Showing papers on "Membrane lipids published in 1995"
TL;DR: HV A has emerged as the most commonly employed paradigm to assess the efficacy of thermal adaptation in biological membranes and to explain patterns of temperature-induced change in membrane lipid composi-
Abstract: The phase behavior and physical properties of lipids in biological membranes are exquisitely sensitive to changes in temperature (50). Because membranes (a) act as physical barriers to solute diffusion, (b) mediate the transmembrane movement of specific solutes, (c) regulate the utilization of energy stored in transmembrane ion gradients, Cd) provide an organizing matrix for the assem bly of multicomponent metabolic and signal transduction pathways, and (e) supply precursors for the generation of lipid-derived second messengers, tem perature-induced perturbations in membrane organization pose a serious chal lenge to the maintenance of physiological function in poikilotherms. However, poikilotherms exploit the diversity of lipid structure to fashion membranes with physical properties appropriate to their thermal circumstance and, in this way, restore membrane function following thermal challenge. Based on the finding that membrane lipids of Escherichia coli grown at 43 and 15°C dis played similar physical properties when compared at their respective growth temperatures, Sinensky concluded that membrane fluidity was defended as growth temperature changes and referred to this cellular homeostatic response as homeoviscous adaptation CHV A) (94). Since the original exposition of this hypothesis, HV A has emerged as the most commonly employed paradigm to assess the efficacy of thermal adaptation in biological membranes and to explain patterns of temperature-induced change in membrane lipid composi-
1,091 citations
TL;DR: The results reviewed suggest that membrane fusion in diverse biological fusion reactions involves formation of some specific intermediates: stalks and pores, and suggest a specific geometry to bent fusion intermediates (stalks and pores) and imply a contribution by lipids to the energy of these intermediates.
Abstract: The results reviewed suggest that membrane fusion in diverse biological fusion reactions involves formation of some specific intermediates: stalks and pores. Energy of these intermediates and, consequently, the rate and extent of fusion depend on the propensity of the corresponding monolayers of membranes to bend in the required directions. Proteins and peptides can control the bending energy of membrane monolayers in a number of ways. Monolayer lipid composition may be altered by different phospholipases [50, 85, 90], flipases and translocases [4, 50]. Proteins and peptides can change monolayer spontaneous curvature or hydrophobic void energy by direct interaction with membrane lipids [20, 32, 111]. Proteins may also provide some barriers for lipid diffusion in the plane of the monolayer [83, 141]. If diffusion of lipids at some specific membrane sites (e.g., in the vicinity of fusion protein) is somehow hindered, the energy of the bent fusion intermediates would reflect the elastic properties of these particular sites rather than the spontaneous curvature of the whole monolayers. Proteins may deform membranes while bringing them locally into close contact. The alteration of the geometric (external) curvature will certainly change the elastic energy of the initial state and, thus affect the energetic barriers of the formation of the intermediates [143]. In addition, the area and the energy of the stalk can be reduced by preliminary bending of the contacting membranes [111]. The possible effects of proteins and polymers on local elastic properties and local shapes of the membranes have been recently analyzed [22, 39, 45, 63]. These studies may provide a good basis for future development of theoretical models of protein-mediated fusion. Various models for biological fusion have been presented as hypothetical sequences of intermediate conformations of proteins, with membrane lipids just covering the empty spaces between the proteins. Although the results discussed above do not allow us to draw an allexplaining cartoon of the fusion mechanism, they do indicate which properties of membrane lipid bilayers (if modified by fusion proteins) would get these bilayers to fuse. In addition, these data suggest a specific geometry to bent fusion intermediates (stalks and pores) and imply a contribution by lipids to the energy of these intermediates. We think that the synthesis of rapidly developing structural information on fusion proteins with the analysis of the physics of membrane rearrangement may soon yield a real understanding of the fascinating and fundamental phenomenon of membrane fusion.
429 citations
TL;DR: It is suggested that unsaturation of fatty acids of phosphatidylglycerol in thylakoid membranes stabilizes the photosynthetic machinery against low-temperature photoinhibition by accelerating the recovery of the photosystem II protein complex.
Abstract: Using tobacco plants that had been transformed with the cDNA for glycerol-3-phosphate acyltransferase, we have demonstrated that chilling tolerance is affected by the levels of unsaturated membrane lipids. In the present study, we examined the effects of the transformation of tobacco plants with cDNA for glycerol-3-phosphate acyltransferase from squash on the unsaturation of fatty acids in thylakoid membrane lipids and the response of photosynthesis to various temperatures. Of the four major lipid classes isolated from the thylakoid membranes, phosphatidylglycerol showed the most conspicuous decrease in the level of unsaturation in the transformed plants. The isolated thylakoid membranes from wild-type and transgenic plants did not significantly differ from each other in terms of the sensitivity of photosystem II to high and low temperatures and also to photoinhibition. However, leaves of the transformed plants were more sensitive to photoinhibition than those of wild-type plants. Moreover, the recovery of photosynthesis from photoinhibition in leaves of wild-type plants was faster than that in leaves of the transgenic tobacco plants. These results suggest that unsaturation of fatty acids of phosphatidylglycerol in thylakoid membranes stabilizes the photosynthetic machinery against low-temperature photoinhibition by accelerating the recovery of the photosystem II protein complex.
259 citations
TL;DR: The absorption and spreading behavior of lipid vesicles composed of either palmitoyloleoylphosphatidylcholine (POPC) or Escherichia coli lipid upon contact with a glass surface was examined, and supported planar bilayers were found to be permeable for small molecules, whereas supported vesicle layers were impermeable and thus represented immobilized, topologically separate compartments.
256 citations
TL;DR: Lipids and proteins were found to contact a nascent type II membrane protein, as well as a nascent secretory protein, during their insertion into the membrane of the endoplasmic reticulum, suggesting that the protein-conducting channel is open laterally toward the lipid bilayer during an early stage of protein insertion.
254 citations
24 Oct 1995
TL;DR: This article classified simple and compound lipids into three groups: simple (triglycerides, steryl esters, and wax esters), compound (phospholipids, sterols, sphingolipid, and lipoproteins), and derived lipids (fatty acids, fatsoluble vitamins and provitamins, sterol, terpenoids, and ethers).
Abstract: Lipids form one of the major bulk constituents in food and other biological systems.
This group of organic biomolecules can be classified into three groups: simple
lipids (triglycerides, steryl esters, and wax esters), compound lipids (phospholipids,
glycolipids, sphingolipids, and lipoproteins), and derived lipids (fatty acids, fatsoluble vitamins and provitamins, sterols, terpenoids, and ethers). Lipids occur in
animals and plants either as storage lipids, which are potential sources of energy
by beta oxidation, or as membrane lipids. Storage lipids are triglycerides, whereas
membrane lipids include phospholipids, sterols, sphingolipids, and glycolipids.
Many foods of plant origin contain highly unsaturated lipids. Lipids of animal
origin have lower levels of unsaturated lipids, but they contain certain amounts of
the higher unsaturated fatty acids.
249 citations
01 Jan 1995
TL;DR: Most biological membranes are fluid at physiological temperatures—a requirement for proper function, although membranes that contain large quantities of Chol can adopt a different fluid-phase known as liquid-ordered.
Abstract: Publisher Summary Biological membranes are fluid (liquid–crystalline) lipid bilayers, into which, proteins can insert or associate at the surface. The membrane research has focused primarily on the protein components, with the lipid portion viewed as a convenient barrier and environment for enzymes. However, biological membranes contain a wide diversity of lipids, far more than are needed to perform structural functions, and these lipids require elaborate metabolic pathways for their synthesis and transport. The main classes of lipids found in eukaryotic biological membranes include the glycerophospholipids, the sphingolipids, and cholesterol (Chol). Of the former group, phosphatidylcholine (PC) is the major lipid, but phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and cardiolipin (CL) are also major lipid species in biological membranes. A representative chemical structure of a common phospholipid is 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The sphingolipids include sphingomyelin (SPM), ceramide (CER), and the glycosphingolipids (GSLs). Most biological membranes are fluid at physiological temperatures—a requirement for proper function. The fluid-membrane phase usually refers to the liquid–crystalline bilayer phase, although membranes that contain large quantities of Chol can adopt a different fluid-phase known as liquid-ordered.
189 citations
TL;DR: The presence of the low-fluidity layer will lower the permeability of the cell wall to lipophilic antibiotics and chemotherapeutic agents and may contribute to the well-known intrinsic resistance of mycobacteria to such compounds.
Abstract: The mycobacterial cell wall contains large amounts of unusual lipids, including mycolic acids that are covalently linked to the underlying arabinogalactan-peptidoglycan complex. Hydrocarbon chains of much of these lipids have been shown to be packed in a direction perpendicular to the plane of the cell surface. In this study, we examined the dynamic properties of the organized lipid domains in the cell wall isolated from Mycobacterium chelonae grown at 30 degrees C. Differential scanning calorimetry showed that much of the lipids underwent major thermal transitions between 30 degree C and 65 degrees C, that is at temperatures above the growth temperature, a result suggesting that a significant portion of the lipids existed in a structure of extremely low fluidity in the growing cells. Spin-labeled fatty acid probes were successfully inserted into the more fluid part of the cell wall. Our model of the cell wall suggests that this domain corresponds to the outermost leaflet, a conclusion reinforced by the observation that labeling of intact cells produced electron spin resonance spectra similar to those of the isolated cell wall. Use of stearate labeled at different positions showed that the fluidity within the outer leaflet increased only slightly as the nitroxide group was placed farther away from the surface. These results are consistent with the model of mycobacterial cell wall containing an asymmetric lipid bilayer, with an internal, less fluid mycolic acid leaflet and an external, more fluid leaflet composed of lipids containing shorter chain fatty acids. The presence of the low-fluidity layer will lower the permeability of the cell wall to lipophilic antibiotics and chemotherapeutic agents and may contribute to the well-known intrinsic resistance of mycobacteria to such compounds.
146 citations
TL;DR: It is concluded that non‐bilayer lipids are essential for efficient protein transport across the plasma membrane of E. coli.
Abstract: The construction of a mutant Escherichia coli strain which cannot synthesize phosphatidylethanolamine provides a tool to study the involvement of non-bilayer lipids in membrane function. This strain produces phosphatidylglycerol and cardiolipin (CL) as major membrane constituents and requires millimolar concentrations of divalent cations for growth. In this strain, the lipid phase behaviour is tightly regulated by adjustment of the level of CL which favours a nonbilayer organization in the presence of specific divalent cations. We have used an in vitro system of inverted membrane vesicles to study the involvement of non-bilayer lipids in protein translocation in the secretion pathway. In this system, protein translocation is very low in the absence of divalent cations but can be enhanced by inclusion of Mg2+, Ca2+ or Sr2+ but not by Ba2+ which is unable to sustain growth of the mutant strain and cannot induce a non-bilayer phase in E. coli CL dispersions. Alternatively, translocation in cation depleted vesicles could be increased by incorporation of the non-bilayer lipid DOPE (18:1) but not by DMPE (14:0) or DOPC (18:1), both of which are bilayer lipids under physiological conditions. We conclude that non-bilayer lipids are essential for efficient protein transport across the plasma membrane of E. coli.
142 citations
TL;DR: Analysis of the binding isotherms of native cytochrome c to negatively charged lipid dispersions of dioleoyl phosphatidylglycerol demonstrates that the apparent saturation effects could arise from a competition between the out-of-plane binding reaction and the lateral in-plane interactions between proteins at the surface.
142 citations
TL;DR: It is demonstrated that these lipid patterns rich in free fatty acids were relevant to the degradation of complex lipids, and confirmed that the diatom, S. costatum, provides a good diet for molluscs, particularly through its high proportion of eJ3 PUFA.
TL;DR: An important role of the lipid component of the cell membrane in signal transduction and its alteration by anthracyclines is revealed, which could explain how anthrACYclines can exert their cytocidal action without entering the cell.
Abstract: Albeit anthracyclines are widely used in the treatment of solid tumors and leukemias, their mechanism of action has not been elucidated. The present study gives relevant information about the role of nonlamellar membrane structures in signaling pathways, which could explain how anthracyclines can exert their cytocidal action without entering the cell [Tritton, T. R. & Yee, G. (1982) Science 217, 248-250]. The anthracycline daunomycin reduced the formation of the nonlamellar hexagonal (HII) phase (i.e., the hexagonal phase propensity), stabilizing the bilayer structure of the plasma membrane by a direct interaction with membrane phospholipids. As a consequence, various cellular events involved in signal transduction, such as membrane fusion and membrane association of peripheral proteins [e.g., guanine nucleotide-binding regulatory proteins (G proteins and protein kinase C-alpha beta)], where nonlamellar structures (negative intrinsic monolayer curvature strain) are required, were altered by the presence of daunomycin. Functionally, daunomycin also impaired the expression of the high-affinity state of a G protein-coupled receptor (ternary complex for the alpha 2-adrenergic receptor) due to G-protein dissociation from the plasma membrane. In vivo, daunomycin also decreased the levels of membrane-associated G proteins and protein kinase C-alpha beta in the heart. The occurrence of such nonlamellar structures favors the association of these peripheral proteins with the plasma membrane and prevents daunomycin-induced dissociation. These results reveal an important role of the lipid component of the cell membrane in signal transduction and its alteration by anthracyclines.
TL;DR: Measurements of the physical strength of the association between membrane bilayer and the membrane-associated skeleton in red blood cells are reported and it is postulated that an important contribution to the energy of association between bilayers and skeleton comes from the increase in chemical potential due to the lateral segregation of lipids and integral proteins.
Abstract: Bilayer membranes are intrinsically fluid in character and require stabilization by association with an underlying cytoskeleton. Instability either in the membrane-associated cytoskeleton or in the association between the bilayer and the skeleton can lead to loss of membrane bilayer and premature cell death. In this report measurements of the physical strength of the association between membrane bilayer and the membrane-associated skeleton in red blood cells are reported. These measurements involve the mechanical formation of long, thin cylinders of membrane bilayer (tethers) from the red cell surface. Ultrastructural evidence is presented indicating that these tethers do not contain membrane skeleton and, furthermore, that they are deficient in at least some integral membrane proteins. By measuring the forces on the cell as the tether is formed and the dimensions of the tether, the energy associated with its formation can be calculated. The minimum force to form a tether was found to be approximately 50 pN corresponding to an energy of dissociation of 0.2-0.3 mJ/m2. Such measurements enable critical evaluation of potential physical mechanisms for the stabilization of the membrane bilayer by the underlying cytoskeleton. It is postulated that an important contribution to the energy of association between bilayer and skeleton comes from the increase in chemical potential due to the lateral segregation of lipids and integral proteins.
Journal Article•
TL;DR: It is shown that LAMs were efficiently inserted into the plasma membranes of human and murine lymphomonocytic cells through their GPI anchor, and both the acyl chains and the mannoside core glycan of the LAM-GPI anchor contribute to the specificity of integration.
Abstract: Lipoarabinomannans (LAMs) are major Ags of the mycobacterial cell envelope where they apparently insert through a glycosylphosphatidylinositol (GPI) anchoring structure. LAMs induce host macrophages to secrete TNF-alpha, IL-1, and IL-6 and inhibit T cell proliferative responses. The mechanisms by which LAMs mediate these effects remain poorly understood. We show that LAMs were efficiently inserted into the plasma membranes of human and murine lymphomonocytic cells through their GPI anchor. Prior deacylation of LAMs abrogated this event. Phosphatidylinositol hexamannoside (PIM6), the GPI anchor of all LAMs, competitively inhibited LAM insertion. Deacylated PIM6 was not inhibitory. The hexamannoside glycan of PIM6 appears to be important for LAM insertion, since phosphatidylinositol from soybean, lacking the glycan core, was not as efficient an inhibitor. Interaction of LAM with target cells was influenced by the gel/fluid phase distribution of membrane lipids, suggesting a direct interaction of the LAM-GPI anchor with the membrane bilayer. The inserted LAMs were mobile in the plane of the membrane and interfered with Ab-mediated mobilization of the GPI-anchored Thy-1 molecules. Further, LAMs were preferentially incorporated into isolated plasma membrane vesicles enriched in Thy-1. Our results strongly suggest that 1) interaction of LAMs with host lymphomonocytic cells is mediated through a preferential integration of LAM-GPI anchor into specialized plasma membrane domains enriched in endogenous GPI-anchored molecules, and 2) both the acyl chains and the mannoside core glycan of the LAM-GPI anchor contribute to the specificity of integration.
TL;DR: A novel finding that membrane lipids modulate βARK activity in vitro in a manner that is analogous and competitive with G is reported, submitting the intriguing possibility that both lipids and G proteins co-regulate the function of GRKs.
TL;DR: The authors' data are consistent with the hypothesis that membrane fusion proceeds through highly bent membrane intermediates (stalks) having a net negative curvature, and suggest inverted cone-shaped lysolipids inhibit and cone- shaped cis-unsaturated fatty acids promote stalk formation and, ultimately, membrane fusion.
Abstract: We have investigated the effects of membrane lipid composition on biological membrane fusion triggered by low pH and mediated by the baculovirus envelope glycoprotein gp64. Lysolipids, either added exogenously or produced in situ by phospholipase A2 treatment of cell membranes, reversibly inhibited syncytium formation. Lysolipids also decreased the baculovirus infection rate. In contrast, oleic and arachidonic acids and monoolein promoted cell-cell fusion. Membrane lipid composition affected pH-independent processes which followed the low-pH-induced change in fusion protein conformation. Inhibition and promotion of membrane fusion by a number of lipids could not be explained by mere binding or incorporation into membranes, but rather was correlated with the effective molecular shape of exogenous lipids. Our data are consistent with the hypothesis that membrane fusion proceeds through highly bent membrane intermediates (stalks) having a net negative curvature. Consequently, inverted cone-shaped lysolipids inhibit and cone-shaped cis-unsaturated fatty acids promote stalk formation and, ultimately, membrane fusion.
TL;DR: It is concluded that membrane binding of the βIΣII spectrin C-terminal region is by means of a direct interaction between the N-Terminal region of the PH domain and membrane lipids and does not require membrane protein.
TL;DR: Results from the quadrupolar splittings for deuterated ethanol bound to cholesterol-containing bilayers showed that ethanol binding decreased with increasing amounts of cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract: The influence of lipid composition on the response of bilayers to ethanol binding was investigated with 2H NMR spectroscopy. The bilayers were composed of various combinations of the lipids most often found in neural cell membranes: phosphatidylcholines (PCs), gangliosides, sphingomyelin, and cholesterol. The PCs, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were chain-perdeuterated to allow the response of bilayer order to ethanol to be monitored at all positions through the depth of the bilayer interior. All bilayers were investigated in the lamellar liquid-crystalline (L alpha) phase. The results from the de-Paked NMR spectra demonstrate that ethanol binding in the lipid-water interface [Barry, J. A., & Gawrisch, K. (1994) Biochemistry 33, 8082-8088] alters order parameter profiles in the bilayer interior differently for the various lipid mixtures. The presence of 10 mol % brain gangliosides enhanced the disordering effect of ethanol and altered the response of the order profile along the PC chains. This effect was apparently caused by sugar-ethanol interactions in the oligosaccharide head group. The impact of the ceramide moiety of brain sphingomyelin (50 mol % in DMPC) was negligible. In bilayers containing cholesterol, the binding of ethanol and its effects on the hydrocarbon interior were found to reflect the phase transition to the liquid-ordered phase at about 25 mol % cholesterol [Thewalt, J. L., & Bloom, M. (1992) Biophys. J. 63, 1176-1181]. Results from the quadrupolar splittings for deuterated ethanol (CH3CD2OH) bound to cholesterol-containing bilayers showed that ethanol binding decreased with increasing amounts of cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The results show that the presence of negatively charged lipids (phospholipid or unprotonated fatty acid) reduces the proportion of lysed vesicles and the modulation of the lytic effect is proposed to originate from the electrostatic interactions between the peptide and the bilayer surface.
TL;DR: It would appear that the above factors impose a tendency for the "extra" portion of the 24-carbon chain to cross the bilayer midplane where it may interact with terminal portions of acyl chains in the opposing monolayer; however, steric constraints, and probably collision events associated with lateral diffusion, induce wide orientation fluctuations in the segment involved.
TL;DR: The results show that 22:4(n-6) is the precursor of 22:5(n -6) but the pathway is independent of an acyl-CoA-dependent 4-desaturase and probably requires intracellular communication between the endoplasmic reticulum and a site for beta-oxidation.
TL;DR: Observations support the hypothesis that the spontaneous curvature of lipid extracts from Acholeplasma laidlawii strain A-EF22 is a functionally important membrane parameter which is regulated by the organism and is likely to be one of the constraints controlling the lipid composition of the bilayer.
TL;DR: The NADPH-UQ reductase in cytosol was presumed to be responsible for maintaining the steady-state redox levels of intrACEllular UQ and thereby to act as an endogenous antioxidant in protecting intracellular membranes from lipid peroxidation that is inevitably induced in aerobic metabolism.
Abstract: Rat liver homogenates reduced ubiquinone (UQ)-10 to ubiquinol (UQH2)-10 in the presence of NADPH rather than NADH. This NADPH-dependent UQ reductase (NADPH-UQ reductase) activity that was not inhibited by antimycin A and rotenone, was located mainly in the cytosol fraction and its activity accounted for 68% of that of the homogenates. Furthermore, the NADPH-UQ reductase from rat liver cytosol efficiently reduced both UQ-10 incorporated into egg yolk lecithin liposomes, and native UQ-9 residing in rat microsomes, to the respective UQH2 form in the presence of NADPH. The gross redox ratios of UQH2-9/(UQ-9 + UQH2-9) in individual tissues of rat correlated positively with the log of their respective cytosolic NADPH-UQ reductase activities, while the redox ratios in every intracellular fraction from liver were at about the same level, irrespective of NADPH-UQ reductase activities in the respective fractions. The combined addition of rat liver cytosol and NADPH inhibited to a great extent 2,2'-azobis(2,4-dimethyl-valeronitrile)-induced lipid peroxidation of UQ-10-fortified lecithin liposomes and completely inhibited such peroxidation in the liposomes in which UQH2-10 replaced UQ-10. The NADPH-UQ reductase activity was clearly separated from DT-diaphorase (EC 1.6.99.2) activity by means of Cibacron Blue-immobilized Bio-Gel A-5m chromatography. In conclusion, the NADPH-UQ reductase in cytosol, which is a novel enzyme to our knowledge, was presumed to be responsible for maintaining the steady-state redox levels of intracellular UQ and thereby to act as an endogenous antioxidant in protecting intracellular membranes from lipid peroxidation that is inevitably induced in aerobic metabolism.
TL;DR: Neither change in membrane lipid asymmetry nor normal levels of the pH-titratable inner monolayer lipids is necessary for cell pH-mediated shape change, according to this study.
TL;DR: The various spectral features monitored for the nAChR reconstituted into lipid membranes either with or without cholesterol are very similar, indicating that cholesterol is not a major structural regulator of the n AChR.
Abstract: FTIR spectra have been recorded both as a function of time and after prolonged exposure to 2H2O buffer in order to study the structural changes that lead to both the ligand- and lipid-dependent channel-inactive states of the nicotinic acetylcholine receptor (nAChR). The hydrogen/deuterium exchange spectra provide insight into both the overall rates and extent of peptide 1H/2H exchange and the individual rates and extent to which peptide hydrogens in alpha-helix and beta-sheet conformations exchange for deuterium. The spectra are also sensitive to the conformation of the polypeptide backbone and thus the secondary structure of the nAChR. The various spectral features monitored in the presence and absence of carbamylcholine and tetracaine are essentially identical, indicating that there are no large net changes in secondary structure in the channel-inactive desensitized state. The various spectral features monitored for the nAChR reconstituted into lipid membranes either with or without cholesterol are very similar, indicating that cholesterol is not a major structural regulator of the nAChR. However, in the absence of both cholesterol and anionic lipids, there is a slightly enhanced rate of exchange of alpha-helical peptide hydrogens for deuterium that occurs as a result of either an increase in nAChR dynamics or an increase in the accessibility of transmembrane peptide hydrogens to 2H2O. The latter may simply be due to an increase in the "fluidity" and thus permeability of the lipid bilayers to aqueous solvent.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Results indicate that SB-β-CyD and S-β,CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent β- CyD and HP- β-cyD.
Abstract: The hemolytic activity of beta-cyclodextrin (beta-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of beta-CyD; the membrane disrupting abilities decreased in the order of beta-CyD > 2-hydroxypropyl-beta-CyD (HP-beta-CyD) > sulfobutyl-beta-CyD (SB-beta-CyD) >> beta-CyD sulfate (S-beta-CyD). Under pre-hemolytic concentrations, both beta-CyD and SB-beta-CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S-beta-CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S-beta-CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike beta-CyD, S-beta-CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three beta-CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB-beta-CyD and S-beta-CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent beta-CyD and HP-beta-CyD.
TL;DR: The agreement suggests that both hydrodynamic and thermodynamic interactions are important determinants of diffusion coefficients of proteins in lipid bilayers, and the role of hydrod dynamic interactions in protein diffusion in reconstituted systems is confirmed.
TL;DR: Data support a postulated accessory role for PI-PLC with LLO in lysing the primary phagosome of a macrophage in a liposome lysis assay and the rate of binding of each protein was not influenced by the presence of the other.
Abstract: We have examined potential cooperative interactions of Listeria monocytogenes phosphatidylinositol-specific phospholipase C (PI-PLC) and listeriolysin O (LLO), a pore-forming hemolysin, in a liposome lysis assay. Large unilamellar vesicles, approximately 0.1 micron in diameter, encapsulating the fluorescent probe calcein, were treated with PI-PLC or LLO at pH 6.0, and each was capable of causing dye release. With phosphatidylcholine/phosphatidylinositol/cholesterol liposomes at 0.1 microM lipid, minimal release of dye was observed on addition of 80 pM LLO or 7 nM PI-PLC. Addition of the two proteins together produced rapid dye release. Unexpectedly, essentially identical results were obtained with phosphatidylcholine/cholesterol liposomes. Thus, the effect of PI-PLC did not depend on lipid hydrolysis. Both proteins also released inulin (M(r) 5200) from liposomes. Membrane permeabilization was not accompanied by membrane fusion. Very little dye release from phosphatidylcholine/phosphatidylinositol/cholesterol liposomes was seen with PI-PLC from Bacillus thuringiensis, and addition of this enzyme to LLO produced no additional dye release; however PI-PLC from L. monocytogenes cooperated with perfringolysin O from Clostridium perfringens. PI-PLC from L. monocytogenes and LLO bind to phosphatidylcholine/cholesterol liposomes, and the rate of binding of each protein was not influenced by the presence of the other. These data support a postulated accessory role for PI-PLC with LLO in lysing the primary phagosome of a macrophage.
Journal Article•
TL;DR: While studies suggest that permanent changes in membrane structure and function may result from radiation-induced injury to the plasma membrane and reconstituted "pure" membranes, reversibility of these defects over time requires additional study.
Abstract: In addition to interacting with genomic DNA, ionizing radiation may directly and indirectly alter the structure and function of components of the plasma membrane of eukaryotic cells. Water radiolysis generates reactive species, including superoxide, hypochlorous acid and chloride radicals that may in turn react with biological membranes, as well as with cellular DNA. Reaction of plasma membrane lipids with molecular oxygen results in lipid peroxidation of both reconstituted membranes and biological membranes, an effect that increases with decreasing dose rate. Both ionizing radiation and ultraviolet light alter functions of membrane-anchored molecules, including adhesion molecules, histocompatibility complex antigens and membrane-bound growth factors. The latter growth factors represent a repertoire of growth and differentiation signals that are expressed in a nondiffusible fashion at the cell surface, and in soluble forms appearing after cleavage of their extracellular domain. The importance of cell-cell signaling via the membrane-anchored form of growth factors is becoming increasingly recognized. Expression of membrane-bound hematopoietic cytokines by eukaryotic cells is impaired after exposure to ultraviolet light, a defect in cell-cell signaling that may lead to impaired hematopoiesis. While studies suggest that permanent changes in membrane structure and function may result from radiation-induced injury to the plasma membrane and reconstituted "pure" membranes, reversibility of these defects over time requires additional study.
TL;DR: The results suggest that the oxidant-induced loss of Na,K-ATPase activity in RCEC results primarily from changes in membrane lipids, and implicate both the inhibition and increases in membrane lipid peroxidation in the mechanism responsible for the delayed free radical-induced increase in RC EC membrane ‘permeability’.
Abstract: Na,K-ATPase activity, membrane lipid peroxidation (TBARM), and membrane 'leakiness' for small molecules were examined in rat cerebromicrovascular endothelial cells (RCEC) following exposure to hydrogen peroxide and xanthine/xanthine oxidase. Whereas short-term (15-30 min) exposure to either oxidant decreased ouabain-sensitive 86Rb uptake and increased TBARM in a concentration-dependent fashion, significant release of 51Cr (30-40%) from cells was observed only after one hour exposure to the oxidants. By comparison, much longer exposure times (i.e., 4 hours) were needed to induce significant lactate dehydrogenase release from oxidant-treated cells. The oxidant-evoked decrease in Na,K-ATPase activity and increases in TBARM and RCEC 'permeability' were abolished in the presence of the steroid antioxidants U-74500A and U-74389G (5-20 microM). Reduced glutathione (4 mM) partially attenuated oxidant-induced changes, whereas ascorbic acid (2 mM) and the disulfide bond-protecting agent, dithiothreitol (1 mM), were ineffective. These results suggest that the oxidant-induced loss of Na,K-ATPase activity in RCEC results primarily from changes in membrane lipids, and implicate both the inhibition of Na,K-ATPase and membrane lipid peroxidation in the mechanism responsible for the delayed free radical-induced increase in RCEC membrane 'permeability'.