1
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Wilson KJ, Nguyen HQ, Gervay-Hague J, Keller SL. Sterol-lipids enable large-scale, liquid-liquid phase separation in bilayer membranes of only two components. Proc Natl Acad Sci U S A 2024; 121:e2401241121. [PMID: 39250661 DOI: 10.1073/pnas.2401241121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Accepted: 07/02/2024] [Indexed: 09/11/2024] Open
Abstract
Despite longstanding excitement and progress toward understanding liquid-liquid phase separation in natural and artificial membranes, fundamental questions have persisted about which molecules are required for this phenomenon. Except in extraordinary circumstances, the smallest number of components that has produced large-scale, liquid-liquid phase separation in bilayers has stubbornly remained at three: a sterol, a phospholipid with ordered chains, and a phospholipid with disordered chains. This requirement of three components is puzzling because only two components are required for liquid-liquid phase separation in lipid monolayers, which resemble half of a bilayer. Inspired by reports that sterols interact closely with lipids with ordered chains, we tested whether phase separation would occur in bilayers in which a sterol and lipid were replaced by a single, joined sterol-lipid. By evaluating a panel of sterol-lipids, some of which are present in bacteria, we found a minimal bilayer of only two components (PChemsPC and diPhyPC) that robustly demixes into micron-scale, liquid phases. It suggests an additional role for sterol-lipids in nature, and it reveals a membrane in which tie-lines (and, therefore, the lipid composition of each phase) are straightforward to determine and will be consistent across multiple laboratories.
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Affiliation(s)
- Kent J Wilson
- Department of Physics, University of Washington-Seattle, Seattle, WA 98195
- Department of Chemistry, University of Washington-Seattle, Seattle, WA 98195
| | - Huy Q Nguyen
- Department of Chemistry, University of California-Davis, Davis, CA 95616
| | | | - Sarah L Keller
- Department of Physics, University of Washington-Seattle, Seattle, WA 98195
- Department of Chemistry, University of Washington-Seattle, Seattle, WA 98195
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2
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Mishra M, Dadhich R, Mogha P, Kapoor S. Mycobacterium Lipids Modulate Host Cell Membrane Mechanics, Lipid Diffusivity, and Cytoskeleton in a Virulence-Selective Manner. ACS Infect Dis 2020; 6:2386-2399. [PMID: 32786287 DOI: 10.1021/acsinfecdis.0c00128] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Microbial lipids play a critical role in the pathogenesis of infectious diseases by modulating the host cell membrane properties, including lipid/protein diffusion and membrane organization. Mycobacterium tuberculosis (Mtb) synthesizes various chemically distinct lipids that are exposed on its outer membrane and interact with host cell membranes. However, the effects of the structurally diverse Mtb lipids on the host cell membrane properties to fine-tune the host cellular response remain unknown. In this study, we employed membrane biophysics and cell biology to assess the effects of different Mtb lipids on cell membrane mechanics, lipid diffusion, and the cytoskeleton of THP-1 macrophages. We found that Mtb lipids modulate macrophage membrane properties, actin cytoskeleton, and biochemical processes, such as protein phosphorylation and lipid peroxidation, in a virulence lipid-selective manner. These results emphasize that Mtb can fine-tune its interactions with the host cells governed by modulating the lipid profile on its surface. These observations provide a novel lipid-centric paradigm of Mtb pathogenesis that is amenable to pharmacological inhibition and could promote the development of robust biomarkers of Mtb infection and pathogenesis.
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Affiliation(s)
- Manjari Mishra
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Ruchika Dadhich
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Pankaj Mogha
- Department of Chemical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Shobhna Kapoor
- Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
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3
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Effect of dipole moment on amphiphile solubility and partition into liquid ordered and liquid disordered phases in lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183157. [PMID: 31846646 DOI: 10.1016/j.bbamem.2019.183157] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Revised: 12/01/2019] [Accepted: 12/12/2019] [Indexed: 12/20/2022]
Abstract
Association of amphiphiles with biomembranes is important for their availability at specific locations in organisms and cells, being critical for their biological function. A prominent role is usually attributed to the hydrophobic effect, and to electrostatic interactions between charged amphiphiles and lipids. This work explores a closely related and complementary aspect, namely the contribution made by dipole moments to the strength of the interactions established. Two xanthene amphiphiles with opposite relative orientations of their dipole and amphiphilic moments have been selected (Rhodamine-C14 and Carboxyfluorescein-C14). The membranes studied have distinct lipid compositions, representing typical cell membrane pools, ranging from internal membranes to the outer and inner leaflet of the plasma membrane. A comprehensive study is reported, including the affinity of the amphiphiles for the different membranes, the stability of the amphiphiles as monomers and their tendency to form small clusters, as well as their transverse location in the membrane. The orientation of the amphiphile dipole moment, which determines whether its interaction with the membrane dipole potential is repulsive or attractive, is found to exert a large influence on the association of the amphiphile with ordered lipid membranes. These interactions are also responsible for the formation of small clusters or stabilization of amphiphile monomers in the membrane. The results obtained allow understanding the prevalence of protein lipidation at the N-terminal for efficient targeting to the plasma membrane, as well as the tendency of GPI-anchored proteins (usually lipidated at the C-terminal) to form small clusters in the membrane ordered domains.
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4
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Allender DW, Giang H, Schick M. Model Plasma Membrane Exhibits a Microemulsion in Both Leaves Providing a Foundation for "Rafts". Biophys J 2020; 118:1019-1031. [PMID: 32023433 DOI: 10.1016/j.bpj.2020.01.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 12/02/2019] [Accepted: 01/03/2020] [Indexed: 12/22/2022] Open
Abstract
We consider a model lipid plasma membrane, one that describes the outer leaf as consisting of sphingomyelin, phosphatidylcholine, and cholesterol and the inner leaf of phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, and cholesterol. Their relative compositions are taken from experiment; the cholesterol freely interchanges between leaves. Fluctuations in local composition are coupled to fluctuations in the local membrane curvature, as in the Leibler-Andelman mechanism. Structure factors of components in both leaves display a peak at nonzero wavevector. This indicates that the disordered fluid membrane is characterized by structure of the corresponding wavelength. The scale is given by membrane properties: its bending modulus and its surface tension, which arises from the membrane's connections to the cytoskeleton. From measurements on the plasma membrane, this scale is on the order of 100 nm. We find that the membrane can be divided into two different kinds of domains that differ not only in their composition but also in their curvature. The first domain in the outer, exoplasmic leaf is rich in cholesterol and sphingomyelin, whereas the inner, cytoplasmic leaf is rich in phosphatidylserine and phosphatidylcholine. The second kind of domain is rich in phosphatidylcholine in the outer leaf and in cholesterol and phosphatidylethanolamine in the inner leaf. The theory provides a tenable basis for the origin of structure in the plasma membrane and an illuminating picture of the organization of lipids therein.
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Affiliation(s)
- David W Allender
- Department of Physics, University of Washington, Seattle, Washington; Department of Physics, Kent State University, Kent, Ohio
| | - Ha Giang
- Department of Physics, University of Washington, Seattle, Washington; Viettel Aerospace Institute, Hanoi, Vietnam
| | - M Schick
- Department of Physics, University of Washington, Seattle, Washington.
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5
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Mishra M, Adhyapak P, Dadhich R, Kapoor S. Dynamic Remodeling of the Host Cell Membrane by Virulent Mycobacterial Sulfoglycolipid-1. Sci Rep 2019; 9:12844. [PMID: 31492926 PMCID: PMC6731295 DOI: 10.1038/s41598-019-49343-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 08/23/2019] [Indexed: 12/31/2022] Open
Abstract
Lipids dictate membrane properties to modulate lateral membrane organization, lipid/protein diffusion and lipid-protein interactions, thereby underpinning proper functioning of cells. Mycobacterium tuberculosis harnesses the power of its atypical cell wall lipids to impact immune surveillance machinery centered at the host cell membrane. However, the role of specific virulent lipids in altering host cellular functions by modulating membrane organization and the associated signaling response are still pertinent unresolved questions. Here, combining membrane biophysics and cell biology, we elucidate how virulent Mtb sulfoglycolipids hijack the host cell membrane, affecting its order, fluidity, and stiffness along with manipulating the linked cytoskeleton. The functional outcome of this perturbation was assayed by monitoring membrane-associated autophagy signaling. These actions form a part of the overall response to commandeer host membrane-associated immune processes during infection. The findings on the mechanism of action of Mtb lipids on host cell membrane structure and downstream signaling will deepen the collective understanding of their functional aspects in membrane-dictated bacterial survival, pathogenesis and drug resistance and reveal suitable membrane driven-therapeutic intervention points and diagnostic tools.
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Affiliation(s)
- Manjari Mishra
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, India
| | - Pranav Adhyapak
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, India
| | - Ruchika Dadhich
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, India
| | - Shobhna Kapoor
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, India.
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6
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Lin X, Gorfe AA, Levental I. Protein Partitioning into Ordered Membrane Domains: Insights from Simulations. Biophys J 2019; 114:1936-1944. [PMID: 29694870 DOI: 10.1016/j.bpj.2018.03.020] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 03/09/2018] [Accepted: 03/22/2018] [Indexed: 11/24/2022] Open
Abstract
Cellular membranes are laterally organized into domains of distinct structures and compositions by the differential interaction affinities between various membrane lipids and proteins. A prominent example of such structures are lipid rafts, which are ordered, tightly packed domains that have been widely implicated in cellular processes. The functionality of raft domains is driven by their selective recruitment of specific membrane proteins to regulate their interactions and functions; however, there have been few general insights into the factors that determine the partitioning of membrane proteins between coexisting liquid domains. In this work, we used extensive coarse-grained and atomistic molecular dynamics simulations, potential of mean force calculations, and conceptual models to describe the partitioning dynamics and energetics of a model transmembrane domain from the linker of activation of T cells. We find that partitioning between domains is determined by an interplay between protein-lipid interactions and differential lipid packing between raft and nonraft domains. Specifically, we show that partitioning into ordered domains is promoted by preferential interactions between peptides and ordered lipids, mediated in large part by modification of the peptides by saturated fatty acids (i.e., palmitoylation). Ordered phase affinity is also promoted by elastic effects, specifically hydrophobic matching between the membrane and the peptide. Conversely, ordered domain partitioning is disfavored by the tight molecular packing of the lipids therein. The balance of these dominant drivers determines partitioning. In the case of the wild-type linker of activation of T cells transmembrane domain, these factors combine to yield enrichment of the peptide at Lo/Ld interfaces. These results define some of the general principles governing protein partitioning between coexisting membrane domains and potentially explain previous disparities among experiments and simulations across model systems.
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Affiliation(s)
- Xubo Lin
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas; School of Biological Science and Medical Engineering, Beihang University, Beijing, China; Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China
| | - Alemayehu A Gorfe
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas.
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas.
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7
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Vermaas JV, Bentley GJ, Beckham GT, Crowley MF. Membrane Permeability of Terpenoids Explored with Molecular Simulation. J Phys Chem B 2018; 122:10349-10361. [DOI: 10.1021/acs.jpcb.8b08688] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Josh V. Vermaas
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Gayle J. Bentley
- National Bioenergy Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Gregg T. Beckham
- National Bioenergy Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Michael F. Crowley
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
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8
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Allender DW, Schick M. The Effect of Solutes on the Temperature of Miscibility Transitions in Multicomponent Membranes. Biophys J 2017; 113:1814-1821. [PMID: 29045875 DOI: 10.1016/j.bpj.2017.08.033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 08/17/2017] [Accepted: 08/21/2017] [Indexed: 12/20/2022] Open
Abstract
We address questions posed by experiments that show small-chain alcohols reduce the miscibility transition temperature when added to giant plasma membrane vesicles (GPMVs), but increase that temperature when added to giant unilamellar vesicles. In giant unilamellar vesicles the change in temperature displays a definite minimum, between decanol and tetradecanol, as a function of alcohol chain length; in GPMVs there is no such minimum. To emphasize the competition between internal entropies of the components and the interactions between them, we model the system as consisting of three different linear polymers. Two of them are the constituents of a liquid, one that can undergo a miscibility transition. To this liquid is added the third polymer component, which represents the short-chain alcohol. We show that, within Flory-Huggins theory, the addition of alcohol causes an increase or decrease of the miscibility transition temperature depending upon the competition of two effects. The first is the dilution of the interactions between the two components of the liquid caused by the introduction of the alcohol. This tends to lower the transition temperature. The second effect is the preferential partitioning of the alcohol into one phase of the liquid or the other. This tends to raise the transition temperature irrespective of which phase the alcohol prefers. This second effect is the smallest, and the decrease in transition temperature the largest, when the alcohol partitions equally between the two phases. Such equal partitioning occurs when the effect of the entropic excluded volume interactions (which cause the alcohol to prefer one phase) just balances the effect of the direct interactions, which cause it to prefer the other. These results allow us to make several predictions, and to propose an explanation for the different behavior of the transition temperature in GPMVs and giant unilamellar vesicles that results from the addition of alcohols.
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Affiliation(s)
- David W Allender
- Department of Physics, Kent State University, Kent, Ohio; Department of Physics, University of Washington, Seattle, Washington
| | - M Schick
- Department of Physics, University of Washington, Seattle, Washington.
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9
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Cornell CE, McCarthy NLC, Levental KR, Levental I, Brooks NJ, Keller SL. n-Alcohol Length Governs Shift in L o-L d Mixing Temperatures in Synthetic and Cell-Derived Membranes. Biophys J 2017; 113:1200-1211. [PMID: 28801104 PMCID: PMC5607138 DOI: 10.1016/j.bpj.2017.06.066] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 06/07/2017] [Accepted: 06/29/2017] [Indexed: 11/30/2022] Open
Abstract
A persistent challenge in membrane biophysics has been to quantitatively predict how membrane physical properties change upon addition of new amphiphiles (e.g., lipids, alcohols, peptides, or proteins) in order to assess whether the changes are large enough to plausibly result in biological ramifications. Because of their roles as general anesthetics, n-alcohols are perhaps the best-studied amphiphiles of this class. When n-alcohols are added to model and cell membranes, changes in membrane parameters tend to be modest. One striking exception is found in the large decrease in liquid-liquid miscibility transition temperatures (Tmix) observed when short-chain n-alcohols are incorporated into giant plasma membrane vesicles (GPMVs). Coexisting liquid-ordered and liquid-disordered phases are observed at temperatures below Tmix in GPMVs as well as in giant unilamellar vesicles (GUVs) composed of ternary mixtures of a lipid with a low melting temperature, a lipid with a high melting temperature, and cholesterol. Here, we find that when GUVs of canonical ternary mixtures are formed in aqueous solutions of short-chain n-alcohols (n ≤ 10), Tmix increases relative to GUVs in water. This shift is in the opposite direction from that reported for cell-derived GPMVs. The increase in Tmix is robust across GUVs of several types of lipids, ratios of lipids, types of short-chain n-alcohols, and concentrations of n-alcohols. However, as chain lengths of n-alcohols increase, nonmonotonic shifts in Tmix are observed. Alcohols with chain lengths of 10-14 carbons decrease Tmix in ternary GUVs of dioleoyl-PC/dipalmitoyl-PC/cholesterol, whereas 16 carbons increase Tmix again. Gray et al. observed a similar influence of the length of n-alcohols on the direction of the shift in Tmix. These results are consistent with a scenario in which the relative partitioning of n-alcohols between liquid-ordered and liquid-disordered phases evolves as the chain length of the n-alcohol increases.
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Affiliation(s)
- Caitlin E Cornell
- University of Washington, Department of Chemistry, Seattle, Washington
| | | | - Kandice R Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School at The University of Texas Medical Center, Houston, Texas
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School at The University of Texas Medical Center, Houston, Texas
| | - Nicholas J Brooks
- Department of Chemistry, Imperial College London, London, United Kingdom
| | - Sarah L Keller
- University of Washington, Department of Chemistry, Seattle, Washington.
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10
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Membrane Curvature and Lipid Composition Synergize To Regulate N-Ras Anchor Recruitment. Biophys J 2017; 113:1269-1279. [PMID: 28738989 DOI: 10.1016/j.bpj.2017.06.051] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 06/26/2017] [Accepted: 06/27/2017] [Indexed: 11/22/2022] Open
Abstract
Proteins anchored to membranes through covalently linked fatty acids and/or isoprenoid groups play crucial roles in all forms of life. Sorting and trafficking of lipidated proteins has traditionally been discussed in the context of partitioning to membrane domains of different lipid composition. We recently showed that membrane shape/curvature can in itself mediate the recruitment of lipidated proteins. However, exactly how membrane curvature and composition synergize remains largely unexplored. Here we investigated how three critical structural parameters of lipids, namely acyl chain saturation, headgroup size, and acyl chain length, modulate the capacity of membrane curvature to recruit lipidated proteins. As a model system we used the lipidated minimal membrane anchor of the GTPase, N-Ras (tN-Ras). Our data revealed complex synergistic effects, whereby tN-Ras binding was higher on planar DOPC than POPC membranes, but inversely higher on curved POPC than DOPC membranes. This variation in the binding to both planar and curved membranes leads to a net increase in the recruitment by membrane curvature of tN-Ras when reducing the acyl chain saturation state. Additionally, we found increased recruitment by membrane curvature of tN-Ras when substituting PC for PE, and when decreasing acyl chain length from 14 to 12 carbons (DMPC versus DLPC). However, these variations in recruitment ability had different origins, with the headgroup size primarily influencing tN-Ras binding to planar membranes whereas the change in acyl chain length primarily affected binding to curved membranes. Molecular field theory calculations recapitulated these findings and revealed lateral pressure as an underlying biophysical mechanism dictating how curvature and composition synergize to modulate recruitment of lipidated proteins. Our findings suggest that the different compositions of cellular compartments could modulate the potency of membrane curvature to recruit lipidated proteins and thereby synergistically regulate the trafficking and sorting of lipidated proteins.
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11
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Gleria I, Mocskos E, Tagliazucchi M. Minimum free-energy paths for the self-organization of polymer brushes. SOFT MATTER 2017; 13:2362-2370. [PMID: 28275766 DOI: 10.1039/c6sm02725c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A methodology to calculate minimum free-energy paths based on the combination of a molecular theory and the improved string method is introduced and applied to study the self-organization of polymer brushes under poor solvent conditions. Polymer brushes in a poor solvent cannot undergo macroscopic phase separation due to the physical constraint imposed by the grafting points; therefore, they microphase separate forming aggregates. Under some conditions, the theory predicts that the homogeneous brush and the aggregates can exist as two different minima of the free energy. The theoretical methodology introduced in this work allows us to predict the minimum free-energy path connecting these two minima as well as the morphology of the system along the path. It is shown that the transition between the homogeneous brush and the aggregates may involve a free-energy barrier or be barrierless depending on the relative stability of the two morphologies and the chain length and grafting density of the polymer. In the case where a free-energy barrier exists, one of the morphologies is a metastable structure and, therefore, the properties of the brush as the quality of the solvent is cycled are expected to display hysteresis. The theory is also applied to study the adhesion/deadhesion transition between two opposing surfaces modified by identical polymer brushes and it is shown that this process may also require surpassing a free-energy barrier.
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Affiliation(s)
- Ignacio Gleria
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Computación, Buenos Aires, Argentina
| | - Esteban Mocskos
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Computación, Buenos Aires, Argentina and CONICET, Centro de Simulación Computacional para Aplicaciones Tecnológicas (CSC), Buenos Aires, Argentina
| | - Mario Tagliazucchi
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Inorgánica, Analítica y Química-Física, Buenos Aires, Argentina. and CONICET-Universidad de Buenos Aires, Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE), Buenos Aires, Argentina
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12
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Schick M. Shift in membrane miscibility transition temperature upon addition of short-chain alcohols. Phys Rev E 2016; 94:062114. [PMID: 28085479 DOI: 10.1103/physreve.94.062114] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Indexed: 11/07/2022]
Abstract
I consider the effect of a small concentration of a molecule, such as a short-chain alcohol, on the miscibility transition temperature of a giant plasma membrane vesicle. For concentrations sufficiently small such that the system can be treated as a dilute solution, the change in transition temperature is known to depend upon the extent of the molecule's partition into the coexisting liquid-disordered and liquid-ordered phases. Preferential partitioning into the former decreases the miscibility temperature, while preferential partitioning into the latter causes an increase. The analysis, combined with calculated values of the partition coefficient of saturated chains, illuminates the results of recent experiments on the change in miscibility transition temperatures with changing alcohol chain length, and makes several testable predictions.
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Affiliation(s)
- M Schick
- Department of Physics, University of Washington, Seattle, Washington 98195, USA
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13
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Membrane curvature enables N-Ras lipid anchor sorting to liquid-ordered membrane phases. Nat Chem Biol 2015; 11:192-4. [DOI: 10.1038/nchembio.1733] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Accepted: 11/14/2014] [Indexed: 11/08/2022]
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14
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Abstract
![]()
Linactants,
molecules that preferentially localize at the boundary
of lipid membrane domains, are attracting considerable attention in
recent years due to the recognition that they might regulate lipid-phase
separation and thereby modulate membrane morphology. Recent studies
have also shown that clustering of some line active agents enhances
their ability to modulate membrane curvature. However, the molecular
origin of this phenomenon, and the degree to which it impacts biological
membranes, remains poorly understood. In this work, we have investigated
how linactants induce shape change in multidomain small unilamallar
vesicles (SUVs) using extensive dissipative particle dynamics simulations.
The linactant was modeled as a two-tailed hybrid lipid with the two
tails differing in preference for different lipid domains. We found
that addition of a small amount of linactants (∼1%) to a two-domain
vesicle leads to substantial reduction in the line tension and neck
curvature at the domain boundary. Using cross-linking as a surrogate
for clustering, we further show that linactant clusters substantially
enhance the boundary preference and therefore the reduction in neck
curvature. Moreover, on the basis of analyses of the corresponding
changes in the membrane energetics, we highlight how linactants might
stabilize nanoscale domains. These results have important implications
for the potential existence and physical explanations of nanosized
domains in biological membranes.
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Affiliation(s)
- Zhenlong Li
- Department of Integrative Biology and Pharmacology, The University of Texas Medical School at Houston , 6431 Fannin Street, Houston, Texas 77030, United States
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15
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Hou S, Grillo D, Williams CL, Wasserstrom JA, Szleifer I, Zhao M. Membrane phospholipid redistribution in cancer micro-particles and implications in the recruitment of cationic protein factors. J Extracell Vesicles 2014; 3:22653. [PMID: 24959330 PMCID: PMC4056184 DOI: 10.3402/jev.v3.22653] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 04/15/2014] [Accepted: 04/23/2014] [Indexed: 11/14/2022] Open
Abstract
Cancer cell-derived micro-particles (MPs) play important regulatory roles on cellular and system levels. These activities are attributed in part to protein factors carried by MPs. However, recruitment strategies for sequestering certain protein factors in MPs are poorly understood. In the current study, using exogenous and endogenously expressed phospholipid-binding probes, we investigated the distribution of membrane phospholipids in MPs as a potential mechanism for electrostatically enriching cationic protein factors in MPs. We detected a significant level of externalised phosphatidylethanolamine (PE) at the outer surface of MPs. This was accompanied, in the inner leaflet of the MP membrane, by a greater density of negatively charged phospholipids, particularly phosphatidylserine (PS). The local enrichment of PS in the inner surface of MPs was correlated with an elevated presence of small GTPases in a polybasic region (PBR)-dependent fashion. By employing a series of RhoA derivatives, including constitutively active and RhoA derivatives lacking a PBR, we could demonstrate that the congregation of RhoA in MPs was dependent on the presence of the PBR. A chimer with the fusion of PBR sequence alone to GFP significantly enhanced GFP localisation in MPs, indicative of a positive contribution of electrostatic interactions in RhoA recruitment to MPs. Using in silico thermodynamic simulations, we characterised the electrostatic interactions between PBR and anionic lipid membrane surface. In summary, the redistribution of membrane phospholipids in MPs has an impact on the local ionic density, and is likely a contributing factor in the electrostatic recruitment of membrane-associated proteins to MPs in a PBR-dependent fashion.
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Affiliation(s)
- Songwang Hou
- Department of Medicine, Northwestern University, Chicago, IL, USA
| | - Doris Grillo
- Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL, USA
| | - Carol L Williams
- Department of Pharmacology, Medical College of Wisconsin, Milwaukee, WI, USA
| | | | - Igal Szleifer
- Department of Medicine, Northwestern University, Chicago, IL, USA ; Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL, USA ; Department of Biomedical Engineering and Department of Chemistry, Northwestern University, Evanston, IL, USA ; Chemistry of Life Processes Institute, Northwestern University, Evanston, IL, USA
| | - Ming Zhao
- Department of Medicine, Northwestern University, Chicago, IL, USA ; Chemistry of Life Processes Institute, Northwestern University, Evanston, IL, USA
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16
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Tagliazucchi M, Rabin Y, Szleifer I. Transport rectification in nanopores with outer membranes modified with surface charges and polyelectrolytes. ACS NANO 2013; 7:9085-9097. [PMID: 24047263 DOI: 10.1021/nn403686s] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
This work reports a comprehensive theoretical study of the transport-rectification properties of cylindrical nanopores with neutral inner walls and chemically modified outer membrane. The chemical species on the two outer sides of the membrane have charges of opposite sign and can be either surface-confined species (i.e., surface charges) or polyelectrolyte brushes. The advantage of this design over other types of rectifying nanopores is that it requires controlling the composition of the outer walls of the pore (which are easy to access) rather than the inner walls, thus simplifying the fabrication process. Ion-current rectification in nanopores with charged outer walls is ascribed to applied-potential-induced changes in the ionic concentration within the pore. The rectification efficiency is studied as a function of pore length, radius, surface charge and bulk electrolyte concentration. An analytical model is derived for the case of surface-confined charges that predicts the current-potential curves in very good agreement with the numerical calculations. Neutral nanopores with polyelectrolyte-modified outer walls have two distinct advantages compared to surface-charged systems: (i) they exhibit higher rectification factors due to the large charge density immobilized by the polyelectrolyte brushes, and (ii) the applied potential deforms the polyelectrolyte chains toward the oppositely charged electrode. This deformation brings the polyelectrolyte brushes into the pore in the low conductivity state and expels them from the pore in the high conductivity regime. Calculations of the potentials of mean-force suggest that the applied-field-induced conformational changes can be used to control the translocation of cargoes larger than ions, such as proteins and nanoparticles.
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Affiliation(s)
- Mario Tagliazucchi
- Department of Biomedical Engineering, Department of Chemistry and Chemistry of Life Processes Institute, Northwestern University , Evanston, Illinois 60208, United States
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Uline MJ, Szleifer I. Mode specific elastic constants for the gel, liquid-ordered, and liquid-disordered phases of DPPC/DOPC/cholesterol model lipid bilayers. Faraday Discuss 2013; 161:177-91; discussion 273-303. [PMID: 23805743 PMCID: PMC3703892 DOI: 10.1039/c2fd20091k] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
Using microscopic molecular theory, we determine the bending and saddle-splay constants of three-component lipid bilayers. The membrane contains cholesterol, dipalmitoyl-phosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) and the predictions of the theory have been shown to qualitatively reproduce phase diagrams of giant unilamellar vesicles (GUVs) of the same three components. The bending and saddle-splay constants were calculated for the gel, liquid-ordered (lo) and liquid-disordered (ld) phases. By proper expansion of the free energy, the molecular theory enables us to determine the effects of the mode of membrane bending deformation on the value of the elastic constants for different phases. In particular, we refer to the ability of the molecules to arrange the composition between the two monolayers upon deformation. The bending and saddle-splay constants obtained from the free energy expansion can be expressed in terms of moments of the local lateral pressures and their derivatives, all evaluated for a symmetric planar bilayer. The effect of blocked vs. free exchange of lipids across the two monolayers on the values of the bending constant is as high as 50 k(B)Tin the ld phase to as high as 200 k(B)T in the lo phase. These results show that one must strongly consider the mode of deformation in determining the mechanical properties of lipid bilayers. We discuss how the different contributions to the lateral pressures affect the values of the elastic constants, including the effects of the cholesterol concentration and temperature on the membrane elastic constants. We also calculate the equilibrium binding concentrations of lipid tail anchors as a function of membrane curvature by explicitly determining the chemical potential difference of species across a curved bilayer. Our results are in excellent agreement with recent experimental results.
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Affiliation(s)
- Mark J. Uline
- Department of Chemical Engineering, University of South Carolina, Columbia, SC, 29208, USA
| | - Igal Szleifer
- Biomedical Engineering Department, Northwestern University, Evanston, IL, 60208, USA
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Weise K, Huster D, Kapoor S, Triola G, Waldmann H, Winter R. Gibbs energy determinants of lipoprotein insertion into lipid membranes: the case study of Ras proteins. Faraday Discuss 2013; 161:549-61; discussion 563-89. [DOI: 10.1039/c2fd20100c] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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Li Z, Janosi L, Gorfe AA. Formation and domain partitioning of H-ras peptide nanoclusters: effects of peptide concentration and lipid composition. J Am Chem Soc 2012; 134:17278-85. [PMID: 22994893 PMCID: PMC3479155 DOI: 10.1021/ja307716z] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Experiments have shown that homologous Ras proteins containing different lipid modification, which is required for membrane binding, form nonoverlapping nanoclusters on the plasma membrane. However, the physical basis for clustering and lateral organization remains poorly understood. We have begun to tackle this issue using coarse-grained molecular dynamics simulations of the H-ras lipid anchor (tH), a triply lipid-modified heptapeptide embedded in a domain-forming mixed lipid bilayer [Janosi L. et al. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 8097]. Here we use the same simulation approach to investigate the effect of peptide concentration and bilayer composition on the clustering and lateral distribution of tH. We found no major difference in the clustering behavior of tH above a certain concentration. However, the simulations predict the existence of a critical concentration below which tH does not form nanoclusters. Moreover, our data demonstrate that cholesterol enhances the stability of tH nanoclusters but is not required for their formation. Finally, analyses of peptide distributions and partition free energies allowed us to quantitatively describe how clustering facilitates the accumulation of tH at the interface between ordered and disordered domains of the simulated bilayer systems. These thermodynamic insights represent some of the key elements for a comprehensive understanding of the molecular basis for the formation and stability of Ras signaling platforms.
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Affiliation(s)
- Zhenlong Li
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 6431 Fannin St., Houston, Texas 77030, USA
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20
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Uline MJ, Schick M, Szleifer I. Phase behavior of lipid bilayers under tension. Biophys J 2012; 102:517-22. [PMID: 22325274 DOI: 10.1016/j.bpj.2011.12.050] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2011] [Revised: 12/19/2011] [Accepted: 12/30/2011] [Indexed: 12/15/2022] Open
Abstract
Given the proposed importance of membrane tension in regulating cellular functions, we explore the effects of a finite surface tension on phase equilibrium using a molecular theory that captures the quantitative structure of the phase diagram of the tensionless DPPC/DOPC/Cholesterol lipid bilayer. We find that an increase in the surface tension decreases the temperature of the transition from liquid to gel in a pure DPPC system by ∼1.0 K/(mN/m), and decreases the liquid-disordered to liquid-ordered transition at constant chemical potentials by approximately the same amount. Our results quantitatively isolate the role of tension in comparison to other thermodynamic factors, such as pressure, in determining the phase behavior of lipid bilayers.
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Affiliation(s)
- Mark J Uline
- Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina, USA.
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Putzel GG, Schick M. Insights on raft behavior from minimal phenomenological models. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:284101. [PMID: 21709324 DOI: 10.1088/0953-8984/23/28/284101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We construct a simple phenomenological theory of phase separation in ternary mixtures of cholesterol and saturated and unsaturated lipids. Such separation is relevant to the formation of 'rafts' in the plasma membrane. We also show how simple cross-linking of proteins which prefer one form of lipid to the other can trigger raft-formation, the first step in a signaling pathway.
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Affiliation(s)
- G Garbès Putzel
- Department of Physics, University of Washington, Seattle, WA 98195-1560, USA
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Putzel GG, Uline MJ, Szleifer I, Schick M. Interleaflet coupling and domain registry in phase-separated lipid bilayers. Biophys J 2011; 100:996-1004. [PMID: 21320444 DOI: 10.1016/j.bpj.2011.01.021] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Revised: 01/08/2011] [Accepted: 01/11/2011] [Indexed: 12/23/2022] Open
Abstract
There is clear evidence of an interleaflet coupling in model lipid/cholesterol membranes exhibiting liquid-liquid phase separation. The strength of this coupling is quantified by the mismatch free energy, γ. We calculate it using a molecular mean-field model of a phase-separated lipid/cholesterol bilayer and obtain values that increase as the concentration of saturated lipids in the coexisting phases is increased. These values lie in the range 0.01-0.03 k(B)T/nm(2). We clarify the relationship between the interleaflet coupling and the extent of interleaflet alignment of liquid domains by analyzing a statistical mechanical model of coupled fluctuating domain interfaces. The model is solved exactly using the correspondence between statistical mechanics and quantum mechanics, yielding an expression for the characteristic size of fluctuations out of domain registry. This length scale depends only weakly on the strength of the interleaflet coupling and inevitably is only of the order of nanometers, which explains the experimental result that fluctuations out of domain registry have not been observed by optical microscopy.
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Affiliation(s)
- G Garbès Putzel
- Department of Biomedical Engineering and Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois, USA
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Schäfer LV, Marrink SJ. Partitioning of lipids at domain boundaries in model membranes. Biophys J 2011; 99:L91-3. [PMID: 21156123 DOI: 10.1016/j.bpj.2010.08.072] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 08/25/2010] [Accepted: 08/26/2010] [Indexed: 10/18/2022] Open
Abstract
Line-active molecules ("linactants") that bind to the boundary interface between different fluid lipid domains in membranes have a strong potential as regulators of the lateral heterogeneity that is important for many biological processes. Here, we use molecular dynamics simulations in combination with a coarse-grain model that retains near-atomic resolution to identify lipid species that can act as linactants in a model membrane that is segregated into two lipid domains of different fluidity. Our simulations predict that certain hybrid saturated/unsaturated chain lipids can bind to the interface and lower the line tension, whereas cone-shaped lysolipids have a less pronounced effect.
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Affiliation(s)
- Lars V Schäfer
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
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