Lipid Bilayer Of Plasma Membrane Research Articles

The Functional Activity of the Human Serotonin 5-HT1A Receptor Is Controlled by Lipid Bilayer Composition

Although the properties of the cell plasma membrane lipid bilayer are broadly understood to affect integral membrane proteins, details of these interactions are poorly understood. This is particularly the case for the large family of G protein-coupled receptors (GPCRs). Here, we examine the lipid dependence of the human serotonin 5-HT1A receptor, a GPCR that is central to neuronal function. We incorporate the protein in synthetic bilayers of controlled composition together with a fluorescent reporting system that detects GPCR-catalyzed activation of G protein to measure receptor-catalyzed oligonucleotide exchange. Our results show that increased membrane order induced by sterols and sphingomyelin increases receptor-catalyzed oligonucleotide exchange. Increasing membrane elastic curvature stress also increases this exchange. These results reveal the broad dependence that the 5-HT1A receptor has on plasma membrane properties, demonstrating that membrane lipid composition is a biochemical control parameter and highlighting the possibility that compositional changes related to aging, diet, or disease could impact cell signaling functions.

Axl Receptor Axis: A New Therapeutic Target in Lung Cancer

Abstract The Axl receptor tyrosine kinase belongs to the TAM (Tyro3, Axl, Mer) family of proteins and is upregulated in multiple types of cancers, including non-small cell lung cancer. In normal tissues, TAM receptor tyrosine kinases contribute to immune regulation. In cancer, Axl expression is associated with poor outcomes and is controlled through various transcriptional and epigenetic mechanisms. Preclinical studies have shown that Axl is involved in cancer cell migration, growth, survival and resistance to chemotherapy through activation of multiple downstream signaling pathways, such as Ras/MAPK, PI3K and Rac1. Axl is also expressed on endothelial cells and plays a role in angiogenesis. In preclinical models, Axl inhibition decreases cancer growth and impedes lung cancer metastases. Small molecule Axl inhibitors have been developed and are currently being used as monotherapy or in combination with cytotoxic chemotherapy or anti-EGFR therapy in early clinical trials. Here, we review Axl structure, functions, regulation, and preclinical and clinical studies in lung cancer.

Molecular insights into cell toxicity of a novel familial amyloidogenic variant of β2-microglobulin.

The first genetic variant of β2‐microglobulin (b2M) associated with a familial form of systemic amyloidosis has been recently described. The mutated protein, carrying a substitution of Asp at position 76 with an Asn (D76N b2M), exhibits a strongly enhanced amyloidogenic tendency to aggregate with respect to the wild‐type protein. In this study, we characterized the D76N b2M aggregation path and performed an unprecedented analysis of the biochemical mechanisms underlying aggregate cytotoxicity. We showed that, contrarily to what expected from other amyloid studies, early aggregates of the mutant are not the most toxic species, despite their higher surface hydrophobicity. By modulating ganglioside GM1 content in cell membrane or synthetic lipid bilayers, we confirmed the pivotal role of this lipid as aggregate recruiter favouring their cytotoxicity. We finally observed that the aggregates bind to the cell membrane inducing an alteration of its elasticity (with possible functional unbalance and cytotoxicity) in GM1‐enriched domains only, thus establishing a link between aggregate‐membrane contact and cell damage.

Modulation by Off-Flavors of CNG Channels in Olfactory Cilia

Olfactory transduction starts at the cilia that display a nano-scale structure (100 nm diameter). Binding of odorants to the receptor protein triggers the activation of G-protein and adenylyl cyclase, which leads to sequential openings of two transduction channels (CNG and Cl(Ca) channel). We have examined the effect of off-flavors that are generated in varieties of foods/beverages. Current responses of cilia were obtained from olfactory cells isolated from the newt using photolysis of caged cAMP under the whole-cell recording. One of the most powerful off-flavors is 2,4,6-trichloroanisole (TCA), which is known for inducing the cork taint in wines. Generally, it has been thought that off-flavor substances induce unpleasant smells exogenously. However, it was shown that TCA suppressed potently the transduction current. The order of potency of CNG suppression by TCA analogues (2,4,6-tribromoanisole) or precursors (2,4,6-trichlorophenol) were identical to that of the human detection of the corresponding off-flavors, suggesting that the cork taint is related to TCA suppression of CNG channels. Furthermore, current suppression by TCA was detected even with atto-molar (10−18 M) concentration. We saw the positive correlation between LogD of TCA derivatives and suppression ratio (SR) of CNG channels. It is likely that CNG channels are inhibited through a partitioning of those substances into the lipid bilayer of plasma membranes. These findings not only reveal a likely mechanism of flavor loss of foods/beverages, but also may suggest certain molecular structures for possible olfactory masking agents and powerful channel blockers.

Amyloid-β adopts a conserved, partially folded structure upon binding to zwitterionic lipid bilayers prior to amyloid formation.

Aggregation at the neuronal cell membrane's lipid bilayer surface is implicated in amyloid-β (Aβ) toxicity associated with Alzheimer's disease; however, structural and mechanistic insights into the process remain scarce. We have identified a conserved binding mode of Aβ40 on lipid bilayer surfaces with a conserved helix containing the self-recognition site (K16-E22).

Characterization of P4 ATPase Phospholipid Translocases (Flippases) in Human and Rat Pancreatic Beta Cells: THEIR GENE SILENCING INHIBITS INSULIN SECRETION

The negative charge of phosphatidylserine in lipid bilayers of secretory vesicles and plasma membranes couples the domains of positively charged amino acids of secretory vesicle SNARE proteins with similar domains of plasma membrane SNARE proteins enhancing fusion of the two membranes to promote exocytosis of the vesicle contents of secretory cells. Our recent study of insulin secretory granules (ISG) (MacDonald, M. J., Ade, L., Ntambi, J. M., Ansari, I. H., and Stoker, S. W. (2015) Characterization of phospholipids in insulin secretory granules in pancreatic beta cells and their changes with glucose stimulation. J. Biol. Chem. 290, 11075-11092) suggested that phosphatidylserine and other phospholipids, such as phosphatidylethanolamine, in ISG could play important roles in docking and fusion of ISG to the plasma membrane in the pancreatic beta cell during insulin exocytosis. P4 ATPase flippases translocate primarily phosphatidylserine and, to a lesser extent, phosphatidylethanolamine across the lipid bilayers of intracellular vesicles and plasma membranes to the cytosolic leaflets of these membranes. CDC50A is a protein that forms a heterodimer with P4 ATPases to enhance their translocase catalytic activity. We found that the predominant P4 ATPases in pure pancreatic beta cells and human and rat pancreatic islets were ATP8B1, ATP8B2, and ATP9A. ATP8B1 and CDC50A were highly concentrated in ISG. ATP9A was concentrated in plasma membrane. Gene silencing of individual P4 ATPases and CDC50A inhibited glucose-stimulated insulin release in pure beta cells and in human pancreatic islets. This is the first characterization of P4 ATPases in beta cells. The results support roles for P4 ATPases in translocating phosphatidylserine to the cytosolic leaflets of ISG and the plasma membrane to facilitate the docking and fusion of ISG to the plasma membrane during insulin exocytosis.

Low-Energy Ultrasound Treatment Improves Regional Tumor Vessel Infarction by Retargeted Tissue Factor.

To enhance the regional antitumor activity of the vascular-targeting agent truncated tissue factor (tTF)-NGR by combining the therapy with low-energy ultrasound (US) treatment. For the in vitro US exposure of human umbilical vein endothelial cells (HUVECs), cells were put in the focus of a US transducer. For analysis of the US-induced phosphatidylserine (PS) surface concentration on HUVECs, flow cytometry was used. To demonstrate the differences in the procoagulatory efficacy of TF-derivative tTF-NGR on binding to HUVECs with a low versus high surface concentration of PS, we performed factor X activation assays. For low-energy US pretreatment, HT1080 fibrosarcoma xenotransplant-bearing nude mice were treated by tumor-regional US-mediated stimulation (ie, destruction) of microbubbles. The therapy cohorts received the tumor vessel-infarcting tTF-NGR protein with or without US pretreatment (5 minutes after US stimulation via intraperitoneal injection on 3 consecutive days). Combination therapy experiments with xenotransplant-bearing nude mice significantly increased the antitumor activity of tTF-NGR by regional low-energy US destruction of vascular microbubbles in tumor vessels shortly before application of tTF-NGR (P < .05). Mechanistic studies proved the upregulation of anionic PS on the outer leaflet of the lipid bilayer of endothelial cell membranes by low-energy US and a consecutive higher potential of these preapoptotic endothelial cells to activate coagulation via tTF-NGR and coagulation factor X as being a basis for this synergistic activity. Combining retargeted tTF to tumor vessels with proapoptotic stimuli for the tumor vascular endothelium increases the antitumor effects of tumor vascular infarction. Ultrasound treatment may thus be useful in this respect for regional tumor therapy.

КВАНТОВО-ХІМІЧНЕ МОДЕЛЮВАННЯ ВЗАЄМОДІЇ МЕТИЛТРЕТБУТИЛОВОГО ЕФІРУ З ЛІПІДНИМ ШАРОМ ПЛАЗМАТИЧНОЇ МЕМБРАНИ

КВАНТОВО-ХІМІЧНЕ МОДЕЛЮВАННЯ ВЗАЄМОДІЇ МЕТИЛТРЕТБУТИЛОВОГО ЕФІРУ З ЛІПІДНИМ ШАРОМ ПЛАЗМАТИЧНОЇ МЕМБРАНИ

How is SR calcium release in muscle modulated by PIP(4,5)2?

Ion channels are embedded in the lipid bilayer of cell membranes; therefore, it is not surprising that their functions can be modulated by membrane phospholipids and their metabolites. Over the last decade, a number of ion channels—including multiple types of potassium channels, voltage-gated

Characterization of Phospholipids in Insulin Secretory Granules and Mitochondria in Pancreatic Beta Cells and Their Changes with Glucose Stimulation

The lipid composition of insulin secretory granules (ISG) has never previously been thoroughly characterized. We characterized the phospholipid composition of ISG and mitochondria in pancreatic beta cells without and with glucose stimulation. The phospholipid/protein ratios of most phospholipids containing unsaturated fatty acids were higher in ISG than in whole cells and in mitochondria. The concentrations of negatively charged phospholipids, phosphatidylserine, and phosphatidylinositol in ISG were 5-fold higher than in the whole cell. In ISG phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin, fatty acids 12:0 and 14:0 were high, as were phosphatidylserine and phosphatidylinositol containing 18-carbon unsaturated FA. With glucose stimulation, the concentration of many ISG phosphatidylserines and phosphatidylinositols increased; unsaturated fatty acids in phosphatidylserine increased; and most phosphatidylethanolamines, phosphatidylcholines, sphingomyelins, and lysophosphatidylcholines were unchanged. Unsaturation and shorter fatty acid length in phospholipids facilitate curvature and fluidity of membranes, which favors fusion of membranes. Recent evidence suggests that negatively charged phospholipids, such as phosphatidylserine, act as coupling factors enhancing the interaction of positively charged regions in SNARE proteins in synaptic or secretory vesicle membrane lipid bilayers with positively charged regions in SNARE proteins in the plasma membrane lipid bilayer to facilitate docking of vesicles to the plasma membrane during exocytosis. The results indicate that ISG phospholipids are in a dynamic state and are consistent with the idea that changes in ISG phospholipids facilitate fusion of ISG with the plasma membrane-enhancing glucose-stimulated insulin exocytosis.

Regioselective synthesis of diacylglycerol rosmarinates and evaluation of their antioxidant activity in fibroblasts

A series of new model of lipophilized phenolic compound derived from the rosmarinic acid was synthesized: 1,2‐diacylglycerol rosmarinate (RDAG) with different alkyl chain lengths from five to eighteen carbons. These RDAG were obtained through a chemo‐enzymatic synthesis: A chemical esterification based on the Mitsunobu reaction, followed by a lipase‐catalyzed transesterification to link the different lipophilic moieties. The antioxidant abilities of these molecules were assessed on reactive oxygen species (ROS) overexpressing fibroblasts. The RDAG12 displayed the best antioxidant activity of the series. Lengthening of the lipid chain beyond twelve carbon atoms leads to a decrease in the antioxidant activity, thus confirming the occurrence of a cut‐off effect. Antioxidant RDAG12 activity was then compared with that of vitamins C and E, rosmarinic acid and decyl rosmarinate (R10). The order of activity was R10 &gt; RDAG12 &gt; RDAG5 &gt; rosmarinic acid ∼ vitamin C ∼ vitamin E. At 5 μM, R10 exhibited an even better antioxidant activity than the combination of vitamins C and E at 5 μM each. These results confirm, firstly, that catechol structure is very effective in terms of antioxidant activity and secondly, that linking an appropriate hydrophobic domain is a powerful strategy to synthesize effective antioxidants.Practical applications: Phenolic compounds (especially phenolic acids and flavonoids) are potent antioxidants that may play an important role as well in biological system (to prevent some risk factors associated with cancers, cardiovascular, and neurodegenerative diseases) as in formulated‐lipid dispersions. However, their activity is often limited by low solubility and stability in such systems. Lipophilization of phenolic compounds may increase their solubility in lipophilic matrices, conferring better antioxidant protection for food or non‐food application. In biological system, lipophilization may contribute to easier penetration of antioxidants through lipid bilayer of cell membranes, which can significantly increase their bioavailability. Thus, lipophilic phenolic derivatives provide a perspective of substances with maintained or improved biological properties for food, cosmetic, and pharmaceutical applications, playing an important role in the development of new drugs or food additives.A series of new model of lipophilized phenolic compound (1,2‐diacylglycerol rosmarinate, RDAG) were synthesized through a chemo‐enzymatic synthesis. In terms of antioxidant activity assessed in fibroblasts, all synthesized RDAG exhibited higher ROS inhibition level than free rosmarinic acid. RDAG with two lauryl chains (RDAG12) displayed the best antioxidant ability of the series, with higher activity than vitamins E and C. These results confirm that linking an appropriate hydrophobic domain is a powerful strategy to synthesize effective antioxidants.

Novel understanding of ABC transporters ABCB1/MDR/P-glycoprotein, ABCC2/MRP2, and ABCG2/BCRP in colorectal pathophysiology.

To evaluate ATP-binding cassette (ABC) transporters in colonic pathophysiology as they had recently been related to colorectal cancer (CRC) development. Literature search was conducted on PubMed using combinations of the following terms: ABC transporters, ATP binding cassette transporter proteins, inflammatory bowel disease, ulcerative, colitis, Crohn's disease, colorectal cancer, colitis, intestinal inflammation, intestinal carcinogenesis, ABCB1/P-glycoprotein (P-gp/CD243/MDR1), ABCC2/multidrug resistance protein 2 (MRP2) and ABCG2/breast cancer resistance protein (BCRP), Abcb1/Mdr1a, abcc2/Mrp2, abcg2/Bcrp, knock-out mice, tight junction, membrane lipid function. Recently, human studies reported that changes in the levels of ABC transporters were early events in the adenoma-carcinoma sequence leading to CRC. A link between ABCB1, high fat diet and gut microbes in relation to colitis was suggested by the animal studies. The finding that colitis was preceded by altered gut bacterial composition suggests that deletion of Abcb1 leads to fundamental changes of host-microbiota interaction. Also, high fat diet increases the frequency and severity of colitis in specific pathogen-free Abcb1 KO mice. The Abcb1 KO mice might thus serve as a model in which diet/environmental factors and microbes may be controlled and investigated in relation to intestinal inflammation. Potential molecular mechanisms include defective transport of inflammatory mediators and/or phospholipid translocation from one side to the other of the cell membrane lipid bilayer by ABC transporters affecting inflammatory response and/or function of tight junctions, phagocytosis and vesicle trafficking. Also, diet and microbes give rise to molecules which are potential substrates for the ABC transporters and which may additionally affect ABC transporter function through nuclear receptors and transcriptional regulation. Another critical role of ABCB1 was suggested by the finding that ABCB1 expression identifies a subpopulation of pro-inflammatory Th17 cells which were resistant to treatment with glucocorticoids. The evidence for the involvement of ABCC2 and ABCG2 in colonic pathophysiology was weak. ABCB1, diet, and gut microbes mutually interact in colonic inflammation, a well-known risk factor for CRC. Further insight may be translated into preventive and treatment strategies.

Usefulness of Screening for Paroxismal Nocturnal Hemoglobinuria in Patients with Undefined Anemia

Background: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare life-threatening blood disease that is characterized by intravascular hemolytic anemia and thrombosis. It may be primary or secondary to other bone marrow diseases. It results from clonal expansion of a multipotent hematolopoietic stem cell harboring a PIG-A mutation. The PIG-A gene product is required for the biosynthesis of glycophosphatidylinositol anchors, a glycolipid moiety that tethers proteins to lipid bilayer of cell membranes. Consequently, the PNH stem cell and its progeny have a reduction or absence of all GPI-anchored proteins. Two of these proteins, CD55 and CD59, are complement regulatory proteins and are fundamental to the pathophysiology of paroxysmal nocturnal hemoglobinuria. CD55 inhibits C3 convertase and CD59 blocks the formation of the membrane attack complex (MAC). The loss of complement regulatory proteins renders PNH erythrocytes susceptible to both intravascular (due to CD59 deficiency) and extravascular (due to CD55 deficiency) hemolysis, but it is the intravascular hemolysis that contributes to much of the morbidity and mortality from the disease. Eculizumab is a humanized monoclonal antibody that is a terminal complement inhibitor and the first therapy approved for the treatment of PNH. In clinical trials in patients with PNH, eculizumab was associated with reductions in chronic hemolysis, thromboembolic events, and transfusion requirements, as well as improvements in PNH symptoms, quality of life, and survival. Methods: In a national observational study, 3162 patients with aplastic anemia, hemoglobinuria, myelodysplastic syndromes, undefined anemia, and atypical thrombosis have been evaluated for the PNH III clone. In a single center study in Reggio Calabria, Italy, 103 of the national registry patients were screened. Diagnostic flow cytometry for CD55 and CD59 on white and red blood cells was performed. Based on the levels of these cell proteins, cells may be classified as type I, II, or III PNH cells. Type I cells have normal levels of CD55 and CD59; type II have reduced levels; and type III have absent levels. Results: Of the national registry, 428 (13,5%) had GPI-linked defects. In the single center registry from Reggio Calabria, 3 cases (3%) with undefined anemia were identified as harboring the PNH III clone. Of the latter, at diagnosis, 2 patients had myelodysplastic syndromes and were red blood cell transfusion-dependent with high serum LDH levels (> 10 times upper normal limits) and one patient presented with cerebral venous thrombosis. They received Eculizumab according to international guidelines. The 2 patients with transfusion requirement obtained an erythroid response with transfusion independence with a significant decrease in serum LDH and the patient with cerebral thrombosis experienced complete recovery. Conclusions: PNH screening is useful among high risk populations. The identification of the PNH clone allows for targeted therapy to obtain clinically meaningful responses. DisclosuresOliva:Celgene: Consultancy, Honoraria; Novartis: Consultancy, Speakers Bureau.

Antagonism and synergy of single chain sphingolipids sphingosine and sphingosine-1-phosphate toward lipid bilayer properties. Consequences for their role as cell fate regulators.

A recurring question in membrane biological chemistry is whether bioactive signaling lipids act only as second messenger ligands or also through an effect on bilayer physical properties. Sphingosine (Sph) and sphingosine-1-phosphate (S1P) are single-chained charged sphingolipids that have antagonistic functions in the "sphingolipid rheostat" which determines cell fate. Sph and S1P respectively promote apoptosis and cell growth. In the present study, potential effects of these bioactive lipids on physicochemical properties of the lipid bilayer of cell membranes were evaluated. We have investigated the effect of both sphingolipids, incorporated separately or, for the first time, together, in large or giant phosphadidylcholine (PC) unilamellar vesicles. Three bilayer properties were examined: membrane surface charge, lipid packing, and formation of membrane microdomains. Sph and S1P appear to have distinct, when not inverse, effects on all three properties. Besides, when both sphingolipids are mixed together, their effects on lipid packing are synergistic, whereas their effects on microdomain formation and zeta-potential are mostly antagonistic. These results are interpreted as arising from different electrostatic interactions between lipid headgroups. In particular, Sph and S1P may interact together electrostatically and form a complex. These mostly inverse and opposing effects of both single-chain phospholipids on membrane physical properties might be involved in their antagonistic role in regulating cell fate. Particularly, the mutual interaction between Sph and S1P as a complex might be able to sequester both molecules in a biologically inactive form and therefore to promote a mutual regulation of their biological activities, depending on their ratio, consistent with the sphingolipid rheostat.

Polyphosphate goes from pedestrian to prominent in the marine P-cycle.

Phosphorus plays a key role in all life (1), from providing the energy that runs the cell machinery, linking nucleotides in RNA and DNA that form the “blueprint” of life, to being an integral part of the cell membrane lipid bilayer, making life possible by compartmentalizing biochemical processes. Polyphosphates (poly-P) are linear or cyclical polymers of a few to many hundreds of phosphate molecules linked with the same type of high-energy bond found in ATP, the key molecule in energy transactions within living cells, and poly-P may in fact act as a substitute for ATP in some enzymatic reactions (2). Poly-P was most likely present in prebiological times of the Earth’s history as these polymers spontaneously form during volcanic, or hydrothermal vent, activity (3). Additionally, it has been speculated that poly-P may have played a role in the origins of life on our planet (4). Although, poly-P appears to be ubiquitous throughout the natural world (5) and has long been recognized as a storage molecule for phosphate, relatively little has been known about its role and function in cells until quite recently (6). As a result, poly-P has sometimes been called a molecular “fossil” (7) due to its obscure and presumably pedestrian role in cell metabolism and hence has not garnered much scientific interest in the past. Nevertheless, over the last decades, it has become increasingly clear that poly-P may in fact be essential for a multitude of cellular functions, including, but not limited to, gene expression regulation, energy storage, motility, and ultimately the survival of the cell (4). However, the presence, distribution, and significance of poly-P in the marine environment and to its microbial inhabitants have been largely lacking, although recent metagenomic studies have suggested their potential importance to microorganisms in the oligotrophic oceans (8). Here, Martin et al. (9) present, to date, the most comprehensive study of poly-P content and distribution in particulate material in the marine environment. Their study transects the temperate western North Atlantic (TWNA) Ocean, which is relatively rich in nutrients, across the Gulf Stream and into the severely phosphorus-limited subtropical Sargasso Sea. Along this transect, which provides a natural gradient in nutrient regimes, they measure the poly-P content, among other phosphorus-relevant parameters, of the microbial communities in the upper water column, as well as the amount of poly-P in particles sinking out of the upper ocean into its deep interior.

A study of the antibacterial activity of l-Phenylalanine and l-Tyrosine esters in relation to their CMCs and their interactions with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC as model membrane

Cationic amino acid-based surfactants are known to interact with the lipid bilayer of cell membranes resulting in depolarization, lysis and cell death through a disruption of the membrane topology. A range of cationic surfactant analogues derived from l-Phenylalanine (C1–C20) and l-Tyrosine (C8–C14) esters have been synthesized and screened for their antibacterial activity. The esters were more active against gram positive than gram negative bacteria. The activity increased with increasing chain length, exhibiting a cut-off effect at C12 for gram positive and C8/C10 for gram negative bacteria. The cut-off effect for gram negative bacteria was observed at a lower alkyl chain length. The CMC was correlated with the MIC, inferring that micellar activity contribute to the cut-off effect in antibacterial activity. The interaction of the cationic surfactants with the phospholipid vesicles (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) in the presence of 1-anilino-8-naphthalene sulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH) as fluorescence probes showed that an increase in ionic interaction causes an increase in antibacterial activity. Increase in hydrophobic interaction increases the antibacterial activity only to a certain chain length, attributing to the cut-off effect. Therefore, both electrostatic and hydrophobic interactions, involving the polar and nonpolar moieties are of paramount importance for the bactericidal properties.

Omega 3 fatty acids and the brain: implications for nursing practice

This article synthesises the current literature regarding the effects of omega 3 polyunsaturated fatty acids (omega 3 PUFAs) in various neurological disorders and suggests implications for nursing practice. Omega 3 PUFAs are essential fatty acids and are crucial in cell functioning. Docosahexaenoic acid is a particularly important omega 3 PUFA that modulates the lipid bilayer of neuronal cell membranes, reduces inflammation and synthesises neuroprotectin D1, which has anti-apoptotic properties (preventing cell death). Omega 3 PUFAs are reported to have neuroprotective properties in Alzheimer's disease, ischaemia, epilepsy and attention-deficit hyperactivity disorder. Because humans are not able to synthesise omega 3 PUFAs, the body's supply comes from consumption. Nursing practice should include assessment for risks of neurological disorders as well as education regarding omega 3 PUFA intake. Knowledge of omega 3 PUFAs allows the nurse to educate patients thoroughly and accurately regarding the importance of these supplements.

2,4,6-Trichloroanisole is a potent suppressor of olfactory signal transduction

We investigated the sensitivity of single olfactory receptor cells to 2,4,6-trichloroanisole (TCA), a compound known for causing cork taint in wines. Such off-flavors have been thought to originate from unpleasant odor qualities evoked by contaminants. However, we here show that TCA attenuates olfactory transduction by suppressing cyclic nucleotide-gated channels, without evoking odorant responses. Surprisingly, suppression was observed even at extremely low (i.e., attomolar) TCA concentrations. The high sensitivity to TCA was associated with temporal integration of the suppression effect. We confirmed that potent suppression by TCA and similar compounds was correlated with their lipophilicity, as quantified by the partition coefficient at octanol/water boundary (pH 7.4), suggesting that channel suppression is mediated by a partitioning of TCA into the lipid bilayer of plasma membranes. The rank order of suppression matched human recognition of off-flavors: TCA equivalent to 2,4,6-tribromoanisole, which is much greater than 2,4,6-trichlorophenol. Furthermore, TCA was detected in a wide variety of foods and beverages surveyed for odor losses. Our findings demonstrate a potential molecular mechanism for the reduction of flavor.

Structural Insights into Clostridium perfringens Delta Toxin Pore Formation

Clostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins.

Arv1 Regulates PM and ER Membrane Structure and Homeostasis But is Dispensable for Intracellular Sterol Transport

The pan-eukaryotic endoplasmic reticulum (ER) membrane protein Arv1 has been suggested to play a role in intracellular sterol transport. We tested this proposal by comparing sterol traffic in wild-type and Arv1-deficient Saccharomyces cerevisiae. We used fluorescence microscopy to track the retrograde movement of exogenously supplied dehydroergosterol (DHE) from the plasma membrane (PM) to the ER and lipid droplets and high performance liquid chromatography to quantify, in parallel, the transport-coupled formation of DHE esters. Metabolic labeling and subcellular fractionation were used to assay anterograde transport of ergosterol from the ER to the PM. We report that sterol transport between the ER and PM is unaffected by Arv1 deficiency. Instead, our results indicate differences in ER morphology and the organization of the PM lipid bilayer between wild-type and arv1Δ cells suggesting a distinct role for Arv1 in membrane homeostasis. In arv1Δ cells, specific defects affecting single C-terminal transmembrane domain proteins suggest that Arv1 might regulate membrane insertion of tail-anchored proteins involved in membrane homoeostasis.