Superresolution microscopy reveals partial preassembly and subsequent bending of the clathrin coat during endocytosis

Eukaryotic cells use clathrin-mediated endocytosis to take up a large range of extracellular cargos. During endocytosis, a clathrin coat forms on the plasma membrane, but it remains controversial when and how it is remodeled into a spherical vesicle. Here, we use 3D superresolution microscopy to determine the precise geometry of the clathrin coat at endocytic sites. Through pseudo-temporal sorting, we determine the average trajectory of clathrin remodeling during endocytosis and find that clathrin coats assemble first on flat membranes to ~50% of the coat area, before they become rapidly and continuously bent. We introduce a mathematical model that assumes a positive feedback for curvature generation of the clathrin coat. This Cooperative Curvature Model agrees excellently with experimental data in three cell lines, and likely describes a general pathway for clathrin coat remodeling during endocytosis.

Ionotropic Gelation of Chitosan Flat Structures and Potential Applications

The capability of some polymers, such as chitosan, to form low cost gels under mild conditions is of great application interest. Ionotropic gelation of chitosan has been used predominantly for the preparation of gel beads for biomedical application. Only in the last few years has the use of this method been extended to the fabrication of chitosan-based flat structures. Herein, after an initial analysis of the major applications of chitosan flat membranes and films and their usual methods of synthesis, the process of ionotropic gelation of chitosan and some recently proposed novel procedures for the synthesis of flat structures are presented.

Preparation of Semipermeable polyvinylpyrrolidone Membranes and Study Their Chemical, Physical and Mechanical Properties: تحضير أغشية نصف نفوذة من بولي فينيل بيروليدون ودراسة خواصها الكيميائية والفيزيائية والميكانيكية

Been we had prepared three semipermeable membranes with different concentration of polyvinylpyrrolidone by the phase inversion process. This way is a basic method to get flat membranes. the membranes were tested for chemical properties (pH rang), and physical properties (viscosity and porosity), and mechanical properties (tensile strength and strain), The results showed that polyvinylpyrrolidone (8%, 12%,15%) membrane having the higher pH range, while the polyvinylpyrrolidone (15%) membrane having the higher tensile strength and strain, but it was having the lowest porosity, viscosity was measured in low concentration was showed that polyvinylpyrrolidone (2%) solution having the higher viscosity.

Biological lipid nanotubes and their potential role in evolution

The membrane of cells and organelles are highly deformable fluid interfaces, and can take on a multitude of shapes. One distinctive and particularly interesting property of biological membranes is their ability to from long and uniform nanotubes. These nanoconduits are surprisingly omnipresent in all domains of life, from archaea, bacteria, to plants and mammals. Some of these tubes have been known for a century, while others were only recently discovered. Their designations are different in different branches of biology, e.g. they are called stromule in plants and tunneling nanotubes in mammals. The mechanical transformation of flat membranes to tubes involves typically a combination of membrane anchoring and external forces, leading to a pulling action that results in very rapid membrane nanotube formation – micrometer long tubes can form in a matter of seconds. Their radius is set by a mechanical balance of tension and bending forces. There also exists a large class of membrane nanotubes that form due to curvature inducing molecules. It seems plausible that nanotube formation and functionality in plants and animals may have been inherited from their bacterial ancestors during endosymbiotic evolution. Here we attempt to connect observations of nanotubes in different branches of biology, and outline their similarities and differences with the aim of providing a perspective on their joint functions and evolutionary origin.

Membrane Shape Remodeling by Protein Crowding

The steric repulsion between proteins on biological membranes is one of the most generic mechanisms that cause membrane shape changes. We present a minimal model where a spontaneous curvature is induced by steric repulsion between membrane-associated proteins. Our results show that the interplay between the induced spontaneous curvature and the membrane tension determine the energy minimizing shapes, which describe the wide range of experimentally observed membrane shapes, i.e. flat membranes, spherical vesicles, elongated tubular protrusions, and pearling structures.

Novel Polyester Amide Membranes Containing Biquinoline Units and Complex with Cu(I): Synthesis, Characterization, and Approbation for n-Heptane Isolation from Organic Mixtures

The wide possibilities of designing a chemical structure and creating complexes with transition metals make polymers of heteroaromatic structure interesting objects, from both scientific and practical aspects. In this work, modern biquinoline-containing polymers, namely polyester amide (PEA) and its metal–polymer complex (PEA–Cu(I)), were synthesized and used to form dense flat membranes. A comparative study of their morphology, same physical properties (density, free volume, and contact angles), and thermomechanical characteristics was carried out. The transport properties of the modern membranes were studied during pervaporation, to solve a problem of n-heptane isolation from its binary mixtures with thiophene and methanol. It was shown that only the PEA membrane is selective for the separation of thiophene impurities from the mixture with n-heptane. In pervaporation of methanol/n-heptane mixture, the РЕА–Cu(I) membrane exhibits significantly higher pervaporation separation index, as compared with that of the РЕА membrane.

Characterization of natural Lebanese clays for the preparation of ceramic membranes designed to water filtration

The potentiality of natural Lebanon minerals for the fabrication of ceramics membranes has been investigated for the first time, opening new perspectives for the development of local, low-cost and sustainable processes for water filtration. Natural clay deposits, originated from North (Kousba, El-Koura), South (Hasbaya) and East (Rashaya, south of the Beqaa valley) regions of Lebanon were collected and investigated in terms of chemical, mineralogical and thermal features. The phase and chemical transformations occurring during heat treatments of these clays were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron spectroscopy (SEM), and X-ray fluorescence (XRF), in view of their uses as membranes for water purification. Flat membranes were prepared by roll-pressing of clay pastes followed by pyrolysis. The mineral membranes were characterized in terms of porosity and water flux.

Phagocytosis is mediated by two-dimensional assemblies of the F-BAR protein GAS7

Phagocytosis is a cellular process for internalization of micron-sized large particles including pathogens. The Bin-Amphiphysin-Rvs167 (BAR) domain proteins, including the FCH-BAR (F-BAR) domain proteins, impose specific morphologies on lipid membranes. Most BAR domain proteins are thought to form membrane invaginations or protrusions by assembling into helical submicron-diameter filaments, such as on clathrin-coated pits, caveolae, and filopodia. However, the mechanism by which BAR domain proteins assemble into micron-scale phagocytic cups was unclear. Here, we show that the two-dimensional sheet-like assembly of Growth Arrest-Specific 7 (GAS7) plays a critical role in phagocytic cup formation in macrophages. GAS7 has the F-BAR domain that possesses unique hydrophilic loops for two-dimensional sheet formation on flat membranes. Super-resolution microscopy reveals the similar assemblies of GAS7 on phagocytic cups and liposomes. The mutations of the loops abolishes both the membrane localization of GAS7 and phagocytosis. Thus, the sheet-like assembly of GAS7 plays a significant role in phagocytosis.