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Feigenson GW, Huang J, Enoki TA. An Unexpected Driving Force for Lipid Order Appears in Asymmetric Lipid Bilayers. J Am Chem Soc 2023; 145:21717-21722. [PMID: 37683131 DOI: 10.1021/jacs.3c05081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/10/2023]
Abstract
An ordered phase in one leaflet of an asymmetric bilayer can induce a precisely superimposed induced order domain in the apposed leaflet. Order is induced in such simple lipid compositions as dioleoylphosphatidylcholine/cholesterol (DOPC)/chol) which is expected to be a uniform and disordered lipid mixture. Dye partitioning can be used to label and identify coexisting liquid-disordered (Ld), liquid-ordered (Lo), or gel-ordered (Lβ) molecules in a phase-separated leaflet. In the other leaflet of an asymmetric bilayer, dye partitioning also labels and identifies any induced order domains created by an Lo or gel phase domain in the apposed leaflet as well as the state of disorder of the lipid surrounding the induced ordered region. We explore a molecular level mechanism by which a disorder-prone uniform mixture of DOPC/chol = 0.8/0.2 would spontaneously separate into ordered regions coexisting with disordered regions. A redistribution of cholesterol seems to take place in the regions apposed to the ordered phase. The precision of the superposition of Lo or gel domains with their induced order domains implies a strong energy penalty that would be incurred if order/disorder interfaces were to form at the bilayer midplane. We conclude that the energy penalty for Lo/Ld or gel/Ld contact in the bilayer midplane is sufficient to drive disorderly DOPC/chol into an ordered state that reduces unfavorable order-disorder contacts at the bilayer midplane interface.
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Affiliation(s)
- Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
| | - Juyang Huang
- Department of Physics and Astronomy, Texas Tech University, Lubbock, Texas 79409, United States
| | - Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
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Feigenson GW, Enoki TA. Nano-scale domains in the plasma membrane are like macroscopic domains in asymmetric bilayers. Biophys J 2023; 122:925-930. [PMID: 36380589 PMCID: PMC10111217 DOI: 10.1016/j.bpj.2022.11.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 11/02/2022] [Accepted: 11/10/2022] [Indexed: 11/16/2022] Open
Abstract
Unfavorable lipid-lipid pairwise interactions between HiTm and LowTm lipids drive liquid-disordered (Ld) + liquid-ordered (Lo) phase separation. Large size of phase domains is opposed by lipid dipole repulsions, which are more significant compared with the pairwise interactions for naturally abundant LowTm lipids such as palmitoyl oleoyl phosphatidylcholine. During the nano-to-macro domain size transition, no lipid phase transition occurs, and measured properties of Ld + Lo nanodomains are found to be essentially the same as those of macrodomains. Use of macrodomains in mixtures to model cell plasma membranes (PM) is helpful, enabling study by optical microscopy. Use of asymmetric giant unilamellar vesicles to model a PM reveals that ordered phase domains in one leaflet induce ordered domains in an otherwise uniform phase in the apposing leaflet that models a cytoplasmic leaflet. Because macro and nano phase properties are so similar, we conclude that a cell PM that has nano-scale Ld + Lo phase domains in the exoplasmic leaflet is likely to induce nano-scale ordered domains in the cytoplasmic leaflet.
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Affiliation(s)
- Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University - Ithaca, Ithaca, New York.
| | - Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University - Ithaca, Ithaca, New York
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3
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Enoki TA, Feigenson GW. Improving our picture of the plasma membrane: Rafts induce ordered domains in a simplified model cytoplasmic leaflet. Biochim Biophys Acta Biomembr 2022; 1864:183995. [PMID: 35753393 DOI: 10.1016/j.bbamem.2022.183995] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2022] [Revised: 06/09/2022] [Accepted: 06/13/2022] [Indexed: 01/06/2023]
Abstract
By study of asymmetric membranes, models of the cell plasma membrane (PM) have improved, with more realistic properties of the asymmetric lipid composition of the membrane being explored. We used hemifusion of symmetric giant unilamellar vesicles (GUVs) with a supported lipid bilayer (SLB) to engineer bilayer leaflets of different composition. During hemifusion, only the outer leaflets of GUV and SLB are connected, exchanging lipids by simple diffusion. aGUVs were detached from the SLB for study. In general these aGUVs are formed with one leaflet that phase-separates into Ld (liquid disordered) + Lo (liquid ordered) phases, and another leaflet with lipid composition that would form a single fluid phase in a symmetric bilayer. We observed that ordered phases of either Lo or Lβ (gel phase) induce an ordered domain in the apposed fluid leaflet that lacks high melting lipids. Results suggest both an inter-leaflet and an intra-leaflet redistribution of cholesterol. We used C-Laurdan spectral images to investigate the lipid packing/order of aGUVs, finding that cholesterol partitions into the induced ordered domains. We suggest this behavior to be commonplace, that when Ld + Lo phase separation occurs in a cell PM exoplasmic leaflet, an induced order domain forms in the cytoplasmic leaflet.
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Affiliation(s)
- Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA.
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, USA
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Feigenson GW. On the small size of liquid-disordered + liquid-ordered nanodomains. Biochim Biophys Acta Biomembr 2021; 1863:183685. [PMID: 34175299 DOI: 10.1016/j.bbamem.2021.183685] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Revised: 06/09/2021] [Accepted: 06/17/2021] [Indexed: 11/15/2022]
Abstract
Four-component phase diagrams reveal that Liquid-disordered + liquid-ordered (Ld + Lo) nanodomains are exclusively found adjacent to a three-phase region, and so cannot be a one-phase microemulsion. Of importance for understanding biological membranes, a small change in lipid bilayer composition can change the size of these coexisting phase domains hundreds of fold, between tens of nanometers and microns. Nanodomain diameter, measured from small angle neutron scattering, is in the range 15-35 nm, consistent with stabilization by repulsive dipole fields. Ld/Lo line tension controls the Ld + Lo domain size transition. Other than size, chemical and physical properties of the phase domains do not seem to change during the transition. Unfavorable lipid-lipid pairwise interactions, rather than phase thickness mismatch, seem to be the main reason for Ld + Lo immiscibility. Pairwise interactions of cholesterol-phospholipid seem to be favorable, whereas pairwise interactions of high-melting phospholipid with low-melting phospholipid are unfavorable. Measured Ld/Lo line tension, like the phase separation, is created mainly by unfavorable lipid-lipid pairwise interactions. Lipid dipole-dipole repulsion opposes these unfavorable lipid-lipid pairwise interactions and thus, in a sense, is the reason that nanodomains form. Bilayer physical and chemical properties measured from macroscopic domains of coexisting Ld + Lo phases should be good approximations for the properties of coexisting nanoscopic domains.
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Affiliation(s)
- Gerald W Feigenson
- Cornell University Department of Molecular Biology and Genetics, Room 201 Biotechnology Building, 215 Tower Rd. Ithaca, New York 14853, United States.
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Enoki TA, Wu J, Heberle FA, Feigenson GW. Dataset of asymmetric giant unilamellar vesicles prepared via hemifusion: Observation of anti-alignment of domains and modulated phases in asymmetric bilayers. Data Brief 2021; 35:106927. [PMID: 33763508 PMCID: PMC7973298 DOI: 10.1016/j.dib.2021.106927] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Revised: 02/26/2021] [Accepted: 03/01/2021] [Indexed: 01/04/2023] Open
Abstract
The data provided with this paper are confocal fluorescence images of symmetric giant unilamellar vesicles (GUVs) and asymmetric giant unilamellar vesicles (aGUVs). In this work, aGUVs were prepared using the hemifusion method and are labelled with two different fluorescent dyes, named TFPC and DiD. Both dyes show strong preference for the liquid-disordered (Ld) phase instead of the liquid-ordered (Lo) phase. The partition of these dyes favoring the Ld phase leads to bright Ld phase and dark Lo phase domains in symmetric GUVs observed by fluorescence microscopy. In symmetric vesicles, the bright and the dark domains of the inner and the outer leaflets are aligned. In aGUVs, the fluorescent probe TFPC exclusively labels the aGUV outer leaflet. Here, we show a dataset of fluorescence micrographs obtained using scanning fluorescence confocal microscopy. For the system chosen, the fluorescence signal of TFPC and DiD show anti-alignment of the brighter domains on aGUVs. Important for this dataset, TFPC and DiD have fluorescence emission centered in the green and far-red region of the visible spectra, respectively, and the dyes’ fluorescence emission bands do not overlap. This dataset were collected in the same conditions of the dataset reported in the co-submitted work (Enoki, et al. 2021) where most of aGUVs show domains alignment. In addition, we show micrographs of GUVs displaying modulated phases and macrodomains. We also compare the modulated phases observed in GUVs and aGUVs. For these datasets, we collected a sequence of micrographs using confocal microscopy varying the z-position, termed a z-stack. Images were collected in a scanning microscope Nikon Eclipse C2+ (Nikon Instruments, Melville, NY). Additional samples used to measure the lipid concentrations and to prepare GUVs with accurate lipid fractions are also provided with this paper.
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Affiliation(s)
- Thais A Enoki
- Cornell University, United States.,University of Tennessee, United State
| | - Joy Wu
- Cornell University, United States
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Enoki TA, Scott HL, Feigenson GW, Heberle FA. Inter- and Intra-Plane Interactions Control the Existence of Macrodomains in Asymmetric Giant Unilamellar Vesicles. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.1080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Abstract
Located at the inner leaflet of the plasma membrane (PM), phosphatidyl-inositol 4,5-bisphosphate [PI(4,5)P2] composes only 1-2 mol% of total PM lipids. With its synthesis and turnover both spatially and temporally regulated, PI(4,5)P2 recruits and interacts with hundreds of cellular proteins to support a broad spectrum of cellular functions. Several factors contribute to the versatile and dynamic distribution of PI(4,5)P2 in membranes. Physiological multivalent cations such as Ca2+ and Mg2+ can bridge between PI(4,5)P2 headgroups, forming nanoscopic PI(4,5)P2-cation clusters. The distinct lipid environment surrounding PI(4,5)P2 affects the degree of PI(4,5)P2 clustering. In addition, diverse cellular proteins interacting with PI(4,5)P2 can further regulate PI(4,5)P2 lateral distribution and accessibility. This review summarizes the current understanding of PI(4,5)P2 behavior in both cells and model membranes, with emphasis on both multivalent cation- and protein-induced PI(4,5)P2 clustering. Understanding the nature of spatially separated pools of PI(4,5)P2 is fundamental to cell biology.
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Affiliation(s)
- Yi Wen
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14850, USA; , ,
| | - Volker M Vogt
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14850, USA; , ,
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14850, USA; , ,
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Mohideen N, Weiner MD, Feigenson GW. Bilayer compositional asymmetry influences the nanoscopic to macroscopic phase domain size transition. Chem Phys Lipids 2020; 232:104972. [PMID: 32941827 DOI: 10.1016/j.chemphyslip.2020.104972] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 08/18/2020] [Accepted: 09/04/2020] [Indexed: 10/23/2022]
Abstract
The eukaryotic plasma membrane (PM) exhibits lipid mixing heterogeneities known as lipid rafts. These lipid rafts, the result of liquid-liquid phase separation, can be modeled by coexisting liquid ordered (Lo) and liquid disordered (Ld) domains. Four-lipid component systems with a high-melting lipid, a nanodomain-inducing low-melting lipid, a macrodomain-inducing low-melting lipid, and cholesterol (chol) can give rise to domains of different sizes. These four-component systems have been characterized in experiments, yet there are few studies that model the asymmetric distribution of lipids actually found in the PM. We used molecular dynamics (MD) simulations to analyze the transition from nanoscopic to macroscopic domains in symmetric and in asymmetric model membranes. Using coarse-grained MD simulations, we found that asymmetry promotes macroscopic domain growth in a case where symmetric systems exhibit nanoscopic domains. Also, macroscopic domain formation in symmetric systems is highly dependent on registration of like phases in the cytoplasmic and exoplasmic leaflets. Using united-atom MD simulations, we found that symmetric Lo domains are only slightly more ordered than asymmetric Lo domains. We also found that large Lo domains in our asymmetric systems induce a slight chain ordering in the apposed cytoplasmic regions. The chol fractions of phase-separated Lo and Ld domains of the exoplasmic leaflet were unchanged whether the system was symmetric or asymmetric.
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Affiliation(s)
- Naveen Mohideen
- Cornell University Department of Physics, 117 Clark Hall, Ithaca, New York, 14853, United States; Johns Hopkins University Department of Molecular Biophysics, 101 Jenkins Hall, 3400 N. Charles Street, Baltimore, Maryland, 21218, United States.
| | - Michael D Weiner
- Cornell University Department of Physics, 117 Clark Hall, Ithaca, New York, 14853, United States; Georgia Institute of Technology Partnership for an Advanced Computing Environment, 756 W. Peachtree St. NW, Atlanta, Georgia, 30332, United States.
| | - Gerald W Feigenson
- Cornell University Department of Molecular Biology and Genetics, Room 201 215 Tower Rd. Ithaca, New York, 14853, United States.
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Abstract
Phosphatidylinositol 4,5-bisphosphate (PIP2) is critical for HIV-1 virus assembly. The viral membrane is enriched in PIP2, suggesting that the virus assembles at PIP2-rich microdomains. We showed previously that in model membranes PIP2 can form nanoscopic clusters bridged by multivalent cations. Here, using purified proteins we quantitated the binding of HIV-1 Gag-related proteins to giant unilamellar vesicles containing either clustered or free PIP2. Myristoylated MA strongly preferred binding to clustered PIP2. By contrast, unmyristoylated HIV-1 MA, RSV MA, and a PH domain all preferred to interact with free PIP2. We also found that HIV-1 Gag multimerization promotes PIP2 clustering. Truncated Gag proteins comprising the MA, CA, and SP domains (MACASP) or the MA and CA domains (MACA) induced self-quenching of acyl chain-labeled fluorescent PIP2 in liposomes, implying clustering. However, HIV-1 MA itself did not induce PIP2 clustering. A CA inter-hexamer dimer interface mutation led to a loss of induced PIP2 clustering in MACA, indicating the importance of protein multimerization. Cryo-electron tomography of liposomes with bound MACA showed an amorphous protein layer on the membrane surface. Thus, it appears that while protein–protein interactions are required for PIP2 clustering, formation of a regular lattice is not. Protein-induced PIP2 clustering and multivalent cation-induced PIP2 clustering are additive. Taken together, these results provide the first evidence that HIV-1 Gag can selectively target pre-existing PIP2-enriched domains of the plasma membrane for viral assembly, and that Gag multimerization can further enrich PIP2 at assembly sites. These effects could explain the observed PIP2 enrichment in HIV-1.
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Affiliation(s)
- Yi Wen
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Gerald W Feigenson
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Volker M Vogt
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Robert A Dick
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY 14853, USA.
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Enoki TA, Heberle FA, Feigenson GW. Experimental Evidence That Bilayer Asymmetry Decreases Lo/Ld Line Tension. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.2202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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Enoki TA, Feigenson GW. Asymmetric Bilayers by Hemifusion: Method and Leaflet Behaviors. Biophys J 2019; 117:1037-1050. [PMID: 31493862 DOI: 10.1016/j.bpj.2019.07.054] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 06/13/2019] [Accepted: 07/08/2019] [Indexed: 01/03/2023] Open
Abstract
We describe a new method to prepare asymmetric giant unilamellar vesicles (aGUVs) via hemifusion. Hemifusion of giant unilamellar vesicles and a supported lipid bilayer, triggered by calcium, promotes the lipid exchange of the fused outer leaflets mediated by lipid diffusion. We used different fluorescent dyes to monitor the inner and the outer leaflets of the unsupported aGUVs. We confirmed that almost all newly exchanged lipids in the aGUVs are found in the outer leaflet of these asymmetric vesicles. In addition, we test the stability of the aGUVs formed by hemifusion in preserving their contents during the procedure. For aGUVs prepared from the hemifusion of giant unilamellar vesicles composed of 1,2-distearoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-phosphocholine/cholesterol = 0.39/0.39/0.22 and a supported lipid bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine/cholesterol = 0.8/0.2, we observed the exchanged lipids to alter the bilayer properties. To access the physical and chemical properties of the asymmetric bilayer, we monitored the dye partition coefficients of individual leaflets and the generalized polarization of the fluorescence probe 6-dodecanoyl-2-[ N-methyl-N-(carboxymethyl)amino] naphthalene, a sensor for the lipid packing/order of its surroundings. For a high percentage of lipid exchange (>70%), the dye partition indicates induced-disordered and induced-ordered domains. The induced domains have distinct lipid packing/order compared to the symmetric liquid-disordered and liquid-ordered domains.
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Affiliation(s)
- Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York.
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
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Shurer CR, Kuo JCH, Roberts LM, Gandhi JG, Colville MJ, Enoki TA, Pan H, Su J, Noble JM, Hollander MJ, O'Donnell JP, Yin R, Pedram K, Möckl L, Kourkoutis LF, Moerner WE, Bertozzi CR, Feigenson GW, Reesink HL, Paszek MJ. Physical Principles of Membrane Shape Regulation by the Glycocalyx. Cell 2019; 177:1757-1770.e21. [PMID: 31056282 PMCID: PMC6768631 DOI: 10.1016/j.cell.2019.04.017] [Citation(s) in RCA: 139] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 02/19/2019] [Accepted: 04/09/2019] [Indexed: 12/12/2022]
Abstract
Cells bend their plasma membranes into highly curved forms to interact with the local environment, but how shape generation is regulated is not fully resolved. Here, we report a synergy between shape-generating processes in the cell interior and the external organization and composition of the cell-surface glycocalyx. Mucin biopolymers and long-chain polysaccharides within the glycocalyx can generate entropic forces that favor or disfavor the projection of spherical and finger-like extensions from the cell surface. A polymer brush model of the glycocalyx successfully predicts the effects of polymer size and cell-surface density on membrane morphologies. Specific glycocalyx compositions can also induce plasma membrane instabilities to generate more exotic undulating and pearled membrane structures and drive secretion of extracellular vesicles. Together, our results suggest a fundamental role for the glycocalyx in regulating curved membrane features that serve in communication between cells and with the extracellular matrix.
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Affiliation(s)
- Carolyn R Shurer
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Joe Chin-Hun Kuo
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | | | - Jay G Gandhi
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | | | - Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Hao Pan
- Field of Biophysics, Cornell University, Ithaca, NY 14853, USA
| | - Jin Su
- Department of Clinical Sciences, Cornell University, Ithaca, NY 14853, USA
| | - Jade M Noble
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Michael J Hollander
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | - John P O'Donnell
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Rose Yin
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Kayvon Pedram
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Leonhard Möckl
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Lena F Kourkoutis
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA; Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA
| | - W E Moerner
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Carolyn R Bertozzi
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Gerald W Feigenson
- Field of Biophysics, Cornell University, Ithaca, NY 14853, USA; Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Heidi L Reesink
- Department of Clinical Sciences, Cornell University, Ithaca, NY 14853, USA
| | - Matthew J Paszek
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853, USA; Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA; Field of Biophysics, Cornell University, Ithaca, NY 14853, USA; Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA.
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Enoki TA, Heberle FA, Feigenson GW. FRET Detects the Size of Nanodomains for Coexisting Liquid-Disordered and Liquid-Ordered Phases. Biophys J 2019; 114:1921-1935. [PMID: 29694869 DOI: 10.1016/j.bpj.2018.03.014] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 02/15/2018] [Accepted: 03/15/2018] [Indexed: 11/18/2022] Open
Abstract
Biomembranes with as few as three lipid components can form coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases. In the coexistence region of Ld and Lo phases, the lipid mixtures 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/chol or brain sphingomyelin (bSM)/DOPC/chol form micron-scale domains that are easily visualized with light microscopy. Although large domains are not observed in the mixtures DSPC/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/chol and bSM/POPC/chol, lateral heterogeneity is nevertheless detected using techniques with nanometer-scale spatial resolution. We propose a simple and accessible method to measure domain sizes below optical resolution (∼200 nm). We measured nanodomain size for the latter two mixtures by combining experimental Förster resonance energy transfer data with a Monte-Carlo-based analysis. We found a domain radius of 7.5-10 nm for DSPC/POPC/chol, similar to values obtained previously by neutron scattering, and ∼5 nm for bSM/POPC/chol, slightly smaller than measurable by neutron scattering. These analyses also detect the domain-size transition that is observed by fluorescence microscopy in the four-component lipid mixture bSM/DOPC/POPC/chol. Accurate measurements of fluorescent-probe partition coefficients are especially important for the analysis; therefore, we exploit three different methods to measure the partition coefficient of fluorescent molecules between Ld and Lo phases.
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Affiliation(s)
- Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Frederick A Heberle
- Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Large Scale Structures Group, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York.
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Usery RD, Enoki TA, Wickramasinghe SP, Nguyen VP, Ackerman DG, Greathouse DV, Koeppe RE, Barrera FN, Feigenson GW. Membrane Bending Moduli of Coexisting Liquid Phases Containing Transmembrane Peptide. Biophys J 2019; 114:2152-2164. [PMID: 29742408 DOI: 10.1016/j.bpj.2018.03.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Revised: 03/19/2018] [Accepted: 03/22/2018] [Indexed: 11/25/2022] Open
Abstract
A number of highly curved membranes in vivo, such as epithelial cell microvilli, have the relatively high sphingolipid content associated with "raft-like" composition. Given the much lower bending energy measured for bilayers with "nonraft" low sphingomyelin and low cholesterol content, observing high curvature for presumably more rigid compositions seems counterintuitive. To understand this behavior, we measured membrane rigidity by fluctuation analysis of giant unilamellar vesicles. We found that including a transmembrane helical GWALP peptide increases the membrane bending modulus of the liquid-disordered (Ld) phase. We observed this increase at both low-cholesterol fraction and higher, more physiological cholesterol fraction. We find that simplified, commonly used Ld and liquid-ordered (Lo) phases are not representative of those that coexist. When Ld and Lo phases coexist, GWALP peptide favors the Ld phase with a partition coefficient of 3-10 depending on mixture composition. In model membranes at high cholesterol fractions, Ld phases with GWALP have greater bending moduli than the Lo phase that would coexist.
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Affiliation(s)
- Rebecca D Usery
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Sanjula P Wickramasinghe
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Vanessa P Nguyen
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Scientific Computing, Howard Hughes Medical Institute, Janelia Research Campus, Ashburn, Virginia
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas
| | - Francisco N Barrera
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York.
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15
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal Leaflet Coupling in Compositionally Asymmetric Phase-Separated Lipid Membranes. J Phys Chem B 2019; 123:3968-3975. [PMID: 31009218 DOI: 10.1021/acs.jpcb.9b03488] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The eukaryotic plasma membrane has an asymmetric distribution of its component lipids. Rafts that result from liquid-liquid phase separation are a feature of its exoplasmic leaflet, but how these exoplasmic leaflet domains are coupled to the cytoplasmic leaflet is not understood. These rafts can be studied in model membranes of three-component mixtures that produce coexisting liquid ordered (Lo) and liquid disordered (Ld) domains. We conducted all-atom molecular dynamics simulations of compositionally asymmetric lipid bilayers that reflect a more realistic model of the plasma membrane. One leaflet contained phase-separated domains with phosphatidylcholine and cholesterol, representing the exoplasmic leaflet, whereas the other contained phosphatidylethanolamine, phosphatidylserine, and cholesterol, which are the predominant components of the cytoplasmic leaflet. Inspired by findings of domain alignment across the two leaflets in compositionally symmetric model membranes, we examined the coupling between the two leaflets to see how the single-phase cytoplasmic leaflet would respond to phase separation in the other leaflet and if information could be communicated across the membrane. We found the region of the single-phase leaflet apposing the Lo domain to be slightly more ordered and thicker than the region apposing the Ld domain. The region across from the Lo domain is somewhat enriched in cholesterol and significantly depleted of polyunsaturated lipids.
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16
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Enoki TA, Feigenson GW. A New Method to Prepare Asymmetric Unilamellar Vesicles: Hemifusion. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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17
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Ashkar R, Doktorova M, Heberle FA, Scott H, Kelley E, Nagao M, Usery R, Barrera FN, Feigenson GW, Katsaras J, Khelashvili G. Cholesterol Affects the Bending Rigidity of DOPC Membranes. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.1780] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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18
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Doktorova M, Heberle FA, Marquardt D, Rusinova R, Sanford RL, Peyear TA, Katsaras J, Feigenson GW, Weinstein H, Andersen OS. Gramicidin Increases Lipid Flip-Flop in Symmetric and Asymmetric Lipid Vesicles. Biophys J 2019; 116:860-873. [PMID: 30755300 PMCID: PMC6400823 DOI: 10.1016/j.bpj.2019.01.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 01/03/2019] [Accepted: 01/09/2019] [Indexed: 01/06/2023] Open
Abstract
Unlike most transmembrane proteins, phospholipids can migrate from one leaflet of the membrane to the other. Because this spontaneous lipid translocation (flip-flop) tends to be very slow, cells facilitate the process with enzymes that catalyze the transmembrane movement and thereby regulate the transbilayer lipid distribution. Nonenzymatic membrane-spanning proteins with unrelated primary functions have also been found to accelerate lipid flip-flop in a nonspecific manner and by various hypothesized mechanisms. Using deuterated phospholipids, we examined the acceleration of flip-flop by gramicidin channels, which have well-defined structures and known functions, features that make them ideal candidates for probing the protein-membrane interactions underlying lipid flip-flop. To study compositionally and isotopically asymmetric proteoliposomes containing gramicidin, we expanded a recently developed protocol for the preparation and characterization of lipid-only asymmetric vesicles. Channel incorporation, conformation, and function were examined with small angle x-ray scattering, circular dichroism, and a stopped-flow spectrofluorometric assay, respectively. As a measure of lipid scrambling, we used differential scanning calorimetry to monitor the effect of gramicidin on the melting transition temperatures of the two bilayer leaflets. The two calorimetric peaks of the individual leaflets merged into a single peak over time, suggestive of scrambling, and the effect of the channel on the transbilayer lipid distribution in both symmetric 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and asymmetric 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles was quantified from proton NMR measurements. Our results show that gramicidin increases lipid flip-flop in a complex, concentration-dependent manner. To determine the molecular mechanism of the process, we used molecular dynamics simulations and further computational analysis of the trajectories to estimate the extent of membrane deformation. Together, the experimental and computational approaches were found to constitute an effective means for studying the effects of transmembrane proteins on lipid distribution in both symmetric and asymmetric model membranes.
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Affiliation(s)
- Milka Doktorova
- Tri-Institutional PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York.
| | - Frederick A Heberle
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas; The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee
| | | | - Radda Rusinova
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - R Lea Sanford
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Thasin A Peyear
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - John Katsaras
- Large Scale Structures Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York; The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, Weill Greenberg Center, New York, New York
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
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19
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Tsai WC, Feigenson GW. Lowering line tension with high cholesterol content induces a transition from macroscopic to nanoscopic phase domains in model biomembranes. Biochim Biophys Acta Biomembr 2018; 1861:478-485. [PMID: 30529459 DOI: 10.1016/j.bbamem.2018.11.010] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 11/26/2018] [Accepted: 11/27/2018] [Indexed: 11/25/2022]
Abstract
Chemically simplified lipid mixtures are used here as models of the cell plasma membrane exoplasmic leaflet. In such models, phase separation and morphology transitions controlled by line tension in the liquid-disordered (Ld) + liquid-ordered (Lo) coexistence regime have been described [1]. Here, we study two four-component lipid mixtures at different cholesterol fractions: brain sphingomyelin (BSM) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). On giant unilamellar vesicles (GUVs) display a nanoscopic-to-macroscopic transition of Ld + Lo phase domains as POPC is replaced by DOPC, and this transition also depends on the cholesterol fraction. Line tension decreases with increasing cholesterol mole fractions in both lipid mixtures. For the ternary BSM/DOPC/Chol mixture, the published phase diagram [19] requires a modification to show that when cholesterol mole fraction is >~0.33, coexisting phase domains become nanoscopic.
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Affiliation(s)
- Wen-Chyan Tsai
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, United States of America
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, United States of America.
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20
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Weiner MD, Feigenson GW. Presence and Role of Midplane Cholesterol in Lipid Bilayers Containing Registered or Antiregistered Phase Domains. J Phys Chem B 2018; 122:8193-8200. [DOI: 10.1021/acs.jpcb.8b03949] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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21
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Usery RD, Enoki TA, Wickramasinghe SP, Nguyen VP, Ackerman DG, Greathouse DV, Koeppe RE, Barrera FN, Feigenson GW. Membrane Bending Moduli of Coexisting Liquid Phases Containing Transmembrane Peptide. Biophys J 2018; 115:164. [PMID: 29972808 DOI: 10.1016/j.bpj.2018.06.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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22
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Feigenson GW. Constructing and using Phase Diagrams of Multi-component Lipid Mixtures. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2227] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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23
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Enoki TA, Feigenson GW. Measuring Partition Coefficient between Liquid-Disordered (LD) and Liquid-Ordered Phases. Why are Phase Diagrams Important to Know? Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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24
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal the Impact of Compositional Asymmetry in Phase-Separated Lipid Membranes on Phospholipid Physical Properties. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.2488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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25
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Doktorova M, Heberle FA, Kingston RL, Khelashvili G, Cuendet MA, Wen Y, Katsaras J, Feigenson GW, Vogt VM, Dick RA. Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties. Biophys J 2017; 113:2004-2015. [PMID: 29117524 DOI: 10.1016/j.bpj.2017.08.055] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 08/07/2017] [Accepted: 08/09/2017] [Indexed: 01/28/2023] Open
Abstract
Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.
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Affiliation(s)
- Milka Doktorova
- Tri-Institutional PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York
| | - Frederick A Heberle
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
| | - Richard L Kingston
- School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Michel A Cuendet
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Yi Wen
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - John Katsaras
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Volker M Vogt
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Robert A Dick
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York.
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26
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Doktorova M, Heberle FA, Kingston RL, Khelashvili G, Cuendet MA, Wen Y, Katsaras J, Feigenson GW, Vogt VM, Dick RA. Cholesterol Promotes Protein Binding by Affecting Membrane Electrostatics and Solvation Properties. Biophys J 2017. [PMID: 29117524 DOI: 10.1016/j.bpj.2017.08.055.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Binding of the retroviral structural protein Gag to the cellular plasma membrane is mediated by the protein's matrix (MA) domain. Prominent among MA-PM interactions is electrostatic attraction between the positively charged MA domain and the negatively charged plasma membrane inner leaflet. Previously, we reported that membrane association of HIV-1 Gag, as well as purified Rous sarcoma virus (RSV) MA and Gag, depends strongly on the presence of acidic lipids and is enhanced by cholesterol (Chol). The mechanism underlying this enhancement was unclear. Here, using a broad set of in vitro and in silico techniques we addressed molecular mechanisms of association between RSV MA and model membranes, and investigated how Chol enhances this association. In neutron scattering experiments with liposomes in the presence or absence of Chol, MA preferentially interacted with preexisting POPS-rich clusters formed by nonideal lipid mixing, binding peripherally to the lipid headgroups with minimal perturbation to the bilayer structure. Molecular dynamics simulations showed a stronger MA-bilayer interaction in the presence of Chol, and a large Chol-driven increase in lipid packing and membrane surface charge density. Although in vitro MA-liposome association is influenced by disparate variables, including ionic strength and concentrations of Chol and charged lipids, continuum electrostatic theory revealed an underlying dependence on membrane surface potential. Together, these results conclusively show that Chol affects RSV MA-membrane association by making the electrostatic potential at the membrane surface more negative, while decreasing the penalty for lipid headgroup desolvation. The presented approach can be applied to other viral and nonviral proteins.
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Affiliation(s)
- Milka Doktorova
- Tri-Institutional PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York
| | - Frederick A Heberle
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
| | - Richard L Kingston
- School of Biological Sciences, The University of Auckland, Auckland, New Zealand
| | - George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Michel A Cuendet
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
| | - Yi Wen
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - John Katsaras
- The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Gerald W Feigenson
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Volker M Vogt
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York
| | - Robert A Dick
- Department of Biochemistry and Molecular Cell Biology, Cornell University, Ithaca, New York.
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27
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Usery RD, Enoki TA, Wickramasinghe SP, Weiner MD, Tsai WC, Kim MB, Wang S, Torng TL, Ackerman DG, Heberle FA, Katsaras J, Feigenson GW. Line Tension Controls Liquid-Disordered + Liquid-Ordered Domain Size Transition in Lipid Bilayers. Biophys J 2017; 112:1431-1443. [PMID: 28402885 DOI: 10.1016/j.bpj.2017.02.033] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/27/2017] [Accepted: 02/16/2017] [Indexed: 12/28/2022] Open
Abstract
To better understand animal cell plasma membranes, we studied simplified models, namely four-component lipid bilayer mixtures. Here we describe the domain size transition in the region of coexisting liquid-disordered (Ld) + liquid-ordered (Lo) phases. This transition occurs abruptly in composition space with domains increasing in size by two orders of magnitude, from tens of nanometers to microns. We measured the line tension between coexisting Ld and Lo domains close to the domain size transition for a variety of lipid mixtures, finding that in every case the transition occurs at a line tension of ∼0.3 pN. A computational model incorporating line tension and dipole repulsion indicated that even small changes in line tension can result in domains growing in size by several orders of magnitude, consistent with experimental observations. We find that other properties of the coexisting Ld and Lo phases do not change significantly in the vicinity of the abrupt domain size transition.
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Affiliation(s)
- Rebecca D Usery
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Thais A Enoki
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Sanjula P Wickramasinghe
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Department of Biochemistry and Biophysics at the University of Pennsylvania, Philadelphia, Pennsylvania
| | | | - Wen-Chyan Tsai
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York
| | - Mary B Kim
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Department of Medicine, Baylor College of Medicine, Houston, Texas
| | - Shu Wang
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Harvard Medical School Library of Integrated Network-based Cellular Signatures Center and Laboratory of Systems Pharmacology, Harvard University, Boston, Massachusetts
| | - Thomas L Torng
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Department of Biochemistry, Geisel School of Medicine at Dartmouth College, Hanover, New Hampshire
| | - David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York; Scientific Computing, Howard Hughes Medical Institute, Janelia Research Campus, Ashburn, Virginia
| | - Frederick A Heberle
- Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee
| | - John Katsaras
- Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York.
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28
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Enoki TA, Heberle FA, Feigenson GW. Probe Partition between Liquid-Disordered (LD) and Liquid-Ordered (Lo) Phases and Investigation of Nanodomain Sizes. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.2040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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29
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Weiner MD, Feigenson GW. Molecular Dynamics Simulations Reveal the Impact of Compositional Asymmetry in Lipid Membranes on Phase Behavior and Leaflet Interactions. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.2049] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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30
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Affiliation(s)
- Gerald W Feigenson
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, New York.
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31
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Heberle FA, Marquardt D, Doktorova M, Geier B, Standaert RF, Heftberger P, Kollmitzer B, Nickels JD, Dick R, Feigenson GW, Katsaras J, London E, Pabst G. Subnanometer Structure of an Asymmetric Model Membrane: Interleaflet Coupling Influences Domain Properties. Langmuir 2016; 32:5195-200. [PMID: 27128636 PMCID: PMC4910133 DOI: 10.1021/acs.langmuir.5b04562] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Cell membranes possess a complex three-dimensional architecture, including nonrandom lipid lateral organization within the plane of a bilayer leaflet, and compositional asymmetry between the two leaflets. As a result, delineating the membrane structure-function relationship has been a highly challenging task. Even in simplified model systems, the interactions between bilayer leaflets are poorly understood, due in part to the difficulty of preparing asymmetric model membranes that are free from the effects of residual organic solvent or osmotic stress. To address these problems, we have modified a technique for preparing asymmetric large unilamellar vesicles (aLUVs) via cyclodextrin-mediated lipid exchange in order to produce tensionless, solvent-free aLUVs suitable for a range of biophysical studies. Leaflet composition and structure were characterized using isotopic labeling strategies, which allowed us to avoid the use of bulky labels. NMR and gas chromatography provided precise quantification of the extent of lipid exchange and bilayer asymmetry, while small-angle neutron scattering (SANS) was used to resolve bilayer structural features with subnanometer resolution. Isotopically asymmetric POPC vesicles were found to have the same bilayer thickness and area per lipid as symmetric POPC vesicles, demonstrating that the modified exchange protocol preserves native bilayer structure. Partial exchange of DPPC into the outer leaflet of POPC vesicles produced chemically asymmetric vesicles with a gel/fluid phase-separated outer leaflet and a uniform, POPC-rich inner leaflet. SANS was able to separately resolve the thicknesses and areas per lipid of coexisting domains, revealing reduced lipid packing density of the outer leaflet DPPC-rich phase compared to typical gel phases. Our finding that a disordered inner leaflet can partially fluidize ordered outer leaflet domains indicates some degree of interleaflet coupling, and invites speculation on a role for bilayer asymmetry in modulating membrane lateral organization.
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Affiliation(s)
- Frederick A. Heberle
- Biology and Soft Matter Division, Joint Institute for
Neutron Sciences, and Biosciences Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
- E-mail:
| | - Drew Marquardt
- Institute
of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
- E-mail:
| | - Milka Doktorova
- Tri-Institutional
PhD Program in Computational Biology and Medicine, Weill Cornell Medical College, New York, New York 10065, United States
- Department
of Molecular Biology and Genetics, Cornell
University, Ithaca, New York 14853, United
States
| | - Barbara Geier
- Institute
of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
| | - Robert F. Standaert
- Biology and Soft Matter Division, Joint Institute for
Neutron Sciences, and Biosciences Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
- Department of Biochemistry and Cellular
& Molecular Biology, and Department of
Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Peter Heftberger
- Institute
of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
| | - Benjamin Kollmitzer
- Institute
of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
| | - Jonathan D. Nickels
- Biology and Soft Matter Division, Joint Institute for
Neutron Sciences, and Biosciences Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Robert
A. Dick
- Department
of Molecular Biology and Genetics, Cornell
University, Ithaca, New York 14853, United
States
| | - Gerald W. Feigenson
- Department
of Molecular Biology and Genetics, Cornell
University, Ithaca, New York 14853, United
States
| | - John Katsaras
- Biology and Soft Matter Division, Joint Institute for
Neutron Sciences, and Biosciences Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
- Department of Biochemistry and Cellular
& Molecular Biology, and Department of
Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Erwin London
- Department
of Biochemistry and Cell Biology, Stony
Brook University, Stony Brook, New York 11794, United States
| | - Georg Pabst
- Institute
of Molecular Biosciences, Biophysics Division, NAWI Graz, University of Graz, Graz 8010, Austria
- BioTechMed-Graz, Graz 8010, Austria
- E-mail:
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32
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Ackerman DG, Feigenson GW. Effects of Transmembrane α-Helix Length and Concentration on Phase Behavior in Four-Component Lipid Mixtures: A Molecular Dynamics Study. J Phys Chem B 2016; 120:4064-77. [PMID: 27081858 DOI: 10.1021/acs.jpcb.6b00611] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We used coarse-grained molecular dynamics simulations to examine the effects of transmembrane α-helical WALP peptides on the behavior of four-component lipid mixtures. These mixtures contain a high-melting temperature (high-Tm) lipid, a nanodomain-inducing low-Tm lipid, a macrodomain-inducing low-Tm lipid and cholesterol to model the outer leaflet of cell plasma membranes. In a series of simulations, we incrementally replace the nanodomain-inducing low-Tm lipid by the macrodomain-inducing low-Tm lipid and measure how lipid and phase properties are altered by the addition of WALPs of different length. Regardless of the ratio of the two low-Tm lipids, shorter WALPs increase domain size and all WALPs increase domain alignment between the two leaflets. These effects are smallest for the longest WALP tested, and increase with increasing WALP concentration. Thus, our simulations explain the experimental observation that WALPs induce macroscopic domains in otherwise nanodomain-forming lipid-only mixtures (unpublished). Since the cell plasma membrane contains a large fraction of transmembrane proteins, these findings link the behavior of lipid-only model membranes in vitro to phase behavior in vivo.
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Affiliation(s)
- David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University , Ithaca, New York 14853, United States
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University , Ithaca, New York 14853, United States
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Mudgal S, Keresztes I, Feigenson GW, Rizvi S. Controlling the taste receptor accessible structure of rebaudioside A via binding to bovine serum albumin. Food Chem 2016; 197:84-91. [DOI: 10.1016/j.foodchem.2015.10.064] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 09/20/2015] [Accepted: 10/14/2015] [Indexed: 11/30/2022]
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34
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Doktorova M, Dick R, Heberle FA, Feigenson GW, Vogt VM. Cholesterol Promotes the Peripheral Binding of Retroviral Proteins to Lipid Bilayers. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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35
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Doktorova M, Feigenson GW, Weinstein H. The Interaction of Proteins with Asymmetric Lipid Bilayers. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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36
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Tsai WC, Feigenson GW. Line Tension and Phase Separation of a Four-Component Phospholipid Bilayer. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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37
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Enoki TA, Kim S, Heberle FA, Feigenson GW. Partition Coefficient of a Transmembrane Peptide, between Lo and Ld Phases: Does the Peptide Distinguish Macro from Nano Domains? Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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38
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Konyakhina TM, Feigenson GW. Phase diagram of a polyunsaturated lipid mixture: Brain sphingomyelin/1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine/cholesterol. Biochim Biophys Acta 2015; 1858:153-61. [PMID: 26525664 DOI: 10.1016/j.bbamem.2015.10.016] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Revised: 09/28/2015] [Accepted: 10/21/2015] [Indexed: 12/17/2022]
Abstract
Phospholipids having a polyunsaturated acyl chain are abundant in biological membranes, but their behavior in lipid mixtures is difficult to study. Here we elucidate the nature of such mixtures with this report of the first ternary phase diagram containing the polyunsaturated lipid SDPC in mixtures of BSM/SDPC/Chol (brain sphingomyelin/1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine/cholesterol). These mixtures show coexisting macroscopic liquid-disordered (Ld) and liquid-ordered (Lo) phase separation, with phase boundaries determined by FRET and by fluorescence microscopy imaging of giant unilamellar vesicles (GUVs). Surprisingly, SDPC mixes with BSM/Chol similarly to how DOPC and POPC mix with BSM/Chol. Notably, intermediate states are produced within the Ld+Lo liquid-liquid immiscibility region upon addition of fourth component POPC. These mixtures of BSM/SDPC/POPC/Chol exhibit nanoscopic Ld+Lo domains over a very large volume of composition space, possibly because Ld/Lo line tension is not high.
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Affiliation(s)
- Tatyana M Konyakhina
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA.
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40
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Ackerman DG, Feigenson GW. Multiscale modeling of four-component lipid mixtures: domain composition, size, alignment, and properties of the phase interface. J Phys Chem B 2015; 119:4240-50. [PMID: 25564922 DOI: 10.1021/jp511083z] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Simplified lipid mixtures are often used to model the complex behavior of the cell plasma membrane. Indeed, as few as four components-a high-melting lipid, a nandomain-inducing low-melting lipid, a macrodomain-inducing low-melting lipid, and cholesterol (chol)-can give rise to a wide range of domain sizes and patterns that are highly sensitive to lipid compositions. Although these systems are studied extensively with experiments, the molecular-level details governing their phase behavior are not yet known. We address this issue by using molecular dynamics simulations to analyze how phase separation evolves in a four-component system as it transitions from small domains to large domains. To do so, we fix concentrations of the high-melting lipid 16:0,16:0-phosphatidylcholine (DPPC) and chol, and incrementally replace the nanodomain-inducing low-melting lipid 16:0,18:2-PC (PUPC) by the macrodomain-inducing low-melting lipid 18:2,18:2-PC (DUPC). Coarse-grained simulations of this four-component system reveal that lipid demixing increases as the amount of DUPC increases. Additionally, we find that domain size and interleaflet alignment change sharply over a narrow range of replacement of PUPC by DUPC, indicating that intraleaflet and interleaflet behaviors are coupled. Corresponding united atom simulations show that only lipids within ∼2 nm of the phase interface are significantly perturbed regardless of domain composition or size. Thus, whereas the fraction of interface-perturbed lipids is negligible for large domains, it is significant for smaller ones. Together, these results reveal characteristic traits of bilayer thermodynamic behavior in four-component mixtures, and provide a baseline for investigation of the effects of proteins and other lipids on membrane phase properties.
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Affiliation(s)
- David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
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41
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Wickramasinghe SP, Ackerman DG, Feigenson GW. Appearance of Modulated Bilayer Morphology for Coexisting LD and LO Phases is Correlated with Line Tension. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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42
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Weiner MD, Feigenson GW. Coarse Grained Molecular Dynamics Simulations to Study Asymmetric Membranes. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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43
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Ackerman DG, Feigenson GW. The Effects of Walp Peptides on Phase Behavior in Quaternary Lipid Mixtures: A Molecular Dynamics Study. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.1334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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44
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Amazon JJ, Feigenson GW. Lattice simulations of phase morphology on lipid bilayers: renormalization, membrane shape, and electrostatic dipole interactions. Phys Rev E Stat Nonlin Soft Matter Phys 2014; 89:022702. [PMID: 25353504 PMCID: PMC4391078 DOI: 10.1103/physreve.89.022702] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Indexed: 06/03/2023]
Abstract
When liquid phases coexist at equilibrium but are not driven to minimize domain interfacial contact energy, the resulting patterns of phase domains can have important implications for living cells. In this study we explore some of the interactions and conditions that produce the stable patterned phases that are observed in model lipid mixtures. By use of Monte Carlo simulations we find that background curvature is important for the formation of patterned (modulated) phases. The interactions that stabilize nanoscopic phase separation are still not well understood. We show that inclusion of an electrostatic dipole repulsion with decay lengths as short as two to four lipid diameters can break up domains at the nanometer scale and that the location of the miscibility critical point is sensitive to this interaction. The use of a coarse-grained simulation raises questions about comparing parameters in simulations performed at different length scales. Using renormalization group techniques we show how to reconcile this problem, treating line tension as a running coupling constant.
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Affiliation(s)
- Jonathan J Amazon
- Field of Biophysics, Cornell University, Ithaca, New York 14850, USA
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45
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Doktorova M, Heberle FA, Goh SL, Standaert RF, Katsaras J, Feigenson GW. Hybrid and Nonhybrid Lipids Exert Common Effects on Membrane Raft Size and Morphology. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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46
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Ackerman DG, Feigenson GW. Multiscale Modeling of Four Component Lipid Mixtures: Coarse Grained and United Atom Simulations Reveal Trends in Phase Separation. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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47
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Heberle FA, Petruzielo RS, Pan J, Drazba P, Kucerka N, Standaert RF, Feigenson GW, Katsaras J. Bilayer Thickness Mismatch Controls Domain Size in Model Membranes. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1686] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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48
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Heberle FA, Doktorova M, Goh SL, Standaert RF, Katsaras J, Feigenson GW. Hybrid and nonhybrid lipids exert common effects on membrane raft size and morphology. J Am Chem Soc 2013; 135:14932-5. [PMID: 24041024 DOI: 10.1021/ja407624c] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nanometer-scale domains in cholesterol-rich model membranes emulate lipid rafts in cell plasma membranes (PMs). The physicochemical mechanisms that maintain a finite, small domain size are, however, not well understood. A special role has been postulated for chain-asymmetric or hybrid lipids having a saturated sn-1 chain and an unsaturated sn-2 chain. Hybrid lipids generate nanodomains in some model membranes and are also abundant in the PM. It was proposed that they align in a preferred orientation at the boundary of ordered and disordered phases, lowering the interfacial energy and thus reducing domain size. We used small-angle neutron scattering and fluorescence techniques to detect nanoscopic and modulated liquid phase domains in a mixture composed entirely of nonhybrid lipids and cholesterol. Our results are indistinguishable from those obtained previously for mixtures containing hybrid lipids, conclusively showing that hybrid lipids are not required for the formation of nanoscopic liquid domains and strongly implying a common mechanism for the overall control of raft size and morphology. We discuss implications of these findings for theoretical descriptions of nanodomains.
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Affiliation(s)
- Frederick A Heberle
- Biology and Soft Matter and §Biosciences Divisions, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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49
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Konyakhina TM, Wu J, Mastroianni JD, Heberle FA, Feigenson GW. Phase diagram of a 4-component lipid mixture: DSPC/DOPC/POPC/chol. Biochim Biophys Acta 2013; 1828:2204-14. [PMID: 23747294 DOI: 10.1016/j.bbamem.2013.05.020] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 05/20/2013] [Accepted: 05/22/2013] [Indexed: 11/15/2022]
Abstract
We report the first 4-component phase diagram for the lipid bilayer mixture, DSPC/DOPC/POPC/chol (distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has macroscopic Ld+Lo phase domains, clearly shows that all phase boundaries determined for the 3-component mixture containing DOPC transition smoothly into the boundaries for the 3-component mixture containing POPC, which has nanoscopic phase domains of Ld+Lo. Our studies start from two published ternary phase diagrams, and show how these can be combined into a quaternary phase diagram by study of a few hundred samples of intermediate compositions.
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Key Words
- 1,1′-didodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate
- 1,1′-dieicosanyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate
- 1,2-Dilauroyl-sn-glycero-3-phosphocholine
- 1,2-Dioleoyl-sn-glycero-3-phosphocholine
- 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine
- 1,2-Distearoyl-sn-glycero-3-phosphocholine
- 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine
- 1-Stearoyl-2-oleoyl-sn-glycero-3-phosphocholine
- 2-(4,4-Difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine
- 3-Dye method
- 4-Component lipid phase diagram
- BoDIPY-PC
- C12:0-DiI
- C20:0-DiI
- Chol
- Cholesterol
- Competing interaction
- DHE
- DLPC
- DOPC
- DPPC
- DSPC
- Ergosta-5,7,9(11),22-tetraen-3β-ol
- FRET
- Förster resonance energy transfer
- GUV
- Giant unilamellar vesicle
- LHS
- Left hand side refers to left side of phase diagram, i.e. at lower χ(DSPC)
- Lipid raft
- Modulated phase
- PC
- POPC
- Phosphatidylcholine
- Quaternary phase diagram
- REE
- RHS
- RRE
- RSE
- Rapid solvent exchange
- Region of enhanced efficiency
- Region of reduced efficiency
- Right hand side, refers to right side of phase diagram, i.e.,, at higher χ(DSPC)
- SAE
- SM
- SOPC
- Sensitized acceptor emission
- Sphingomyelin
- T1–T6
- TLC
- TOE
- Thin-layer chromatography
- Trajectories 1–6. bSM, sphingomyelin derived from porcine brain
- Trp-Oleoyl Ester, N-oleoyl-dl-tryptophan ethyl ester
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Affiliation(s)
- Tatyana M Konyakhina
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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50
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Ackerman DG, Heberle FA, Feigenson GW. Limited perturbation of a DPPC bilayer by fluorescent lipid probes: a molecular dynamics study. J Phys Chem B 2013; 117:4844-52. [PMID: 23548205 DOI: 10.1021/jp400289d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The properties of lipid bilayer nanometer-scale domains could be crucial for understanding cell membranes. Fluorescent probes are often used to study bilayers, yet their effects on host lipids are not well understood. We used molecular dynamics simulations to investigate perturbations in a fluid DPPC bilayer upon incorporation of three indocarbocyanine probes: DiI-C18:0, DiI-C18:2, or DiI-C12:0. We find a 10-12% decrease in chain order for DPPC in the solvation shell nearest the probe but smaller effects in subsequent shells, indicating that the probes significantly alter only their local environment. We also observe order perturbations of lipids directly across from the probe in the opposite leaflet. Additionally, the DPPC headgroup phosphorus-to-nitrogen vector of lipids nearest the probe exhibits preferential orientation pointing away from the DiI. We show that, while DiI probes perturb their local environment, they do not strongly influence the average properties of "nanoscopic" domains containing a few hundred lipids.
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Affiliation(s)
- David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, United States
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