Key Role of Polyphosphoinositides in Dynamics of Fusogenic Nuclear Membrane Vesicles

The role of phosphoinositides has been thoroughly described in many signalling and membrane trafficking events but their function as modulators of membrane structure and dynamics in membrane fusion has not been investigated. We have reconstructed models that mimic the composition of nuclear envelope precursor membranes with naturally elevated amounts of phosphoinositides. These fusogenic membranes (membrane vesicle 1(MV1) and nuclear envelope remnants (NER) are critical for the assembly of the nuclear envelope. Phospholipids, cholesterol, and polyphosphoinositides, with polyunsaturated fatty acid chains that were identified in the natural nuclear membranes by lipid mass spectrometry, have been used to reconstruct complex model membranes mimicking nuclear envelope precursor membranes. Structural and dynamic events occurring in the membrane core and at the membrane surface were monitored by solid-state deuterium and phosphorus NMR. “MV1-like” (PC∶PI∶PIP∶PIP2, 30∶20∶18∶12, mol%) membranes that exhibited high levels of PtdIns, PtdInsP and PtdInsP2 had an unusually fluid membrane core (up to 20% increase, compared to membranes with low amounts of phosphoinositides to mimic the endoplasmic reticulum). “NER-like” (PC∶CH∶PI∶PIP∶PIP2, 28∶42∶16∶7∶7, mol%) membranes containing high amounts of both cholesterol and phosphoinositides exhibited liquid-ordered phase properties, but with markedly lower rigidity (10–15% decrease). Phosphoinositides are the first lipids reported to counterbalance the ordering effect of cholesterol. At the membrane surface, phosphoinositides control the orientation dynamics of other lipids in the model membranes, while remaining unchanged themselves. This is an important finding as it provides unprecedented mechanistic insight into the role of phosphoinositides in membrane dynamics. Biological implications of our findings and a model describing the roles of fusogenic membrane vesicles are proposed

Sequestering Hydrated Fluoride in a Three-Dimensional Non-Interpenetrated Octahedral Coordination Polymer via a Single-Crystal-to-Single-Crystal Fashion

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Aminosilane/Oleic Acid Vesicles as Model Membranes of Protocells

Oleic acid vesicles represent good models of membrane protocells that could have existed in prebiotic times. Here, we report the formation, growth polymorphism, and dynamics of oleic acid spherical vesicles (1-10 μm), stable elongated vesicles (>50 μm length; 1-3 μm diameter), and chains of vesicles (pearl necklaces, >50 μm length; 1-3 μm diameter) in the presence of aminopropyl triethoxysilane and guanidine hydrochloride. These vesicles exhibit a remarkable behavior with temperature: spherical vesicles only are observed when keeping the sample at 4 °C for 2 h, and self-aggregated spherical vesicles occur upon freezing/unfreezing (-20/20 °C) samples. Rather homogeneous elongated vesicles are reformed upon heating samples at 80 °C. The phenomenon is reversible through cycles of freezing/heating or cooling/heating of the same sample. Deuterium NMR evidences a chain packing rigidity similar to that of phospholipid bilayers in cellular biomembranes. We expect these bilayered vesicles to be surrounded by a layer of aminosilane oligomers, offering a variant model for membrane protocells

Nucleotide-Promoted Morphogenesis in Amphiphile Assemblies: Kinetic Control of Micrometric Helix Formation †

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Industrial Crops and Products

(E)-(R)-4-Thujanol present in thyme essential oils is an important aromatic ingredient for food, cosmetic and pharmaceutical applications. Until now, its extraction was challenging due to its low content in classical aromatic plants such as thyme or marjoram. Although this molecule is synthetically available, there is no production on an industrial scale because of very time-consuming and expensive chemical processes. We report here for the first time a new eco-responsible method to produce (E)-(R)-4-thujanol crystals on a kilogram scale. This new milestone is based on 2 fundamental research gaps: i) the selection of a wild thyme (Thymus vulgaris) for its high content of (E)-(R)-4-thujanol and its careful harvesting in the hills of French Provence and ii) a steam distillation producing an organic aromatic oil which aggregates spontaneously due to a favorable amphipathic partition at the air-water interface. Gas chromatography revealed a composition made of (E)-(R)-4-thujanol (76%), thymol (5%), β-myrcene (2,8%) and other minor monoterpenes. The white aggregate submitted to a cycle of sublimation/crystallization, led to accumulating translucent fibers made of (E)-(R)-4-thujanol (98%). X-ray diffraction unambiguously demonstrated that crystals of (E)-(R)-4-thujanol form a trimer (monoclinic asymmetric (C2)) unit composed of three independent (E)-(R)-4-thujanol molecules. The trimer is further organized into a chiral P-type supramolecular helix of trimers through a network of intermolecular hydrogen bonds. This study is based on the cheap, easy and eco-responsible kilogram production of (E)-(R)-4-thujanol crystals may open up new opportunities for the flavor, fragrance and pharmaceutical industries. Fibers of (E)-(R)-4-thujanol may also have applications as bio-active fibrous assemblies

Biophysical Insight on the Membrane Insertion of an Arginine-Rich Cell-Penetrating Peptide

International audienceCell-penetrating peptides (CPPs) are short peptides that can translocate and transport cargoes into the intracellular milieu by crossing biological membranes. The mode of interaction and internalization of cell-penetrating peptides has long been controversial. While their interaction with anionic membranes is quite well understood, the insertion and behavior of CPPs in zwitterionic membranes, a major lipid component of eukaryotic cell membranes, is poorly studied. Herein, we investigated the membrane insertion of RW16 into zwitterionic membranes, a versatile CPP that also presents antibacterial and antitumor activities. Using complementary approaches, including NMR spectroscopy, fluorescence spectroscopy, circular dichroism, and molecular dynamic simulations, we determined the high-resolution structure of RW16 and measured its membrane insertion and orientation properties into zwitterionic membranes. Altogether, these results contribute to explaining the versatile properties of this peptide toward zwitterionic lipids

The unprecedented membrane deformation of the human nuclear envelope, in a magnetic field, indicates formation of nuclear membrane invaginations

International audienceHuman nuclear membrane (hNM) invaginations are thought to be crucial in fusion, fission and remodeling of cells and present in many human diseases. There is however little knowledge, if any, about their lipid composition and dynamics. We therefore isolated nuclear envelope lipids from human kidney cells, analyzed their composition and determined the membrane dynamics after resuspension in buffer. The hNM lipid extract was composed of a complex mixture of phospholipids, with high amounts of phosphatidylcholines, phosphatidylinositols (PI) and cholesterol. hNM dynamics was determined by solid-state NMR and revealed that the lamellar gel-to-fluid phase transition occurs below 0 °C, reflecting the presence of elevated amounts of unsaturated fatty acid chains. Fluidity was higher than the plasma membrane, illustrating the dual action of Cholesterol (ordering) and PI lipids (disordering). The most striking result was the large magnetic field-induced membrane deformation allowing to determine the membrane bending elasticity, a property related to hydrodynamics of cells and organelles. Human Nuclear Lipid Membranes were at least two orders of magnitude more elastic than the classical plasma membrane suggesting a physical explanation for the formation of nuclear membrane invaginations

High-Temperature Behavior of Early Life Membrane Models

International audienceOrigin of life scenarios generally assume an onset of cell formation in terrestrial hot springs or in the deep oceans close to hot vents, where energy was available for non-enzymatic reactions. Membranes of the protocells had therefore to withstand extreme conditions different from what is found on Earth's surface today. We present here an exhaustive study of temperature stability up to 80 °C of vesicles formed by a mixture of short-chain fatty acids and alcohols, which are plausible candidates for membranes permitting the compartmentalization of protocells. We confirm that the presence of alcohol has a strong structuring and stabilizing impact on the lamellar structures. Moreover and most importantly, at high temperature (> 60 °C) we observe a conformational transition in the vesicles, which results from vesicular fusion. Because all the most likely environments for the origin of life involve high temperature, our results imply the need to take into account such a transition and its effect when studying a protomembrane model's behaviour