Behavior Of Model Membranes Research Articles

Gb3 Glycosphingolipids with Fluorescent Oligoene Fatty Acids: Synthesis and Phase Behavior in Model Membranes.

Glycosphingolipids are involved in a number of physiological and pathophysiological processes, and they serve as receptors for a variety of bacterial toxins and viruses. To investigate their function in lipid membranes, fluorescently labeled glycosphingolipids are highly desirable. Herein, a synthetic route to access Gb3 glycosphingolipids with fluorescently labeled fatty acids, consisting of pentaene and hexaene moieties either at the terminus or in the middle of the acyl chain, has been developed. The fluorescent properties of the Gb3 derivatives were investigated in small unilamellar vesicles composed of a raft-like mixture. Phase-separated giant unilamellar vesicles (GUVs) allowed the quantification of the apparent partitioning coefficients of the Gb3 compounds by means of confocal fluorescence laser scanning microscopy. The determined partition coefficients demonstrate that the Gb3 derivatives are preferentially localized in the liquid-disordered (ld ) phase. To analyze whether the compounds behave like their physiological counterparts, Cy3-labeled (Cy: cyanine) Shiga toxin B subunits (STxB) were specifically bound to Gb3 -doped GUVs. However, the protein was favorably localized in the ld phase, in contrast to results reported for STxB bound to naturally occurring Gb3 , which is discussed in terms of the packing density of the lipids in the liquid-ordered (lo ) phase.

Fluorescent Sterols and Cholesteryl Esters as Probes for Intracellular Cholesterol Transport.

Cholesterol transport between cellular organelles comprised vesicular trafficking and nonvesicular exchange; these processes are often studied by quantitative fluorescence microscopy. A major challenge for using this approach is producing analogs of cholesterol with suitable brightness and structural and chemical properties comparable with those of cholesterol. This review surveys currently used fluorescent sterols with respect to their behavior in model membranes, their photophysical properties, as well as their transport and metabolism in cells. In the first part, several intrinsically fluorescent sterols, such as dehydroergosterol or cholestatrienol, are discussed. These polyene sterols (P-sterols) contain three conjugated double bonds in the steroid ring system, giving them slight fluorescence in ultraviolet light. We discuss the properties of P-sterols relative to cholesterol, outline their chemical synthesis, and explain how to image them in living cells and organisms. In particular, we show that P-sterol esters inserted into low-density lipoprotein can be tracked in the fibroblasts of Niemann–Pick disease using high-resolution deconvolution microscopy. We also describe fluorophore-tagged cholesterol probes, such as BODIPY-, NBD-, Dansyl-, or Pyrene-tagged cholesterol, and eventual esters of these analogs. Finally, we survey the latest developments in the synthesis and use of alkyne cholesterol analogs to be labeled with fluorophores by click chemistry and discuss the potential of all approaches for future applications.

Rafts defined: a report on the Keystone symposium on lipid rafts and cell function

The recent Keystone Symposium on Lipid Rafts and Cell Function (March 23-28, 2006 in Steamboat Springs, CO) brought together biophysicists, biochemists, and cell biologists to discuss the structure and function of lipid rafts. What emerged from the meeting was a consensus definition of a membrane raft: "Membrane rafts are small (10-200 nm), heterogeneous, highly dynamic, sterol- and sphingolipid-enriched domains that compartmentalize cellular processes. Small rafts can sometimes be stabilized to form larger platforms through protein-protein and protein-lipid interactions." This definition helps to clarify current thinking in a field that has been plagued by the heterogeneous and sometimes ephemeral nature of its subject.

Time-Dependent Absorption Evidence of Phenylurea-Derived Herbicides on Model Biomembranes: A DSC Study

Environmental Context. The need to improve the quality of agricultural cultivation and to control the weed growth of non-cultivated area has brought herbicides to wide-scale use. Unfortunately, these compounds have been proved to be toxic for many organisms, humans included. With an aim to a better knowledge of the mobility and fate of environmental pollutants, it becomes very important to have an exact knowledge of the role that the medium in which these products are dissolved or dispersed plays on the absorption of these products by biological membranes as a complement to information on the interaction between these compounds and cells. Abstract. Phenylurea derivatives are used as herbicides that inhibit photosynthesis. These materials enter plants via their roots and are employed for selective control of germinating grass and broad-leaved weeds in many crops as well as for total weed control of non-cultivated areas such as roads, railways, and parks. The study of the interaction between the herbicide and lipid membrane is interesting in assessing the relevance of the dispersing medium in the absorption processes. Differential scanning calorimetry (DSC), which detects the effect of foreign molecules on the phase transition from an ordered to a disordered lipid structure when submitted to heating, was employed to study such an interaction. Effects exerted by four phenylurea herbicides (difenoxuron, diuron, metoxuron, and linuron) on the thermotropic behavior of model membranes were here investigated. Aqueous dispersions of dimyristoylphosphatidylcholine (DMPC) were used as model membranes to study herbicide–membrane interactions. Experiments carried out by leaving herbicides, in a powdered form, in contact with DMPC-based multilamellar or unilamellar vesicles show that all the examined herbicides are able, but in different ways, to migrate through the aqueous medium and interact with model membranes. Experiments on herbicide-loaded liposomes in contact with empty ones indicate that the compounds are able to migrate from a loaded membrane to an empty one. The obtained data seem to validate the use of the DSC in demonstrating that bioactive and potentially toxic compounds not only to interact with biological membranes but also adsorb into a cell when dispersed in a lipophilic medium.

Docosahexaenoic acid (DHA) alters the phospholipid molecular species composition of membranous vesicles exfoliated from the surface of a murine leukemia cell line

Previously, we presented evidence that the vesicles routinely exfoliated from the surface of T27A tumor cells arise from vesicle-forming regions of the plasma membrane and possess a set of lateral microdomains distinct from those of the plasma membrane as a whole. We also showed that docosahexaenoic acid (DHA, or 22:6n-3), a fatty acyl chain known to alter microdomain structure in model membranes, also alters the structure and composition of exfoliated vesicles, implying a DHA-induced change in microdomain structure on the cell surface. In this report we show that enrichment of the cells with DHA reverses some of the characteristic differences in composition between the parent plasma membrane and shed microdomain vesicles, but does not alter their phospholipid class composition. In untreated cells, DHA-containing species were found to be a much greater proportion of the total phosphatidylethanolamine (PE) pool than the total phosphatidylcholine (PC) pool in both the plasma membrane and the shed vesicles. After DHA treatment, the proportion of DHA-containing species in the PE and PC pools of the plasma membrane were elevated, and unlike in untreated cells, their proportions were equal in the two pools. In the vesicles shed from DHA-loaded cells, the proportion of DHA-containing species of PE was the same as in the plasma membrane. However, the proportion of DHA-containing species of PC in the vesicles (0.089) was much lower than that found in the plasma membrane (0.194), and was relatively devoid of species with 16-carbon acyl components. These data suggested that DHA-containing species of PC, particularly those having a 16-carbon chain in the sn-1 position, were preferentially retained in the plasma membrane. The data can be interpreted as indicating that DHA induces a restructuring of lateral microdomains on the surface of living cells similar to that predicted by its behavior in model membranes.

How trehalose affects the lipid phase behavior of model membranes

How trehalose affects the lipid phase behavior of model membranes

N-Pyrene dodecanoyl sulfatide as membrane probe: a study of glycolipid dynamic behavior in model membranes

An N-linked pyrene-dodecanoyl sulfatide was employed to measure the ratio of excimer fluorescence to monomer fluoresence intensities ( E/M). The E/M values provided information about both the dynamic behavior and the structural distribution of the labelled glycolipid in note dispersion of micellar sulfatides and multilamellar vesicles of different phospholipids. Most of the labelled sulfatide seems to be located in domains sequestered from the surrounding phospholipids still above the phase transition temperature of the vesicles. The glycolipids sequestered in these domain environment are less sensitive to the structural changes that the addition of cholesterol or Ca 2+ can induce in the phospholipid regions during the phase transition.