Opioid peptide interactions with lipid bilayer membranes.

The interaction of the delta-opioid receptor selective peptides, cyclic [D-Pen2, D-Pen5]-enkephalin [DPDPE] and its acyclic analog, DPDPE(SH)2, with neutral phospholipid bilayer membranes was examined by permeability and calorimetry measurements. The permeabilities were accomplished by entrapping either peptide inside of unilamellar liposomes (composed of a mixture of a molar ratio 65:25:10 phosphatidylcholine/phosphatidylethanolamine/cholesterol) then monitoring the peptide efflux through the bilayer. The initial permeability of DPDPE (first 12 h) averaged over four experiments was (0.91 +/- 0.47).10(-12) cm s-1. In contrast the average permeability of the acylic DPDPE(SH)2 was (4.26 +/- 0.23).10(-12) cm s-1. The effect of these peptides on the phase transition, Tm, of 1,2-dipalmitoylphosphatidylcholine (DPPC) bilayers was examined by high sensitivity differential scanning calorimetry. The Tm, the calorimetric enthalpy, and the van 't Hoff enthalpy of DPPC were not significantly altered by the presence of DPDPE, whereas the calorimetric data for DPPC with DPDPE(SH)2 showed a small, yet significant, increase (0.2 degrees C) in the Tm with a 30% decrease in the cooperative unit. Both the permeability and calorimetry data reveal a stronger peptide-membrane interaction in the case of the more flexible acyclic peptide.     

Lipid-polypeptide interactions in bilayer lipid membranes

Summary The modifications of the electrical properties of bilayer lipid membranes (BLM) composed of cholesterol and an ionic surfactant upon interaction with charged polypeptides were studied. The addition of 10^–8 m polylysine (Ps⁺) to one side of anionic cholesterol dodecylphosphate BLM increases the specific membrane conductance over 1000-fold (from 10^–8 to 10^–5 mho/cm²) and develops a cationic transmembrane potential larger than 50 mV. This potential is reverted by addition of polyanions such as RNA, polyglutamic or polyadenilic acid to the same side on which Ps⁺ is present, by addition of Ps⁺ to the opposite side, or by addition of trypsin to either side. Both conductance and potential changes are hindered by increasing the ionic strength or by raising the pH of the bathing medium, disappearing above pH 11.5 where it is known that Ps⁺ folds into an -helix. The interaction of polyglutamic acid (PGA) with a cationic cholesterol-hexadecyltrimethylammonium bromide BLM results in increased membrane conductance and development of an anionic transmembrane potential which is reverted by addition of polycations to the same aqueous phase where PGA is present. Addition of either Ps⁺ or PGA to one or both sides of a neutral BLM composed of 7-dehydrocholesterol induces no significant change. The observations suggest the formation of a lipid polymer membrane resultant from the interaction, predominantly electrostatic, of the isolated components. The implications of these results are discussed in terms of the current models of membrane structure.     

Flexoelectric and steric interactions between two bilayer lipid membranes resulting from their curvature fluctuations

Steric repulsion of lipid membranes due to their thermally stimulated out-of-plane fluctuations has been calculated by Helfrich. In the present paper another method of calculation has been used and the fluctuating curvature-induced (flexoelectric) polarization of the membranes has been taken into account as well. This polarization leads to an attractive contribution to the interaction force. At a great distance the flexoelectric effect has modified the Helfrich's law of repulsion while at a short distance and big enough value of the flexoelectric coefficient a first order phase transition, similar to the onset of condensation in a non-ideal gas under higher pressure, has been predicted.     

古尼拟青霉表型多样性及其与活性成分的关系

目的研究表型多样性与活性成分之间的联系。方法研究10株古尼拟青霉菌株的培养特性,观察菌落形态,测定其产孢量和粗蛋白、多糖、甘露醇、麦角甾醇、腺苷等主要活性成分含量。结果A类菌株菌落背面褶皱不平,中央为棕色环状,周边为淡黄色,是生长性状优良、活性成分含量高,适于大规模工业化生产的优质菌株。结论不同菌株具有不同的形态特征,且形态特征与其产孢量及主要活性成分存在一定内在联系。     

Implicit solvent simulations of peptide interactions with anionic lipid membranes

A recently developed implicit membrane model (IMM1) is supplemented with a Gouy-Chapman term describing counterion-screened electrostatic interactions of a solute with negatively charged membrane lipids. The new model is tested on peptides that bind to anionic membranes. Pentalysine binds just outside the plane of negative charge, whereas Lys-Phe peptides insert their aromatic rings into the hydrophobic core. Melittin and magainin 2 bind more strongly to anionic than to neutral membranes and in both cases insert their hydrophobic residues into the hydrocarbon core. The third domain of Antennapedia homeodomain (penetratin) binds as an alpha-helix in the headgroup region. Cardiotoxin II binds strongly to anionic membranes but marginally to neutral ones. In all cases, the location and configuration of the peptides are consistent with experimental data, and the effective energy changes upon binding compare favorably with experimental binding free energies. The model opens the way to exploring the effect of membrane charge on the location, conformation, and dynamics of a large variety of biologically active peptides on membranes.     

Computer analyses suggest interactions of non-muscle filamin with lipid membranes

It is concluded from structure predictions of the primary amino acid sequence by computer analyses that two segments of non-muscle filamin could facilitate lipid membrane attachment or anchoring. Residues 49–71 of the amino-terminal may attach to phospholipid membranes, and residues 131–155 may anchor in the hydrophobic region of lipid membranes.     

The monolayer technique: a potent tool for studying the interfacial properties of antimicrobial and membrane-lytic peptides and their interactions with lipid membranes

Erudites of the antiquity already knew the calming effect of oil films on the sea waves. But one had to wait until 1774 to read the first scientific report on oil films from B. Franklin and again 1878 to learn the thermodynamic analysis on adsorption developed by J. Gibbs. Then, in 1891, Agnes Pockels described a technique to manipulate oil films by using barriers. Finally, in 1917, I. Langmuir introduced the experimental and theoretical modern concepts on insoluble monolayers. Since that time, and because it has been found to provide invaluable information at the molecular scale, the monolayer technique has been more and more extensively used, and, during the past decade, an explosive increase in the number of publications has occurred. Over the same period, considerable and ever-increasing interest in the antimicrobial peptides of various plants, bacteria, insects, amphibians and mammals has grown. Because many of these antimicrobial peptides act at the cell membrane level, the monolayer technique is entirely suitable for studying their physicochemical and biological properties. This review describes monolayer experiments performed with some of these antimicrobial peptides, especially gramicidin A, melittin, cardiotoxins and defensin A. After giving a few basic notions of surface chemistry, the surface-active properties of these peptides and their behavior when they are arranged in monomolecular films are reported and discussed in relation to their tridimensional structure and their amphipathic character. The penetration of these antimicrobial peptides into phospholipid monolayer model membranes, as well as their interactions with lipids in mixed films, are also emphasized.     

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.     

The role of spontaneous lipid curvature in the interaction of interfacially active peptides with membranes

Research on antimicrobial peptides is in part driven by urgent medical needs such as the steady increase in pathogens being resistant to antibiotics. Despite the wealth of information compelling structure–function relationships are still scarce and thus the interfacial activity model has been proposed to bridge this gap. This model also applies to other interfacially active (membrane active) peptides such as cytolytic, cell penetrating or antitumor peptides. One parameter that is strongly linked to interfacial activity is the spontaneous lipid curvature, which is experimentally directly accessible. We discuss different parameters such as H-bonding, electrostatic repulsion, changes in monolayer surface area and lateral pressure that affect induction of membrane curvature, but also vice versa how membrane curvature triggers peptide response. In addition, the impact of membrane lipid composition on the formation of curved membrane structures and its relevance for diverse mode of action of interfacially active peptides and in turn biological activity are described. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.     

Atomic force microscopy of supported lipid membranes and their complexes with polycations

The method of atomic force microscopy has been used to investigate the morphology of mica-supported bilayer lipid membranes and stability of their complexes with a cationic polymer, poly-(N-ethyl-4-vinylpyridinium bromide). Lipid bilayers with a minimum of defects were obtained by the fusion of monolamellar neutral or mixed anionic bilayer vesicles (liposomes) on the mica surface, followed by excessive solvent removal by means of rapid rotation of a plate in horizontal plane (spin-coating). It has been shown that the cationic polymer does not interact with the bilayers, where the outer leaflet (i.e., the monolayer exposed to the surrounding aqueous solution) is made of an electroneutral phosphatidylcholine (PC). At the same time, the polymer irreversibly binds to the bilayer containing an anionic lipid.     

植物提取物及其活性成分抑制细菌生物被膜的研究进展北大核心CSCD

大量研究报道生物被膜细菌对抗生素的耐药性是浮游菌的10–1 000倍,据报道细菌生物被膜是80%以上细菌感染的罪魁祸首,对医疗保健领域构成了严峻的挑战。植物提取物及其活性成分对细菌生物被膜有明显的抑制作用,包括减少生物被膜量、生物被膜活菌数以及清除已经成熟的生物被膜等。该文对这些有效的植物提取物及其活性成分进行了总结,并分析了其抗细菌生物被膜的作用机制。旨在为防治细菌生物被膜感染的植物类药物的开发提供参考。     

Electrostatic interactions at charged lipid membranes. Calcium binding

A quantitative study of calcium-ion binding by the negatively-charged phospholipid methylphosphatidic acid is presented. Experimental results are compared with the predictions of the Gouy-Chapman theory, taking into account both the ions bound at the membrane surface and the ions held in the diffuse layer. This theory suffices to explain the titration of the calcium/lipid system, but fails to explain completely the behaviour of the ordered-fluid transition temperature, which shows a splitting that according to electrostatic theory alone should not occur. The dependence of the calcium-lipid binding constant. upon 1: 1 electrolyte concentration is correctly predicted by the theory; the latter however gives equations which can only be solved numerically. A simple, approximate equation is therefore given (in the text, eq. 34) for the prediction of the degree of calcium binding to a negatively-charged lipid membrane.     

Evaluation of Magainin I interactions with lipid membranes: An optical and electrochemical study

Most antimicrobial peptides (AMPs) have shown clear activity related to the disruption of lipid bilayers. In order to improve knowledge of this subject, the interaction of Magainin I (MagI) with phospholipid layers (PLs), uncoated or coated with synperonic (Synp), was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) techniques. MagI peptide was immobilized on gold electrode via a self-assembling monolayer obtained from liposomes and liposomes covered by Synp. MagI induces pores in the supported lipid membranes, which are reflected in an increased amperometric-response and also a decreased electron-transfer resistance (R(CT)). In addition, MagI showed a significant interaction with the PL-Synp-modified gold electrode, but MagI showed a reliable contact with the PL-modified gold electrode, leading to a decrease in the relative resistance charge transfer value of -17.38%. Our results demonstrated that Synp acts as a membrane sealant after exposure of the lipid membrane to MagI. A parallel reaction model was proposed for the interaction of MagI and a hybrid layer that result in a complex bimolecular interaction. In short, the importance of triblock copolymer to stabilize liposomes for future applications as drug delivery systems for MagI was demonstrated.     

Current-voltage characteristics of planar lipid membranes with attached Halobacterium cell-envelope vesicles

We have studied the photoactivity of a system consisting of large, planar, essentially solvent free bilayers bearing adsorbed cell-envelope vesicles prepared from Halobacterium halobium (strain L 33). The system was made conductive by addition of a proton carrier (SF-6847). We observed photocurrents which were linearly dependent upon transmembrane voltage. Current-voltage curves were found to be well described by an equivalent circuit with the following significant parameters: planar bilayer conductance, planar bilayer-vesicle contact area conductance, cell-envelope vesicle conductance, and chloride pump equivalent voltage-generator potential. These parameters are uniquely obtained as a result of a few independent current measurements. The stationary photovoltage was dependent upon chloride concentration, and from this dependence an active transport (pump) affinity of the system for chloride was calculated to be about 50 mM.     

Coating of magnetic nanoparticles affects their interactions with model cell membranes

BackgroundThe use of functionalized iron oxide nanoparticles of various chemical properties and architectures offers a new promising direction in theranostic applications. The increasing applications of nanoparticles in medicine require that these engineered nanomaterials will contact human cells without damaging essential tissues. Thus, efficient delivery must be achieved, while minimizing cytotoxicity during passage through cell membranes to reach intracellular target compartments.MethodsDifferential Scanning Calorimetry (DSC), molecular modeling, and atomistic Molecular Dynamics (MD) simulations were performed for two magnetite nanoparticles coated with polyvinyl alcohol (PVA) and polyarabic acid (ARA) in order to assess their interactions with model DPPC membranes.ResultsDSC experiments showed that both nanoparticles interact strongly with DPPC lipid head groups, albeit to a different degree, which was further confirmed and quantified by MD simulations. The two systems were simulated, and dynamical and structural properties were monitored. A bimodal diffusion was observed for both nanoparticles, representing the diffusion in the water phase and in the proximity of the lipid bilayer. Nanoparticles did not enter the bilayer, but caused ordering of the head groups and reduced the area per lipid compared to the pure bilayer, with MAG-PVA interacting more strongly and being closer to the lipid bilayer.ConclusionsResults of DSC experiments and MD simulations were in excellent agreement. Our findings demonstrate that the external coating is a key factor that affects nanoparticle-membrane interactions. Magnetite nanoparticles coated with PVA and ARA did not destabilize the model membrane and can be considered promising platforms for biomedical applications.General significanceUnderstanding the physico-chemical interactions of different nanoparticle coatings in contact with model cell membranes is the first step for assessing toxic response and could lead to predictive models for estimating toxicity. DSC in combination with MD simulations is an effective strategy to assess physico-chemical interactions of coated nanoparticles with lipid bilayers.     

Characterization of lipopolysaccharide fractions and their interactions with cells and model membranes.

The role of the length of the O-antigen polysaccharide side chain of bacterial lipopolysaccharide (LPS) in biological and model membrane systems was investigated. LPS from Salmonella typhimurium ATCC 14028 was chromatographed on a Sephadex G-200 column in the presence of sodium deoxycholate and separated into three fractions on the basis of molecular size. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot (immunoblot), and chemical analyses indicated that these fractions differed from each other primarily in the number of repeating units in the O-antigen polysaccharide side chain. In a biological system fractions 2 and 3 had the same effects to induce mitogenesis in murine lymphocytes, but fraction 1 was less effective than the other two fractions. In a model membrane system, LPS induced changes in small unilamellar vesicles (SUVs) which were measured by changes in the behavior of a fluorescent probe, 1,6-diphenylhexa-1,3,5-triene (DPH), and interaction of increasing amounts of all LPS fractions with SUVs gradually increased DPH anisotropy. Fractions 2 and 3 had similar effects on the SUVs as detected by changes in DPH anisotropy, while fraction 1 had almost twice as much activity as the other two fractions. These results suggest that the polysaccharide side chain of LPS may modulate the ability of biologically active lipid A to interact with cells and model membranes. In addition, factors other than changes in membrane fluidity may play a role in mediating LPS-induced cell activation.     

The interactions of bilirubin with model and biological membranes

The partitioning of bilirubin between albumin and model and biological membranes and the differential partitioning of bilirubin between membranes with different lipid and protein compositions were measured. Partition coefficients were independent of the concentration of bilirubin in membranes up to at least 7 mol of bilirubin/mol of phospholipid. The avidity of albumin for bilirubin was greater than that of membranes, but the avidity of the latter for bilirubin depended on the composition of the membrane. Bilirubin partitioned preferentially into model membranes comprised of microsomal lipids greater than dioleoylphosphatidylcholine = plasma membrane lipids much greater than egg phosphatidylcholine = dimyristoylphosphatidylcholine. Partitioning into membranes was increased if these contained proteins, but the effect of proteins could not be attributed to specific binding to sites on proteins, as reflected by the temperature independence of partition coefficients. Differential partitioning of bilirubin into different membranes of pure lipids also was independent of temperature. Differences in the bulk phase fluidity of membranes does not appear to account for the preferential partitioning of bilirubin into some membranes. It appears that bilirubin partitions into elements of free volume of differing sizes in membranes with variable lipid compositions and that the size of these elements can be increased by adding proteins to membranes.     

Electrostatic interactions at charged lipid membranes. Hydrogen bonds in lipid membrane surfaces

Hydrogen-bonded structures within lipid membrane surfaces are not disrupted by water and are of thermodynamic and therefore potential structural importance in biological systems.     

The interaction of detergents with bilayer lipid membranes

Detergents are widely used for extracting and purifying membrane proteins. Four such detergents have been studied to find the extent to which they alone can alter black lipid film conductances. The slope of the plot of conductivity versus concentration for Triton X-100 is 4.54 in the range 0.025–0.15 mM; dodecyl sulphate 0.82 in the range 0.01–1 mM; sodium deoxycholate 1.03 in the range 0.01–1 mM and sodium cholate 1.37 in the range 0.1–10 mM. These ranges are below the respective critical micelle concentrations; above these concentrations the membranes break. Bilayer lipid membrane conductivity measured at constant detergent concentration increases with the conductivity of the bathing salt solution with a slope greater than 1, indicating an effect on the putative pore structures induced by detergents.