Influence of N-dodecyl-N,N-dimethylamine N-oxide on the activity of sarcoplasmic reticulum Ca2+-transporting ATPase reconstituted into diacylphosphatidylcholine vesicles: Effects of bilayer physical parameters

Mild Hyperthermia-Induced Thermogenesis in the Endoplasmic Reticulum Defines Stress Response Mechanisms

Previous studies reported that a mild, non-protein-denaturing, fever-like temperature increase induced the unfolded protein response (UPR) in mammalian cells. Our dSTORM super-resolution microscopy experiments revealed that the master regulator of the UPR, the IRE1 (inositol-requiring enzyme 1) protein, is clustered as a result of UPR activation in a human osteosarcoma cell line (U2OS) upon mild heat stress. Using ER thermo yellow, a temperature-sensitive fluorescent probe targeted to the endoplasmic reticulum (ER), we detected significant intracellular thermogenesis in mouse embryonic fibroblast (MEF) cells. Temperatures reached at least 8 °C higher than the external environment (40 °C), resulting in exceptionally high ER temperatures similar to those previously described for mitochondria. Mild heat-induced thermogenesis in the ER of MEF cells was likely due to the uncoupling of the Ca2+/ATPase (SERCA) pump. The high ER temperatures initiated a pronounced cytosolic heat-shock response in MEF cells, which was significantly lower in U2OS cells in which both the ER thermogenesis and SERCA pump uncoupling were absent. Our results suggest that depending on intrinsic cellular properties, mild hyperthermia-induced intracellular thermogenesis defines the cellular response mechanism and determines the outcome of hyperthermic stress.

Coarse-Grained Molecular Dynamics of pH-Sensitive Lipids

pH-sensitive lipids represent a class of lipids that can be protonated and destabilized in acidic environments, as they become positively charged in response to low-pH conditions. They can be incorporated into lipidic nanoparticles such as liposomes, which are able to change their properties and allow specific drug delivery at the acidic conditions encountered in some pathological microenvironments. In this work, we used coarse-grained molecular-dynamic simulations to study the stability of neutral and charged lipid bilayers containing POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and various kinds of ISUCA ((F)2-(imidazol-1-yl)succinic acid)-derived lipids, which can act as pH-sensitive molecules. In order to explore such systems, we used a MARTINI-derived forcefield, previously parameterized using all-atom simulation results. We calculated the average area per lipid, the second-rank order parameter and the lipid diffusion coefficient of both lipid bilayers made of pure components and mixtures of lipids in different proportions, under neutral or acidic conditions. The results show that the use of ISUCA-derived lipids disturbs the lipid bilayer structure, with the effect being particularly marked under acidic conditions. Although more-in depth studies on these systems must be carried out, these initial results are encouraging and the lipids designed in this research could be a good basis for developing new pH-sensitive liposomes.

Cyclic and Acyclic Amine Oxide Alkyl Derivatives as Potential Adjuvants in Antimicrobial Chemotherapy against Methicillin-Resistant Staphylococcus aureus with an MDR Profile

The dramatic intensification of antimicrobial resistance occurrence in pathogenic bacteria concerns the global community. The revitalisation of inactive antibiotics is, at present, the only way to go through this health system crisis and the use of antimicrobial adjuvants is turning out the most promising approach. Due to their low toxicity, eco-friendly characteristics and antimicrobial activity, amphoteric surfactants are good candidates. This study investigated the adjuvant potentialities of commercial acyclic and newly cyclic N-oxide surfactants combined with therapeutically available antibiotics against MDR methicillin-resistant Staphylococcus aureus (MRSA). The safety profile of the new cyclic compounds, compared to commercial surfactants, was preliminarily assessed, evaluating the cytotoxicity on human peripheral mononuclear blood cells and the haemolysis in human red blood cells. The compounds show an efficacious antimicrobial activity strongly related to the length of the carbon atom chain. In drug–drug interaction assays, all surfactants act synergistically, restoring sensitivity to oxacillin in MRSA, with dodecyl acyclic and cyclic derivatives being the most effective. After evaluating the cytotoxicity and considering the antimicrobial action, the most promising compound is the L-prolinol amine-oxide C12NOX. These findings suggest that the combination of antibiotics with amphoteric surfactants is a valuable therapeutic option for topical infections sustained by multidrug-resistant S. aureus.

pH-Sensitive N,N-Dimethylalkane-1-amine N-Oxides in DNA Delivery: From Structure to Transfection Efficiency

pH-sensitive liposomes composed of homologues of series of N,N-dimethylalkane-1-amine N-oxides (CnNO, n = 8-18, where n is the number of carbon atoms in the alkyl substituent) and neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) were prepared at two molar ratios (CnNO/DOPE = 0.4:1 and 1:1) and tested for their in vitro transfection activity. Several techniques (SAXS/WAXS, UV-vis, zeta potential measurements, confocal microscopy) were applied to characterize the system in an effort to unravel the relationship among the transfection efficiency, structure, and composition of the lipoplexes. The transfection efficiency of CnNO/DOPE for plasmid DNA in U2OS cells follows a quasi-parabolic dependence on CnNO's alkyl substituent length with a maximum at n = 16. The transfection efficiency of CnNO/DOPE (n = 12-18) lipoplexes was found to be higher than that of commercially available Lipofectamine 2000. C16NO/DOPE also positively transfected HEK 293T and HeLa cells. Small-angle X-ray scattering (SAXS) shows large structural diversity depending on the complex's composition and pH. Transfection efficiencies mediated by two structures, either a condensed lamellar (L_α^c) or epitaxially connected L_α^c and a condensed inverted hexagonal (H_II^c) phase (L_α^c & H_II^c), were found to be very similar. The change in pH from acidic to neutral induces phase transition L_α^c & H_II^c → Q_II + L_α, with cubic phase Q_II of the Pn3m space group. Q_II detected in lipoplexes of most efficient composition CnNO/DOPE (n = 16 and 18) facilitates DNA release and promotes its internalization in the cell.

Effects of Dipole Potential Modifiers on Heterogenic Lipid Bilayers

In this work, we examine the ability of dipole modifiers, flavonoids, and RH dyes to affect the dipole potential (φ d) and phase separation in membranes composed of ternary mixtures of POPC with different sphingolipids and sterols. Changes in the steady-state conductance induced by cation-ionophore complexes have been measured to evaluate the changes in dipole potential of planar lipid bilayers. Confocal fluorescence microscopy has been employed to investigate lipid segregation in giant unilamellar vesicles. The effects of flavonoids on φ d depend on lipid composition and dipole modifier type. The effectiveness of RH dyes to increase φ d depends on sphingolipid type but is not influenced by sterol content. Tested modifiers lead to partial or complete disruption of gel domains in bilayers composed of POPC, sphingomyelin, and cholesterol. Substitution of cholesterol to ergosterol or 7-dehydrocholesterol leads to a loss of fluidizing effects of modifiers except phloretin. This may be due to various compositions of gel domains. The lack of influence of modifiers on phase scenario in vesicles composed of ternary mixtures of POPC, cholesterol, and phytosphingosine or sphinganine is related to an absence of gel-like phase. It was concluded that the membrane lateral heterogeneity affects the dipole-modifying abilities of the agents that influence the magnitude of φ d by intercalation into the bilayer and orientation of its own large dipole moments (phloretin and RH dyes). The efficacy of modifiers that do not penetrate deeply and affect φ d through water adsorption (phlorizin, quercetin, and myricetin) is not influenced by lateral heterogeneity of membrane.

Structural Significance of Lipid Diversity as Studied by Small Angle Neutron and X-ray Scattering

We review recent developments in the rapidly growing field of membrane biophysics, with a focus on the structural properties of single lipid bilayers determined by different scattering techniques, namely neutron and X-ray scattering. The need for accurate lipid structural properties is emphasized by the sometimes conflicting results found in the literature, even in the case of the most studied lipid bilayers. Increasingly, accurate and detailed structural models require more experimental data, such as those from contrast varied neutron scattering and X-ray scattering experiments that are jointly refined with molecular dynamics simulations. This experimental and computational approach produces robust bilayer structural parameters that enable insights, for example, into the interplay between collective membrane properties and its components (e.g., hydrocarbon chain length and unsaturation, and lipid headgroup composition). From model studies such as these, one is better able to appreciate how a real biological membrane can be tuned by balancing the contributions from the lipid's different moieties (e.g., acyl chains, headgroups, backbones, etc.).

Caloric restriction induces energy-sparing alterations in skeletal muscle contraction, fiber composition and local thyroid hormone metabolism that persist during catch-up fat upon refeeding

Weight regain after caloric restriction results in accelerated fat storage in adipose tissue. This catch-up fat phenomenon is postulated to result partly from suppressed skeletal muscle thermogenesis, but the underlying mechanisms are elusive. We investigated whether the reduced rate of skeletal muscle contraction-relaxation cycle that occurs after caloric restriction persists during weight recovery and could contribute to catch-up fat. Using a rat model of semistarvation-refeeding, in which fat recovery is driven by suppressed thermogenesis, we show that contraction and relaxation of leg muscles are slower after both semistarvation and refeeding. These effects are associated with (i) higher expression of muscle deiodinase type 3 (DIO3), which inactivates tri-iodothyronine (T₃), and lower expression of T₃-activating enzyme, deiodinase type 2 (DIO2), (ii) slower net formation of T₃ from its T₄ precursor in muscles, and (iii) accumulation of slow fibers at the expense of fast fibers. These semistarvation-induced changes persisted during recovery and correlated with impaired expression of transcription factors involved in slow-twitch muscle development. We conclude that diminished muscle thermogenesis following caloric restriction results from reduced muscle T₃ levels, alteration in muscle-specific transcription factors, and fast-to-slow fiber shift causing slower contractility. These energy-sparing effects persist during weight recovery and contribute to catch-up fat.

Rutin stimulates sarcoplasmic reticulum Ca(2+)-ATPase activity (SERCA1) and protects SERCA1 from peroxynitrite mediated injury

In this study we analyzed the protective action of the flavonoid rutin on peroxynitrite (ONOO(-)) mediated impairment of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1 isoform), especially related to posttranslational and conformational changes. Rutin concentration dependently protected ONOO(-) induced SERCA1 activity decrease with effective concentration EC50 of 18 ± 1.5 µM. Upon treatment with ONOO(-), this flavonoid also prevented SERCA1 from thiol group oxidation and significantly reduced tyrosine nitration and protein carbonyl formation. In the absence of ONOO(-), rutin (250 and 350 µM) stimulated SERCA1 activity at 2.1 mM [ATP] and 10 µM [Ca(2+)]free. According to changes in the kinetic parameters V max and K m with regard to [ATP], rutin (250 µM) increased the rate of enzyme catalysis and decreased the affinity of SERCA1 to ATP. FITC fluorescence decreased in the presence of rutin (150 and 250 µM), indicating conformational changes in the cytosolic ATP binding region of SERCA1. In silico study confirmed the binding of rutin in the cytosolic region of SERCA1, in the vicinity of the ATP binding site. Residue Glu183 localized within the conserved TGES loop was identified to play a key role in rutin-SERCA1 interaction (H-bond length of 1.7 Å), elucidating the ability of rutin to affect the affinity of SERCA1 to ATP. The binding of rutin in the proximity of Lys515 is likely to cause a decrease in FITC fluorescence.

The influence of halogen derivatives of thyronine and fluorescein on the dipole potential of phospholipid membranes

The effects of halogen derivatives of thyronine (tetraiodotironine and triiodothyronine) and fluorescein (Rose Bengal, phloxine B, erythrosin, eosin Y, and fluorescein) on the dipole potential of membranes composed of diphytanoylphosphocholine, diphytanoylphosphoserine, and diphytanoylphosphoethanolamine were investigated. A quantitative description of the modifying action of the agents was presented as characteristic parameters of the Langmuir adsorption isotherm: the maximum changes in the dipole potential of the membrane at an infinitely high concentration of modifiers and the desorption constant, characterizing their inverse affinities to the lipid phase. It was shown that the iodine-containing hormones led to a less significant reduction in the dipole potential of phospholipid membranes compared to the xanthene dyes, Rose Bengal, phloxine B, and erythrosin. The latter were characterized by the highest affinity for the lipid membranes compared to tetraiodotironine and triiodothyronine. It was found that the effect of iodine-containing hormones and xanthene dyes on the membrane dipole potential was caused by their uncharged and charged forms, respectively.

Modulation of rabbit muscle sarcoplasmic reticulum Ca(2+)-ATPase activity by novel quercetin derivatives

Sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) is the pump crucial for calcium homeostasis and its impairment results in pathologies such as myopathy, heart failure or diabetes. Modulation of SERCA activity may represent an approach to the therapy of diseases with SERCA impairment involvment. Quercetin is flavonoid known to modulate SERCA activity. We examined the effect of nine novel quercetin derivatives on the activity of the pump. We found that 5-morpholinohydroxypoxyquercetin, di(prenylferuoyl)quercetin, di(diacetylcaffeoyl)-mono-(monoacetylcaffeoyl)quercetin and monoacetylferuloylquercetin stimulated the activity of SERCA. On the contrary, monochloropivaloylquercetin, tri(chloropivaloyl)quercetin, pentaacetylquercetin, tri(trimethylgalloyl)quercetin and diquercetin inhibited the activity of the pump. To identify compounds with a potential to protect SERCA against free radicals, we assessed the free radical scavenging activity of quercetin derivatives. We also related lipophilicity, an index of the ability to incorporate into the membrane of sarcoplasmic reticulum, to the modulatury effect of quercetin derivatives on SERCA activity. In addition to its ability to stimulate SERCA, di(prenylferuloyl)quercetin showed excellent radical scavenging activity.

Novel quercetin derivatives in treatment of peroxynitrite-oxidized SERCA1

Sarco/endoplasmic reticulum calcium ATP-ase (SERCA) is regulated by low concentrations of peroxynitrite and inhibited by high levels, as indicated in human diseases. We studied quercetin (Q) and its novel derivatives monochloropivaloylquercetin (MPQ) and chloronaphthoquinonequercetin (CHQ) as agents with expected preventive properties against peroxynitrite-induced SERCA impairment. Q and MPQ protected the SERCA1 against peroxynitrite induced activity decrease, while CHQ potentiated the inhibitory effect of peroxynitrite. Quercetin derivatives were found to be weaker antioxidants compared with Q, as indicated by their ability to scavenge peroxynitrite and prevent of SERCA1 carbonylation, both decreasing in the order (Q > MPQ > CHQ). Quantum-chemical values of theoretical parameter E HOMO also indicated lower antioxidant capacities for MPQ and CHQ. Prooxidant properties estimated by calculations of frontier molecular orbitals (E LUMO) correlated with experimentally determined SH-group decrease induced by the compounds studied. Both methods showed a decrease of prooxidant properties as follows: CHQ > MPQ > Q. In addition, experimentally measured half-wave potentials indicated stronger prooxidant properties of quercetin derivatives as compared to Q. More expressive alterations of conformation in the transmembrane region of SERCA1 induced by quercetin derivatives, as compared with Q, may at least partially correlate with their higher lipophilicities. The protective effects of Q and MPQ on different isoforms of SERCA activity may be useful in prevention and treatment of inflammation or muscle diseases. The inhibitory effect of CHQ on SERCA isoforms may be beneficial in therapeutic approaches aimed at anti-tumor treatment.

Effect of dipole modifiers on the magnitude of the dipole potential of sterol-containing bilayers

The effects of various subclasses of flavonoids, Rose Bengal, and different styrylpyridinium dyes on the magnitude of the dipole potential of membranes composed of pure phospholipids and sterol-containing bilayers were investigated. Changes in the steady-state membrane conductance induced by cation-ionophore complexes were measured to examine the changes in the dipole potential of lipid bilayers. The characteristic parameters of the Langmuir adsorption isotherm for different flavonoids and Rose Bengal and the slope of the linear dependence of the dipole potential change on the aqueous concentrations of RH dyes were estimated. Chalcones (phloretin and phloridzin) and flavonols (quercetin and myricetin) strictly decrease the dipole potential of phospholipid- and sterol-containing membranes; the unsaturation of the C-ring and the hydrophobicity of the molecule contribute to the ability of the flavonoid to reduce the bilayer dipole potential. Rose Bengal decreases the magnitude of the bilayer dipole potential to a similar extent, but its affinity for membrane lipids is higher; the effects of RH dyes, chalcones, and phloroglucinol are determined by sterol concentration and type.

Model-based approaches for the determination of lipid bilayer structure from small-angle neutron and X-ray scattering data

Some of our recent work has resulted in the detailed structures of fully hydrated, fluid phase phosphatidylcholine (PC) and phosphatidylglycerol (PG) bilayers. These structures were obtained from the joint refinement of small-angle neutron and X-ray data using the scattering density profile (SDP) models developed by Kučerka et al. (Biophys J 95:2356-2367, 2008; J Phys Chem B 116:232-239, 2012). In this review, we first discuss models for the standalone analysis of neutron or X-ray scattering data from bilayers, and assess the strengths and weaknesses inherent to these models. In particular, it is recognized that standalone data do not contain enough information to fully resolve the structure of naturally disordered fluid bilayers, and therefore may not provide a robust determination of bilayer structure parameters, including the much-sought-after area per lipid. We then discuss the development of matter density-based models (including the SDP model) that allow for the joint refinement of different contrast neutron and X-ray data, as well as the implementation of local volume conservation within the unit cell (i.e., ideal packing). Such models provide natural definitions of bilayer thicknesses (most importantly the hydrophobic and Luzzati thicknesses) in terms of Gibbs dividing surfaces, and thus allow for the robust determination of lipid areas through equivalent slab relationships between bilayer thickness and lipid volume. In the final section of this review, we discuss some of the significant findings/features pertaining to structures of PC and PG bilayers as determined from SDP model analyses.

Fluid phase lipid areas and bilayer thicknesses of commonly used phosphatidylcholines as a function of temperature

The structural parameters of fluid phase bilayers composed of phosphatidylcholines with fully saturated, mixed, and branched fatty acid chains, at several temperatures, have been determined by simultaneously analyzing small-angle neutron and X-ray scattering data. Bilayer parameters, such as area per lipid and overall bilayer thickness have been obtained in conjunction with intrabilayer structural parameters (e.g. hydrocarbon region thickness). The results have allowed us to assess the effect of temperature and hydrocarbon chain composition on bilayer structure. For example, we found that for all lipids there is, not surprisingly, an increase in fatty acid chain trans-gauche isomerization with increasing temperature. Moreover, this increase in trans-gauche isomerization scales with fatty acid chain length in mixed chain lipids. However, in the case of lipids with saturated fatty acid chains, trans-gauche isomerization is increasingly tempered by attractive chain-chain van der Waals interactions with increasing chain length. Finally, our results confirm a strong dependence of lipid chain dynamics as a function of double bond position along fatty acid chains.

Pycnogenol and Ginkgo biloba extract: effect on peroxynitrite-oxidized sarcoplasmic reticulum Ca-ATPase

The effect of two natural standardized plant extracts, Pycnogenol(®) and EGb 761, on sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) activity and posttranslational modifications induced by peroxynitrite was investigated to assess their possible protective role. EGb 761 was found to have a protective effect on SERCA activity in the concentration range of 5-40 µg/ml. On the other hand, Pycnogenol(®) caused a decrease of SERCA activity at concentrations of 25 µg/ml. EGb 761 did not prevent protein carbonyl formation upon oxidation with peroxynitrite. On the contrary, Pycnogenol(®) at the concentrations of 5 and 10 µg/ml significantly decreased the level of protein carbonyls by 44% and 54%, respectively. Neither Pycnogenol(®) nor EGb 761 exerted a protective effect against thiol group oxidation.The plant extracts studied modulated peroxynitrite-injured SERCA activity by different ways and failed to correlate with posttranslational modifications. Their effect seems to be associated with their ability to change SERCA conformation rather than by their antioxidant capacity.

Surfactin activity depends on the membrane dipole potential

The effect of dipole modifying agents phloretin and RH 421 on the membrane conductance induced by surfactin, a lipopeptide antibiotic from Bacillus subtilis, was studied. Surfactin added on both sides of a bilayer formed from diphytanoylphosphocholine in 1 M KCl (pH 6.5) leads to the formation of voltage-independent channels of different conductance levels. The conductance of different states of SA channels varies from tens of picosiemens for small pores up to tens of nanosiemens for large ones. Small channels demonstrate pronounced cationic selectivity, whereas large ones practically lose their K(+)/Cl(-) selectivity, most probably because of their large effective radii. The addition of phloretin to the bilayer bathing solution, the agent known to decrease the membrane dipole potential, results in a decrease in the surfactin-induced membrane conductance. At the same time, increasing the membrane dipole potential because of the introduction of RH 421 leads to a rise in the steady-state conductance. Increasing dipole potential is accompanied by increases in both the number of open channels and their conductance. The observed changes in the channel-forming activity of surfactin might be caused by varying the partition coefficient of lipopeptide between the lipid and aqueous phases.

Bio-organoclays based on phospholipids as immobilization hosts for biological species

A new type of hybrid biomaterials based on the clay minerals montmorillonite and sepiolite as well as phosphatidylcholine, acting as environment-friendly biomodifier, was prepared. The biohybrids were characterized by sampling of adsorption isotherms in different organic solvents. The results suggest bilayer formation both on the external sepiolite surface as well as in the intracrystalline space of the montmorillonite. The obtained supported lipid membranes were further investigated by X-ray diffraction, multinuclear solid state NMR, Fourier transformed IR spectroscopy and thermal analysis. From these results an adsorption model based on electrostatic interaction between the polar phospholipid headgroups and the silicate surface could be postulated. The versatility of bio-organoclays as immobilization host for biological species was demonstrated in a mycotoxin retention study.

Areas of monounsaturated diacylphosphatidylcholines

We have studied the structural properties of monounsaturated diacylphosphatidylcholine lipid bilayers (i.e., diCn:1PC, where n = 14, 16, 18, 20, 22, and 24 is the number of acyl chain carbons). High-resolution x-ray scattering data were analyzed in conjunction with contrast-varied neutron scattering data using a technique we recently developed. Analyses of the data show that the manner by which bilayer thickness increases with increasing n in monounsaturated diacylphosphatidylcholines is dependent on the double bond's position. For commonly available monounsaturated diacylphosphatidylcholines, this results in the nonlinear behavior of both bilayer thickness and lipid area, whereas for diC18:1PC bilayers, lipid area assumes a maximum value. It is worthwhile to note that compared to previous data, our results indicate that lipid areas are smaller by approximately 10%. This observation highlights the need to revisit lipid areas, as they are often used in comparisons with molecular dynamics simulations. Moreover, simulators are encouraged to compare their results not only to x-ray scattering data, but to neutron data as well.

Hydrophobic thickness, lipid surface area and polar region hydration in monounsaturated diacylphosphatidylcholine bilayers: SANS study of effects of cholesterol and beta-sitosterol in unilamellar vesicles

The influence of a mammalian sterol cholesterol and a plant sterol beta-sitosterol on the structural parameters and hydration of bilayers in unilamellar vesicles made of monounsaturated diacylphosphatidylcholines (diCn:1PC, n=14-22 is the even number of acyl chain carbons) was studied at 30 degrees C using small-angle neutron scattering (SANS). Recently published advanced model of lipid bilayer as a three-strip structure was used with a triangular shape of polar head group probability distribution (Kucerka et al., Models to analyze small-angle neutron scattering from unilamellar lipid vesicles, Physical Review E 69 (2004) Art. No. 051903). It was found that 33 mol% of both sterols increased the thickness of diCn:1PC bilayers with n=18-22 similarly. beta-sitosterol increased the thickness of diC14:1PC and diC16:1PC bilayers a little more than cholesterol. Both sterols increased the surface area per unit cell by cca 12 A(2) and the number of water molecules located in the head group region by cca 4 molecules, irrespective to the acyl chain length of diCn:1PC. The structural difference in the side chain between cholesterol and beta-sitosterol plays a negligible role in influencing the structural parameters of bilayers studied.

Protective effect of antioxidants against sarcoplasmic reticulum (SR) oxidation by Fenton reaction, however without prevention of Ca-pump activity

The Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA) of rabbit skeletal muscle was oxidized by Fe2+/H2O2/ascorbic acid (AA), a system which generates HO(.) radicals according to the Fenton reaction: (Fe2(+)+H2O2-->HO(.)+OH(-)+Fe(3+)) under conditions similar to the pathological state of inflammation. Under these conditions, when hydroxyl-radicals and/or ferryl-radicals are generated, a 50% decrease of the SERCA activity was observed, a significant decrease of SH groups and an increase of protein carbonyl groups and lipid peroxidation were identified. Two new bands, time dependent in density, appeared in the SERCA protein electrophoresis after incubation with the Fenton system (at approximately 50 and 75kDa), probably due to structural changes as supported also by trypsin digestion. Immunoblotting of DNPH derivatized protein bound carbonyls detected a time dependent increase after incubation of SERCA with the Fenton system. Trolox and the pyridoindole stobadine (50microM) protected SR against oxidation induced via the Fenton system by preventing SH group oxidation and lipid peroxidation. Pycnogenol((R)) and EGb761 (40microg/ml) protected SERCA in addition against protein bound carbonyl formation. In spite of the antioxidant effects, trolox and stobadine were not able to prevent a decrease in the SERCA Ca(2+)-ATPase activity. Pycnogenol and EGb761 even enhanced the decrease of the Ca(2+)-ATPase activity induced by the Fenton system, probably by secondary oxidative reactions.

The effect of cholesterol on short- and long-chain monounsaturated lipid bilayers as determined by molecular dynamics simulations and X-ray scattering

We investigate the structure of cholesterol-containing membranes composed of either short-chain (diC14:1PC) or long-chain (diC22:1PC) monounsaturated phospholipids. Bilayer structural information is derived from all-atom molecular dynamics simulations, which are validated via direct comparison to x-ray scattering experiments. We show that the addition of 40 mol % cholesterol results in a nearly identical increase in the thickness of the two different bilayers. In both cases, the chain ordering dominates over the hydrophobic matching between the length of the cholesterol molecule and the hydrocarbon thickness of the bilayer, which one would expect to cause a thinning of the diC22:1PC bilayer. For both bilayers there is substantial headgroup rearrangement for lipids directly in contact with cholesterol, supporting the so-called umbrella model. Importantly, in diC14:1PC bilayers, a dynamic network of hydrogen bonds stabilizes long-lived reorientations of some cholesterol molecules, during which they are found to lie perpendicular to the bilayer normal, deep within the bilayer's hydrophobic core. Additionally, the simulations show that the diC14:1PC bilayer is significantly more permeable to water. These differences may be correlated with faster cholesterol flip-flop between the leaflets of short-chain lipid bilayers, resulting in an asymmetric distribution of cholesterol molecules. This asymmetry was observed experimentally in a case of unilamellar vesicles (ULVs), and reproduced through a set of novel asymmetric simulations. In contrast to ULVs, experimental data for oriented multilamellar stacks does not show the asymmetry, suggesting that it results from the curvature of the ULV bilayers.

Altering the activity of syringomycin E via the membrane dipole potential

The membrane dipole potential is responsible for the modulation of numerous biological processes. It was previously shown (Ostroumova, O. S.; Kaulin, Y. A.; Gurnev, P. A.; Schagina, L. V. Langmuir 2007, 23, 6889-6892) that variations in the dipole potential lead to changes in the channel properties of the antifungal lipodepsipeptide syringomycin E (SRE). Here, data are presented demonstrating the effect of the membrane dipole potential on the channel-forming activity of SRE. A rise in the dipole potential is accompanied by both an increase in the minimum SRE concentration required for the detection of single channels at fixed voltage and a decrease in the steady-state number of open SRE channels at a given SRE concentration and voltage. These alterations are determined by several factors: gating charge, connected with translocations of lipid and SRE dipoles during channel formation, the bilayer-water solution partitioning of SRE, and the chemical work related to conformational changes during channel formation.

Influence of cholesterol on the bilayer properties of monounsaturated phosphatidylcholine unilamellar vesicles

The influence of cholesterol on the structure of unilamellar-vesicle (ULV) phospholipid bilayers is studied using small-angle neutron scattering. ULVs made up of short-, mid- and long-chain monounsaturated phospholipids (diCn :1PC, n = 14 , 18, 22, respectively) are examined over a range (0-45 mol %) of cholesterol concentrations. Cholesterol's effect on bilayer structure is characterized through changes to the lipid's transmembrane thickness, lateral area and headgroup hydration. For all three lipids, analysis of the experimental data shows that the addition of cholesterol results in a monotonic increase of these parameters. In the case of the short- and mid-chain lipids, this is an expected result, however, such a finding was unexpected for the long-chain lipid. This implies that cholesterol has a pronounced effect on the lipid's hydrocarbon chain organization.

Effect of agents modifying the membrane dipole potential on properties of syringomycin E channels

We evaluated the effect of agents modifying the membrane dipole potential: phloretin, 6-ketocholestanol and RH 421 on the properties of single channels formed by lipodepsipeptide syringomycin E (SRE) in planar lipid bilayers. SRE forms two conductive states in lipid bilayers: "small" and "large." Large SRE channels are clusters of several small ones, demonstrating synchronous openings and closures. The increase in the membrane dipole potential led to (i) an increase in SRE channel conductance, (ii) an increase in the channel's lifetime, and (iii) a decrease in a number of synchronously operating small channels in the clusters. Overall, the results support the model of the small SRE channel synchronization in the cluster as voltage-dependent orientation of the lipid dipoles associated with the channel pores.