Assembly of the enveloped bacteriophage phi 6 in environments which perturb the host cell membranes.

The effects of known membrane-perturbing agents (pH, Na+, Ca2+, and a small lipid-soluble molecule) on the enveloped bacteriophage phi 6 host cell system were investigated at the levels of cellular growth, virus assembly and stability, and the physical and chemical properties of host cell membranes. Spin-label probes of cellular membranes indicate that growth in high levels of Na+ or the small spherical hydrophobic molecule adamantanone results in membranes having increased "fluidity," while growth in high levels of Ca2+ results in slightly greater rigidity of the membranes. In addition, the phospholipid composition of the cellular membranes is dependent on the NaCl concentration in the growth medium. None of these membrane alterations, however, prevent the production of infectious phi 6 virus particles.     

Fatty Acids Regulate Stress Resistance and Virulence Factor Production for Listeria monocytogenes

Fatty acids (FAs) are the major structural component of cellular membranes, which provide a physical and chemical barrier that insulates intracellular reactions from environmental fluctuations. The native composition of membrane FAs establishes the topological and chemical parameters for membrane-associated functions and is therefore modulated diligently by microorganisms especially in response to environmental stresses. However, the consequences of altered FA composition during host-pathogen interactions are poorly understood. The food-borne pathogen Listeria monocytogenes contains mostly saturated branched-chain FAs (BCFAs), which support growth at low pH and low temperature. In this study, we show that anteiso-BCFAs enhance bacterial resistance against phagosomal killing in macrophages. Specifically, BCFAs protect against antimicrobial peptides and peptidoglycan hydrolases, two classes of phagosome antimicrobial defense mechanisms. In addition, the production of the critical virulence factor, listeriolysin O, was compromised by FA modulation, suggesting that FAs play a key role in virulence regulation. In summary, our results emphasize the significance of FA metabolism, not only in bacterial virulence regulation but also in membrane barrier function by providing resistance against host antimicrobial stress.     

Differential temperature acclimatization responses in the membrane phospholipids of Posthodiplostomum minimum and its second intermediate host, Lepomis macrochirus

The effects of temperature change on phospholipid content in metacercariae of Posthodiplostomum minimum and their second intermediate hosts, Lepomis macrochirus, were examined to gauge similarities in the homeoviscous adaptation of host and parasite membranes to environmental thermal change. Heart, liver, and muscle tissues from individual L. macrochirus responded to environmental temperature declines with a decrease in the ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC). Increases in membrane PE concentration increase membrane fluidity, maintaining fish membrane function as environmental temperature declines. However, the metacercariae of P. minimum exhibit changes in cholesterol levels, total lipid levels, and lipid composition (PE/PC) that contrast the normal changes for homeoviscous membrane adaptation exhibited by their fish intermediate hosts. The parasites seem to rely on their hosts for homeoviscous adaptation within normal developmental temperature ranges, pooling both cholesterol and PE as energetic stores for development and ontological transitions signaled by elevated temperatures.     

Alcohol and the heart: theoretical considerations

It is now well established that consumption of ethyl alcohol, both acute and chronic, exerts deleterious effects on the heart. Evidence is presented that the initial event that precipitates both acute and chronic changes reflects the physical effects of alcohol on membrane phospholipids and perhaps proteins. The presence of alcohol increases membrane fluidity, a condition that leads to an adaptive change in the phospholipid composition of the membranes, with resultant greater rigidity of the membranes. The effects of alcohol on the lipid bilayer of the plasma membrane, when combined with other nonspecific insults, may lead to a drastic increase in calcium permeability; the resulting calcium influx may cause cell necrosis and initiate irreversibly cardiomyopathy. It is likely that changes in membrane fluidity also exert profound effects on enzyme and transport activities of membrane-bound proteins. In addition, alcohol may interact directly with the hydrophobic regions of proteins. Such interactions may play an important role not only in membrane-bound proteins, but also in alcohol-induced changes in contractile proteins of the heart. It is suggested that, in general, the effects of alcohol are similar to those of other anesthetic agents, and that the elucidation of the pathogenesis of alcoholic cardiomyopathy may require a deeper understanding of the physical interaction among alcohol, phospholipids, and proteins.     

Regulatory role of membrane fluidity in gene expression and physiological functions

Plants, algae, and photosynthetic bacteria experience frequent changes in environment. The ability to survive depends on their capacity to acclimate to such changes. In particular, fluctuations in temperature affect the fluidity of cytoplasmic and thylakoid membranes. The molecular mechanisms responsible for the perception of changes in membrane fluidity have not been fully characterized. However, the understanding of the functions of the individual genes for fatty acid desaturases in cyanobacteria and plants led to the directed mutagenesis of such genes that altered the membrane fluidity of cytoplasmic and thylakoid membranes. Characterization of the photosynthetic properties of the transformed cyanobacteria and higher plants revealed that lipid unsaturation is essential for protection of the photosynthetic machinery against environmental stresses, such as strong light, salt stress, and high and low temperatures. The unsaturation of fatty acids enhances the repair of the damaged photosystem II complex under stress conditions. In this review, we summarize the knowledge on the mechanisms that regulate membrane fluidity, on putative sensors that perceive changes in membrane fluidity, on genes that are involved in acclimation to new sets of environmental conditions, and on the influence of membrane properties on photosynthetic functions.     

Effects of weight loss on erythrocyte membrane composition and fluidity in overweight and moderately obese women

A previous study showed chemical and physical impairment of the erythrocyte membrane of overweight and moderately obese women. The present study investigated the effects of a low-calorie diet (800 kcal/day deficit for 8 weeks) on erythrocyte membrane properties in 70 overweight and moderately obese (body mass index, 25-33 kg/m²) normotensive, nondiabetic women. At the end of dietary intervention, 24.3% of women dropped out, 45.7% lost less than 5% of their initial weight (Group I) and only 30% of patients lost at least 5% of their initial body weight (Group II). Group I showed no significant changes in erythrocyte membrane composition and function. The erythrocyte membranes of Group II showed significant reductions in malondialdehyde, lipofuscin, cholesterol, sphingomyelin, palmitic acid and nervonic acid and an increase in di-homo-γ-linolenic acid, arachidonic acid and membrane fluidity. Moreover, Group II showed an improvement in total cholesterol, low-density lipoprotein cholesterol, glycemia and insulin resistance. These changes in erythrocyte membrane composition could reflect a virtuous cycle resulting from the reduction in insulin resistance associated with increased membrane fluidity that, in turn, results in a sequence of metabolic events that concur to further improve membrane fluidity.     

Regional influences on the physical properties of T cell membranes

Differences in the composition of membrane lipids are well documented between cells from distinct tissues. These differences may be manifested by changes in the motional freedom or fluidity of lipid molecules within plasma membranes and may predispose to alterations in cellular function. Regional influences on immune function have been implied by the finding that thymic-derived cells from murine spleen and lymph nodes are differentially responsive to antigen priming. The possibility that microenvironment also shapes the physical properties of T lymphocyte membranes has not been explored and is the focus of this study. Using mice as the experimental model, differences were found in fluidity and in the resting level of intracellular free-ionized Ca2+ between splenic and lymph node T cells from immunologically normal mice and from autoimmune-prone MRL-lpr/lpr mice. The results indicate that T cells are more heterogeneous than previously recognized and suggest a potential role for microenvironment in determining immune responsiveness.     

Heat death and cellular heat injury

1. 1.|Evidence is presented implicating cellular membranes in cellular heat injury. It is proposed this is the site of the primary lesion.

2. 2.|Secondary and tertiary events, resulting from the primary lesion, cause organism death. Those events may be unique to the life style and grade of organisation of the organism.

3. 3.|Thus hyperthermia may cause “excessive” fluidisation of membranes and so cause impairment of membrane permeability and disrupt the stability of membrane enzymes.

4. 4.|Homeoviscous adaptation of membrane fluidity may well have an important role in resistance acclimation as well as resistance adaptation.

Use of fluorescence polarization to monitor intracellular membrane changes during temperature acclimation. Correlation with lipid compositional and ultrastructural changes.

Fluorescence polarization of 1,6-diphenylhexatriene (DPH) was used to study the effects of temperature acclimation on Tetrahymena membranes. The physical properties of membrane lipids were found to be highly dependent on cellular growth temperature. DPH polarization in lipids from three different membrane fractions correlated well with earlier freeze-fracture and electron spin resonance observations showing that membrane fluidity progressively decreases in the order microsomes greater than pellicles greater than cilia throughout a wide range of growth temperatures. Changes in membrane lipid fluidity following a shift from high to low growth temperatures proceed rapidly in the microsomes, whereas there is a pronounced lag in the changes of peripheral cell membrane lipids. These data support previous observations that adaptive changes in membrane fluidity proceed via lipid modifications in the endoplasmic reticulum, followed by dissemination of lipid components to other cell membranes. The rapid changes in polarization observed in the microsomal lipids following a temperature shift correspond closely with the time-dependent alterations in both lipid fatty acid composition and freeze-fracture patterns of membrane particle distribution, suggesting that, in the endoplasmic reticulum, lipid phase separation is the primary cause of membrane particle rearrangements.     

Membrane adaptation in phospholipids and cholesterol in the widely distributed,freeze-tolerant wood frog,Rana sylvatica

Maintaining proper membrane phase and fluidity is important for preserving membrane structure and function, and by altering membrane lipid composition many organisms can adapt to changing environmental conditions. We compared the phospholipid and cholesterol composition of liver and brain plasma membranes in the freeze-tolerant wood frog, Rana sylvatica, from southern Ohio and Interior Alaska during summer, fall, and winter. We also compared membranes from winter-acclimatized frogs from Ohio that were either acclimated to 0, 4, or 10 °C, or frozen to ?2.5 °C and sampled before or after thawing. Lipids were extracted from isolated membranes, separated by one-dimensional thin-layer chromatography, and analyzed via densitometry. Liver membranes underwent seasonal changes in phospholipid composition and lipid ratios, including a winter increase in phosphatidylethanolamine, which serves to increase fluidity. However, whereas Ohioan frogs decreased phosphatidylcholine and increased sphingomyelin, Alaskan frogs only decreased phosphatidylserine, indicating that these phenotypes use different adaptive strategies to meet the functional needs of their membranes. Liver membranes showed no seasonal variation in cholesterol abundance, though membranes from Alaskan frogs contained relatively less cholesterol, consistent with the need for greater fluidity in a colder environment. No lipid changed seasonally in brain membranes in either population. In the thermal acclimation experiment, cold exposure induced an increase in phosphatidylethanolamine in liver membranes and a decrease in cholesterol in brain membranes. No changes occurred during freezing and thawing in membranes from either organ. Wood frogs use tissue-specific membrane adaptation of phospholipids and cholesterol to respond to changing environmental factors, particularly temperature, though not with freezing.     

Effects of acclimation temperature on enzymatic capacities and mitochondrial membranes from the body wall of the earthworm Lumbricus terrestris

Many ectotherms respond to low temperature by adjusting capacities of enzymes from energy metabolism, restructuring membrane phospholipids and modulating membrane fluidity. Although much is known about the temperature biology of earthworms, it is not known to what extent earthworms employ compensatory changes in enzymatic capacities and membrane physical properties after exposure to low temperature. We examined activities of enzymes from glycolysis and central oxidative pathways as well as fluidity and phospholipid fatty acid composition of mitochondrial membranes prepared from the body wall of the temperate oligochaete Lumbricus terrestris after a one month acclimation to 5 degrees and 15 degrees C. No compensation occurs in central pathways of oxidative metabolism since activities of cytochrome-c oxidase and citrate synthase, when measured at a common temperature, are similar for 5 degrees C and 15 degrees C-acclimated animals. In contrast, activity of pyruvate kinase is elevated 1.3-fold after acclimation to 5 degrees C. Mitochondrial membranes display inverse compensation with respect to temperature (membranes from 5 degrees C animals are more ordered than membranes from 15 degrees C animals). Our results, in combination with earlier reports, indicate that routine metabolism in L. terrestris may be maintained at reduced temperatures with little or no change in enzymatic capacities and inverse compensation of mitochondrial membranes.     

Alcohol stress,membranes, and chaperones

Ethanol, which affects all body organs, exerts a number of cytotoxic effects, most of them independent of cell type. Ethanol treatment leads to increased membrane fluidity and to changes in membrane protein composition. It can also interact directly with membrane proteins, causing conformational changes and thereby influencing their function. The cytotoxic action may include an increased level of oxidative stress. Heat shock protein molecular chaperones are ubiquitously expressed evolutionarily conserved proteins which serve as critical regulators of cellular homeostasis. Heat shock proteins can be induced by various forms of stresses such as elevated temperature, alcohol treatment, or ischemia, and they are also upregulated in certain pathological conditions. As heat shock and ethanol stress provoke similar responses, it is likely that heat shock protein activation also has a role in the protection of membranes and other cellular components during alcohol stress.     

Effects of membrane lipids on ion channel structure and function

Biologic membranes are not simply inert physical barriers, but complex and dynamic environments that affect membrane protein structure and function. Residing within these environments, ion channels control the flux of ions across the membrane through conformational changes that allow transient ion flux through a central pore. These conformational changes may be modulated by changes in transmembrane electrochemical potential, the binding of small ligands or other proteins, or changes in the local lipid environment. Ion channels play fundamental roles in cellular function and, in higher eukaryotes, are the primary means of intercellular signaling, especially between excitable cells such as neurons. The focus of this review is to examine how the composition of the bilayer affects ion channel structure and function. This is an important consideration because the bilayer composition varies greatly in different cell types and in different organellar membranes. Even within a membrane, the lipid composition differs between the inner and outer leaflets, and the composition within a given leaflet is both heterogeneous and highly dynamic. Differential packing of lipids (and proteins) leads to the formation of microdomains, and lateral diffusion of these microdomains or "lipid rafts" serve as mobile platforms for the clustering and organization of bilayer constituents including ion channels. The structure and function of these channels are sensitive to specific chemical interactions with neighboring components of the membrane and also to the biophysical properties of their membrane microenvironment (e.g., fluidity, lateral pressure profile, and bilayer thickness). As specific examples, we have focused on the K+ ion channels and the ligand-gated nicotinicoid receptors, two classes of ion channels that have been well-characterized structurally and functionally. The responsiveness of these ion channels to changes in the lipid environment illustrate how ion channels, and more generally, any membrane protein, may be regulated via cellular control of membrane composition.     

A σW-dependent stress response in Bacillus subtilis that reduces membrane fluidity

Bacteria respond to physical and chemical stresses that affect the integrity of the cell wall and membrane by activating an intricate cell envelope stress response. The ability of cells to regulate the biophysical properties of the membrane by adjusting fatty acid composition is known as homeoviscous adaptation. Here, we identify a homeoviscous adaptation mechanism in Bacillus subtilis regulated by the extracytoplasmic function σ factor σ(W). Cell envelope active compounds, including detergents, activate a sense-oriented, σ(W)-dependent promoter within the first gene of the fabHa fabF operon. Activation leads to a decrease in the amount of FabHa coupled with an increase in FabF, the initiation and elongation condensing enzymes of fatty acid biosynthesis respectively. Downregulation of FabHa results in an increased reliance on the FabHb paralogue leading to a greater proportion of straight chain fatty acids in the membrane, and the upregulation of FabF increases the average fatty acid chain length. The net effect is to reduce membrane fluidity. The inactivation of the σ(W)-dependent promoter within fabHa increased sensitivity to detergents and to antimicrobial compounds produced by other Bacillus spp. Thus, the σ(W) stress response provides a mechanism to conditionally decrease membrane fluidity through the opposed regulation of FabHa and FabF.     

Modulation of the in vitro activity of lysosomal phospholipase A1 by membrane lipids

Lysosomal phospholipases play a critical role for degradation of cellular membranes after their lysosomal segregation. We investigated the regulation of lysosomal phospholipase A1 by cholesterol, phosphatidylethanolamine, and negatively-charged lipids in correlation with changes of biophysical properties of the membranes induced by these lipids. Lysosomal phospholipase A1 activity was determined towards phosphatidylcholine included in liposomes of variable composition using a whole-soluble lysosomal fraction of rat liver as enzymatic source. Phospholipase A1 activity was then related to membrane fluidity, lipid phase organization and membrane potential as determined by fluorescence depolarization of DPH, 31P NMR and capillary electrophoresis. Phospholipase A1 activity was markedly enhanced when the amount of negatively-charged lipids included in the vesicles was increased from 10 to around 30% of total phospholipids and the intensity of this effect depended on the nature of the acidic lipids used (ganglioside GM1相似文献   

Non steroidal anti-inflammatory drugs modulate the physicochemical properties of plasma membrane in experimental colorectal cancer: a fluorescence spectroscopic study

According to "fluid-mosaic model," plasma membrane is a bilayer constituted by phospholipids which regulates the various cellular activities governed by many proteins and enzymes. Any chemical, biochemical, or physical factor has to interact with the bilayer in order to regulate the cellular metabolism where various physicochemical properties of membrane, i.e., polarization, fluidity, electrostatic potential, and phase state may get affected. In this study, we have observed the in vivo effects of a pro-carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) and the two non steroidal anti-inflammatory drugs (NSAIDs); sulindac and celecoxib on various properties of the plasma membrane of colonocytes, i.e., electric potential, fluidity, anisotropy, microviscosity, lateral diffusion, and phase state in the experimentally induced colorectal cancer. A number of fluorescence probes were utilized like membrane fluidity and anisotropy by 1,6-diphenyl-1,3,5-hexatriene, membrane microviscosity by Pyrene, membrane electric potential by merocyanine 540, lateral diffusion by N-NBD-PE, and phase state by Laurdan. It is observed that membrane phospholipids are less densely packed and therefore, the membrane is more fluid in case of carcinogenesis produced by DMH than control. But NSAIDs are effective in reverting back the membrane toward normal state when co-administered with DMH. The membrane becomes less fluid, composed of low electric potential phospholipids whose lateral diffusion is being prohibited and the membrane stays mostly in relative gel phase. It may be stated that sulindac and celecoxib, the two NSAIDs may exert their anti-neoplastic role in colorectal cancer via modifying the physicochemical properties of the membranes.     

Cultured human skin fibroblasts modify their plasma membrane lipid composition and fluidity according to growth temperature suggesting homeoviscous adaptation at hypothermic (30 degrees C) but not at hyperthermic (40 degrees C) temperatures.

Mammalian cell metabolism is responding to changes in temperature. Body temperature is regulated around 37 degrees C, but temperatures of exposed skin areas may vary between 20 degrees C and 40 degrees C for extended periods of time without apparent disturbance of adequate cellular functions. Cellular membrane functions are depending from temperatures but also from their lipid environment, which is a major component of membrane fluidity. Temperature-induced changes of membrane fluidity may be counterbalanced by adaptive modification of membrane lipids. Temperature-dependent changes of whole cell- and of purified membrane lipids and possible homeoviscous adaptation of membrane fluidity have been studied in human skin fibroblasts cultured at 30 degrees C, 37 degrees C, and 40 degrees C for ten days. Membrane anisotropy was measured by polarized fluorescence spectroscopy using TMA-DPH for superficial and DPH for deeper membrane layers. Human fibroblasts were able to adapt themselves to hypothermic temperatures (30 degrees C) by modifying the fluidity of the deeper apolar regions of the plasma membranes as reported by changes of fluorescence anisotropy due to appropriate changes of their plasma membrane lipid composition. This could not be shown for the whole cells. At 40 degrees C growth temperature, adaptive changes of the membrane lipid composition, except for some changes in fatty acid compositions, were not seen. Independent from the changes of the membrane lipid composition, the fluorescence anisotropy of the more superficial membrane layers (TMA-DPH) increased in cells growing at 30 degrees C and decreased in cells growing at 40 degrees C.     

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism--an electron paramagnetic resonance investigation

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, L-arginine and S-nitroso-N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N(G)-nitro-L-arginine-methyl-ester (L-NAME) and asymmetric dimethyl-L-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.     

Biosurfactants

Abstract

Lipids are known as a part of an effective adaptation mechanism reflecting the changes in the extracellular environment. The fluidity of biological membranes is influenced by the lipid structure and the portion of saturated, unsaturated, branched, or cyclic fatty acids in individual phospholipids. For all living organisms undergoing environmental adaptation, the fluidity can be changed only to a relatively small extent. This range is genetically determined and it is specific for every microorganism. This article presents recent knowledge about the influence of some environmental parameters (temperature, osmotic pressure, pH, the presence of salt or ethanol in medium) on a microbial membrane with the emphasis on regulation aspect in fatty acid biosynthesis. The main tools for regulation of membrane fluidity, for example, fatty acid desaturation or incorporation of branched and cyclic fatty acids into phospholipids, are discussed in more detail.