Phospholipid Polar Head Group Research Articles

Polar Glycerolipids and Membrane Lipid Rafts.

Current understanding of the structure and functioning of biomembranes is impossible without determining the mechanism of formation of membrane lipid rafts. The formation of liquid-ordered and disordered phases (Lo and Ld) and lipid rafts in membranes and their simplified models is discussed. A new consideration of the processes of formation of lipid phases Lo and Ld and lipid rafts is proposed, taking into account the division of each of the glycerophospholipids into several groups. Generally accepted three-component schemes for modeling the membrane structure are critically considered. A four-component scheme is proposed, which is designed to more accurately assume the composition of lipids in the resulting Lo and Ld phases. The role of the polar head groups of phospholipids and, in particular, phosphatidylethanolamine is considered. The structure of membrane rafts and the possible absence of a clear boundary between the Lo and Ld phases are discussed.

Antibacterial activity and mechanisms of α-terpineol against foodborne pathogenic bacteria.

This study aimed to evaluate the antibacterial activities of α-terpineol against common foodborne pathogenic bacteria by agar well diffusion, broth microdilution, and colony counting assay. Propulsive research was conducted to reveal the antibacterial mechanisms, including morphology, infrared spectroscopy, membrane fluidity, membrane permeability, proton motive force, and oxidative phosphorylation. Results indicated that the antibacterial activity of α-terpineol decreased in the following order: Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus. With an initial cell count of 8 log CFU/mL, α-terpineol at 0.8% (v/v) reduced E. coli O157:H7 and S. aureus by approximately 5.6 and 3.9 log CFU/mL within 1 h, respectively. Remarkable destruction in cell envelopes and intracellular organizations was observed. The hydroxyl of α-terpineol might form glycosidic bonds with carbohydrates and hydrogen bonds with PO2- and COO- via infrared spectroscopy analysis. Generalized polarization of Laurdan revealed that the polar head groups of phospholipids transformed into close packed. The anisotropy variations of trimethyl amino-diphenylhexatriene (TMA-DPH) and DPH suggested membrane fluidity decreased. The N-phenyl-1-naphthylamine intake assay indicated that α-terpineol impairedthe cell wall. Propidium iodide staining was indicative of damaged plasma membranes. Electron transport in the cytoplasmic membrane was impaired, inducing reactive oxygen species accumulation. Both membrane electrical potential and membrane pH gradient collapsed. The disruption of proton motive force and the leakage of ATP resulted in a deficit of intracellular ATP. Our research revealed the interaction between the hydroxyl group of α-terpineol and bacteria affects membrane function contributing to the bacteria's death. KEY POINTS: • α-Terpineol hydroxy formed glycosidic bonds and hydrogen bonds with bacteria • α-Terpineol increased the membrane gelation and reduced the membrane fluidity • Proton motive force and oxidative phosphorylation were impaired.

Nucleoside Analog Reverse-Transcriptase Inhibitors in Membrane Environment: Molecular Dynamics Simulations.

The behavior of four drugs from the family of nucleoside analog reverse-transcriptase inhibitors (zalcitabine, stavudine, didanosine, and apricitabine) in a membrane environment was traced using molecular dynamics simulations. The simulation models included bilayers and monolayers composed of POPC and POPG phospholipids. It was demonstrated that the drugs have a higher affinity towards POPG membranes than POPC membranes due to attractive long-range electrostatic interactions. The results obtained for monolayers were consistent with those obtained for bilayers. The drugs accumulated in the phospholipid polar headgroup region. Two adsorption modes were distinguished. They differed in the degree of penetration of the hydrophilic headgroup region. Hydrogen bonds between drug molecules and phospholipid heads were responsible for adsorption. It was shown that apricitabine penetrated the hydrophilic part of the POPC and POPG membranes more effectively than the other drugs. Van der Waals interactions between S atoms and lipids were responsible for this.

A mechanistic understanding of the effects of polyethylene terephthalate nanoplastics in the zebrafish (Danio rerio) embryo

Plastic pollution, especially by nanoplastics (NPs), has become an emerging topic due to the widespread existence and accumulation in the environment. The research on bioaccumulation and toxicity mechanism of NPs from polyethylene terephthalate (PET), which is widely used for packaging material, have been poorly investigated. Herein, we report the first use of high-resolution magic-angle spinning (HRMAS) NMR based metabolomics in combination with toxicity assay and behavioural end points to get systems-level understanding of toxicity mechanism of PET NPs in intact zebrafish embryos. PET NPs exhibited significant alterations on hatching and survival rate. Accumulation of PET NPs in larvae were observed in liver, intestine, and kidney, which coincide with localization of reactive oxygen species in these areas. HRMAS NMR data reveal that PET NPs cause: (1) significant alteration of metabolites related to targeting of the liver and pathways associated with detoxification and oxidative stress; (2) impairment of mitochondrial membrane integrity as reflected by elevated levels of polar head groups of phospholipids; (3) cellular bioenergetics as evidenced by changes in numerous metabolites associated with interrelated pathways of energy metabolism. Taken together, this work provides for the first time a comprehensive system level understanding of toxicity mechanism of PET NPs exposure in intact larvae.

Phospholipid headgroups govern area per lipid and emergent elastic properties of bilayers

Phospholipid bilayers are liquid-crystalline materials whose intermolecular interactions at mesoscopic length scales have key roles in the emergence of membrane physical properties. Here we investigated the combined effects of phospholipid polar headgroups and acyl chains on biophysical functions of membranes with solid-state 2H NMR spectroscopy. We compared the structural and dynamic properties of phosphatidylethanolamine and phosphatidylcholine with perdeuterated acyl chains in the solid-ordered (so) and liquid-disordered (ld) phases. Our analysis of spectral lineshapes of 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE-d62) and 1,2-diperdeuteriopalmitoyl-sn-glycero-3-phosphocholine (DPPC-d62) in the so (gel) phase indicated an all-trans rotating chain structure for both lipids. Greater segmental order parameters (SCD) were observed in the ld (liquid-crystalline) phase for DPPE-d62 than for DPPC-d62 membranes, while their mixtures had intermediate values irrespective of the deuterated lipid type. Our results suggest the SCD profiles of the acyl chains are governed by methylation of the headgroups and are averaged over the entire system. Variations in the acyl chain molecular dynamics were further investigated by spin-lattice (R1Z) and quadrupolar-order relaxation (R1Q) measurements. The two acyl-perdeuterated lipids showed distinct differences in relaxation behavior as a function of the order parameter. The R1Z rates had a square-law dependence on SCD, implying collective mesoscopic dynamics, with a higher bending rigidity for DPPE-d62 than for DPPC-d62 lipids. Remodeling of lipid average and dynamic properties by methylation of the headgroups thus provides a mechanism to control the actions of peptides and proteins in biomembranes.

Metal Ion-Mediated Pro-oxidative Reactions of Different Lipid Molecules: Revealed by Nontargeted Lipidomic Approaches.

Unsaturated fatty acids are easily affected by metal ions, leading to the changes of their flavor, nutrition, and safety through lipid oxidation. Nevertheless, there is a lack of comprehensive evaluation of the pro-oxidative ability of different metal ions, which have different effects on different lipids. Thus, in this work, crude lipids extracted from abalone were incubated with different metal ions, and the comprehensive lipid oxidation products were analyzed by nontargeted lipidomics approaches using an ultra-high-performance liquid chromatography-Q-Exactive HF-X Orbitrap Mass Spectrometer (UPLC-Q-Exactive HF-X). Results showed that the overall pro-oxidative ability from strong to weak was Fe3+, Fe2+, Cu2+, Zn2+, Mn2+, Mg2+, Na+, and K+. Among them, Fe3+ and Fe2+ could promote the accumulation of oxidation intermediates and branched fatty acid esters of hydroxy fatty acids. Na+, K+, Cu2+, and Mg2+ could accelerate the oxidation of N-acyl ethanolamines and ceramides. K+ and Na+ had more influences on the free fatty acids than Zn2+ and Mn2+. Slow oxidation of triglyceride may be attributed to its long distance from the oil-water interface and the restriction of the polar headgroups of phospholipids on free radicals.

Influence of the lipid bilayer composition on interaction of polyanions with the alpha-toxin ion channel

The mechanism of interaction among polyanions and Staphylococcal alpha hemolysin (αHL) ion channel still was not elucidated completely. The initial interaction of polyanions with surface membrane of phospholipids is based in Ca2+ bridge formation. Such interaction increases polyanion concentration close to membrane surface that, in turn, increases the probability of polyanion enter into a channel and blocks it. Thus, this study proposed to investigate the role of the lipid membrane composition on interaction of polyanions, such as heparin, with αHL channel. It was found that the effectiveness of heparin to block αHL channels was significantly dependent on the lipid composition of the bilayers. The lipids on their ability to support heparin influence were ranked as follows: PC >> PI » PS > DPhPS ³ PE ³ DPhPC > OChol. These results indicate that the interaction of Ca2+ with lipid membranes depends on the exposure and density of phosphate groups in phospholipids at membrane surface. On the other hand, the effectiveness of heparin to block αHL channel was more strongly correlated with the length of the hydrocarbons chain of fatty acids of the phospholipids. Thus, we demonstrate that the polar head group of phospholipids in the membranes affects their interaction with divalent ions by changing their surface potential, and therefore influences the effectiveness of heparin blockage in the formed channels. The results might be of interest for pharmacology, biomedicine, and research aiming to design mesoscopic pore blockers.

Advances in the delivery of COVID-19 vaccines

Several systems are being developed and investigated for the delivery of COVID-19 vaccines. A crucial challenge is the ability to maintain vaccine efficacy through the use of an effective delivery system. Some of these vaccine delivery systems such as lipid nanoparticles (LNPs) have been approved for the use by regulatory authorities in numerous countries. LNPs are currently used for the delivery of Moderna and Pfizer/BioNtech vaccines. LNPs consist of four constituents: Cholesterol for LNP stabilization, cationic lipids for the protection of messenger RNA (mRNA) molecules from nuclease degradation, and helper phospholipids that aid the formation and intracellular release of mRNA and PEGylated lipids that reduce nonspecific interactions. Researchers have also used virus-like particles (VLPs) for COVID-19 vaccine delivery. VLPs consist of several hollow viral proteins without the viral genome. VLPs are structurally identical to the native virus and can activate the human adaptive immune response. The nanosized VLPs self-assemblies have investigated as potential platforms for the delivery of COVID-19 vaccines. Liposomal vesicles are amphiphilic since the polar headgroups of phospholipids are oriented toward water molecules and the hydrophobic chains are in the internal area of the vesicles. The rationale behind the utilization of liposomes as vaccine delivery systems is their versatility and flexibility. Messenger RNA coding for SARS-CoV-2 spike protein can be entrapped into liposomes that are designed to remain stable in the bloodstream until their uptake by phagocytic cells. Other vaccine delivery approaches such as the use of microneedles and electroporation provide transdermal vaccine transport enable COVID-19 vaccines to cross the skin but not the cells of deep-lying tissues.

P.725 ACC neurometabolites in Bipolar Disorder are influenced by mood state and medication: a systematic review and meta-analysis of 1H-MRS studies

Local anesthetics promote analgesia by interacting with excitable membranes. Articaine (ATC) has a unique composition among local anesthetics as it possesses a thiophene instead of the typical phenyl ring. Aiming to characterize the interaction of neutral articaine (nATC) with phospholipid membranes, we have employed a synergistic approach of experimental and computational techniques. Fluorescence measurements supported nATC partitioning into the membranes, since its intrinsic fluorescence anisotropy increased from 0.03 in water to 0.29 in the presence of egg phosphatidylcholine (EPC) liposomes, and the fluorescence of AHBA, a probe that monitors the water-membrane interface, was quenched by nATC. 1H NMR experiments revealed changes in the chemical shifts of articaine and EPC hydrogens after partitioning, and shorter T1 values of nATC hydrogens when inserted into the EPC vesicles. Contacts of nATC and the phospholipid polar head group were inferred from 2D-NOE. Taken together, these results indicate a superficial insertion of the nATC molecules inside EPC bilayers. This conclusion was confirmed by molecular dynamics simulations, which allowed the identification of the key interactions underlying the preferential location of nATC in the bilayer. Contrary to what is often stated (that articaine is a high lipophilic local anesthetic agent) our results place ATC among the hydrophilic ones, such as lidocaine, prilocaine, and mepivacaine, for which the water/membrane interface is the preferred location.

Articaine interaction with phospholipid bilayers

Local anesthetics promote analgesia by interacting with excitable membranes. Articaine (ATC) has a unique composition among local anesthetics as it possesses a thiophene instead of the typical phenyl ring. Aiming to characterize the interaction of neutral articaine (nATC) with phospholipid membranes, we have employed a synergistic approach of experimental and computational techniques. Fluorescence measurements supported nATC partitioning into the membranes, since its intrinsic fluorescence anisotropy increased from 0.03 in water to 0.29 in the presence of egg phosphatidylcholine (EPC) liposomes, and the fluorescence of AHBA, a probe that monitors the water-membrane interface, was quenched by nATC. 1H NMR experiments revealed changes in the chemical shifts of articaine and EPC hydrogens after partitioning, and shorter T1 values of nATC hydrogens when inserted into the EPC vesicles. Contacts of nATC and the phospholipid polar head group were inferred from 2D-NOE. Taken together, these results indicate a superficial insertion of the nATC molecules inside EPC bilayers. This conclusion was confirmed by molecular dynamics simulations, which allowed the identification of the key interactions underlying the preferential location of nATC in the bilayer. Contrary to what is often stated (that articaine is a high lipophilic local anesthetic agent) our results place ATC among the hydrophilic ones, such as lidocaine, prilocaine, and mepivacaine, for which the water/membrane interface is the preferred location.

Effects of Curcumin on Lipid Membranes: an EPR Spin-label Study

Curcumin is a yellow–orange dye widely used as a spice, food coloring and food preservative. It also exhibits a broad range of therapeutic effects against different disorders such as cancer, diabetes, or neurodegenerative diseases. As a compound insoluble in water curcumin accumulates in cell membranes and due to this location it may indirectly lead to the observed effects by structurally altering the membrane environment. To exert strong structural effects on membrane curcumin needs to adopt a transbilayer orientation. However, there is no agreement in literature as to curcumin’s orientation and its structural effects on membranes. Here, we investigated the effects of curcumin on lipid order, lipid phase transition, and local polarity in a model liposome membranes made of DMPC or DSPC using electron paramagnetic resonance (EPR) spin labeling technique. Curcumin affected lipid order at different depths within the membrane: it slightly increased the phospholipid polar headgroup mobility as monitored by spectral parameters of T-PC, while along the acyl chain the ordering effect was observed in terms of order parameter S. Also, rotational correlation times τ2B and τ2C of 16-PC in the membrane center were increased by curcumin. Polarity measurements performed in frozen suspensions of liposomes revealed enhancement of water penetration by curcumin in the membrane center (16-PC) and in the polar headgroup region (T-PC) while the intermediate positions along the acyl chain (5-PC and 10-PC) were not significantly affected. Curcumin at a lower concentration (5 mol%) shifted the temperature of the DMPC main phase transition to lower values and increased the transition width, and at a higher concentration (10 mol%) abolished the transition completely. The observed effects suggest that curcumin adopts a transbilayer orientation within the membrane and most probably form oligomers of two molecules, each of them spanning the opposite bilayer leaflets. The effects are also discussed in terms of curcumin’s protective activity and compared with those imposed on membranes by other natural dyes known for their protective role, namely polar carotenoids, lutein and zeaxanthin.

Disruptive effect of tocopherol oxalate on DPPC liposome structure: DSC, SAXS, and fluorescence anisotropy studies

α-Tocopherol oxalate (TO), a tocopherol ester derivative, was investigated for its effect on the structural changes of fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes, as a function of concentration and temperature, by applying differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), and DPH fluorescence anisotropy methods. The DSC and DPH anisotropy data indicated that TO embedded into DPPC membrane lowered the enthalpy (ΔHm) and temperature (Tm) of the main phase transition as well its cooperativity. Fluidization of the membrane at a lowered temperature was accompanied by formation of mixed structures of tocopherol-enriched domains. SAXS studies showed the formation of various ordered structures in DPPC gel-phase during incorporation of TO into the bilayer, as evidenced by the existence of lamellar phases with repeat distances (d) of 6.13 and 6.87 nm, assigned to TO-enriched domains and a lamellar, liquid-ordered DPPC phase with d = 8.45 nm at increasing TO concentrations with lowering and broadening of the Bragg peaks, and diffuse scattering, characteristic of a fluid Lα phase, were observed. In DPPC fluid-phase, the increasing presence of TO at low concentrations resulted in the appearance of a liquid-ordered phase with repeat d = 6.9 nm coexistent with a lamellar structure with d = 9.2 nm, assigned to liquid-disordered structures. An increasing repeat distance observed with raising the TO amount in the DPPC bilayer evolved from an increasing interlamellar water layer of increasing thickness. Presence of TO facilitated penetration of water molecules into the acyl chain region which decreased van der Waals interactions in the bilayer. The DSC, SAXS, and fluorescence anisotropy data established that TO exhibited pronounced disruptive activity in DPPC membranes compared to α-tocopherol. The driving force of the observed action was attributed to electrostatic and dipole interactions of the acidic moiety with the polar head group of phospholipids in the interface region of the bilayer.

Differential interaction of α-synuclein N-terminal segment with mitochondrial model membranes

Alpha-synuclein (α-syn) is an intrinsically-disordered protein that has been associated with Parkinson's disease through its deposition in an amyloid fibril form within Lewy Body. Several lines of evidence suggest that the physical association of α-syn with the mitochondrial membranes may cause membrane damage and mitochondrial dysfunction, playing an important role in disease progression. Although there is strong evidence that the N-terminus part of α-syn is essential for membrane affinity, cooperative formation of helical domains and regulation of mitochondria membrane permeability, the amino acids involve in this membrane binding is still controversial. Fluorescence spectroscopy, circular dichroism and Langmuir monolayer technique were used to elucidate this recognition process of mitochondrial membrane system by synthetic peptides derived from α-syn N-terminal segment. The results obtained in this work show that the first 15 amino acid of the α-syn N-terminal segment mainly participate in the anchoring, perturbing the membrane hydrophobic region, while the peptide corresponding to 16–30 residues interacts only with the phospholipid polar headgroup, confirming that the binding affinity of the N-terminus is nonuniform.

Enterodiol is Actively Transported by Rat Liver Cell Membranes.

The interaction of enterodiol and the well-described polyphenol epigallocatechin gallate (EGCG) with hepatic membranes has been matter of interest in the last few years. On one hand, EGCG is only able to bind to the phospholipid polar head groups, as it has been already described in synthetic lipid bilayers and erythrocyte membranes but cannot get inserted into the hydrophobic core or be transported into the lumen of membrane vesicles. On the other, enterodiol has no interaction with non-energized membranes either, but it is able to interact and even be transported upon addition of ATP. In fact, the ATPase activity undergoes a twofold increase in the presence of enterodiol but not in the presence of EGCG. This is the first report on the transport of enterodiol by liver membranes, and it may help explain the rather high blood concentrations of this estrogenic enterolignan compared to EGCG, which is extensively metabolized by the intestine and the liver. The present results suggest that a fraction of enterodiol may escape the liver inactivation by being pumped out from the hepatocytes to the bloodstream.

Characterization of Pegylated Liposomal Mitomycin C Lipid-Based Prodrug (Promitil) by High Sensitivity Differential Scanning Calorimetry and Cryogenic Transmission Electron Microscopy.

The effect of a lipidated prodrug of mitomycin C (MLP) on the membrane of a pegylated liposome formulation (PL-MLP), also known as Promitil, was characterized through high-sensitivity differential scanning calorimetry (DSC) and cryo-TEM. The thermodynamic analysis demonstrated that MLP led to the formation of heterogeneous domains in the membrane plane of PL-MLP. MLP concentrated in prodrug-rich domains, arranged in high-ordered crystal-like structures, as suggested by the sharp and high enthalpy endotherm in the first heating scanning. After thiolytic cleavage of mitomycin C from MLP by dithiothreitol (DTT) treatment, the crystal-like prodrug domain disappears and a homogeneous membrane with stronger lipid interactions and higher phase transition temperature compared with the blank (MLP-free) liposomes is observed by DSC. In parallel, the rod-like discoid liposomes and the "kissing liposomes" seen by cryo-TEM in the PL-MLP formulation disappear, and liposome mean size and polydispersity increase after DTT treatment. Both MLP and the residual postcleavage lipophilic moiety of the prodrug increased the rigidity of the liposome membrane as indicated by DSC. These results confirm that MLP is inserted in the PL-MLP liposome membrane via its lipophilic anchor, and its mitomycin C moiety located mainly at the region of the phospholipid glycerol backbone and polar headgroup. We hypothesize that π-π stacking between the planar aromatic rings of the mitomycin C moieties leads to the formation of prodrug-rich domains with highly ordered structure on the PL-MLP liposome membrane. This thermodynamically stable conformation may explain the high stability of the PL-MLP formulation. These results also provide us with an interesting example of the application of high sensitivity DSC in understanding the composition-structure-behavior dynamics of liposomal nanocarriers having a lipid-based drug as pharmaceutical ingredient.

Interaction of chitosan and self‐assembled distearoylphosphatidic acid molecules at liquid/liquid and air/water interfaces. Effect of temperature

The effect of the polyelectrolyte, chitosan (CHI), on distearoylphosphatidic acid (DSPA) films was analyzed by cyclic voltammetry, surface pressure‐area isotherm, and Brewster angle microscopy. Distearoylphosphatidic acid films formed at liquid/liquid interface produced a blocking effect to the electrochemical transfer of tetraethylammonium (TEA+) cation from the aqueous to the organic phase, as can be deduced from the cyclic voltammetry experiments. Monolayers of DSPA were performed at different experimental conditions, temperature, subphase solutions (LiCl or CaCl2), and CHI concentration. Both aqueous electrolytes studied exert strong interaction with the negative‐charged polar head groups of phospholipids, which enhance the lateral interactions of the hydrocarbon chains, forming a very structured film. Under these conditions the presence of CHI produces a shift of TEA+ transfer potential toward more positive values because of the less availability of negative sites of the phospholipids for TEA+ adsorption, because they are occupied by the positive‐charged amine groups in CHI chain.Surface pressure‐molecular area isotherms for DSPA monolayers change in the presence of CHI, demonstrating that this polymer produces an expansion of the DSPA film and modifies the surface elasticity of the film. The effect of the temperature was also studied; an exothermic phase transition was observed in the surface pressure‐molecular area isotherms for DSPA‐CHI monolayers, which involves the rupture of interactions between them. Images of Brewster angle microscopy evidence an increase in the optical thickness of the DSPA films in presence of CHI that indicates that the polymer interacts with DSPA molecules at all molecular areas. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous analysis of polar and non-polar components of cell membrane phospholipids by GC-MS

AbstractA rapid and selective GC-MS method was optimised for the simultaneous analysis of fatty acids, phosphoethanolamine, phosphoglycerol and phosphoserine, which comprise the polar headgroups of phospholipids. Enzymatic hydrolysis was used for sample preparation to selectively release fatty acids and prevent cleavage of the phosphoester bonds of the polar headgroups. A two-step consecutive derivatisation of the fatty acids and polar headgroups was applied to enable the simultaneous analysis of the selected analytes. The method was tested on samples of cell membrane phospholipids of

Crystal structure of vespid phospholipase A1 reveals insights into the mechanism for cause of membrane dysfunction

Vespid phospholipase A1 (vPLA1) from the black-bellied hornet (Vespa basalis) catalyzes the hydrolysis of emulsified phospholipids and shows potent hemolytic activity that is responsible for its lethal effect. To investigate the mechanism of vPLA1 towards its function such as hemolysis and emulsification, we isolated vPLA1 from V. basalis venom and determined its crystal structure at 2.5 Å resolution. vPLA1 belongs to the α/β hydrolase fold family. It contains a tightly packed β-sheet surrounded by ten α-helices and a Gly-X-Ser-X-Gly motif, characteristic of a serine hydrolyase active site. A bound phospholipid was modeled into the active site adjacent to the catalytic Ser-His-Asp triad indicating that Gln95 is located at hydrogen-bonding distance from the substrate's phosphate group. Moreover, a hydrophobic surface comprised by the side chains of Phe53, Phe62, Met91, Tyr99, Leu197, Ala167 and Pro169 may serve as the acyl chain-binding site. vPLA1 shows global similarity to the N-terminal domain of human pancreatic lipase (HPL), but with some local differences. The lid domain and the β9 loop responsible for substrate selectivity in vPLA1 are shorter than in HPL. Thus, solvent-exposed hydrophilic residues can easily accommodate the polar head groups of phospholipids, thereby accounting for the high activity level of vPLA1. Our result provides a potential explanation for the ability of vPLA1 to hydrolyze phospholipids of cell membrane.

Effect of Erythrodiol, A Natural Pentacyclic Triterpene from Olive Oil, on the Lipid Membrane Properties.

The effect of erythrodiol, a natural pentacyclic triterpene to which humans are exposed through nutrients, on the lipid membranes is studied using liposomes as a membrane model. Empty and erythrodiol-loaded liposomes were prepared by the reverse phase evaporation method followed by the extrusion and by the thin film hydration method. Liposomes were characterized in terms of size and zeta potential and were imaged by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The effect of erythrodiol on thermotropic behavior of DPPC bilayers is also examined by differential scanning calorimetry (DSC). The DSC thermograms suggested that erythrodiol interacted with the polar head groups of phospholipids and may produce a disruption of the ordering of the alkyl chains. The diffraction light scattering analysis showed that erythrodiol-loaded liposomes presented a decrease in the vesicle size when compared to blank liposomes. Images obtained by TEM confirmed the formation of unilamellar and spherical liposomes. AFM images showed spherical vesicles and single lipid bilayers. The latter were more abundant in the preparations containing erythrodiol than in the blank ones. Moreover, erythrodiol-loaded liposomes tended to rupture into single lipid bilayers during scanning. The study may provide a better understanding of pentacyclic triterpenes-membrane interaction.

Lipid-dependent pore formation by antimicrobial peptides arenicin-2 and melittin demonstrated by their proton transfer activity

This work presents a comparative study of proton transfer activity (PTA) of two cationic (+6) antimicrobial peptides, β-structural arenicin-2 and α-helical melittin. A new approach was proposed for the detection of passive proton transfer by using proteoliposomes containing bacteriorhodopsin, which creates a small light-induced electrochemical proton gradient ∆ΔpH. Addition of several nanomoles of the peptides lowers ∆ΔpH that is proximately indicative of the pore formation. The quantitative analysis of sigmoidal dependences of ∆pH on the peptides concentration was carried out using liposomes prepared from PC, PC/PE, PC/PE/PI and PC/PG. Substitution of PC-containing liposomes with PE-containing ones, having negative spontaneous curvature, reduced the PTA of α-helical melittin and increased that of β-structural arenicin-2. This result indicates an essential difference in the pore formation by these peptides. Further increase of PTA in response to arenicin-2 (in contrast to melittin) was observed in the liposomes prepared from PC/PE/PI. The data analysis leads to the conclusion that PTA is influenced by (i) efficiency of the pore assemblage, which depends on the structure of pore-forming peptides, and the spontaneous curvature of lipids and (ii) the presence of mobile protons in the polar head groups of phospholipids.