Membrane Lipid Order Research Articles

Molecular dynamics simulations of the human ocular lens with age and cataract

The human ocular lens consists primarily of elongated, static fibers characterized by high stability and low turnover, which differ dramatically in their composition and properties from other biological membranes. Cholesterol (Chol) and sphingolipids (SL) are present at high concentrations, including saturated SLs, such as dihyrosphingomyelin (DHSM). Past molecular dynamics simulations demonstrated that the presence of DHSM and high Chol concentration contributes to higher order in lipid membranes. This current study simulated more complex models of human lens membranes. Models were developed representing physiological compositions in cataractous lenses aged 74 ± 6 years and in healthy lenses aged 22 ± 4, 41 ± 6, and 69 ± 3 years. With older age, Chol and ceramide concentrations increase and glycerophospholipid concentration decreases. With cataract, ceramide concentration increases and Chol and glycerophospholipid concentrations decrease. Surface area per lipid, deuterium order parameters (SCD), sterol tilt angle, electron density profiles, bilayer thickness, chain interdigitation, two-dimensional radial distribution functions (2D-RDF), lipid clustering, and hydrogen bonding were calculated for all simulations. All systems exhibited low surface area per lipid and high bilayer thickness, indicative of strong vertical packing. SCD parameters suggest similarly, with saturated tails in the hydrophobic core of the membrane having elevated order. Vertical packing and acyl tail order increased with both age and cataract condition. Lateral diffusion decreased with age and cataracts, with the older and cataractous models demonstrating increased long-range structure by the 2D-RDF analysis. In future work examining the membrane proteins of the lens, these models can serve as a physiologically accurate representation of the lens lipidome.

Role of Surface Tension in Microrobot Penetration in Membranes.

cell-membrane fusion using microrobots can be a useful technique for delivering bioactive compounds to cellular systems. The role of membrane curvature and lipid ordering in the cell membrane penetration process is well known. However, once the fusion into the cell membrane is already initiated, the fluid dynamics of microrobot penetration based on tension difference of the microrobot solution and membrane curvature at the fusion pore has not been explored yet. Here, we demonstrate how surface tension difference among merging interfaces plays role in microrobot droplet penetration into a liquid bath, mimicking cell membrane fusion. The maximum penetration of a microrobot droplet into a liquid bath depends on the positive difference of surface tension between the droplet and liquid bath, longitudinal curvature of the bridge region, and the size of the droplet.

Enzymatic synthesis and characterization of aryl iodides of some phenolic acids with enhanced antibacterial properties

Phenolic acids represent a class of drugs with mild antibacterial properties. We have synthesized iodinated gallic and ferulic acids and together with commercially available iodinated forms of salicylic acids studied their cytotoxicity, bacteriostatic and anti-virulence action. Out of these, iodogallic acid had lowest minimal inhibitory concentration (MIC) against Staphylococcus aureus (MIC = 0.4 mM/118.8 μg/ml). Yet, it had strong effect on erythrocyte membrane lipid ordering and on α-hemolysin secretion by the bacteria at lower non-bacteriostatic and non-cytotoxic concentrations (<0.1 mM). Iodogallic acid formed static complexes with α-hemolysin in solutions (logKb = 4.69 ± 0.07) and inhibited its nano-pore conduction in artificial lipid bilayers (IC50 = 37.9 ± 5.3 μM). These effects of iodogallic acid converged on prevention of hemolysis induced by α-hemolysin (IC50 = 41.5 ± 4.2 μM) and pointed to enhanced and diverse anti-virulence properties of some aryl iodides. The analysis of molecular surface electrostatic charge distribution, molecular hydrophilicity, electronegativity, and dipole moment of studied compounds suggested the importance of the number of hydroxyl groups and their proximity to iodine in anti-virulence activity manifestation. In iodogallic acid, charge redistribution resulted in higher hydrophilicity without concomitant change in overall molecular electronegativity and dipole moment compared to non-iodinated gallic acid. This study shows new directions for the development of antibacterial/antivirulence therapeutics.

Oxidized Lipids Control Lipid Order and Phospholipase A2 Activity in Model Membranes

Oxidative stress is an important etiologic factor in the pathogenesis of various diseases. The formation of oxidized phospholipid species in vivo induces membrane remodelling with direct pathological implications with a prominent inflammatory component. Secretory phospholipases A2 (sPLA2) are involved in the regulation of inflammation and immune response. Their activity is highly dependent on the lipid membrane composition, structure and organization. In this work, we studied the impact of oxidized phosphatidylcholines (OxPCs) on the membrane lipid order and the sPLA2 activity. The effects of two of the most physiologically active OxPCs, 1-palmitoyl-2-(5′-oxo-valeroyl)-sn-glycero- 3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-3- phosphocholine (PGPC) were compared using 1-palmitoyl-2-oleoyl-sn-glycero- 3-phosphocholine (POPC) vesicles. Both OxPCs reduce the membrane lipid order and sPLA2 activity at physiological temperature. Moreover, these changes depend on the chemical nature of the oxidized chains.

PUFA-rich phospholipid classes and subclasses of ram spermatozoa are unevenly affected by cryopreservation with a soybean lecithin-based extender

Cryopreservation is known to affect spermatozoa structure and function. Ram sperm are among the most highly sensitive mammalian gametes to freezing, due to their lipid composition, which limit their efficiency in artificial insemination programs. The aim of this study was to investigate the effects of cryopreservation with a chemically defined soybean lecithin-based extender on ram spermatozoa functionality on the one hand, and quantifiable changes in lipid and fatty acid profile on the other. Freeze-thawing decreased sperm quality, as indicated by post-thaw parameters related to membrane integrity, mitochondrial viability and sperm motility. The most relevant lipid change after cryopreservation was a remarkable loss of all glycerophospholipids containing 22:6n-3. Species of sphingomyelin with very long chain polyunsaturated fatty acids (VLC-PUFA), that are exclusively located in the sperm head, where responsible of its reduction after cryostorage. Freezing caused a reduction in mitochondrial function, which was confirmed by significantly decreased of mitochondrial membrane potential and by the generation of 4-HNE. Mitochondria damage was accompanied by a loss in cardiolipin with 18:2n-6 and phosphatidylethanolamine with 20:4n-6, two well-known lipids that are critical components for mitochondrial membrane functionality. Loss of sterols after cryopreservation occurred along with a decrease in the order of sperm membrane lipids. Our research provides new insights on deleterious effects of cryopreservation on PUFA-rich phospholipids of ram sperm and highlight their importance as biomarkers of ultrastructural, biochemical and functional damage that ram spermatozoa undergo after freezing-thawing.

Lipid-driven CFTR clustering is impaired in cystic fibrosis and restored by corrector drugs.

ABSTRACTMembrane proteins often cluster in nanoscale membrane domains (lipid rafts) that coalesce into ceramide-rich platforms during cell stress, however the clustering mechanisms remain uncertain. The cystic fibrosis transmembrane conductance regulator (CFTR), which is mutated in cystic fibrosis (CF), forms clusters that are cholesterol dependent and become incorporated into long-lived platforms during hormonal stimulation. We report here that clustering does not involve known tethering interactions of CFTR with PDZ domain proteins, filamin A or the actin cytoskeleton. It also does not require CFTR palmitoylation but is critically dependent on membrane lipid order and is induced by detergents that increase the phase separation of membrane lipids. Clustering and integration of CFTR into ceramide-rich platforms are abolished by the disease mutations F508del and S13F and rescued by the CFTR modulators elexacaftor plus tezacaftor. These results indicate CF therapeutics that correct mutant protein folding restore both trafficking and normal lipid interactions in the plasma membrane.This article has an associated First Person interview with the first author of the paper.

Myconoside interacts with the plasma membranes and the actin cytoskeleton and provokes cytotoxicity in human lung adenocarcinoma A549 cells.

Studies have been carried out on the effects of the phenyl glycoside myconoside, extracted from the relict, Balkan endemic resurrection plant Haberlea rhodopensis on the plasma membrane structural organization and the actin cytoskeleton. Because the plasma membrane is the first target of exogenous bioactive compounds, we focused our attention on the influence of myconoside on the membrane lipid order and actin cytoskeleton in human lung adenocarcinoma A549 cells, using fluorescent spectroscopy and microscopy techniques. We found that low myconoside concentration (5μg/ml) did not change cell viability but was able to increase plasma membrane lipid order of the treated cells. Higher myconoside concentration (20μg/ml) inhibited cell viability by decreasing plasma membrane lipid order and impairing actin cytoskeleton. We hypothesize that the observed changes in the plasma membrane structural organization and the actin cytoskeleton are functionally connected to cell viability. Biomimetic membranes were used to demonstrate that myconoside is able to reorganize the membrane lipids by changing the fraction of sphingomyelin-cholesterol enriched domains. Thus, we propose a putative mechanism of action of myconoside on A549 cells plasma membrane lipids as well as on actin filaments in order to explain its cytotoxic effect at high myconoside concentration.

Hemodynamic Forces, Endothelial Mechanotransduction, and Vascular Diseases.

Cells in the tissues and organs of a living body are subjected to mechanical forces, such as pressure, friction, and tension from their surrounding environment. Cells are equipped with a mechanotransduction mechanism by which they perceive mechanical forces and transmit information into the cell interior, thereby causing physiological or pathogenetic mechano-responses. Endothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to shear stress caused by blood flow and a cyclic strain caused by intravascular pressure. A number of studies have shown that ECs are sensitive to changes in these hemodynamic forces and alter their morphology and function, sometimes by modifying gene expression. The mechanism of endothelial mechanotransduction has been elucidated, and the plasma membrane has recently been shown to act as a mechanosensor. The lipid order and cholesterol content of plasma membranes change immediately upon the exposure of ECs to hemodynamic forces, resulting in a change in membrane fluidity. These changes in a plasma membrane's physical properties affect the conformation and function of various ion channels, receptors, and microdomains (such as caveolae and primary cilia), thereby activating a wide variety of downstream signaling pathways. Such endothelial mechanotransduction works to maintain circulatory homeostasis; however, errors in endothelial mechanotransduction can cause abnormalities in vascular physiological function, leading to the initiation and progression of various vascular diseases, such as hypertension, thrombosis, aneurysms, and atherosclerosis. Recent advances in detailed imaging technology and computational fluid dynamics analysis have enabled us to evaluate the hemodynamic forces acting on vascular tissue accurately, contributing greatly to our understanding of vascular mechanotransduction and the pathogenesis of vascular diseases, as well as the development of new therapies for vascular diseases.

Semi-Refined Carrageenan Attenuates Lipopolysaccharide-Induced Reactive Oxygen Species Production in Peripheral Blood Mononuclear Cells and Cell Membrane Alterations in Leukocytes

Aim: To assess the effects of semi-refined carrageenan (E407a) on lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) generation in peripheral blood mononuclear cells (PBMCs) and LPS-mediated cell membrane alterations in leukocytes. Methods: Blood samples collected from 8 intact rats were incubated with E407a (10 mg/ml), E407a (50 mg/ml), LPS (1 µg/ml), E407a (10 mg/ml) + LPS (1 µg/ml), E407a (50 mg/ml) + LPS (1 µg/ml) and without those compounds (controls) for 2 h in RPMI 1640 medium enriched with 5% fetal bovine serum. ROS generation in PBMCs obtained from the incubated samples was estimated by flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) staining. The impact of E407a, LPS and their mixture on leukocyte cell membranes was evaluated spectrofluorimetrically using the fluorescent probe 2-(2¢-hydroxy-phenyl)-5-phenyl-1,3-oxazole. Results: Expectedly, incubation with LPS induced ROS generation in PBMCs and decreased the lipid order of cell membranes in leukocytes. E407a alone was found to alter neither ROS production in PBMCs, nor membrane lipid order in leukocytes. Semi-refined carrageenan partially reduced LPS-mediated ROS overproduction in PBMCs and cell membrane alterations in leukocytes. Conclusion: E407a attenuates LPS-induced alterations of redox homeostasis in rat PBMCs and LPS-mediated modifications of cell membrane lipid order in leukocytes.

Quantitative Measurements of Membrane Lipid Order in Yeast and Fungi.

Membrane lateral heterogeneity, historically referred to as the lipid raft hypothesis, has been extensively investigated through physiochemical experiments on model membranes. Currently, the basic principles are well understood; however, the physiological relevance of these structures in living organisms is still not clear. Thus, studying membrane organization in vivo is extremely important and elucidates the role of such structures in various membrane-associated processes. This is particularly true when a whole single-celled organism can be studied rather than an isolated cell. The ordered and disordered membrane phases are characterized by the degree of acyl chain packing in the lipid bilayer. Polar water molecules can penetrate into the low-density lipid packing of the disordered phase, but are more excluded from the tightly packed ordered phase. Here, polarity-sensitive probes, embedded in the lipid bilayer, are used to report on membrane organization and to quantitate this parameter via 2-channel fluorescence microscopy. Coupling genetic approaches, which are easily accessible in yeast model organisms, with the imaging approach described here provides a great opportunity to investigate how membrane heterogeneity impacts physiology.

Potentiation of plant defense by bacterial outer membrane vesicles is mediated by membrane nanodomains.

Outer membrane vesicles (OMVs) are released from the outer membranes of Gram-negative bacteria during infection and modulate host immunity during host-pathogen interactions. The mechanisms by which OMVs are perceived by plants and affect host immunity are unclear. Here, we used the pathogen Xanthomonas campestris pv. campestris to demonstrate that OMV-plant interactions at the Arabidopsis thaliana plasma membrane (PM) modulate various host processes, including endocytosis, innate immune responses, and suppression of pathogenesis by phytobacteria. The lipid phase of OMVs is highly ordered and OMVs directly insert into the Arabidopsis PM, thereby enhancing the plant PM's lipid order; this also resulted in strengthened plant defenses. Strikingly, the integration of OMVs into the plant PM is host nanodomain- and remorin-dependent. Using coarse-grained simulations of molecular dynamics, we demonstrated that OMV integration into the plant PM depends on the membrane lipid order. Our computational simulations further showed that the saturation level of the OMV lipids could fine-tune the enhancement of host lipid order. Our work unraveled the mechanisms underlying the ability of OMVs produced by a plant pathogen to insert into the host PM, alter host membrane properties, and modulate plant immune responses.

The ability of carbon nanoparticles to increase transmembrane current of cations coincides with impaired synaptic neurotransmission

Here, carbon nanodots synthesized from β-alanine (Ala-CDs) and detonation nanodiamonds (NDs) were assessed using (1) radiolabeled excitatory neurotransmitters L-[14C]glutamate, D-[2,33H]aspartate, and inhibitory ones [3H]GABA, [3H]glycine for registration of their extracellular concentrations in rat cortex nerve terminals; (2) the fluorescent ratiometric probe NR12S and pH-sensitive probe acridine orange for registration of the membrane lipid order and synaptic vesicle acidification, respectively; (3) suspended bilayer lipid membrane (BLM) to monitor changes in transmembrane current. In nerve terminals, Ala-CDs and NDs increased the extracellular concentrations of neurotransmitters and decreased acidification of synaptic vesicles, whereas have not changed sufficiently the lipid order of membrane. Both nanoparticles, Ala-CDs and NDs, were capable of increasing the conductance of the BLM by inducing stable potential-dependent cation-selective pores. Introduction of divalent cations, Zn2+ or Cd2+ on the particles` application side (cis-side) increased the rate of Ala-CDs pore-formation in the BLM. The application of positive potential (+100 mV) to the cis-chamber with Ala-CDs or NDs also activated the insertion as compared with the negative potential (−100 mV). The Ala-CD pores exhibited a wide-range distribution of conductances between 10 and 60 pS and consecutive increase in conductance of each major peak by ~10 pS, which suggest the clustering of the same basic ion-conductive structure. NDs also formed ion-conductive pores ranging from 6 pS to 60 pS with the major peak of conductance at ~12 pS in cholesterol-containing membrane. Observed Ala-CDs and NDs-induced increase in transmembrane current coincides with disturbance of excitatory and inhibitory neurotransmitter transport in nerve terminals.

A selective Nile Red based solvatochromic probe: A study of fluorescence in LUVs and GUVs model membranes

In this work, a membrane probe (NR18) with a Nile Red-based chromophore, a long tail of 18 carbon atoms and a zwitterionic head was synthesized. The probe is optimized to remain anchored to the phospholipid bilayer without internalizing. NR18 was fully characterized chemically and optically and showed marked solvatochromism. Incorporation into model membranes of LUVs and GUVs having different compositions, demonstrated that the probe could be used to discriminate the lipid order in membranes, based on the fluorescent radiation emitted. Spectrophotometric and fluorimetric measurements on LUVs showed that the emission wavelength increases with temperature, confirming the increase in fluidity and hydration in membranes at higher temperatures. DFT simulations helped us to clarify the impact of NR18 on the membrane thickness and the order parameter showing that NR18 does not cause substantial perturbation in the bilayer. Moreover, we demonstrated that the presence of an enaminic terminal group is mainly responsible for the ability of NR18 to have a different fluorescence in Ld and Lo membranes.

(INVITED) Fluorescent probes for optical investigation of the plasma membrane

The biological functions of the cell membrane are regulated by its physicochemical properties, such as the transmembrane potential, phase state and hydration. Therefore, the in situ investigation of these properties is attracting a rising interest in the field of membrane biophysics. In these regards, a wide variety of fluorescent membrane probes has been developed, providing powerful tools for fluorescence microscopy and/or fluorescence spectroscopy to study the microscopic analogs of viscosity, polarity, and hydration, as well as the molecular order and electrostatic potential at the sites of their location. Despite the success of this approach, further developments rely on the design of fluorescence probes with optimized photophysical properties. This review discusses the most successful fluorescent molecular probes and their application to the study of the plasma membrane viscosity, lipid order and potential.

Cholesterol-dependent plasma membrane order (Lo) is critical for antigen-specific clonal expansion of CD4+ T cells

Early “T cell activation” events are initiated within the lipid microenvironment of the plasma membrane. Role of lipid membrane order (Lo) in spatiotemporal signaling through the antigen receptor in T cells is posited but remains unclear. We have examined the role of membrane order (Lo)/disorder (Ld) in antigen specific CD4+ T cell activation and clonal expansion by first creating membrane disorder, and then reconstituting membrane order by inserting cholesterol into the disordered plasma membrane. Significant revival of antigen specific CD4+ T cell proliferative response was observed after reconstituting the disrupted membrane order with cholesterol. These reconstitution experiments illustrate Koch’s postulate by demonstrating that cholesterol-dependent membrane order (Lo) is critical for responses generated by CD4+ T cells and point to the importance of membrane order and lipid microenvironment in signaling through T cell membrane antigen receptors.

Abstract 2886: The mechanistic effect of DHA on FABP7 associated membrane lipid order &amp; nanodomain distribution in glioblastoma migration

Abstract Glioblastoma (GBM) is the most common primary brain malignancy. Brain fatty acid binding protein (B-FABP, FABP7) promotes glioblastoma (GBM) migration and correlates to dismal prognosis in GBM patients. Long chain polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and arachidonic acid (AA) are abundant in brain cell membranes. DHA and AA are preferred ligands of FABP7, with DHA having the stronger affinity for FABP7. Previous studies have shown that DHA inhibits GBM migration in an FABP7-dependent manner. In the current study, we have demonstrated that DHA dramatically altered membrane FABP7 nanoscale distribution pattern, which resulting from plasma membrane lipid ordered domain disruption in GBM cells and neurosphere cultures. We used quantitative membrane order assay to show that FABP7-expressing cells has increased membrane lipid order which is tightly correlated with higher GBM migration property. Using stimulated emission depletion (STED) microscopy, we observed lipid ordered domain was associated with FABP7 nanoscale domain formation. Interestingly, super-resolution microscopy quantitative image analysis revealed that FABP7 membrane nanodomains distribution was dramatically altered upon DHA treatment, which is associated with DHA inhibitory effect on membrane lipid order. Furthermore, STED microscopy has also revealed that reduced FABP7 nanodomain formation in slow migrating GBM cells are similar as FABP7-expressing GBM cells upon DHA treatment. Therefore, we hypothesize that these alterations are likely to be the mechanism of FABP7-mediated DHA inhibitory role in GBM migration. Citation Format: Xia Xu, Yixiong Wang, Wonshik Choi, Roseline Godbout. The mechanistic effect of DHA on FABP7 associated membrane lipid order &amp; nanodomain distribution in glioblastoma migration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2886.

Biomolecular changes and subsequent time-dependent recovery in hippocampal tissue after experimental mild traumatic brain injury

Traumatic brain injury (TBI) is the main cause of disability and mortality in individuals under the age of 45 years. Elucidation of the molecular and structural alterations in brain tissue due to TBI is crucial to understand secondary and long-term effects after traumatic brain injury, and to develop and apply the correct therapies. In the current study, the molecular effects of TBI were investigated in rat brain at 24 h and 1 month after the injury to determine acute and chronic effects, respectively by Fourier transform infrared imaging. This study reports the time-dependent contextual and structural effects of TBI on hippocampal brain tissue. A mild form of TBI was induced in 11-week old male Sprague Dawley rats by weight drop. Band area and intensity ratios, band frequency and bandwidth values of specific spectral bands showed that TBI causes significant structural and contextual global changes including decrease in carbonyl content, unsaturated lipid content, lipid acyl chain length, membrane lipid order, total protein content, lipid/protein ratio, besides increase in membrane fluidity with an altered protein secondary structure and metabolic activity in hippocampus 24 h after injury. However, improvement and/or recovery effects in these parameters were observed at one month after TBI.

LXR directly regulates glycosphingolipid synthesis and affects human CD4+ T cell function

The liver X receptor (LXR) is a key transcriptional regulator of cholesterol, fatty acid, and phospholipid metabolism. Dynamic remodeling of immunometabolic pathways, including lipid metabolism, is a crucial step in T cell activation. Here, we explored the role of LXR-regulated metabolic processes in primary human CD4+ T cells and their role in controlling plasma membrane lipids (glycosphingolipids and cholesterol), which strongly influence T cell immune signaling and function. Crucially, we identified the glycosphingolipid biosynthesis enzyme glucosylceramide synthase as a direct transcriptional LXR target. LXR activation by agonist GW3965 or endogenous oxysterol ligands significantly altered the glycosphingolipid:cholesterol balance in the plasma membrane by increasing glycosphingolipid levels and reducing cholesterol. Consequently, LXR activation lowered plasma membrane lipid order (stability), and an LXR antagonist could block this effect. LXR stimulation also reduced lipid order at the immune synapse and accelerated activation of proximal T cell signaling molecules. Ultimately, LXR activation dampened proinflammatory T cell function. Finally, compared with responder T cells, regulatory T cells had a distinct pattern of LXR target gene expression corresponding to reduced lipid order. This suggests LXR-driven lipid metabolism could contribute to functional specialization of these T cell subsets. Overall, we report a mode of action for LXR in T cells involving the regulation of glycosphingolipid and cholesterol metabolism and demonstrate its relevance in modulating T cell function.

The Agonist Action of Alkylphenols on TRPA1 Relates to Their Effects on Membrane Lipid Order: Implications for TRPA1-Mediated Chemosensation.

The Transient Receptor Potential Ankyrin 1 cation channel (TRPA1) is a broadly-tuned chemosensor expressed in nociceptive neurons. Multiple TRPA1 agonists are chemically unrelated non-electrophilic compounds, for which the mechanisms of channel activation remain unknown. Here, we assess the hypothesis that such chemicals activate TRPA1 by inducing mechanical perturbations in the plasma membrane. We characterized the activation of mouse TRPA1 by non-electrophilic alkylphenols (APs) of different carbon chain lengths in the para position of the aromatic ring. Having discarded oxidative stress and the action of electrophilic mediators as activation mechanisms, we determined whether APs induce mechanical perturbations in the plasma membrane using dyes whose fluorescence properties change upon alteration of the lipid environment. APs activated TRPA1, with potency increasing with their lipophilicity. APs increased the generalized polarization of Laurdan fluorescence and the anisotropy of the fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH), also according to their lipophilicity. Thus, the potency of APs for TRPA1 activation is an increasing function of their ability to induce lipid order and membrane rigidity. These results support the hypothesis that TRPA1 senses non-electrophilic compounds by detecting the mechanical alterations they produce in the plasma membrane. This may explain how structurally unrelated non-reactive compounds induce TRPA1 activation and support the role of TRPA1 as an unspecific sensor of potentially noxious compounds.

Asymmetric glycerophospholipids impart distinctive biophysical properties to lipid bilayers

Phospholipids are a diverse group of biomolecules consisting of a hydrophilic headgroup and two hydrophobic acyl tails. The nature of the head and length and saturation of the acyl tails are important for defining the biophysical properties of lipid bilayers. It has recently been shown that the membranes of certain yeast species contain high levels of unusual asymmetric phospholipids consisting of one long and one medium-chain acyl moiety, a configuration not common in mammalian cells or other well-studied model yeast species. This raises the possibility that structurally asymmetric glycerophospholipids impart distinctive biophysical properties to the yeast membranes. Previously, it has been shown that lipids with asymmetric length tails form a mixed interdigitated gel phase and exhibit unusual endotherm behavior upon heating and cooling. Here, however, we address physiologically relevant temperature conditions and, using atomistic molecular dynamics simulations and environmentally sensitive fluorescent membrane probes, characterize key biophysical parameters (such as lipid packing, diffusion coefficient, membrane thickness, and area per lipid) in membranes composed of both length-asymmetric glycerophospholipids and ergosterol. Interestingly, we show that saturated but asymmetric glycerophospholipids maintain membrane lipid order across a wide range of temperatures. We also show that these asymmetric lipids can substiture of unsaturated symmetric lipids in the phase behaviour of ternary lipid bilayers. This may allow cells to maintain membrane fluidity, even in environments that lack oxygen, which is required for the synthesis of unsaturated lipids and sterols.