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He H, Rahimi K, Zhong M, Mourran A, Luebke DR, Nulwala HB, Möller M, Matyjaszewski K. Cubosomes from hierarchical self-assembly of poly(ionic liquid) block copolymers. Nat Commun 2017; 8:14057. [PMID: 28091605 PMCID: PMC5241804 DOI: 10.1038/ncomms14057] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 11/24/2016] [Indexed: 01/29/2023] Open
Abstract
Cubosomes are micro- and nanoparticles with a bicontinuous cubic two-phase structure, reported for the self-assembly of low molecular weight surfactants, for example, lipids, but rarely formed by polymers. These objects are characterized by a maximum continuous interface and high interface to volume ratio, which makes them promising candidates for efficient adsorbents and host-guest applications. Here we demonstrate self-assembly to nanoscale cuboidal particles with a bicontinuous cubic structure by amphiphilic poly(ionic liquid) diblock copolymers, poly(acrylic acid)-block-poly(4-vinylbenzyl)-3-butyl imidazolium bis(trifluoromethylsulfonyl)imide, in a mixture of tetrahydrofuran and water under optimized conditions. Structure determining parameters include polymer composition and concentration, temperature, and the variation of the solvent mixture. The formation of the cubosomes can be explained by the hierarchical interactions of the constituent components. The lattice structure of the block copolymers can be transferred to the shape of the particle as it is common for atomic and molecular faceted crystals.
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Affiliation(s)
- Hongkun He
- Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
| | - Khosrow Rahimi
- DWI-Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, Aachen 52074, Germany
| | - Mingjiang Zhong
- Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, USA
| | - Ahmed Mourran
- DWI-Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, Aachen 52074, Germany
| | - David R Luebke
- National Energy Technology Laboratory, United States Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236, USA
| | - Hunaid B Nulwala
- Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.,National Energy Technology Laboratory, United States Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236, USA
| | - Martin Möller
- DWI-Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, Aachen 52074, Germany
| | - Krzysztof Matyjaszewski
- Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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Debnath A, Thakkar FM, Maiti PK, Kumaran V, Ayappa KG. Laterally structured ripple and square phases with one and two dimensional thickness modulations in a model bilayer system. SOFT MATTER 2014; 10:7630-7637. [PMID: 25130991 DOI: 10.1039/c4sm01031k] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Molecular dynamics simulations of bilayers in a surfactant/co-surfactant/water system with explicit solvent molecules show formation of topologically distinct gel phases depending upon the bilayer composition. At low temperatures, the bilayers transform from the tilted gel phase, Lβ', to the one dimensional (1D) rippled, Pβ' phase as the surfactant concentration is increased. More interestingly, we observe a two dimensional (2D) square phase at higher surfactant concentration which, upon heating, transforms to the gel Lβ' phase. The thickness modulations in the 1D rippled and square phases are asymmetric in two surfactant leaflets and the bilayer thickness varies by a factor of ∼2 between maximum and minimum. The 1D ripple consists of a thinner interdigitated region of smaller extent alternating with a thicker non-interdigitated region. The 2D ripple phase is made up of two superimposed square lattices of maximum and minimum thicknesses with molecules of high tilt forming a square lattice translated from the lattice formed with the thickness minima. Using Voronoi diagrams we analyze the intricate interplay between the area-per-head-group, height modulations and chain tilt for the different ripple symmetries. Our simulations indicate that composition plays an important role in controlling the formation of low temperature gel phase symmetries and rippling accommodates the increased area-per-head-group of the surfactant molecules.
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Affiliation(s)
- Ananya Debnath
- Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, India.
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Abstract
Abstract
Cubosomes are lipid bilayer particles that can be formed by dispersing minimal surface-shaped infinite lipid bilayers in water. The structures of cubosomes of the D, G and P types of minimal surfaces are described by mathematical functions on the exponential scale, and the shape and internal structure of the calculated D-type cubosome is compared to electron microscopy studies, showing good correlation.
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Chapter 6 Salt‐Induced Morphological Transitions in Nonequimolar Catanionic Systems. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s1554-4516(09)09006-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Allan E, Hoischen C, Gumpert J. Chapter 1 Bacterial L‐Forms. ADVANCES IN APPLIED MICROBIOLOGY 2009; 68:1-39. [DOI: 10.1016/s0065-2164(09)01201-5] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Literature Alerts. J Microencapsul 2008. [DOI: 10.3109/02652049109071495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Ces O, Mulet X. Physical coupling between lipids and proteins: a paradigm for cellular control. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/sita.200500079] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Yang L, Fukuto M. Modulated phase of phospholipids with a two-dimensional square lattice. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:010901. [PMID: 16089928 DOI: 10.1103/physreve.72.010901] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Indexed: 05/03/2023]
Abstract
We report an observation of a modulated phase of phospholipids in which intrabilayer density modulations form an in-plane square lattice. Similar to the well-known ripple (P'(beta)) phase, this phase can be induced by either dehydration or cooling from the liquid crystalline (L(alpha)) phase. However, further lowering of hydration or temperature induces either an untilted straight-chain gel phase (L(beta)) , or the tilted L'(beta) phase after a brief appearance of the P'(beta) phase. The structural characteristics of this phase support the notion that the coupling between variations in local chain tilt and bilayer shape plays an important role in the formation of modulated phases.
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Affiliation(s)
- Lin Yang
- National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA
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Dommersnes PG, Fournier JB. The many-body problem for anisotropic membrane inclusions and the self-assembly of "saddle" defects into an "egg carton". Biophys J 2002; 83:2898-905. [PMID: 12496066 PMCID: PMC1302374 DOI: 10.1016/s0006-3495(02)75299-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
We calculate the many-body, nonpairwise interaction between N rigid, anisotropic membrane inclusions by modeling them as point-like constraints on the membrane's curvature tensor and by minimizing the membrane's curvature energy. Because multipolar distortions of higher-order decay on very short distances, our calculation gives the correct elastic interaction energy for inclusions separated by distances of the order of several times their size. As an application, we show by thermally equilibrating the many-body elastic energy using a Monte Carlo algorithm, that inclusions shaped as "saddles" attract each other and build an "egg-carton" structure. The latter is reminiscent of some patterns observed in membranes obtained from biological extracts, the origin of which is still mysterious.
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Affiliation(s)
- Paul G Dommersnes
- Department of Physics, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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Abstract
Freeze-fracture electron microscopy is especially useful for investigation of lipid structures by the advantageous fracture course within hydrophobic zones. Freezing is, on the other hand, a restriction because the structures of lamellar and non-lamellar phase states with disordered acyl chains (L(alpha), H(II,) cubic) are difficult to preserve. An important aspect of this method is therefore the lipid structure of phase states with ordered acyl chains (crystal, gel), and with a different degree of hydration. Freeze-fracture of pure lipid systems creates a valid representation of the structure of non-lamellar phases and of the general structure of the "lamellar" lipid bilayer, and lamellar phases with characteristic deformations (ripples, curvatures, plane sectors) can be identified. Fracture through the hydrophobic bilayer centre of biological membranes reveals characteristic protein components, the intramembraneous particles (IMPs). The lateral distribution of the IMPs is a helpful marker for fluid and rigid phase states, also without deformation of the lamella. The overall history and the present state of knowledge concerning the different structures revealed by the freeze-fracture and freeze-etch techniques in lipid systems, and to a limited extent in biological membranes, is reviewed, taking into account studies from our own laboratory.
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Affiliation(s)
- H W Meyer
- Institut für Ultrastrukturforschung, Klinikum der Friedrich-Schiller-Universität Jena, D-07740 Jena, Germany.
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Piotto SP. Novel mathematical description of surfactants macroaggregates. Colloids Surf A Physicochem Eng Asp 2001. [DOI: 10.1016/s0927-7757(00)00674-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Meyer HW, Semmler K, Rettig W, Pohle W, Ulrich AS, Grage S, Selle C, Quinn PJ. Hydration of DMPC and DPPC at 4 degrees C produces a novel subgel phase with convex-concave bilayer curvatures. Chem Phys Lipids 2000; 105:149-66. [PMID: 10823463 DOI: 10.1016/s0009-3084(00)00124-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Hydration of dimyristoyl- and dipalmitoylphosphatidylcholines at 4 degrees C results in the formation of a characteristic subgel phase designated Pcc. Examination of the phase by freeze-fracture electron microscopy shows convex-concave deformations of the planar bilayer which are of two types. A smaller type with a radius of curvature of about 20 nm predominates in DMPC, and a larger type with about 70 nm radii of curvatures dominates in DPPC. The Pcc phase can also be formed in samples hydrated at temperatures above the main phase transition if the dispersion is frozen slowly and subsequently incubated at 4 degrees C for several days. The subgel Pcc phase was distinguished from the subgel Lc phase by the temperature of transition, packing of the acyl chains on the basis of wide-angle X-ray diffraction, and 2H-NMR spectra characteristic of a 'solid-ordered' phase. Vibrational spectra of the carbonyl and phosphate regions are consistent with a partially reduced hydration state. The origin of the convex-concave bilayer deformation is believed to result from constraints imposed by limiting hydration of the headgroup and a frustration arising from the spontaneous curvature of both monolayers.
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Affiliation(s)
- H W Meyer
- Institut für Ultrastrukturforschung des Klinikums der Friedrich-Schiller-Universität Jena, Germany.
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Meyer HW, Bunjes H, Ulrich AS. Morphological transitions of brain sphingomyelin are determined by the hydration protocol: ripples re-arrange in plane, and sponge-like networks disintegrate into small vesicles. Chem Phys Lipids 1999; 99:111-23. [PMID: 10390835 DOI: 10.1016/s0009-3084(99)00029-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The phase transition of hydrated brain sphingomyelin occurs at around 35 degrees C, which is close to the physiological temperature. Freeze-fracture electron microscopy is used to characterize different gel state morphologies in terms of solid-ordered and liquid-ordered phase states, according to the occurrence of ripples and other higher-dimensional bilayer deformations. Evidently, the natural mixed-chain sphingomyelin does not assume the flat L beta, phase but instead the rippled P beta, phase, with symmetric and asymmetric ripples as well as macroripples and an egg-carton pattern, depending on the incubation conditions. An unexpected difference was observed between samples that are hydrated above and below the phase transition temperature. When the lipid is hydrated at low temperature, a sponge-like network of bilayers is formed in the gel state, next to some normal lamellae. The network loses its ripples during cold-incubation, which indicates the formation of a liquid-ordered (lo) gel phase. Ripples re-appear upon warming and the sponge-like network disintegrates spontaneously and irreversibly into small vesicles above the phase transition.
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Affiliation(s)
- H W Meyer
- Institut für Ultrastrukturforschung, Klinikums der Friedrich-Schiller-Universität Jena, Germany.
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Meyer HW, Westermann M, Stumpf M, Richter W, Ulrich AS, Hoischen C. Minimal radius of curvature of lipid bilayers in the gel phase state corresponds to the dimension of biomembrane structures "caveolae". J Struct Biol 1998; 124:77-87. [PMID: 9931276 DOI: 10.1006/jsbi.1998.4042] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Caveolae are membrane invaginations with a radius of curvature in the range of 40 nm for the bulb; 10-15 nm is the minimal radius for lipid bilayers in the liquid-crystalline Lalpha (liquid-disordered: ld) phase state. A minimal radius of 20-30 nm could be detected for the gel phase state by analysis of convex-concave bilayer deformations. Circular protrusions with a diameter in the range of only about 40 nm are closed by a flat lid, and those with diameters of 60 nm or more are closed by hemispherical caps. These structures are found primarily in phosphatidylcholine/sterol mixtures, where the gel phase state "liquid ordered" (lo) has been introduced. As a further example the mixture of dimyristoylphosphatidylcholine (DMPC) with an unusual sterol (diflucortolon-21-valerat) is presented. In the usual hydration at temperatures above the phase transition the deformation requires an incubation at 4 degrees C for several weeks or months to form. Using a low temperature hydration procedure (at 4 degrees C), surprisingly bilayers of pure DMPC and DPPC (dipalmitoylphosphatidylcholine) are found to deform in the same convex-concave manner, and this takes place within hours and days. The dependence on hydration protocol is also observed for formation of a sponge-like bilayer network with 30-35 nm radius of curvature in brain sphingomyelin and its mixtures with cholesterol. Caveolae are microdomains enriched in cholesterol and sphingomyelin and are simultaneously discussed to be in the lo state. Direct evidence by investigation of bilayers formed by the lipids isolated from caveolae is still lacking, but structures similar to caveolae which are in the gel phase state (very probably the lo state) are also formed by lipids extracted from bacterial membranes. A further analogy exists because both natural lipid mixtures (brain sphingomyelin and bacterial lipids) transform during heating from the curved bilayer structures into microvesicles above the phase transition. Internalization of caveolae is a process of vesicle formation.
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Affiliation(s)
- H W Meyer
- Institut für Ultrastrukturforschung des Klinikums, Friedrich-Schiller-Universität Jena, Jena, D-07740, Germany
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Brandenburg K, Richter W, Koch MH, Meyer HW, Seydel U. Characterization of the nonlamellar cubic and HII structures of lipid A from Salmonella enterica serovar Minnesota by X-ray diffraction and freeze-fracture electron microscopy. Chem Phys Lipids 1998; 91:53-69. [PMID: 9488999 DOI: 10.1016/s0009-3084(97)00093-5] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The aggregate structures of lipid A, the 'endotoxic principle' of bacterial lipopolysaccharide (LPS), from rough mutant Salmonella enterica sv. Minnesota R595 was analyzed at different water content, cation (Mg2+) concentration, and temperature applying synchrotron radiation X-ray diffraction and, in selected cases, freeze-fracture electron microscopy. The X-ray diffraction spectra prove the existence of different lamellar, mixed lamellar/cubic, various cubic, and inverted hexagonal (HII) structures depending on ambient conditions. The three mainly bicontinuous cubic phases Q224, Q229, and Q230 can be observed between 30 and 50 degrees C in narrow water and cation concentration ranges. Above 50 degrees C, Q212 an intermediate phase between bicontinuous and micellar is adopted. In freeze-fracture electron microscopic experiments, cubic structures of these symmetries are not readily detected, which can be understood in the light of changes in hydration during freezing and the metastability of these phases. However, 'lipidic particles' closely related to cubic phases are observed. Above 65-70 degrees C, the existence of the HII phase with hexagonal periodicities dH between 4.0 and 6.0 nm for different hydration states is shown using both techniques. Possible biological implications for the preference of lipid A for nonlamellar structures are discussed.
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Affiliation(s)
- K Brandenburg
- Research Center Borstel, Center for Medicine and Biosciences, Germany
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Klösgen B, Helfrich W. Cryo-transmission electron microscopy of a superstructure of fluid dioleoylphosphatidylcholine (DOPC) membranes. Biophys J 1997; 73:3016-29. [PMID: 9414216 PMCID: PMC1181207 DOI: 10.1016/s0006-3495(97)78330-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Using cryo-transmission electron microscopy, we have obtained abundant and reproducible evidence for a superstructure of dioleoylphosphatidylcholine (DOPC) bilayers. Dispersions of vesicles were prepared by gentle shaking of a 2% suspension of DOPC in water followed in part by extrusion through a porous technical membrane. Sampling and cryofixation took place at various times within 3 weeks after the preparation. From the micrographs we infer that the small fraction of vesicles enclosing one another develop passages (connections) between the bilayers. In contrast, the superstructure is basically a feature of disconnected membranes. Among its modifications are isolated membrane bends or folds and a grainy membrane texture with a minimal grain spacing of 4-6 nm. In the extruded dispersions the passages and the superstructure seem to be formed mostly within the first day. The fraction of smooth and unilamellar vesicles is large at all times and in all dispersions.
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Affiliation(s)
- B Klösgen
- Freie Universität Berlin, Fachbereich Physik, Germany.
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Meyer HW, Semmler K, Quinn PJ. The effect of sterols on structures formed in the gel/subgel phase state of dipalmitoylphosphatidylcholine bilayers. Mol Membr Biol 1997; 14:187-93. [PMID: 9491370 DOI: 10.3109/09687689709048181] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effect of cholesterol and lanosterol on the formation of structures in the gel/subgel phase of 1,2-dipalmitoylphosphatidylcholine was investigated using freeze-fracture electron microscopy and X-ray diffraction. Mixtures with up to 25 mol% sterol were analysed after annealing for between several days and some months at 4 degrees C. Bilayers of DPPC with 5 or 10 mol% sterol showed a domain structure in the gel state. There are rounded or lens-like and often inclined plates within less smooth either plane or striped bilayer areas. The stripes are formed by parallel lines separated by a distance of 30-60 nm. Parallel lines can be induced also in the less smooth but plane areas by warming up to 25 degrees C. X-ray diffraction showed two lamellar repeat spacings at 6.45 and 8.3 nm in both 5 and 10 mol% samples. The plates are interpreted as domains of (nearly) pure DPPC within the sterol containing bilayer. Stripes are present if the concentration of cholesterol is below a critical value (approx. 15 mol%). With time of incubation at 4 degrees C curved deformations appear in parts of the bilayers. Two main types are formed. The small type has a repeat distance of about 100 nm and the large type of about 400 nm. The curved deformations were progressively flattened by warming up to 25-32 degrees C with an accompanying reappearance of stripes but no plates. After prolonged annealing at 4 degrees C there is also the formation of regular ripples. It is concluded that in presence of 5 and 10 mol% sterol in bilayers of 1,2-dipalmitoy-phosphatidylcholine the immiscibility of gel phase and subgel phase changes during prolonged annealing at 4 degrees C. We assume a rearrangement of the molecules into a homogeneous phase state with liquid-ordered properties.
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Affiliation(s)
- H W Meyer
- Institute of Ultrastructure Research, Friedrich-Schiller-University Jena, Germany
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Abstract
Cell membranes can form cubic arrangements and there is evidence for the occurrence of periodic curvature in simple membranes. The periodicity of the bilayer implies a standing wave character of vibrational motions. It is proposed that the periodic curvature reflects a dominating mode of standing wave oscillations, with the different cubic bilayer structures representing alternative standing wave conformations of the bilayer. The wave motions in lamellar liquid-crystalline phases, as well as in vesicles and membranes, which lack lateral periodicity, are known to exhibit statistically distributed undulations. The standing wave character of conformational fluctuations of periodically curved membranes, on the other hand, results in an organisation in time and space. Calculated models of standing wave conformations of membranes are demonstrated, and functional aspects of such biomembranes are discussed.
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Affiliation(s)
- K Larsson
- Camurus Lipid Research, Ideon Science Park, Lund, Sweden
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MacKintosh FC. Internal structures in membranes: Ripples, hats, saddles, and egg cartons. Curr Opin Colloid Interface Sci 1997. [DOI: 10.1016/s1359-0294(97)80080-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Hoischen C, Gura K, Luge C, Gumpert J. Lipid and fatty acid composition of cytoplasmic membranes from Streptomyces hygroscopicus and its stable protoplast-type L form. J Bacteriol 1997; 179:3430-6. [PMID: 9171384 PMCID: PMC179132 DOI: 10.1128/jb.179.11.3430-3436.1997] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cells of an L-form strain of Streptomyces hygroscopicus have been grown for 20 years without a cell wall. Their cytoplasmic membranes have high stability and an unusual structural polymorphism. To clarify the importance of the lipid components for these membrane properties, a comparative analysis has been carried out with purified membranes of L-form cells, of parent vegetative hyphal cells (N-form cells), and of protoplasts derived from the latter. The phospholipid classes and fatty acids were determined by thin-layer chromatography (TLC), two-dimensional TLC, high-performance liquid chromatography, gas chromatography, and mass spectrometry. The qualitative compositions of cardiolipin (CL), lyso-cardiolipin (LCL), phosphatidylethanolamine (PE1 and PE2), lyso-phosphatidylethanolamine (LPE), phosphatidylinositolmannoside (PIM), phosphatidic acid (PA), dilyso-cardiolipin-phosphatidylinositol (DLCL-PI), and the 13 main fatty acids were the same in the three membrane types. However, significant quantitative differences were observed in the L-form membrane. They consist of a three- to fourfold-higher content of total, extractable lipids, 20% more phospholipids, an increased content of CL and PIM, and a reduced amount of the component DLCL-PI. Furthermore, the L-form membrane is characterized by a higher content of branched anteiso 15:0 and anteiso 17:0 fatty acids compared to that of the membranes of the walled vegetative cells. These fatty acids have lower melting points than their straight and iso-branched counterparts and make the membrane more fluid. The phospholipid composition of the protoplast membrane differs quantitatively from that of the N form and the L form. Whereas the phospholipid classes are mostly similar to that of the N form, the fatty acid pattern tends to be closer to that of the L-form membrane. The membranes of both the L-form cells and the protoplasts need to be more fluid because of their spherical cell shape and higher degree of curvature compared with N-form membranes.
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Affiliation(s)
- C Hoischen
- Institut für Molekulare Biotechnologie, Jena, Germany
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Meyer HW, Richter W, Brezesinski G. Convex-concave curvatures in bilayers of dipalmitoylphosphatidylcholine and cholesterol induced by amphotericin B/deoxycholate after prolonged storage. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1190:9-19. [PMID: 8110823 DOI: 10.1016/0005-2736(94)90029-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Freeze-fracture investigations on the influence of amphotericin B/deoxycholate on multilamellar vesicles (MLV) of DPPC containing cholesterol have revealed a new phase structure. Alternating convex and concave curvatures are observed after storage of the vesicles at temperatures below 25 degrees C for at least 4 weeks. Three types of these patterns occur, a small-dimensional (repeat distance approximately 100 nm), an intermediate-dimensional (repeat distance approximately 400 nm) and a large-dimensional (repeat distance approximately 700 nm). The types can be formed on the same bilayer side by side. Additionally, the types differ in the morphology of the tops. In the case of the small-dimensional type the shape of the top can be described as a circular flat plane or opening and in the other cases as a hemispherical cap. The large dimensional type differs from the others by involvement of bilayer stacks. The formation of this new phase after prolonged storage could be confirmed by DSC measurements. The new structure can be explained in the framework of bicontinuous cubic phases and periodically curved bilayer structures. From the electron micrographs a lo (liquid ordered) phase is suggested.
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Affiliation(s)
- H W Meyer
- Institut für Ultrastrukturforschung Klinikums der Friedrich-Schiller-Universität Jena, Germany
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Norris V, Manners B. Deformations in the cytoplasmic membrane of Escherichia coli direct the synthesis of peptidoglycan. The hernia model. Biophys J 1993; 64:1691-700. [PMID: 8369402 PMCID: PMC1262504 DOI: 10.1016/s0006-3495(93)81541-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
To explain the growth of the Gram-negative envelope and in particular how it could be strengthened where it is weakest, we propose in the hernia model that local weakening of the peptidoglycan sacculus allows turgor pressure to cause the envelope to bulge outwards in a hernia; the consequent local alteration in the radius of curvature of the cytoplasmic membrane causes local alterations in phospholipid structure and composition that determine both the synthesis and hydrolysis of peptidoglycan. This proposal is supported by evidence that phospholipid composition determines the activity of phospho-N-acetylmuramic acid pentapeptide translocase, UDP-N-acetylglucosamine:N-acetylmuramic acid-(pentapeptide)-P-P-bactoprenyl-N-acetylglucosamine transferase, bactoprenyl phosphate phosphokinase, and N-acetylmuramyl-L-alanine amidase. We also propose that the shape of Escherichia coli is maintained by contractile proteins acting at the hernia. Given the universal importance of membranes, these proposals have implications for the determination of shape in eukaryotic cells.
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Affiliation(s)
- V Norris
- Department of Microbiology, University of Leicester, UK
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