Showing papers on "Membrane lipids published in 2001"
TL;DR: The notion that in biomembranes selected lipids could laterally aggregate to form more ordered, detergent-resistant lipid rafts into which glycosphingolipid- and cholesterol-rich lipid domains partition is strongly supported by this study.
1,357 citations
TL;DR: Organelles in the endocytic pathway are composed of a mosaic of structural and functional regions, indicating that membrane organization might be modular.
Abstract: Organelles in the endocytic pathway are composed of a mosaic of structural and functional regions. These regions consist, at least in part, of specialized protein-lipid domains within the plane of the membrane, or of protein complexes associated with specific membrane lipids. Whereas some of these molecular assemblies can be found in more than one compartment, a given combination seems to be unique to each compartment, indicating that membrane organization might be modular.
742 citations
TL;DR: It is described here how the distribution of lipids is directed by proteins, and, conversely, how lipids influence the distribution and function of proteins.
Abstract: Cells determine the bilayer characteristics of different membranes by tightly controlling their lipid composition. Local changes in the physical properties of bilayers, in turn, allow membrane deformation, and facilitate vesicle budding and fusion. Moreover, specific lipids at specific locations recruit cytosolic proteins involved in structural functions or signal transduction. We describe here how the distribution of lipids is directed by proteins, and, conversely, how lipids influence the distribution and function of proteins.
566 citations
TL;DR: Current understanding of photodynamic (UVA- or visible light-induced) lipid peroxidation with a special focus on LOOH generation and reactivity is reviewed and future goals in this area, many of which depend on continued development of state-of-the-art analytical techniques, are discussed.
Abstract: Unsaturated lipids in cell membranes, including phospholipids and cholesterol, are well-known targets of oxidative modification, which can be induced by a variety of stresses, including ultraviolet A (UVA)- and visible light-induced photodynamic stress. Photodynamic lipid peroxidation has been associated with pathological conditions such as skin phototoxicity and carcinogenesis, as well as therapeutic treatments such as antitumor photodynamic therapy (PDT). Lipid hydroperoxides (LOOHs), including cholesterol hydroperoxides (ChOOHs), are important non-radical intermediates of the peroxidative process which can (i) serve as in situ reporters of type I vs. type II chemistry; (ii) undergo one-electron or two-electron reductive turnover which determines whether peroxidative injury is respectively intensified or suppressed; and (iii) mediate signaling cascades which either fortify antioxidant defenses of cells or evoke apoptotic death if oxidative pressure is too great. The purpose of this article is to review current understanding of photodynamic (UVA- or visible light-induced) lipid peroxidation with a special focus on LOOH generation and reactivity. Future goals in this area, many of which depend on continued development of state-of-the-art analytical techniques, will also be discussed.
548 citations
TL;DR: It is suggested that the ability of cationic lipids to promote nonbilayer structures in combination with anionic phospholipids leads to disruption of the endosomal membrane following uptake of nucleic acid–cationic lipid complexes into cells, thus facilitating cytoplasmic release of the plasmid or oligonucleotide.
Abstract: The mechanism whereby cationic lipids destabilize cell membranes to facilitate the intracellular delivery of macromolecules such as plasmid DNA or antisense oligonucleotides is not well understood. Here, we show that cationic lipids can destabilize lipid bilayers by promoting the formation of nonbilayer lipid structures. In particular, we show that mixtures of cationic lipids and anionic phospholipids preferentially adopt the inverted hexagonal (H(II)) phase. Further, the presence of 'helper' lipids such as dioleoylphosphatidylethanolamine or cholesterol, lipids that enhance cationic lipid-mediated transfection of cells also facilitate the formation of the H(II)phase. It is suggested that the ability of cationic lipids to promote nonbilayer structures in combination with anionic phospholipids leads to disruption of the endosomal membrane following uptake of nucleic acid-cationic lipid complexes into cells, thus facilitating cytoplasmic release of the plasmid or oligonucleotide.
521 citations
TL;DR: It is proposed that these rates of mechanochemical processes, such as endocytosis, membrane extension and membrane resealing after cell wounding, are also controlled physically, through an apparently continuous adhesion between plasma membrane lipids and cytoskeletal proteins.
Abstract: The rates of mechanochemical processes, such as endocytosis, membrane extension and membrane resealing after cell wounding, are known to be controlled biochemically, through interaction with regulatory proteins. Here, I propose that these rates are also controlled physically, through an apparently continuous adhesion between plasma membrane lipids and cytoskeletal proteins.
430 citations
TL;DR: Subfractionation and confocal immunofluorescence microscopy reveal that, in lung tissue and in cultured endothelial and epithelial cells, heterotrimeric G proteins target discrete cell surface microdomains and the G(q)-caveolin complex without G(betagamma) for trafficking, signaling, and mechanotransduction is discussed.
Abstract: Select lipid-anchored proteins such as glycosylphosphatidylinositol (GPI)-anchored proteins and nonreceptor tyrosine kinases may preferentially partition into sphingomyelin-rich and cholesterol-rich plasmalemmal microdomains, thereby acquiring resistance to detergent extraction. Two such domains, caveolae and lipid rafts, are morphologically and biochemically distinct, contain many signaling molecules, and may function in compartmentalizing cell surface signaling. Subfractionation and confocal immunofluorescence microscopy reveal that, in lung tissue and in cultured endothelial and epithelial cells, heterotrimeric G proteins (Gi, Gq, Gs, and Gβγ) target discrete cell surface microdomains. Gq specifically concentrates in caveolae, whereas Gi and Gs concentrate much more in lipid rafts marked by GPI-anchored proteins (5′ nucleotidase and folate receptor). Gq, apparently without Gβγ subunits, stably associates with plasmalemmal and cytosolic caveolin. Gi and Gs interact with Gβγ subunits but not caveolin. Gi and Gs, unlike Gq, readily move out of caveolae. Thus, caveolin may function as a scaffold to trap, concentrate, and stabilize Gq preferentially within caveolae over lipid rafts. In N2a cells lacking caveolae and caveolin, Gq, Gi, and Gs all concentrate in lipid rafts as a complex with Gβγ. Without effective physiological interaction with caveolin, G proteins tend by default to segregate in lipid rafts. The ramifications of the segregated microdomain distribution and the Gq-caveolin complex without Gβγ for trafficking, signaling, and mechanotransduction are discussed.
388 citations
TL;DR: A novel mechanism for proton leakage through lipid bilayers is proposed and a structure-function rationale for distinguishing the structures of the phytosterols as inhibitors of proton leaks from that of cholesterol which is proposed to inhibit leaks of Na(+).
367 citations
TL;DR: It is shown that treatment of Jurkat T cells with polyunsaturated eicosapentaenoic acid results in marked enrichment of PUFAs (20:5; 22:5) in lipids from isolated rafts, which provides strong evidence that displacement of acylated proteins from rafts in PUFA-treated T cells is predominantly due to altered raft lipid composition.
338 citations
01 Jun 2001
TL;DR: The current knowledge of the metabolic mechanisms involved in the divergence from the membrane-lipid biosynthetic pathway during storage lipid formation is presented and sequence information for genes encoding most of the enzymes involved is available.
Abstract: ▪ Abstract In many plants lipids represent up to 80% of dry weight of storage tissues. In seeds, lipids accumulate as triacylglycerols (TAGs), which are formed by an extension of the membrane-lipid biosynthetic pathway common to all plant tissues. In contrast to the conserved fatty acid (FA) composition of membrane lipids, the observed divergence in seed oil acyl chains among different species is very high. The acyl groups of seed TAGs can vary in their chain length (from 8 to 24) as well as in their degree of unsaturation. In addition to methylene-interrupted double bonds, many seeds contain TAGs that have unusual functional groups in their FAs, such as hydroxyl, oxirane, or acetylene groups. All of the major steps in the biosynthetic pathway to TAG are now known and sequence information for genes encoding most of the enzymes involved is available. Here we present the current knowledge of the metabolic mechanisms involved in the divergence from the membrane-lipid biosynthetic pathway during storage lipid...
329 citations
TL;DR: Using a novel x-ray absolute-scale refinement method, this work determines the location, orientation, and likely conformation of monomeric melittin in oriented phosphocholine lipid multilayers and provides direct structural evidence that self-association of amphipathic helices may be the crucial initial step toward membrane lysis.
TL;DR: A wave of studies using GFP-tagged membrane binding domains as reporters has led to new quantitative insights into the kinetics of these signaling mechanisms.
TL;DR: The molecular basis for the polymorphic phase behavior of lipids is outlined and some of the uses of nonbilayer lipids in the preparation of lipid-based delivery systems are highlighted.
TL;DR: It is suggested that the ABCA1-induced modification of the lipid distribution in the membrane, evidenced by the phosphatidylserine exofacial flopping, generates a biophysical microenvironment required for the docking of apoA-I at the cell surface.
TL;DR: It is demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress.
Abstract: In this study, the tolerance to salt stress of the photosynthetic machinery was examined in relation to the effects of the genetic enhancement of the unsaturation of fatty acids in membrane lipids in wild-type and desA+ cells of Synechococcus sp. PCC 7942. Wild-type cells synthesized saturated and mono-unsaturated fatty acids, whereas desA+ cells, which had been transformed with the desA gene for the Delta12 acyl-lipid desaturase of Synechocystis sp. PCC 6803, also synthesized di-unsaturated fatty acids. Incubation of wild-type and desA+ cells with 0.5 M NaCl resulted in the rapid loss of the activities of photosystem I, photosystem II, and the Na+/H+ antiport system both in light and in darkness. However, desA+ cells were more tolerant to salt stress and osmotic stress than the wild-type cells. The extent of the recovery of the various photosynthetic activities from the effects of 0.5 M NaCl was much greater in desA+ cells than in wild-type cells. The photosystem II activity of thylakoid membranes from desA+ cells was more resistant to 0.5 M NaCl than that of membranes from wild-type cells. These results demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress. The enhanced tolerance was due both to the increased resistance of the photosynthetic machinery to the salt-induced damage and to the increased ability of desA+ cells to repair the photosynthetic and Na+/H+ antiport systems.
TL;DR: Cholesterol and sphingomyelin-rich membrane rafts do not provide lipid for efflux promoted by apolipoproteins through theABCA1-mediated lipid secretory pathway and that ABCA1 is not associated with these domains.
TL;DR: It is suggested that the insertion of the toxin channel could imply the formation in the bilayer of a nonlamellar structure, a toroidal lipid pore, as in the case of PC/SM mixtures, where permeabilization was optimal when the molar ratio of PA/SM was ~1.
TL;DR: The results are relevant not only to the permeation of water and polar solutes into membranes and their permeabilities, but also to depth determinations of site-specifically spin-labeled protein residues by using paramagnetic relaxation agents.
Abstract: The isotropic 14N-hyperfine coupling constant, a, of nitroxide spin labels is dependent on the local environmental polarity. The dependence of a in fluid phospholipid bilayer membranes on the C-atom position, n, of the nitroxide in the sn-2 chain of a spin-labeled diacyl glycerophospholipid therefore determines the transmembrane polarity profile. The polarity variation in phospholipid membranes, with and without equimolar cholesterol, is characterized by a sigmoidal, trough-like profile of the form {1 + exp [(n − no)/λ]}−1, where n = no is the point of maximum gradient, or polarity midpoint, beyond which the free energy of permeation decreases linearly with n, on a characteristic length-scale, λ. Integration over this profile yields a corresponding expression for the permeability barrier to polar solutes. For fluid membranes without cholesterol, no ≈ 8 and λ ≈ 0.5–1 CH2 units, and the permeability barrier introduces an additional diffusive resistance that is equivalent to increasing the effective membrane thickness by 35–80%, depending on the lipid. For membranes containing equimolar cholesterol, no ≈ 9–10, and the total change in polarity is greater than for membranes without cholesterol, increasing the permeability barrier by a factor of 2, whereas the decay length remains similar. The permeation of oxygen into fluid lipid membranes (determined by spin-label relaxation enhancements) displays a profile similar to that of the transmembrane polarity but of opposite sense. For fluid membranes without cholesterol no ≈ 8 and λ ≈ 1 CH2 units, also for oxygen. The permeation profile for polar paramagnetic ion complexes is closer to a single exponential decay, i.e., no lies outside the acyl-chain region of the membrane. These results are relevant not only to the permeation of water and polar solutes into membranes and their permeabilities, but also to depth determinations of site-specifically spin-labeled protein residues by using paramagnetic relaxation agents.
TL;DR: Analysis of individual insertion steps of the polytopic E. coli membrane protein MtlA targeted as ribosome‐nascent chain complexes to inner membrane vesicles suggests that YidC forms a contiguous integration unit with the SecYE translocon and functions as an assembly site for polytopic membrane proteins mediating the formation of helix bundles prior to their release into the membrane lipids.
Abstract: Like its mitochondrial homolog Oxa1p, the inner membrane protein YidC of Escherichia coli is involved in the integration of membrane proteins. We have analyzed individual insertion steps of the polytopic E. coli membrane protein MtlA targeted as ribosome-nascent chain complexes to inner membrane vesicles. YidC can accommodate at least the first two transmembrane segments of MtlA at the protein lipid interface and retain them even though the length of the nascent chain would amply allow insertion into membrane lipids. An even longer insertion intermediate of MtlA is described that still has the first transmembrane helix bound to YidC while the third contacts SecE and YidC during integration. Our findings suggest that YidC forms a contiguous integration unit with the SecYE translocon and functions as an assembly site for polytopic membrane proteins mediating the formation of helix bundles prior to their release into the membrane lipids.
TL;DR: The purification and detailed characterization of microdomains from Golgi membranes show a brefeldin A-sensitive and temperature-sensitive localization to the Golgi complex and indicate that the microdomain scaffold is not required for protein interactions between these GIC proteins but instead might modulate their affinity.
Abstract: Sphingomyelin- and cholesterol-enriched microdomains can be isolated as detergent-resistant membranes from total cell extracts (total-DRM). It is generally believed that this total-DRM represents microdomains of the plasma membrane. Here we describe the purification and detailed characterization of microdomains from Golgi membranes. These Golgi-derived detergent-insoluble complexes (GICs) have a low buoyant density and are highly enriched in lipids, containing 25% of total Golgi phospholipids including 67% of Golgi-derived sphingomyelin, and 43% of Golgi-derived cholesterol. In contrast to total-DRM, GICs contain only 10 major proteins, present in nearly stoichiometric amounts, including the alpha- and beta-subunits of heterotrimeric G proteins, flotillin-1, caveolin, and subunits of the vacuolar ATPase. Morphological data show a brefeldin A-sensitive and temperature-sensitive localization to the Golgi complex. Strikingly, the stability of GICs does not depend on its membrane environment, because, after addition of brefeldin A to cells, GICs can be isolated from a fused Golgi-endoplasmic reticulum organelle. This indicates that GIC microdomains are not in a dynamic equilibrium with neighboring membrane proteins and lipids. After disruption of the microdomains by cholesterol extraction with cyclodextrin, a subcomplex of several GIC proteins including the B-subunit of the vacuolar ATPase, flotillin-1, caveolin, and p17 could still be isolated by immunoprecipitation. This indicates that several of the identified GIC proteins localize to the same microdomains and that the microdomain scaffold is not required for protein interactions between these GIC proteins but instead might modulate their affinity.
TL;DR: Results indicate that the limiting mobility of the midplane hydrocarbon region of the membranes formed by macrocyclic archaeol and caldarchaeol lipids play a significant role in reducing the permeability properties of the lipid membrane.
TL;DR: The presence of the capsular polysaccharide turned out to be essential for viability without LPS, as demonstrated by using a strain in which LPS biosynthesis could be switched on or off through a tac promoter‐controlled lpxA gene.
Abstract: In the pathogen Neisseria meningitidis, a completely lipopolysaccharide (LPS)-deficient but viable mutant can be obtained by insertional inactivation of the lpxA gene, encoding UDP-GlcNAc acyltransferase required for the first step of lipid A biosynthesis. To study how outer membrane structure and biogenesis are affected by the absence of this normally major component, inner and outer membranes were separated and their composition analysed. The expression and assembly of integral outer membrane proteins appeared largely unaffected. However, the expression of iron limitation-inducible, cell surface-exposed lipoproteins was greatly reduced. Major changes were seen in the phospholipid composition, with a shift towards phosphatidylethanolamine and phosphatidylglycerol species containing mostly shorter chain, saturated fatty acids, one of which was unique to the LPS-deficient outer membrane. The presence of the capsular polysaccharide turned out to be essential for viability without LPS, as demonstrated by using a strain in which LPS biosynthesis could be switched on or off through a tac promoter-controlled lpxA gene. Taken together, these results can help to explain why meningococci have the unique ability to survive without LPS.
TL;DR: Stored curvature strain energy is an important determinant of CT activation and may reflect an increased surface hydrophobicity of class II lipid membranes, implying a role for surface dehydration in CT's interactions with membranes containing class II lipids.
Abstract: CTP:Phosphocholine cytidylyltransferase (CT) catalyzes the key step in phosphatidylcholine (PC) synthesis. CT is activated by binding to certain lipid membranes. The membrane binding affinity of CT can vary from micromolar to millimolar K(d), depending on the lipid composition of the target membrane. Class II CT activators like diacylglycerols and unsaturated phosphatidylethanolamines (PE) favor inverted lipid phase formation. The mechanism(s) governing CT's association with class II lipid membranes and subsequent activation are relatively unknown. We measured CT activation by vesicles composed of PC and one of three unsaturated PEs, dioleoylglycerol (DOG), or cholesterol. For each lipid system, we estimated the stored curvature strain energy of the monolayer when confined to a relatively flat bilayer. CT binding and activation correlate very well with the curvature strain energy of several chemically distinct class II lipid systems, with the exception of those containing cholesterol, in which CT activation was less than the increase in curvature strain. CT activation by membranes containing DOG was reversed by inclusion of specific lysolipids, which reduce curvature strain energy. LysoPC, which has a larger positive curvature than lysoPE, produced greater inhibition of CT activation. Stored curvature strain energy is thus an important determinant of CT activation. Membrane interfacial polarity was investigated using a membrane-anchored fluorescent probe. Decreases in quenching of this interfacial probe by doxyl-PCs in class II membranes suggest the probe adopts a more superficial membrane location. This may reflect an increased surface hydrophobicity of class II lipid membranes, implying a role for surface dehydration in CT's interactions with membranes containing class II lipids. Cholesterol, a poor activator of CT, did not affect the positioning of the polarity-sensitive probe, suggesting that one reason for its ineffectiveness is an inability to enhance surface hydrophobicity.
TL;DR: Catabolism of all major HDL lipids can occur via SR-BI with the relative selective uptake rate constants for CE, free cholesterol, triglycerides, and phosphatidylcholine being 1, 1.6, 0.7, and 0.2, respectively.
TL;DR: Flaws determining the location of the fluorophore in the lipid water interface are discussed and a slight preference of the NBD group for the lipid-water interface is found for C12-NBD-PC in comparison with C6-N BD-PC.
TL;DR: Analysis of pre- and post-field fluorescent vesicles images, as well as images from negatively stained electron micrographs, indicate that pore formation is associated with a partial loss of the phospholipid bilayer from the vesicle membrane.
TL;DR: It is proposed that the SLOT domain in the viral membrane is the cholesterol-rich raft domain stabilized by the trimers of hemagglutinin and/or the tetramers of neuraminidase, which represents about one-third of the membrane area.
TL;DR: The results show that the dimerization process is stringently controlled by a narrow window of membrane thickness, which could be significant in membranes that have very low cholesterol content, such as the endoplasmic reticulum and the inner mitochondrial membrane, and in trafficking and sorting of cellular cholesterol.
TL;DR: Evidence is presented suggesting that phospholipid-rich, liquid-crystalline phase domains and sphingolipids-rich and liquid-ordered phase domains (rafts) can exist in equilibrium in biological membranes, especially the plasma membrane.
TL;DR: Results from X-ray crystallography are shedding new light on the precise molecular details of the protein-lipid interface.