optimal surface topology is defined as a geometry that gives the membrane a minimum energy shape. A dimensionless parameter, the cell interaction index, was proposed to describe the interplay between the cell membrane bending, the intrinsic curvature, and the strength of cell adhesion. Model simulation shows that an optimal nanotube diameter ranging from 20 nm to 100 nm (cell interaction index between 0.2 and 1, respectively) is feasible within a certain range of parameters describing cell membrane adhesion and bending. The results indicate a possibility to tune the topology of a nanostructural surface in order to enhance the proliferation and differentiation of cells mechanically compatible with the given surface geometry while suppressing the growth of other mechanically incompatible cells.
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Affiliation(s)
- Matej Daniel
- Faculty of Mechanical Engineering, Czech Technical University in Prague, Prague, Czechia
| | | | - Eva Filová
- Institute of Experimental Medicine of the Czech Academy of Sciences, Prague, Czechia
| | | | - Jaroslav Fojt
- Faculty of Chemical Technology, University of Chemistry and Technology Prague, Prague, Czechia
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16
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Baccouch R, Shi Y, Vernay E, Mathelié-Guinlet M, Taib-Maamar N, Villette S, Feuillie C, Rascol E, Nuss P, Lecomte S, Molinari M, Staneva G, Alves ID. The impact of lipid polyunsaturation on the physical and mechanical properties of lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184084. [PMID: 36368636 DOI: 10.1016/j.bbamem.2022.184084] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 10/21/2022] [Accepted: 10/25/2022] [Indexed: 11/09/2022]
Abstract
The lipid composition of cellular membranes and the balance between the different lipid components can be impacted by aging, certain pathologies, specific diets and other factors. This is the case in a subgroup of individuals with psychiatric disorders, such as schizophrenia, where cell membranes of patients have been shown to be deprived in polyunsaturated fatty acids (PUFAs), not only in brain areas where the target receptors are expressed but also in peripheral tissues. This PUFA deprivation thus represents a biomarker of such disorders that might impact not only the interaction of antipsychotic medications with these membranes but also the activation and signaling of the targeted receptors embedded in the lipid membrane. Therefore, it is crucial to understand how PUFAs levels alterations modulate the different physical properties of membranes. In this paper, several biophysical approaches were combined (Laurdan fluorescence spectroscopy, atomic force microscopy, differential scanning calorimetry, molecular modeling) to characterize membrane properties such as fluidity, elasticity and thickness in PUFA-enriched cell membranes and lipid model systems reflecting the PUFA imbalance observed in some diseases. The impact of both the number of unsaturations and their position along the chain on the above properties was investigated. Briefly, data revealed that PUFA presence in membranes increases membrane fluidity, elasticity and flexibility and decreases its thickness and order parameter. Both the level of unsaturation and their position affect these membrane properties.
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Affiliation(s)
- Rim Baccouch
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Yarong Shi
- Laboratoire de Recherche en Nanosciences, LRN EA4682, University of Reims Champagne Ardenne, France
| | - Emilie Vernay
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Marion Mathelié-Guinlet
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Nada Taib-Maamar
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Sandrine Villette
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Cécile Feuillie
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Estelle Rascol
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Philippe Nuss
- Centre de Recherche Saint-Antoine, INSERM UMRS 938, Sorbonne Université, Paris, France; Service de psychiatrie et de psychologie médicale, Sorbonne Université, Hôpital Saint-Antoine, AP-HP, Paris, France
| | - Sophie Lecomte
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Michael Molinari
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France
| | - Galya Staneva
- Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.21, 1113 Sofia, Bulgaria
| | - Isabel D Alves
- Univ. Bordeaux, CNRS, Bordeaux INP, CBMN, UMR 5248, Bat B14, allée Geoffroy St. Hilaire, F-33600 Pessac, France.
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17
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Schachter I, Harries D. Capturing Lipid Nanodisc Shape and Properties Using a Continuum Elastic Theory. J Chem Theory Comput 2023; 19:1360-1369. [PMID: 36724052 PMCID: PMC9979604 DOI: 10.1021/acs.jctc.2c01054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Lipid nanodiscs are nanometric bilayer patches enveloped by confining structures, commonly composed of membrane scaffolding proteins (MSPs). To resolve the interplay between MSP geometry, lipid confinement, and membrane material properties on the nanodisc shape, we apply a continuum elastic theory accounting for lipid bending, tilting, and area deformations. The equilibrium nanodisc shape is then determined by minimizing the elastic free energy functional. Analytic expressions derived under simplifying assumptions demonstrate that the nanodisc shape is sensitive to its size, lipid density, and the lipid tilt and thickness imposed at the contact with the MSP. Under matching physical parameters, these expressions quantitatively reproduce the shape of nanodiscs seen in molecular dynamics simulations, but only if lipid tilt is explicitly considered. We further demonstrate how the bending rigidity can be extracted from the membrane shape profile by fitting the numerically minimized full elastic functional to the membrane shape found in simulations. This fitting procedure faithfully informs on the bending rigidity of nanodiscs larger than ca. 5 nm in radius. The fitted profiles accurately reproduce the increase in bending modulus found using real-space fluctuation analysis of simulated nanodiscs and, for large nanodiscs, also accurately resolve its spatial variations. Our study shows how deformations in lipid patches confined in nanodiscs can be well described by a continuum elastic theory and how this fit can be used to determine local material properties from shape analysis of nanodiscs in simulations. This methodology could potentially allow direct determination of lipid properties from experiments, for example cryo-electron microscopy images of lipid nanodiscs, thereby allowing to guide the development of future nanodisc formulations with desired properties.
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Affiliation(s)
- Itay Schachter
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nám. 542/2, CZ-16000Prague 6, Czech Republic,Institute
of Chemistry, the Fritz Haber Research Center, and the Harvey M. Kruger
Center for Nanoscience & Nanotechnology, The Hebrew University, Jerusalem9190401, Israel
| | - Daniel Harries
- Institute
of Chemistry, the Fritz Haber Research Center, and the Harvey M. Kruger
Center for Nanoscience & Nanotechnology, The Hebrew University, Jerusalem9190401, Israel,E-mail:
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18
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Nanoscale Bending Dynamics in Mixed-Chain Lipid Membranes. Symmetry (Basel) 2023. [DOI: 10.3390/sym15010191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Lipids that have two tails of different lengths are found throughout biomembranes in nature, yet the effects of this asymmetry on the membrane properties are not well understood, especially when it comes to the membrane dynamics. Here we study the nanoscale bending fluctuations in model mixed-chain 14:0–18:0 PC (MSPC) and 18:0–14:0 PC (SMPC) lipid bilayers using neutron spin echo (NSE) spectroscopy. We find that despite the partial interdigitation that is known to persist in the fluid phase of these membranes, the collective fluctuations are enhanced on timescales of tens of nanoseconds, and the chain-asymmetric lipid bilayers are softer than an analogous chain-symmetric lipid bilayer with the same average number of carbons in the acyl tails, di-16:0 PC (DPPC). Quantitative comparison of the NSE results suggests that the enhanced bending fluctuations at the nanosecond timescales are consistent with experimental and computational studies that showed the compressibility moduli of chain-asymmetric lipid membranes are 20% to 40% lower than chain-symmetric lipid membranes. These studies add to growing evidence that the partial interdigitation in mixed-chain lipid membranes is highly dynamic in the fluid phase and impacts membrane dynamic processes from the molecular to mesoscopic length scales without significantly changing the bilayer thickness or area per lipid.
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19
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Doole FT, Gupta S, Kumarage T, Ashkar R, Brown MF. Biophysics of Membrane Stiffening by Cholesterol and Phosphatidylinositol 4,5-bisphosphate (PIP2). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1422:61-85. [PMID: 36988877 DOI: 10.1007/978-3-031-21547-6_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Cell membranes regulate a wide range of phenomena that are implicated in key cellular functions. Cholesterol, a critical component of eukaryotic cell membranes, is responsible for cellular organization, membrane elasticity, and other critical physicochemical parameters. Besides cholesterol, other lipid components such as phosphatidylinositol 4,5-bisphosphate (PIP2) are found in minor concentrations in cell membranes yet can also play a major regulatory role in various cell functions. In this chapter, we describe how solid-state deuterium nuclear magnetic resonance (2H NMR) spectroscopy together with neutron spin-echo (NSE) spectroscopy can inform synergetic changes to lipid molecular packing due to cholesterol and PIP2 that modulate the bending rigidity of lipid membranes. Fundamental structure-property relations of molecular self-assembly are illuminated and point toward a length and time-scale dependence of cell membrane mechanics, with significant implications for biological activity and membrane lipid-protein interactions.
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Affiliation(s)
- Fathima T Doole
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA
| | - Sudipta Gupta
- Department of Physics and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA, USA
| | - Teshani Kumarage
- Department of Physics and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA, USA
| | - Rana Ashkar
- Department of Physics and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA, USA.
| | - Michael F Brown
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA.
- Department of Physics, University of Arizona, Tucson, AZ, USA.
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20
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Heller WT. Small-Angle Neutron Scattering for Studying Lipid Bilayer Membranes. Biomolecules 2022; 12:1591. [PMID: 36358941 PMCID: PMC9687511 DOI: 10.3390/biom12111591] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 10/18/2022] [Accepted: 10/26/2022] [Indexed: 09/23/2023] Open
Abstract
Small-angle neutron scattering (SANS) is a powerful tool for studying biological membranes and model lipid bilayer membranes. The length scales probed by SANS, being from 1 nm to over 100 nm, are well-matched to the relevant length scales of the bilayer, particularly when it is in the form of a vesicle. However, it is the ability of SANS to differentiate between isotopes of hydrogen as well as the availability of deuterium labeled lipids that truly enable SANS to reveal details of membranes that are not accessible with the use of other techniques, such as small-angle X-ray scattering. In this work, an overview of the use of SANS for studying unilamellar lipid bilayer vesicles is presented. The technique is briefly presented, and the power of selective deuteration and contrast variation methods is discussed. Approaches to modeling SANS data from unilamellar lipid bilayer vesicles are presented. Finally, recent examples are discussed. While the emphasis is on studies of unilamellar vesicles, examples of the use of SANS to study intact cells are also presented.
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Affiliation(s)
- William T Heller
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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21
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Lee G, Hadinoto K, Park JW. Changes in Mechanical Properties of Vesicles by Mucin in Aqueous Solution. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:3683. [PMID: 36296873 PMCID: PMC9607402 DOI: 10.3390/nano12203683] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 10/14/2022] [Accepted: 10/14/2022] [Indexed: 06/16/2023]
Abstract
The mechanical properties of vesicles were investigated as they were prepared, according to the ratio of mucin to dipalmitoylphosphatidylcholine (DPPC), using an atomic force microscope (AFM). After the confirmation of the vesicle adsorption on a mica surface, an AFM-tip deflection, caused by the interaction between the tip and the vesicle, was measured. The deflection showed that the tip broke through into the vesicle twice. Each break meant a tip-penetration into the upper and lower portion of the vesicle. Only the first penetration allowed the Hertzian model available to estimate the vesicle mechanical moduli. Two moduli reduced as the ratio of mucin to DPPC increased to 0.5, but the moduli were little changed above the 0.5 ratio. These results seem to be a platform for the effect of the mucin on the plasma-membrane anchoring and cellular signaling.
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Affiliation(s)
- Gaeul Lee
- Department of Chemical and Biomolecular Engineering, College of Energy and Biotechnology, Seoul National University of Science and Technology, Seoul 01811, Korea
| | - Kunn Hadinoto
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore
| | - Jin-Won Park
- Department of Chemical and Biomolecular Engineering, College of Energy and Biotechnology, Seoul National University of Science and Technology, Seoul 01811, Korea
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22
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Fu L, Li X, Zhang S, Dong Y, Fang W, Gao L. Polymyxins induce lipid scrambling and disrupt the homeostasis of Gram-negative bacteria membrane. Biophys J 2022; 121:3486-3498. [PMID: 35964158 PMCID: PMC9515121 DOI: 10.1016/j.bpj.2022.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Revised: 08/01/2022] [Accepted: 08/10/2022] [Indexed: 11/30/2022] Open
Abstract
Polymyxins are increasingly used as the last-line therapeutic option for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. However, efforts to address the resistance in superbugs are compromised by a poor understanding of the bactericidal modes because high-resolution detection of the cell structure is still lacking. By performing molecular dynamics simulations at a coarse-grained level, here we show that polymyxin B (PmB) disrupts Gram-negative bacterial membranes by altering lipid homeostasis and asymmetry. We found that the binding of PmBs onto the asymmetric outer membrane (OM) loosens the packing of lipopolysaccharides (LPS) and induces unbalanced bending torque between the inner and outer leaflets, which in turn triggers phospholipids to flip from the inner leaflet to the outer leaflet to compensate for the stress deformation. Meanwhile, some LPSs may be detained on the inner membrane (IM). Then, the lipid-scrambled OM undergoes phase separation. Defects are created at the boundaries between LPS-rich domains and phospholipid-rich domains, which consequently facilitate the uptake of PmB across the OM. Finally, PmBs target LPSs detained on the IM and similarly perturb the IM. This lipid Scramble, membrane phase Separation, and peptide Translocation model depicts a novel mechanism by which polymyxins kill bacteria and sheds light on developing a new generation of polymyxins or antibiotic adjuvants with improved killing activities and higher therapeutic indices.
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Affiliation(s)
- Lei Fu
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China
| | - Xiangyuan Li
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China
| | - Shan Zhang
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China
| | - Yi Dong
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China
| | - Weihai Fang
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China
| | - Lianghui Gao
- Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, China.
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23
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Himbert S, Rheinstädter MC. Structural and mechanical properties of the red blood cell's cytoplasmic membrane seen through the lens of biophysics. Front Physiol 2022; 13:953257. [PMID: 36171967 PMCID: PMC9510598 DOI: 10.3389/fphys.2022.953257] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Accepted: 08/15/2022] [Indexed: 11/27/2022] Open
Abstract
Red blood cells (RBCs) are the most abundant cell type in the human body and critical suppliers of oxygen. The cells are characterized by a simple structure with no internal organelles. Their two-layered outer shell is composed of a cytoplasmic membrane (RBC cm ) tethered to a spectrin cytoskeleton allowing the cell to be both flexible yet resistant against shear stress. These mechanical properties are intrinsically linked to the molecular composition and organization of their shell. The cytoplasmic membrane is expected to dominate the elastic behavior on small, nanometer length scales, which are most relevant for cellular processes that take place between the fibrils of the cytoskeleton. Several pathologies have been linked to structural and compositional changes within the RBC cm and the cell's mechanical properties. We review current findings in terms of RBC lipidomics, lipid organization and elastic properties with a focus on biophysical techniques, such as X-ray and neutron scattering, and Molecular Dynamics simulations, and their biological relevance. In our current understanding, the RBC cm 's structure is patchy, with nanometer sized liquid ordered and disordered lipid, and peptide domains. At the same time, it is surprisingly soft, with bending rigidities κ of 2-4 kBT. This is in strong contrast to the current belief that a high concentration of cholesterol results in stiff membranes. This extreme softness is likely the result of an interaction between polyunsaturated lipids and cholesterol, which may also occur in other biological membranes. There is strong evidence in the literature that there is no length scale dependence of κ of whole RBCs.
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Affiliation(s)
- Sebastian Himbert
- Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada
- Origins Institute, McMaster University, Hamilton, ON, Canada
| | - Maikel C. Rheinstädter
- Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada
- Origins Institute, McMaster University, Hamilton, ON, Canada
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24
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DiPasquale M, Nguyen MHL, Pabst G, Marquardt D. Partial Volumes of Phosphatidylcholines and Vitamin E: α-Tocopherol Prefers Disordered Membranes. J Phys Chem B 2022; 126:6691-6699. [PMID: 36027485 DOI: 10.1021/acs.jpcb.2c04209] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Despite its discovery over 95 years ago, the biological and nutritional roles of vitamin E remain subjects of much controversy. Though it is known to possess antioxidant properties, recent assertions have implied that vitamin E may not be limited to this function in living systems. Through densitometry measurements and small-angle X-ray scattering we observe favorable interactions between α-tocopherol and unsaturated phospholipids, with more favorable interactions correlating to an increase in lipid chain unsaturation. Our data provide evidence that vitamin E may preferentially associate with oxygen sensitive lipids─an association that is considered innate for a viable membrane antioxidant.
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Affiliation(s)
- Mitchell DiPasquale
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Michael H L Nguyen
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Georg Pabst
- Institute of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria.,BioTechMed-Graz, Graz 8010, Austria
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada.,Department of Physics, University of Windsor, Windsor, Ontario N9B 3P4, Canada
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25
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Shimolina L, Gulin A, Khlynova A, Ignatova N, Druzhkova I, Gubina M, Zagaynova E, Kuimova M, Shirmanova M. Development of resistance to 5-fluorouracil affects membrane viscosity and lipid composition of cancer cells. Methods Appl Fluoresc 2022; 10. [PMID: 35970177 DOI: 10.1088/2050-6120/ac89cd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 08/15/2022] [Indexed: 11/12/2022]
Abstract
The investigations reported here were designed to determine whether the bulk plasma membrane is involved in mechanisms of acquired resistance of colorectal cancer cells to 5-fluorouracil (5-FU). Fluorescence lifetime imaging microscopy (FLIM) of live cultured cells stained with viscosity-sensitive probe BODIPY 2 was exploited to non-invasively assess viscosity in the course of treatment and adaptation to the drug. In parallel, lipid composition of membranes was examined with the time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results showed that a single treatment with 5-FU induced only temporal changes of viscosity in 5-FU sensitive cells immediately after adding the drug. Acquisition of chemoresistance was accompanied by persistent increase of viscosity, which was preserved upon treatment without any changes. Lipidomic analysis revealed that the resistant cells had a lower level of monounsaturated fatty acids and increased sphingomyelin or decreased phosphatidylcholine in their membranes, which partly explain increase of the viscosity. Thus, we propose that a high membrane viscosity mediates the acquisition of resistance to 5-FU.
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Affiliation(s)
- Liubov Shimolina
- Privolzhsky Research Medical University, 10/1 Minin and Pozharsky Sq., Niznij Novgorod, Nižegorodskaâ, 603005, RUSSIAN FEDERATION
| | - Aleksandr Gulin
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygin st. 4, Moskva, Moskva, 119991, RUSSIAN FEDERATION
| | - Aleksandra Khlynova
- Institute of Experimental Oncology and Biomedical Technologies, Privolzhsky Research Medical University, 10/1 Minin and Pozharsky Sq., Niznij Novgorod, Nižegorodskaâ, 603005, RUSSIAN FEDERATION
| | - Nadezhda Ignatova
- Privolzhsky Research Medical University, 10/1 Minin and Pozharsky Sq., Niznij Novgorod, Nižegorodskaâ, 603005, RUSSIAN FEDERATION
| | - Irina Druzhkova
- Privolzhsky Research Medical University, 10/1 Minin and Pozharsky Sq., Niznij Novgorod, Nižegorodskaâ, 603005, RUSSIAN FEDERATION
| | - Margarita Gubina
- Russian Academy of Sciences, Kosygin st. 4, Moskva, Moskva, 119991, RUSSIAN FEDERATION
| | - Elena Zagaynova
- Lobachevsky State University of Nizhny Novgorod, Gagarin Avenue 23, Niznij Novgorod, Nižegorodskaâ, 603950, RUSSIAN FEDERATION
| | - Marina Kuimova
- Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London , SW7 2AZ, London, SW7 2AZ, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Marina Shirmanova
- Privolzhsky Research Medical University, 10/1 Minin and Pozharsky Sq., Niznij Novgorod, Nižegorodskaâ, 603005, RUSSIAN FEDERATION
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26
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Vishvakarma V, Engberg O, Huster D, Maiti S. The effect of cholesterol on highly curved membranes measured by nanosecond Fluorescence Correlation Spectroscopy. Methods Appl Fluoresc 2022; 10. [PMID: 35940167 DOI: 10.1088/2050-6120/ac87ea] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Accepted: 08/08/2022] [Indexed: 11/11/2022]
Abstract
Small lipid vesicles (with diameter ≤ 100nm) with their highly curved membranes comprise a special class of biological lipid bilayers. The mechanical properties of such membranes are critical for their function, e.g. exocytosis. Cholesterol is a near-universal regulator of membrane properties in animal cells. Yet measurements of the effect of cholesterol on the mechanical properties of membranes have remained challenging, and the interpretation of such measurements has remained a matter of debate. Here we show that nanosecond fluorescence correlation spectroscopy (FCS) can directly measure the ns-microsecond rotational correlation time (τr) of a lipid probe in high curvature vesicles with extraordinary sensitivity. Using a home-built 4-Pi fluorescence cross-correlation spectrometer containing polarization-modulating elements, we measure the rotational correlation time (τr) of Nile Red in neurotransmitter vesicle mimics. As the cholesterol mole fraction increases from 0 to 50 %, τr increases from 17 ± 1 to 112 ± 12 ns, indicating a viscosity change of nearly a factor of 7. These measurements are corroborated by solid-state NMR results, which show that the order parameter of the lipid acyl chains increases by about 50% for the same change in cholesterol concentration. Additionally, we measured the spectral parameters of polarity-sensitive fluorescence dyes, which provide an indirect measure of viscosity. The green/red ratio of Nile Red and the generalized polarization of Laurdan show consistent increases of 1.3x and 2.6x, respectively. Our results demonstrate that rotational FCS can directly measure the viscosity of highly curved membranes with higher sensitivity and wider dynamic range compared to other conventional techniques. Significantly, we observe that the viscosity of neurotransmitter vesicle mimics is remarkably sensitive to their cholesterol content.
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Affiliation(s)
- Vicky Vishvakarma
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Navy Nagar Colaba, MUMBAI, Mumbai, Maharashtra, 400005, INDIA
| | - Oskar Engberg
- Institut für Medizinische Physik und Biophysik Universität Leipzig, Universität Leipzig Medizinische Fakultät, Härtelstr. 16-18 04107 Leipzig Germany, Leipzig, Sachsen, 04107, GERMANY
| | - Daniel Huster
- Institut für Medizinische Physik und Biophysik, Universität Leipzig Medizinische Fakultät, Härtelstr. 16-18 04107 Leipzig, Leipzig, Sachsen, 04107, GERMANY
| | - Sudipta Maiti
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Navy Nagar Colaba, Mumbai, 400005, INDIA
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27
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Himbert S, D’Alessandro A, Qadri SM, Majcher MJ, Hoare T, Sheffield WP, Nagao M, Nagle JF, Rheinstädter MC. The bending rigidity of the red blood cell cytoplasmic membrane. PLoS One 2022; 17:e0269619. [PMID: 35913930 PMCID: PMC9342732 DOI: 10.1371/journal.pone.0269619] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 05/24/2022] [Indexed: 11/19/2022] Open
Abstract
An important mechanical property of cells is the membrane bending modulus, κ. In the case of red blood cells (RBCs) there is a composite membrane consisting of a cytoplasmic membrane and an underlying spectrin network. Literature values of κ are puzzling, as they are reported over a wide range, from 5 kBT to 230 kBT. To disentangle the contribution of the cytoplasmic membrane from the spectrin network, we investigated the bending of red blood cell cytoplasmic membranes (RBCcm) in the absence of spectrin and adenosine triphosphate (ATP). We used a combination of X-ray diffuse scattering (XDS), neutron spin-echo (NSE) spectrometry and Molecular Dynamics (MD) simulations. Our results indicate values of κ of order 4 kBT to 6 kBT, relatively small compared to literature values for most single component lipid bilayers. We suggest two ways this relative softness might confer biological advantage.
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Affiliation(s)
- Sebastian Himbert
- Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada
- Origins Institute, McMaster University, Hamilton, ON, Canada
| | - Angelo D’Alessandro
- Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons and New York-Presbyterian Hospital, New York, New York, United States of America
- University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado, United States of America
| | - Syed M. Qadri
- Faculty of Health Sciences, Ontario Tech University, Oshawa, ON, Canada
| | - Michael J. Majcher
- Department of Chemical Engineering, McMaster University, Hamilton, ON, Canada
| | - Todd Hoare
- Department of Chemical Engineering, McMaster University, Hamilton, ON, Canada
| | - William P. Sheffield
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada
- Centre for Innovation, Canadian Blood Services, Hamilton, ON, Canada
| | - Michihiro Nagao
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, United States of America
- Department of Materials Science and Engineering, University of Maryland, College Park, MD, United States of America
- Department of Physics and Astronomy, University of Delaware, Newark, DE, United States of America
| | - John F. Nagle
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA, United States of America
| | - Maikel C. Rheinstädter
- Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada
- Origins Institute, McMaster University, Hamilton, ON, Canada
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28
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Sharma VK, Mamontov E. Multiscale lipid membrane dynamics as revealed by neutron spectroscopy. Prog Lipid Res 2022; 87:101179. [PMID: 35780913 DOI: 10.1016/j.plipres.2022.101179] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 06/25/2022] [Accepted: 06/27/2022] [Indexed: 12/22/2022]
Abstract
The plasma membrane is one of the principal structural components of the cell and, therefore, one of the key components of the cellular life. Because the membrane's dynamics links the membrane's structure and function, the complexity and the broad range of the membrane's motions are essential for the enormously diverse functionality of the cell membrane. Even for the main membrane component, the lipid bilayer, considered alone, the range and complexity of the lipid motions are remarkable. Spanning the time scale from sub-picosecond to minutes and hours, the lipid motion in a bilayer is challenging to study even when a broad array of dynamic measurement techniques is employed. Neutron scattering plays a special role among such dynamic measurement techniques, particularly, because it involves the energy transfers commensurate with the typical intra- and inter- molecular dynamics and the momentum transfers commensurate with intra- and inter-molecular distances. Thus, using neutron scattering-based techniques, the spatial and temporal information on the lipid motion can be obtained and analysed simultaneously. Protium vs. deuterium sensitivity and non-destructive character of the neutron probe add to the remarkable prowess of neutron scattering for elucidating the lipid dynamics. Herein we present an overview of the neutron scattering-based studies of lipid dynamics in model membranes, with a discussion of the direct relevance and implications to the real-life cell membranes. The latter are much more complex systems than simple model membranes, consisting of heterogeneous non-stationary domains composed of lipids, proteins, and other small molecules, such as carbohydrates. Yet many fundamental aspects of the membrane behavior and membrane interactions with other molecules can be understood from neutron scattering measurements of the model membranes. For example, such studies can provide a great deal of information on the interactions of antimicrobial compounds with the lipid matrix of a pathogen membrane, or the interactions of drug molecules with the plasma membrane. Finally, we briefly discuss the recently emerging field of neutron scattering membrane studies with a reach far beyond the model membrane systems.
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Affiliation(s)
- V K Sharma
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Mumbai 400094, India.
| | - E Mamontov
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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29
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Gilbert J, Ermilova I, Nagao M, Swenson J, Nylander T. Effect of encapsulated protein on the dynamics of lipid sponge phase: a neutron spin echo and molecular dynamics simulation study. NANOSCALE 2022; 14:6990-7002. [PMID: 35470842 DOI: 10.1039/d2nr00882c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Lipid membranes are highly mobile systems with hierarchical, time and length scale dependent, collective motions including thickness fluctuations, undulations, and topological membrane changes, which play an important role in membrane interactions. In this work we have characterised the effect of encapsulating two industrially important enzymes, β-galactosidase and aspartic protease, in lipid sponge phase nanoparticles on the dynamics of the lipid membrane using neutron spin echo (NSE) spectroscopy and molecular dynamics (MD) simulations. From NSE, reduced membrane dynamics were observed upon enzyme encapsulation, which were dependent on the enzyme concentration and type. By fitting the intermediate scattering functions (ISFs) with a modified Zilman and Granek model including nanoparticle diffusion, an increase in membrane bending rigidity was observed, with a larger effect for β-galactosidase than aspartic protease at the same concentration. MD simulations for the system with and without aspartic protease showed that the lipids relax more slowly in the system with protein due to the replacement of the lipid carbonyl-water hydrogen bonds with lipid-protein hydrogen bonds. This indicates that the most likely cause of the increase in membrane rigidity observed in the NSE measurements was dehydration of the lipid head groups. The dynamics of the protein itself were also studied, which showed a stable secondary structure of protein over the simulation, indicating no unfolding events occurred.
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Affiliation(s)
- Jennifer Gilbert
- Division of Physical Chemistry, Department of Chemistry, Naturvetarvägen 14, Lund University, 22362 Lund, Sweden.
- NanoLund, Lund University, Professorsgatan 1, 223 63 Lund, Sweden
| | - Inna Ermilova
- Department of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
| | - Michihiro Nagao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA
| | - Jan Swenson
- Department of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
| | - Tommy Nylander
- Division of Physical Chemistry, Department of Chemistry, Naturvetarvägen 14, Lund University, 22362 Lund, Sweden.
- NanoLund, Lund University, Professorsgatan 1, 223 63 Lund, Sweden
- Lund Institute of Advanced Neutron and X-Ray Science, Scheelevägen 19, 223 70 Lund, Sweden
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30
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Castillo SR, Rickeard BW, DiPasquale M, Nguyen MHL, Lewis-Laurent A, Doktorova M, Kav B, Miettinen MS, Nagao M, Kelley EG, Marquardt D. Probing the Link between Pancratistatin and Mitochondrial Apoptosis through Changes in the Membrane Dynamics on the Nanoscale. Mol Pharm 2022; 19:1839-1852. [PMID: 35559658 DOI: 10.1021/acs.molpharmaceut.1c00926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pancratistatin (PST) is a natural antiviral alkaloid that has demonstrated specificity toward cancerous cells and explicitly targets the mitochondria. PST initiates apoptosis while leaving healthy, noncancerous cells unscathed. However, the manner by which PST induces apoptosis remains elusive and impedes the advancement of PST as a natural anticancer therapeutic agent. Herein, we use neutron spin-echo (NSE) spectroscopy, molecular dynamics (MD) simulations, and supporting small angle scattering techniques to study PST's effect on membrane dynamics using biologically representative model membranes. Our data suggests that PST stiffens the inner mitochondrial membrane (IMM) by being preferentially associated with cardiolipin, which would lead to the relocation and release of cytochrome c. Second, PST has an ordering effect on the lipids and disrupts their distribution within the IMM, which would interfere with the maintenance and functionality of the active forms of proteins in the electron transport chain. These previously unreported findings implicate PST's effect on mitochondrial apoptosis.
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Affiliation(s)
- Stuart R Castillo
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Brett W Rickeard
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Mitchell DiPasquale
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Michael H L Nguyen
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Aislyn Lewis-Laurent
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Milka Doktorova
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, Virginia 22903, United States
| | - Batuhan Kav
- Max-Planck Institute of Colloids and Interfaces, Potsdam 14476, Germany.,Institute of Biological Information Processing: Structural Biochemistry (IBI-7), Forschungszentrum Julich, Julich 52428, Germany
| | | | - Michihiro Nagao
- National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland 20899, United States.,Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States.,Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, United States
| | - Elizabeth G Kelley
- National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland 20899, United States
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada.,Department of Physics, University of Windsor, Windsor, Ontario N9B 3P4, Canada
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31
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Faizi HA, Dimova R, Vlahovska PM. A vesicle microrheometer for high-throughput viscosity measurements of lipid and polymer membranes. Biophys J 2022; 121:910-918. [PMID: 35176271 PMCID: PMC8943812 DOI: 10.1016/j.bpj.2022.02.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 01/08/2022] [Accepted: 02/09/2022] [Indexed: 11/02/2022] Open
Abstract
Viscosity is a key property of cell membranes that controls mobility of embedded proteins and membrane remodeling. Measuring it is challenging because existing approaches involve complex experimental designs and/or models, and the applicability of some methods is limited to specific systems and membrane compositions. As a result there is scarcity of systematic data, and the reported values for membrane viscosity vary by orders of magnitude for the same system. Here, we show how viscosity of membranes can be easily obtained from the transient deformation of giant unilamellar vesicles. The approach enables a noninvasive, probe-independent, and high-throughput measurement of the viscosity of membranes made of lipids or polymers with a wide range of compositions and phase state. Using this novel method, we have collected a significant amount of data that provides insights into the relation between membrane viscosity, composition, and structure.
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Affiliation(s)
- Hammad A Faizi
- Department of Mechanical Engineering, Northwestern University, Evanston, Illinois
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Science Park Golm, Potsdam, Germany
| | - Petia M Vlahovska
- Department of Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, Illinois.
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32
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Nagao M, Kelley EG, Faraone A, Saito M, Yoda Y, Kurokuzu M, Takata S, Seto M, Butler PD. Relationship between Viscosity and Acyl Tail Dynamics in Lipid Bilayers. PHYSICAL REVIEW LETTERS 2021; 127:078102. [PMID: 34459628 DOI: 10.1103/physrevlett.127.078102] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
Membrane viscosity is a fundamental property that controls molecular transport and structural rearrangements in lipid membranes. Given its importance in many cell processes, various experimental and computational methods have been developed to measure the membrane viscosity, yet the estimated values depend highly on the method and vary by orders of magnitude. Here we investigate the molecular origins of membrane viscosity by measuring the nanoscale dynamics of the lipid acyl tails using x-ray and neutron spectroscopy techniques. The results show that the membrane viscosity can be estimated from the structural relaxation times of the lipid tails.
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Affiliation(s)
- Michihiro Nagao
- National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, Maryland 20899-6102, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA
| | - Elizabeth G Kelley
- National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, Maryland 20899-6102, USA
| | - Antonio Faraone
- National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, Maryland 20899-6102, USA
| | - Makina Saito
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Osaka, 590-0494, Japan
| | - Yoshitaka Yoda
- Japan Synchrotron Radiation Research Institute, Sayo, Hyogo, 679-5198, Japan
| | - Masayuki Kurokuzu
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Osaka, 590-0494, Japan
| | - Shinichi Takata
- J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
| | - Makoto Seto
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Osaka, 590-0494, Japan
| | - Paul D Butler
- National Institute of Standards and Technology Center for Neutron Research, Gaithersburg, Maryland 20899-6102, USA
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, USA
- Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, USA
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33
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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.
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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
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34
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Bochicchio D, Cantu L, Cadario MV, Palchetti L, Natali F, Monticelli L, Rossi G, Del Favero E. Polystyrene perturbs the structure, dynamics, and mechanical properties of DPPC membranes: An experimental and computational study. J Colloid Interface Sci 2021; 605:110-119. [PMID: 34311305 DOI: 10.1016/j.jcis.2021.07.069] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 06/16/2021] [Accepted: 07/09/2021] [Indexed: 12/14/2022]
Abstract
Synthetic plastic oligomers can interact with the cells of living organisms by different ways. They can be intentionally administered to the human body as part of nanosized biomedical devices. They can be inhaled by exposed workers, during the production of multicomponent, polymer-based nanocomposites. They can leak out of food packaging. Most importantly, they can result from the degradation of plastic waste, and enter the food chain. A physicochemical characterization of the effects of synthetic polymers on the structure and dynamics of cell components is still lacking. Here, we combine a wide spectrum of experimental techniques (calorimetry, x-ray, and neutron scattering) with atomistic Molecular Dynamics simulations to study the interactions between short chains of polystyrene (25 monomers) and model lipid membranes (DPPC, in both gel and fluid phase). We find that doping doses of polystyrene oligomers alter the thermal properties of DPPC, stabilizing the fluid lipid phase. They perturb the membrane structure and dynamics, in a concentration-dependent fashion. Eventually, they modify the mechanical properties of DPPC, reducing its bending modulus in the fluid phase. Our results call for a systematic, interdisciplinary assessment of the mechanisms of interaction of synthetic, everyday use polymers with cell membranes.
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Affiliation(s)
- Davide Bochicchio
- Department of Physics, University of Genoa, Via Dodecaneso 33, 16146 Genoa, Italy
| | - Laura Cantu
- Department of Medical Biotechnology and Translational Medicine, University of Milan, LITA V.le F.lli Cervi 93, 20090 Segrate, Italy
| | - Maria Vittoria Cadario
- Department of Medical Biotechnology and Translational Medicine, University of Milan, LITA V.le F.lli Cervi 93, 20090 Segrate, Italy
| | - Leonardo Palchetti
- Department of Medical Biotechnology and Translational Medicine, University of Milan, LITA V.le F.lli Cervi 93, 20090 Segrate, Italy
| | - Francesca Natali
- Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
| | - Luca Monticelli
- IBCP, CNRS, UMR 5086, 7 Passage du Vercors, 69007 Lyon, France
| | - Giulia Rossi
- Department of Physics, University of Genoa, Via Dodecaneso 33, 16146 Genoa, Italy.
| | - Elena Del Favero
- Department of Medical Biotechnology and Translational Medicine, University of Milan, LITA V.le F.lli Cervi 93, 20090 Segrate, Italy.
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35
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Benedetto A, Kearley GJ. Experimental demonstration of the novel "van-Hove integral method (vHI)" for measuring diffusive dynamics by elastic neutron scattering. Sci Rep 2021; 11:14093. [PMID: 34238981 PMCID: PMC8266890 DOI: 10.1038/s41598-021-93463-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 06/24/2021] [Indexed: 11/09/2022] Open
Abstract
Quasi-elastic neutron scattering (QENS)-based on the seminal work of Nobel Laureate Brockhouse-has been one of the major methods for studying pico-second to nano-second diffusive dynamics over the past 70 years. This is regarded as an "inelastic" method for dynamics. In contrast, we recently proposed a new neutron-scattering method for dynamics, which uses the elastic line of the scattering to access system dynamics directly in the time domain (Benedetto and Kearley in Sci Rep 9:11284, 2019). This new method has been denoted "vHI" that stands for "van Hove Integral". The reason is that, under certain conditions, the measured elastic intensity corresponds to the running-time integral of the intermediate scattering function, [Formula: see text], up to a time that is inversely proportional to the energy band-width incident on the sample. As a result, [Formula: see text] is accessed from the time derivative of the measured vHI profile. vHI has been supported by numerical and Monte-Carlo simulations, but has been difficult to validate experimentally due to the lack of a suitable instrument. Here we show that vHI works in practice, which we achieved by using a simple modification to the standard QENS backscattering spectrometer methodology. Basically, we varied the neutron-energy band-widths incident at the sample via a step-wise variation of the frequency of the monochromator Doppler-drive. This provides a measurement of the vHI profile at the detectors. The same instrument and sample were also used in standard QENS mode for comparison. The intermediate scattering functions, [Formula: see text], obtained by the two methods-vHI and QENS-are strikingly similar providing a direct experimental validation of the vHI method. Perhaps surprisingly, the counting statistics of the two methods are comparable even though the instrument used was expressly designed for QENS. This shows that the methodology modification adopted here can be used in practice to access vHI profiles at many of the backscattering spectrometers worldwide. We also show that partial integrations of the measured QENS spectrum cannot provide the vHI profile, which clarifies a common misconception. At the same time, we show a novel approach which does access [Formula: see text] from QENS spectra.
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Affiliation(s)
- Antonio Benedetto
- School of Physics, University College Dublin, Dublin 4, Ireland.
- Conway Institute, University College Dublin, Dublin 4, Ireland.
- Department of Sciences, University of Roma Tre, Rome, Italy.
- Laboratory for Neutron Scattering, Paul Scherrer Institute, Villigen, Switzerland.
| | - Gordon J Kearley
- School of Physics, University College Dublin, Dublin 4, Ireland
- School of Chemistry, University College Dublin, Dublin 4, Ireland
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36
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Kumari P, Faraone A, Kelley EG, Benedetto A. Stiffening Effect of the [Bmim][Cl] Ionic Liquid on the Bending Dynamics of DMPC Lipid Vesicles. J Phys Chem B 2021; 125:7241-7250. [PMID: 34169716 PMCID: PMC8279542 DOI: 10.1021/acs.jpcb.1c01347] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The elastic properties of the cellular lipid membrane play a crucial role for life. Their alteration can lead to cell malfunction, and in turn, being able to control them holds the promise of effective therapeutic and diagnostic approaches. In this context, due to their proven strong interaction with lipid bilayers, ionic liquids (ILs)-a vast class of organic electrolytes-may play an important role. This work focuses on the effect of the model imidazolium-IL [bmim][Cl] on the bending modulus of DMPC lipid vesicles, a basic model of cellular lipid membranes. Here, by combining small-angle neutron scattering and neutron spin-echo spectroscopy, we show that the IL, dispersed at low concentrations at the bilayer-water interface, (i) diffuses into the lipid region, accounting for five IL-cations for every 11 lipids, and (ii) causes an increase of the lipid bilayer bending modulus, up to 60% compared to the neat lipid bilayer at 40 °C.
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Affiliation(s)
- Pallavi Kumari
- Department of Sciences, University of Roma Tre, 00146 Rome, Italy.,School of Physics and Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland
| | - Antonio Faraone
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Elizabeth G Kelley
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Antonio Benedetto
- Department of Sciences, University of Roma Tre, 00146 Rome, Italy.,School of Physics and Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin 4, Ireland.,Laboratory for Neutron Scattering, Paul Scherrer Institute, 5232 Villigen, Switzerland
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37
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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.
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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
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Reply to Nagle et al.: The universal stiffening effects of cholesterol on lipid membranes. Proc Natl Acad Sci U S A 2021; 118:2102845118. [PMID: 33952694 PMCID: PMC8157964 DOI: 10.1073/pnas.2102845118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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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.
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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
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Lee CT, Akamatsu M, Rangamani P. Value of models for membrane budding. Curr Opin Cell Biol 2021; 71:38-45. [PMID: 33706232 DOI: 10.1016/j.ceb.2021.01.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Revised: 01/27/2021] [Accepted: 01/30/2021] [Indexed: 12/16/2022]
Abstract
The budding of membranes and curvature generation is common to many forms of trafficking in cells. Clathrin-mediated endocytosis, as a prototypical example of trafficking, has been studied in great detail using a variety of experimental systems and methods. Recently, advances in experimental methods have led to great strides in insights on the molecular mechanisms and the spatiotemporal dynamics of the protein machinery associated with membrane curvature generation. These advances have been ably supported by computational models, which have given us insights into the underlying mechanical principles of clathrin-mediated endocytosis. On the other hand, targeted experimental perturbation of membranes has lagged behind that of proteins in cells. In this area, modeling is especially critical to interpret experimental measurements in a mechanistic context. Here, we discuss the contributions made by these models to our understanding of endocytosis and identify opportunities to strengthen the connections between models and experiments.
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Affiliation(s)
- Christopher T Lee
- Department of Mechanical and Aerospace Engineering, University of California San Diego Jacobs School of Engineering, 9500 Gilman Drive #0411, La Jolla, CA, 92093, USA
| | - Matthew Akamatsu
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
| | - Padmini Rangamani
- Department of Mechanical and Aerospace Engineering, University of California San Diego Jacobs School of Engineering, 9500 Gilman Drive #0411, La Jolla, CA, 92093, USA.
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Nagao M, Bradbury R, Ansar SM, Kitchens CL. Effect of gold nanoparticle incorporation into oil-swollen surfactant lamellar membranes. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2020; 7:065102. [PMID: 33344674 PMCID: PMC7744122 DOI: 10.1063/4.0000041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Accepted: 11/25/2020] [Indexed: 05/08/2023]
Abstract
An oil-swollen surfactant membrane is employed to measure the effects of incorporated hydrophobically functionalized gold nanoparticles (AuNPs) on the structure and dynamics of the membranes. While maintaining an average AuNP diameter of approximately 5 nm, the membrane thickness was varied from 5 nm to 7.5 nm by changing the amount of oil in the membrane. The membranes become softer as the proportion of oil is increased, while the thickness fluctuations become slower. We attribute this to an increased fluctuation wavelength. Incorporation of AuNPs in the membrane induces membrane thinning and softening. Oil molecules surround the nanoparticles in the membrane and help their relatively homogeneous distribution. AuNPs significantly alter the membrane's structure and dynamics through thinning of the membrane, increased compressibility, and possible diffusion of AuNPs inside the membrane.
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Affiliation(s)
| | | | - Siyam M. Ansar
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634, USA
| | - Christopher L. Kitchens
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634, USA
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