Properties Of Biological Membranes Research Articles

(p)ppGpp Buffers Cell Division When Membrane Fluidity Decreases in Escherichia coli.

Fluidity is an inherent property of biological membranes and its maintenance (homeoviscous adaptation) is important for optimal functioning of membrane-associated processes. The fluidity of bacterial cytoplasmic membrane increases with temperature or an increase in the proportion of unsaturated fatty acids and vice versa. We found that strains deficient in the synthesis of guanine nucleotide analogs (p)ppGpp and lacking FadR, a transcription factor involved in fatty acid metabolism exhibited a growth defect that was rescued by an increase in growth temperature or unsaturated fatty acid content. The strain lacking (p)ppGpp was sensitive to genetic or chemical perturbations that decrease the proportion of unsaturated fatty acids over saturated fatty acids. Microscopy showed that the growth defect was associated with cell filamentation and lysis and rescued by combined expression of cell division genes ftsQ, ftsA, and ftsZ from plasmid or the gain-of-function ftsA* allele but not over-expression of ftsN. The results implicate (p)ppGpp in positive regulation of cell division during membrane fluidity loss through enhancement of FtsZ proto-ring stability. To our knowledge, this is the first report of a (p)ppGpp-mediated regulation needed for adaptation to membrane fluidity loss in bacteria.

Coordination of bilayer properties by an inward-rectifier K+ channel is a cooperative process driven by protein-lipid interaction

Physical properties of biological membranes directly or indirectly govern biological processes. Yet, the interplay between membrane and integral membrane proteins is difficult to assess due to reciprocal effects between membrane proteins, individual lipids, and membrane architecture. Using solid-state NMR (SSNMR) we previously showed that KirBac1.1, a bacterial Inward-Rectifier K+ channel, nucleates bilayer ordering and microdomain formation through tethering anionic lipids. Conversely, these lipids cooperatively bind cationic residues to activate the channel and initiate K+ flux. The mechanistic details governing the relationship between cooperative lipid loading and bilayer ordering are, however, unknown. To investigate, we generated KirBac1.1 samples with different concentrations of 13C-lableded phosphatidyl glycerol (PG) lipids and acquired a full suite of SSNMR 1D temperature series experiments using the ordered all-trans (AT) and disordered trans-gauche (TG) acyl conformations as markers of bilayer dynamics. We observed increased AT ordered signal, decreased TG disordered signal, and increased bilayer melting temperature with increased PG concentration. Further, we identified cooperativity between ordering and direct binding of PG lipids, indicating KirBac1.1-driven bilayer ordering and microdomain formation is a classically cooperative Hill-type process driven by and predicated upon direct binding of PG lipids. Our results provide unique mechanistic insight into how proteins and lipids in tandem contribute to supramolecular bilayer heterogeneity in the lipid membrane.

Unveiling the consequences of early human saliva contamination on membranes for guided bone regeneration.

GBR membranes have various surface properties designed to elicit positive responses in regenerative clinical procedures; dental clinicians attempt to employ techniques to prevent the direct interaction of contaminated oral fluids with these biomaterials. However, saliva is uninterruptedly exhibited in oral surgical procedures applying GBR membranes, suggesting a persistent interaction with biomaterials and the surrounding oral tissues. This fundamental study aimed to investigate potential alterations in the physical, chemical, and key biological properties of membranes for guided bone regeneration (GBR) caused by isolated early interaction with human saliva. A reproducible step-by-step protocol for collecting and interacting human saliva with membranes was developed. Subsequently, membranes were evaluated for their physicochemical properties, protein quantification, DNA, and 16S rRNA levels viability of two different cell lines at 1 and 7 days, and ALP activity. Non-interacted membranes and pure saliva of donors were applied as controls. Qualitative morphological alterations were noticed; DNA extraction and 16S quantification revealed significantly higher values. Furthermore, the viability of HGF-1 and MC3T3-E1 cells was significantly (p < .05) reduced following saliva interaction with biodegradable membranes. Saliva contamination did not prejudice PTFE membranes significantly in any biological assay. These outcomes demonstrated a susceptible response of biodegradable membranes to isolated early human saliva interaction, suggesting impairment of structural morphology, reduced viability to HGF-1 and MC3T3-E1, and higher absorption/adherence of DNA/16S rRNA. As a result, clinical oral procedures may need corresponding refinements.

The intracellular growth of the vacuolar pathogen Legionella pneumophila is dependent on the acyl chain composition of host membranes

Legionella pneumophila is an accidental human bacterial pathogen that infects and replicates within alveolar macrophages causing a severe atypical pneumonia known as Legionnaires’ disease. As a prototypical vacuolar pathogen L. pneumophila establishes a unique endoplasmic reticulum (ER)-derived organelle within which bacterial replication takes place. Bacteria-derived proteins are deposited in the host cytosol and in the lumen of the pathogen-occupied vacuole via a type IVb (T4bSS) and a type II (T2SS) secretion system respectively. These secretion system effector proteins manipulate multiple host functions to facilitate intracellular survival of the bacteria. Subversion of host membrane glycerophospholipids (GPLs) by the internalized bacteria via distinct mechanisms feature prominently in trafficking and biogenesis of the Legionella-containing vacuole (LCV). Conventional GPLs composed of a glycerol backbone linked to a polar headgroup and esterified with two fatty acids constitute the bulk of membrane lipids in eukaryotic cells. The acyl chain composition of GPLs dictates phase separation of the lipid bilayer and therefore determines the physiochemical properties of biological membranes - such as membrane disorder, fluidity and permeability. In mammalian cells, fatty acids esterified in membrane GPLs are sourced endogenously from de novo synthesis or via internalization from the exogenous pool of lipids present in serum and other interstitial fluids. Here, we exploited the preferential utilization of exogenous fatty acids for GPL synthesis by macrophages to reprogram the acyl chain composition of host membranes and investigated its impact on LCV homeostasis and L. pneumophila intracellular replication. Using saturated fatty acids as well as cis- and trans- isomers of monounsaturated fatty acids we discovered that under conditions promoting lipid packing and membrane rigidification L. pneumophila intracellular replication was significantly reduced. Palmitoleic acid – a C16:1 monounsaturated fatty acid – that promotes membrane disorder when enriched in GPLs significantly increased bacterial replication within human and murine macrophages but not in axenic growth assays. Lipidome analysis of infected macrophages showed that treatment with exogenous palmitoleic acid resulted in membrane acyl chain reprogramming in a manner that promotes membrane disorder and live-cell imaging revealed that the consequences of increasing membrane disorder impinge on several LCV homeostasis parameters. Collectively, we provide experimental evidence that L. pneumophila replication within its intracellular niche is a function of the lipid bilayer disorder and hydrophobic thickness.

The effect of structural changes on the self-assembly of novel green pyridinium-carboxylate gemini surfactants in Langmuir and Langmuir-Blodgett films.

Engineered molecules with tailored molecular structures have the potential to advance various disciplines by enhancing the properties of biological membranes. In this study, we investigated the fundamental interfacial behavior of newly synthesized, water insoluble, cationic pyridinium-carboxylate based gemini surfactants (GSs) using picolinic acid (PA), nicotinic acid (NA), and isonicotinic acid (INA) and their interactions with dipalmitoylphosphatidylcholine (DPPC) in Langmuir and Langmuir-Blodgett (LB) films. Two synthetic methodologies were employed: (a) connecting two alkyl pyridinecarboxylates through the nitrogen atoms with a xylenyl spacer, namely, PAGS, NAGS1, and INAGS; and (b) dimerizing two nicotinic acid molecules through ester linkages with 1,4-benzenedimethanol, and then quaternizing the pyridine nitrogens with hexadecyl chains to yield NAGS2. A combination of Brewster angle microscopy (BAM) and atomic force microscopy (AFM) imaging techniques yielded valuable insights into the morphology of the GS films and their mixtures with DPPC. Density functional theory (DFT) calculations were used to gain further information on the GSs structures and understand their assembly. The results indicate that the film of INAGS is the most hydrophobic film, and its monolayer is the least compressible. When the nitrogen atom and a carboxylate group of the headgroup are positioned closer to each other, the GS molecules tend to form aggregates instead of a continuous film which is observed for the INAGS surfactant. This observation is consistent with the DFT energy values of pair interactions, indicating that both PAGS and NAGS1 have closely packed conformations with high stabilization energy.

Changes in Ion Transport across Biological Membranes Exposed to Particulate Matter.

The cells of living organisms are surrounded by the biological membranes that form a barrier between the internal and external environment of the cells. Cell membranes serve as barriers and gatekeepers. They protect cells against the entry of undesirable substances and are the first line of interaction with foreign particles. Therefore, it is very important to understand how substances such as particulate matter (PM) interact with cell membranes. To investigate the effect of PM on the electrical properties of biological membranes, a series of experiments using a black lipid membrane (BLM) technique were performed. L-α-Phosphatidylcholine from soybean (azolectin) was used to create lipid bilayers. PM samples of different diameters (<4 (SRM-PM4.0) and <10 μm (SRM-PM10) were purchased from The National Institute of Standards and Technology (USA) to ensure the repeatability of the measurements. Lipid membranes with incorporated gramicidin A (5 pg/mL) ion channels were used to investigate the effect of PM on ion transport. The ionic current passing through the azolectin membranes was measured in ionic gradients (50/150 mM KCl on cis/trans side). In parallel, the electric membrane capacitance measurements, analysis of the conductance and reversal potential were performed. Our results have shown that PM at concentration range from 10 to 150 μg/mL reduced the basal ionic current at negative potentials while increased it at positive ones, indicating the interaction between lipids forming the membrane and PM. Additionally, PM decreased the gramicidin A channel activity. At the same time, the amplitude of channel openings as well as single channel conductance and reversal potential remained unchanged. Lastly, particulate matter at a concentration of 150 μg/mL did not affect the electric membrane capacity to any significant extent. Understanding the interaction between PM and biological membranes could aid in the search for effective cytoprotective strategies. Perhaps, by the use of an artificial system, we will learn to support the consequences of PM-induced damage.

Small-angle scattering from flat bilayers containing correlated scattering length density inhomogeneities.

Model lipid bilayers have been widely employed as a minimal system to investigate the structural properties of biological membranes by small-angle X-ray (SAXS) and neutron scattering (SANS) techniques. These have nanometre resolution and can give information regarding membrane thickness and scattering length densities (SLDs) of polar and apolar regions. However, biological membranes are complex systems containing different lipids and protein species, in which lipid domains can be dynamically assembled and disassembled. Therefore, SLD variations can occur within the biomembrane. In this work, a novel method has been developed to simulate SAXS and SANS profiles obtained from large unilamellar vesicles containing SLD inhomogeneities that are spatially correlated over the membrane surface. Such inhomogeneities are represented by cylindrical entities with equivalent SLDs. Stacking of bilayers is also included in the model, with no correlation between horizontal and vertical order. The model is applied to a lipid bilayer containing SLD inhomogeneities representing pores, lipid domains, and transmembrane, partially immersed and anchored proteins. It is demonstrated that all the structural information from the host lipid bilayer and from the SLD inhomogeneity can be consistently retrieved by a combined analysis of experimental SAXS and SANS data through the methodology proposed here.

Comparative analysis of drought stress-induced physiological and transcriptional changes of two black sesame cultivars during anthesis.

Sesame production is severely affected by unexpected drought stress during flowering stage. However, little is known about dynamic drought-responsive mechanisms during anthesis in sesame, and no particular attention was given to black sesame, the most common ingredient in East Asia traditional medicine. Herein, we investigated drought-responsive mechanisms of two contrasting black sesame cultivars (Jinhuangma, JHM, and Poyanghei, PYH) during anthesis. Compared to PYH, JHM plants showed higher tolerance to drought stress through the maintenance of biological membrane properties, high induction of osmoprotectants' biosynthesis and accumulation, and significant enhancement of the activities of antioxidant enzymes. For instance, the drought stress induced a significant increase in the content of soluble protein (SP), soluble sugar (SS), proline (PRO), glutathione (GSH), as well as the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in leaves and roots of JHM plants compared to PYH plants. RNA sequencing followed by differentially expressed genes (DEGs) analysis revealed that more genes were significantly induced under drought in JHM than in PYH plants. Functional enrichment analyses disclosed that several pathways related to drought stress tolerance, such as photosynthesis, amino acids and fatty acid metabolisms, peroxisome, ascorbate and aldarate metabolism, plant hormone signal transduction, biosynthesis of secondary metabolites, and glutathione metabolism, were highly stimulated in JHM than in PYH plants. Thirty-one (31) key highly induced DEGs, including transcription factors and glutathione reductase and ethylene biosynthetic genes, were identified as potential candidate genes for improving black sesame drought stress tolerance. Our findings show that a strong antioxidant system, biosynthesis and accumulation of osmoprotectants, TFs (mainly ERFs and NACs), and phytohormones are essential for black sesame drought tolerance. Moreover, they provide resources for functional genomic studies toward molecular breeding of drought-tolerant black sesame varieties.

Physical properties of phospholipids at low temperatures through Slipid force field

Slipid (Stockholm lipids) force field is suitable for the description of the physical properties of biological membranes composed of phospholipids at room temperature. So far, its accuracy to reproduce the behavior of the thermodynamic and structural quantities of membranes at low temperatures has not yet been tested in sufficient details. In the present study, we compute some characteristic quantities of SOPC (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) using GROMACS in conjunction with Slipid force field. The initial configuration of the SOPC system composed of 128 lipid molecules distributed equally in each monolayer and 5120 water molecules was generated with the aid of CHARMM-GUI. Atomistic molecular dynamic (MD) simulations were performed at several temperatures. By virtue of a statistical analysis of trajectories, we computed the main structural parameters of the lipid molecules and thermodynamic quantities characterizing the phase behavior of the bilayer. The results are compared to available experimental data, as well as theoretical predictions. The Slipid force field was found to describe fairly well the structural behavior of the lipids at low temperatures.

ВЛИЯНИЕ ЭКСТРАКТА RUMEX CONFERTUS НА МЕТАБОЛИЧЕСКИЕ ПРОЦЕССЫ В ОРГАНИЗМЕ

Vital physiological and metabolic processes occurring in the human body are associated with free radical oxidation, which affects the structure, permeability and physico-chemical properties of biological membranes. Horse sorrel is used for scurvy, gout, diabetes, jaundice, hypertension, rheumatism, skin diseases – scabies, lichen, eczema, burns, as well as diseases of the digestive and cardiovascular systems. The purpose of the research: to study the technology of obtaining liquid extract of horse sorrel roots and to study its antioxidant activity on the body. Liquid extract of horse sorrel roots and auxiliary substances were used as the object of the study: dimethyl sulfoxide DMSO, ethyl alcohol 96%, quercetin, lecithin. When performing the work, equipment was used: liquid chromatograph "Color Yauza-01-AA", SF-LEKISS 1207UV. The object of the study of the total antioxidant activity were extracts of horse sorrel roots obtained using ethyl alcohol in concentration: 30%, 40%, 50%, 60%, 70%, 80%. The total content of antioxidants in the studied liquid extracts of horse sorrel roots was determined by two methods: using a liquid chromatograph "Color Yauza-01-AA" with an amperometric detector. The quantitative content of antioxidants was determined according to the calibration schedule. The conversion was carried out for gallic acid and quercetin. Using a model of iron-induced lipid peroxidation in the system of lecithin (phosphotidylcholine) liposomes, the studied liquid extracts were evaluated by reducing the accumulation of peroxide compounds. The study was carried out at a concentration of 200 mcg/ml to 500 mcg/ml of horse sorrel extract and increasing the dose.

Amphiphilic Liquid Crystalline Polymer Micelles That Exhibit a Phase Transition at Body Temperature

Liquid crystalline polymers (LCPs), which exhibit unique structures and properties intermediate between those of liquids and solids, are widely utilized as functional and advanced materials for fabricating optical devices and high-performance fibers. This utility stems from their ability to abruptly change their organized structures and mobilities at their liquid crystalline-isotropic phase transition temperatures, similar to the properties of biological membranes. Despite these numerous potential applications of LCPs, no study on their use in medical applications such as drug delivery has been reported. In the present study, we synthesized amphiphilic side-chain LCPs (LCP-g-OEGs, where OEG is oligo(ethylene glycol)) for medical applications, where the LCP-g-OEGs undergo a nematic-isotropic phase transition at body temperature. The LCP-g-OEGs formed micelles with a diameter of approximately 130 nm in aqueous media. The micelles were stable and did not dissociate in aqueous media even when the temperature exceeded the nematic-isotropic phase transition temperature (TNI). Although the release of a dye as a model drug from micelles was suppressed at temperatures lower than TNI, their dye release was drastically enhanced at temperatures higher than TNI. The LCP-g-OEG micelles regulated dye release reversibly in accordance with stepwise changes in temperature, without undergoing dissociation, differing from the behavior of standard temperature-responsive micelles. The temperature-responsive dye release behavior is induced by dramatic changes in their well-organized and dynamic structures as a result of the nematic-isotropic phase transition. These results demonstrate that the LCP-g-OEG micelles have a lot of medical applications as reversibly stimuli-responsive drug carriers.

Curvature-based sorting of eight lipid types in asymmetric buckled plasma membrane models

Curvature is a fundamental property of biological membranes and has essential roles in cellular function. Bending of membranes can be induced by their lipid and protein compositions, as well as peripheral proteins, such as those that make up the cytoskeleton. An important aspect of membrane function is the grouping of lipid species into microdomains, or rafts, which serve as platforms for specific biochemical processes. The fluid mosaic model of membranes has evolved to recognize the importance of curvature and leaflet asymmetry, and there are efforts toward evaluating their functional roles. This work investigates the effect of curvature on the sorting of lipids in buckled asymmetric bilayers containing eight lipid types, approximating an average mammalian plasma membrane, through coarse-grained (CG) molecular dynamics (MD) simulations with the Martini force field. The simulations reveal that 1) leaflet compositional asymmetry can induce curvature asymmetry, 2) lipids are sorted by curvature to different extents, and 3) curvature-based partitioning trends show moderate to strong correlations with lipid molecular volumes and head to tail bead ratios, respectively. The findings provide unique insights into the role of curvature in membrane organization, and the curvature-based sorting trends should be useful references for later investigations and potentially interpreting the functional roles of specific lipids.

Laurdan in live cell imaging: Effect of acquisition settings, cell culture conditions and data analysis on generalized polarization measurements.

Cell function is highly dependent on membrane structure, organization, and fluidity. Therefore, methods to probe the biophysical properties of biological membranes are required. Determination of generalized polarization (GP) values using Laurdan in fluorescence microscopy studies is one of the most widely-used methods to investigate changes in membrane fluidity in vitro and in vivo. In the last couple of decades, there has been a major increase in the number of studies using Laurdan GP, where several different methodological approaches are used. Such differences interfere with data interpretation inasmuch as it is difficult to validate if Laurdan GP variations actually reflect changes in membrane organization or arise from biased experimental approaches. To address this, we evaluated the influence of different methodological details of experimental data acquisition and analysis on Laurdan GP. Our results showed that absolute GP values are highly dependent on several of the parameters analyzed, showing that incorrect data can result from technical and methodological inconsistencies. Considering these differences, we further analyzed the impact of cell variability on GP determination, focusing on basic cell culture conditions, such as cell confluency, number of passages and media composition. Our results show that GP values can report alterations in the biophysical properties of cell membranes caused by cellular adaptation to the culture conditions. In summary, this study provides thorough analysis of the factors that can lead to Laurdan GP variability and suggests approaches to improve data quality, which would generate more precise interpretation and comparison within individual studies and among the literature on Laurdan GP.

Structural determination of model phospholipid membranes by Raman spectroscopy: Laboratory experiment.

In an upper-division interdisciplinary laboratory experiment, students use Raman spectroscopy to highlight how the overall structure and conformational order of lipid bilayers can be influenced by their individual phospholipid composition. Students prepare a supported lipid bilayer, as a model cell membrane, by spreading liposomes made of various phospholipids on a solid support. The characterization of phospholipid bilayers, a major component of cellular membranes, can advance our fundamental understanding of important biological phenomena, with significant implications in various fields including drug delivery and development. We use Raman spectroscopy as an analytical tool to investigate the structural and packing properties of model cell membranes. The spectral frequency, intensity, and line-width of lipid Raman bands are extremely sensitive to structural alterations. This experimental module effectively exposes students to the fundamentals of Raman spectroscopy and teaches students the importance of interdisciplinary education as they integrate concepts from chemical structure, molecular interactions, and analytical spectroscopic techniques to gain a more holistic understanding of biological membrane properties.

Biomimetic Membranes without Proteins but with Aqueous Nanochannels and Facilitated Transport. Minireview

Imitation of biological membranes and aqueous channels attracts more and more attention. In this review, we mention both the early and very recent papers in this area. Still, we concentrate our attention on less known biomimetic membranes, which are commercial nitrocellulose ultrafilters, impregnated by esters of fatty acids. Pores in filters are filled with lipid-like oils, but aqueous nanochannels are spontaneously formed on the inner pore surfaces with carboxylic groups fixed on nitrocellulose. This combination imitates the most fundamental barrier properties of biological membranes, including specific (per unit thickness) permeability of respiratory gases, transport of nonelectrolytes, water, and ions, cation/anion selectivity, electric impedance, etc. The activation energy for water transport in nanochannels is similar to that in aquaporin. In the presence of fatty acids and other carriers, it is possible to observe facilitated and coupled active counter transport of different metal cations in exchange to H+ and without any transmembrane pressure, voltage or ATP. When quinones are dissolved in oils, light-sensitive co-transport of electrons and H+ through oil is possible. In this case, redox-active substances are separated by the membrane. They are not mixed, but they still react. Small biomimetic membranes can be used as electrochemical drug sensors in drug detection and screening, medium size membranes—for smart transdermal drug -delivery, and large membranes—for industrial separation and purification. For example, after small modifications, they can be used for metal recovery, including radioactive strontium removal from nuclear waste accumulated and stored since the Cold War.

Lipid flippases as key players in plant adaptation to their environment.

Lipid flippases (P4 ATPases) are active transporters that catalyse the translocation of lipids between the two sides of the biological membranes in the secretory pathway. This activity modulates biological membrane properties, contributes to vesicle formation, and is the trigger for lipid signalling events, which makes P4 ATPases essential for eukaryotic cell survival. Plant P4 ATPases (also known as aminophospholipid ATPases (ALAs)) are crucial for plant fertility and proper development, and are involved in key adaptive responses to biotic and abiotic stress, including chilling tolerance, heat adaptation, nutrient deficiency responses and pathogen defence. While ALAs present many analogies to mammalian and yeast P4 ATPases, they also show characteristic features as the result of their independent evolution. In this Review, the main properties, roles, regulation and mechanisms of action of ALA proteins are discussed.

The membrane transporter lactose permease increases lipid bilayer bending rigidity

Cellular life relies on membranes, which provide a resilient and adaptive cell boundary. Many essential processes depend upon the ease with which the membrane is able to deform and bend, features that can be characterized by the bending rigidity. Quantitative investigations of such mechanical properties of biological membranes have primarily been undertaken in solely lipid bilayers and frequently in the absence of buffers. In contrast, much less is known about the influence of integral membrane proteins on bending rigidity under physiological conditions. We focus on an exemplar member of the ubiquitous major facilitator superfamily of transporters and assess the influence of lactose permease on the bending rigidity of lipid bilayers. Fluctuation analysis of giant unilamellar vesicles (GUVs) is a useful means to measure bending rigidity. We find that using a hydrogel substrate produces GUVs that are well suited to fluctuation analysis. Moreover, the hydrogel method is amenable to both physiological salt concentrations and anionic lipids, which are important to mimic key aspects of the native lactose permease membrane. Varying the fraction of the anionic lipid in the lipid mixture DOPC/DOPE/DOPG allows us to assess the dependence of membrane bending rigidity on the topology and concentration of an integral membrane protein in the lipid bilayer of GUVs. The bending rigidity gradually increases with the incorporation of lactose permease, but there is no further increase with greater amounts of the protein in the membrane.

Ceramide and Related Molecules in Viral Infections.

Ceramide is a lipid messenger at the heart of sphingolipid metabolism. In concert with its metabolizing enzymes, particularly sphingomyelinases, it has key roles in regulating the physical properties of biological membranes, including the formation of membrane microdomains. Thus, ceramide and its related molecules have been attributed significant roles in nearly all steps of the viral life cycle: they may serve directly as receptors or co-receptors for viral entry, form microdomains that cluster entry receptors and/or enable them to adopt the required conformation or regulate their cell surface expression. Sphingolipids can regulate all forms of viral uptake, often through sphingomyelinase activation, and mediate endosomal escape and intracellular trafficking. Ceramide can be key for the formation of viral replication sites. Sphingomyelinases often mediate the release of new virions from infected cells. Moreover, sphingolipids can contribute to viral-induced apoptosis and morbidity in viral diseases, as well as virus immune evasion. Alpha-galactosylceramide, in particular, also plays a significant role in immune modulation in response to viral infections. This review will discuss the roles of ceramide and its related molecules in the different steps of the viral life cycle. We will also discuss how novel strategies could exploit these for therapeutic benefit.

Biophysical impact of sphingosine and other abnormal lipid accumulation in Niemann-Pick disease type C cell models

Niemann-Pick disease type C (NPC) is a complex and rare pathology, which is mainly associated to mutations in the NPC1 gene. This disease is phenotypically characterized by the abnormal accumulation of multiple lipid species in the acidic compartments of the cell. Due to the complexity of stored material, a clear molecular mechanism explaining NPC pathophysiology is still not established. Abnormal sphingosine accumulation was suggested as the primary factor involved in the development of NPC, followed by the accumulation of other lipid species. To provide additional mechanistic insight into the role of sphingosine in NPC development, fluorescence spectroscopy and microscopy were used to study the biophysical properties of biological membranes using different cellular models of NPC. Addition of sphingosine to healthy CHO-K1 cells, in conditions where other lipid species are not yet accumulated, caused a rapid decrease in plasma membrane and lysosome membrane fluidity, suggesting a direct effect of sphingosine rather than a downstream event. Changes in membrane fluidity caused by addition of sphingosine were partially sustained upon impaired trafficking and metabolization of cholesterol in these cells, and could recapitulate the decrease in membrane fluidity observed in NPC1 null Chinese Hamster Ovary (CHO) cells (CHO-M12) and in cells with pharmacologically induced NPC phenotype (treated with U18666A). In summary, these results show for the first time that the fluidity of the membranes is altered in models of NPC and that these changes are in part caused by sphingosine, supporting the role of this lipid in the pathophysiology of NPC.

Water Pores in Planar Lipid Bilayers at Fast and Slow Rise of Transmembrane Voltage.

Basic understanding of the barrier properties of biological membranes can be obtained by studying model systems, such as planar lipid bilayers. Here, we study water pores in planar lipid bilayers in the presence of transmembrane voltage. Planar lipid bilayers were exposed to fast and slow linearly increasing voltage and current signals. We measured the capacitance, breakdown voltage, and rupture time of planar lipid bilayers composed of 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), 1-pamitoyl 2-oleoyl phosphatidylserine (POPS), and a mixture of both lipids in a 1:1 ratio. Based on the measurements, we evaluated the change in the capacitance of the planar lipid bilayer corresponding to water pores, the radius of water pores at membrane rupture, and the fraction of the area of the planar lipid bilayer occupied by water pores.planar lipid bilayer capacitance, which corresponds to water pores, water pore radius at the membrane rupture, and a fraction of the planar lipid bilayer area occupied by water pores. The estimated pore radii determining the rupture of the planar lipid bilayer upon fast build-up of transmembrane voltage are 0.101 nm, 0.110 nm, and 0.106 nm for membranes composed of POPC, POPS, and POPC:POPS, respectively. The fraction of the surface occupied by water pores at the moment of rupture of the planar lipid bilayer The fraction of an area that is occupied by water pores at the moment of planar lipid bilayer rupture is in the range of 0.1–1.8%.