Check out our New Publishers' Select for Free Articles

BBA - Biomembranes (v.1808, #11)

Editorial Board (pp. i).

Structural characterization of the interaction of the polyene antibiotic Amphotericin B with DODAB bicelles and vesicles by Tiago R. Oliveira; Carlos R. Benatti; M. Teresa Lamy (pp. 2629-2637).

Amphotericin B (AmB) is widely used in the treatment of systemic fungal infections, despite its toxic effects. Nephrotoxicity, ascribed as the most serious toxic effect, has been related to the state of aggregation of the antibiotic. In search of the increase in AmB antifungal activity associated with low toxicity, several AmB-amphiphile formulations have been proposed. This work focuses on the structural characterization of a specific AmB formulation: AmB associated with sonicated dioctadecyl dimethylammonium bromide (DODAB) aggregates. Here, it was confirmed that sonicated DODAB dispersion is constituted by DODAB bicelles, and that monomeric AmB is much more soluble in bicelles than in DODAB vesicles. A new optical parameter is proposed for the estimation of the relative amount of amphiphile-bound monomeric AmB. With theoretical simulations of the spectra of spin labels incorporated in DODAB bicelles it was possible to prove that monomeric AmB binds preferentially to lipids located at the edges of DODAB bicelles, rigidifying them, and decreasing the polarity of the region. That special binding of monomeric AmB along the borders of bicelles, where the lipids are highly disorganized, could be used in the formulation of other carriers for the antibiotic, including mixtures of natural lipids which are known to form bicelles.► A new optical parameter for the relative quantitation of amphiphilic-bound monomeric AmB. ► Calculation of maximum monomeric AmB bound to DODAB bicelles and vesicles. ► Optical absorption, DSC and ESR show AmB aggregates are in water in DODAB dispersions. ► ESR spectra analysis clearly shows that AmB binds at DODAB bicelle edges. ► ESR analysis discussed here could be used with other drugs or other AmB carriers.

Keywords: Abbreviations; (AmB); Amphotericin B; (DODAB); dioctadecyl dimethylammonium bromide; (DODAB; ^NS; ); Non-sonicated DODAB dispersion; (DODAB; ^S; ); sonicated DODAB dispersion; (ESR); Electron Spin Resonance; (DPPG); dipalmitoyl phosphatidylglycerol; (DPPC); dipalmitoyl phosphatidylcholine; (5- and 16-MESL); spin labels 5- and 16-doxyl stearic acid methyl ester derivativesAmphotericin B; DODAB; Spin label; DSC; Optical spectrum; Drug carrier

Structural characterization of the interaction of the polyene antibiotic Amphotericin B with DODAB bicelles and vesicles by Tiago R. Oliveira; Carlos R. Benatti; M. Teresa Lamy (pp. 2629-2637).

In search of a novel target — Phosphatidylserine exposed by non-apoptotic tumor cells and metastases of malignancies with poor treatment efficacy by Sabrina Riedl; Beate Rinner; Martin Asslaber; Helmut Schaider; Sonja Walzer; Alexandra Novak; Karl Lohner; Dagmar Zweytick (pp. 2638-2645).

This study was performed in the aim to identify potential targets for the development of novel therapy to treat cancer with poor outcome or treatment efficacy. We show that the negatively charged phospholipid phosphatidylserine (PS) is exposed in the outer leaflet of their plasma membrane not only in tumor cell lines, but also in metastases and primary cultures thereof, which contrasts with a lack of PS exposure by differentiated non-tumorigenic counterparts. Studied tumor cell lines were derived from non-tumorigenic and malignant melanomas, prostate- and renal cancer, glioblastoma and a rhabdomyosarcoma. Importantly, also metastases of melanoma expose PS and there is a correlation between malignancy of melanoma cell lines from different stages of tumor progression and PS exposure. The PS exposure we found was neither of apoptotic nor of experimental artificial origin. Finally potentially malignant and non-malignant cells could be differentiated by sorting of a primary cell culture derived from a glioblastoma based on PS exposure, which has so far not been possible within one culture due to lack of a specific marker. Our data provide clear evidence that PS could serve as uniform marker of tumor cells and metastases as well as a target for novel therapeutic approaches based on e.g. PS-specific host defense derived peptides.► Novel marker of glioblastoma, renal cancer, rhabdomyosarcoma ► Novel marker of metastasis ► Marker also present in primary cultures ► Increase of exposure of marker with malignancy ► Demonstration of universality of a novel target for antitumor therapy

Keywords: Cancer plasma membrane; Phosphatidylserine exposure; Tumor marker; Peptide target

Nanoscale structural and mechanical effects of beta-amyloid (1–42) on polymer cushioned membranes: A combined study by neutron reflectometry and AFM Force Spectroscopy by Silvia Dante; Hauss Thomas Hauß; Roland Steitz; Claudio Canale; Norbert A. Dencher (pp. 2646-2655).

The interaction of beta-amyloid peptides with lipid membranes is widely studied as trigger agents in Alzheimer's disease. Their mechanism of action at the molecular level is unknown and their interaction with the neural membrane is crucial to elucidate the onset of the disease. In this study we have investigated the interaction of water soluble forms of beta-amyloid Aβ(1–42) with lipid bilayers supported by polymer cushion. A reproducible protocol for the preparation of a supported phospholipid membrane with composition mimicking the neural membrane and in physiological condition (PBS buffer, pH=7.4) was refined by neutron reflectivity. The change in structure and local mechanical properties of the membrane in the presence of Aβ(1–42) was investigated by neutron reflectivity and Atomic Force Microscopy (AFM) Force Spectroscopy. Neutron reflectivity evidenced that Aβ(1–42) interacts strongly with the supported membrane, causing a change in the scattering length density profile of the lipid bilayer, and penetrates into the membrane. Concomitantly, the local mechanical properties of the bilayer are deeply modified by the interaction with the peptide as seen by AFM Force Spectroscopy. These results may be of great importance for the onset of the Alzheimer's disease, since a simultaneous change in the structural and mechanical properties of the lipid matrix could influence all membrane based signal cascades.► The interaction of amyloid-beta peptide on lipid membranes was investigated. ► Polymer cushioned lipid bilayers used as model membranes. ► Neutron reflectivity showed penetration of the peptide into the membranes. ► AFM Force Spectroscopy showed that amyloid-beta affects mechanical stability of the membrane.

Keywords: Abbreviations; AD; Alzheimer's disease; Aβ(1–42); β-amyloid (1–42); Aβs; soluble amyloid-beta; APP; amyloid precursor protein; AFM-FS; Atomic Force Microscopy Force Spectroscopy; DLS; dynamic light scattering; NR; neutron reflectivity; PBS; phosphate buffer saline; PAH; polyallylamine hydrochloride; PEI; polyethylenemine; PEM; polyelectrolyte multilayer; PSS; polystyrene sulfonate; POPC; 1-palmitoyl-2-oleoyl-phosphatidylcholine; (POPS); 1-palmitoyl-2-oleoyl-phosphatidyl serine; (POPC-D31); 1-palmitoyl(D31)-2-oleoyl-phosphatidylcholine; POPS-D31; 1-palmitoyl(D31)-2-oleoylphosphatidyl serine; QENS; Quasi Elastic Neutron Scattering; SANS; small-angle-neutron scattering; SLD; scattering length density; SLM; supported lipid membranes; TFA; trifluoroacetic acid; ULV; unilamellar lipid vesiclesBeta-amyloid; Lipid bilayer; Polymer cushion; Neutron reflectivity; Force spectroscopy

Human cells and cell membrane molecular models are affected in vitro by the nonsteroidal anti-inflammatory drug ibuprofen by Marcela Manrique-Moreno; Fernando Villena; Carlos P. Sotomayor; Ana M. Edwards; Munoz Marcelo A. Muñoz; Patrick Garidel; Mario Suwalsky (pp. 2656-2664).

This report presents evidence that ibuprofen interacts with red cell membranes as follows: a) in scanning electron microscopy (SEM) studies on human erythrocytes induced shape changes at a concentration as low as 10μM; b) in isolated unsealed human erythrocyte membranes (IUM) induced mild increase in the water content or in their molecular dynamics at the hydrophobic–hydrophilic interphase, while a corresponding ordering decrease at the deep phospholipids acyl chain level; c) at physiological temperature (37°C), 300μM ibuprofen induced a significant increase in the generalized polarization (GP) of dimyristoylphosphatidylcholine (DMPC) large unilamellar vesicles (LUV), an indication that ibuprofen molecules locate in the head polar group region of DMPC; d) X-ray diffraction studies showed that ibuprofen concentrations≥300μM induced increasing structural perturbation to DMPC bilayers; e) differential scanning calorimetry (DSC) data showed that ibuprofen was able to alter the cooperativity of DMPC phase transition in a concentration-dependent manner, to destabilize the gel phase and that ibuprofen did not significantly perturb the organization of the lipid hydrocarbon chains. Additionally, the effect on the viability of both human promyelocytic leukemia HL-60 and human cervical carcinoma HeLa cells was studied.► Ibuprofen induced in vitro morphological changes to human erythrocytes. ► Interacted with class of lipid present in the outer monolayer of the erythrocyte membrane. ► Produced a strong toxic dose-response effect in human promyelocytic leukemia cells.

Keywords: Nonsteroidal anti-inflammatory drug; Ibuprofen; Cell membrane; Drug–membrane interaction; Erythrocyte

Cyclotide–membrane interactions: Defining factors of membrane binding, depletion and disruption by Robert Burman; Stromstedt Adam A. Strömstedt; Martin Malmsten; Goransson Ulf Göransson (pp. 2665-2673).

The cyclotide family of plant-derived peptides is defined by a cyclic backbone and three disulfide bonds locked into a cyclic cystine knot. They display a diverse range of biological activities, many of which have been linked to an ability to target biological membranes. In the current work, we show that membrane binding and disrupting properties of prototypic cyclotides are dependent on lipid composition, using neutral (zwitterionic) membranes with or without cholesterol and/or anionic lipids. Cycloviolacin O2 (cyO2) caused potent membrane disruption, and showed selectivity towards anionic membranes, whereas kalata B1 and kalata B2 cyclotides were significantly less lytic towards all tested model membranes. To investigate the role of the charged amino acids of cyO2 in the membrane selectivity, these were neutralized using chemical modifications. In contrast to previous studies on the cytotoxic and antimicrobial effects of these derivatives, the Glu6 methyl ester of cyO2 was more potent than the native peptide. However, using membranes of Escherichia coli lipids gave the opposite result: the activity of the native peptide increased 50-fold. By using a combination of ellipsometry and LC-MS, we demonstrated that this unusual membrane specificity is due to native cyO2 extracting preferentially phosphatidylethanolamine-lipids from the membrane, i.e., PE-C16:0/cyC17:0 and PE-C16:0/C18:1.Display Omitted► Prototypic cyclotides bind to and disrupt lipid membranes. ► The bracelet cyclotide cycloviolacin O2 is more potent than the Möbius kalata B1 and B2. ► Potency is dependent on electrostatics and on cyclotide secondary and tertiary structure. ► A conserved glutamic acid has a key role for PE-lipid specific extraction. ► A 100-fold difference in bacteria to human model membrane selectivity was observed.

Keywords: Abbreviations; cyO2; cycloviolacin O2; DOPA; Sodium 1,2-dioleoyl-; sn; -glycero-3-phosphate; DOPC; 1,2-dioleoyl-; sn; -glycero-3-phosphocholine; kB1; kalata B1; kB2; kalata B2; PE; PhosphatidylethanolamineCyclotide; Cycloviolacin O2; Kalata; Membrane; Phosphatidylethanolamine; Lipid extraction

Comparative NMR analysis of an 80-residue G protein-coupled receptor fragment in two membrane mimetic environments by L.S. Cohen; B. Arshava; A. Neumoin; J.M. Becker; Guntert P. Güntert; O. Zerbe; F. Naider (pp. 2674-2684).

Fragments of integral membrane proteins have been used to study the physical chemical properties of regions of transporters and receptors. Ste2p(G31-T110) is an 80-residue polypeptide which contains a portion of the N-terminal domain, transmembrane domain 1 (TM1), intracellular loop 1, TM2 and part of extracellular loop 1 of the α-factor receptor (Ste2p) from Saccharomyces cerevisiae. The structure of this peptide was previously determined to form a helical hairpin in lyso-palmitoylphosphatidyl-glycerol micelles (LPPG) [1]. Herein, we perform a systematic comparison of the structure of this protein fragment in micelles and trifluoroethanol (TFE):water in order to understand whether spectra recorded in organic:aqueous medium can facilitate the structure determination in a micellar environment. Using uniformly labeled peptide and peptide selectively protonated on Ile, Val and Leu methyl groups in a perdeuterated background and a broad set of 3D NMR experiments we assigned 89% of the observable atoms. NOEs and chemical shift analysis were used to define the helical regions of the fragment. Together with constraints from paramagnetic spin labeling, NOEs were used to calculate a transiently folded helical hairpin structure for this peptide in TFE:water. Correlation of chemical shifts was insufficient to transfer assignments from TFE:water to LPPG spectra in the absence of further information.► NMR analysis of a double transmembrane fragment of a GPCR, Ste2p(G31-T110). ► Ste2p(G31-T110) in TFE:water (1:1) resulted in a transiently folded helical hairpin. ► Comparison of NMR structures of Ste2p(G31-T110) in micelles and TFE:water. ► Chemical shift correlation analysis of shifts derived in two membrane mimetics.

Keywords: GPCR; Membrane protein structure; Fragment; Transmembrane

Mechanistic insights into the translocation of full length HIV-1 Tat across lipid membranes by Annegret Boll; Aline Jatho; Nadine Czudnochowski; Matthias Geyer; Claudia Steinem (pp. 2685-2693).

The mechanism of how full length Tat (aa 1–86) crosses artificial lipid membranes was elucidated by means of fluorescence spectroscopy and fluorescence microscopy. It was shown that full length Tat (aa 1–86) neither forms pores in large unilamellar vesicles (LUVs) nor in giant unilamellar vesicles (GUVs) composed of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC). In contrast, an N-terminally truncated Tat protein (aa 35–86) that lacks the structurally defined proline- and cysteine-rich region as well as the highly conserved tryptophan residue at position 11 generates pores in artificial POPC-membranes, through which a water-soluble dye up to a size of 10kDa can pass. By means of fluorescence microscopy, the transfer of fluorescently labeled full length Tat across POPC-bilayers was unambiguously visualized with a concomitant accumulation of the protein in the membrane interface. However, if the dye was attached to the protein, also pore formation was induced. The size of the pores was, however smaller than the protein size, i.e. the labeled protein with a mass of 11.6kDa passed the membrane, while a fluorescent dye with a mass of 10kDa was excluded from the vesicles' interior. The results demonstrate that pore formation is not the prime mechanism by which full length Tat crosses a membrane.► Full length Tat protein does not form pores in POPC bilayers ► Truncated Tat, lacking the N-terminus, forms pores in POPC membranes ► Fluorescently labeled full length Tat translocates across lipid membranes

Keywords: Abbreviations; AF633; Alexa Fluor 633 maleimide; AF488; Alexa Fluor 488 maleimide; D3-AF488; 3; kDa dextran coupled AF488; D10-AF488; 10; kDa dextran coupled AF488; Tat-AF633; AF633 labeled full length Tat protein; ARM; arginine rich motif; CF; 5(6)-carboxyfluorescein; CPP; cell penetrating peptide; GUV; giant unilamellar vesicle; LUV; large unilamellar vesicle; PB-DMPE; pacific blue-1,2-ditetradecanoyl-; sn; -glycero-3-phosphoethanolamine, triethylammonium salt; ROI; region of interest; TR-DHPE; sulforhodamine 101 dihexadecanoylphosphatidylethanolamine; IPTG; isopropyl-β-; D; -1-thiogalactopyranoside; PMSF; phenylmethanesulfonylfluoride; GSH; glutathione; TEV; Tobacco etch virus; SDS-PAGE; sodium dodecylsulfate polyacrylamide gel electrophoresisArginine-rich motif; Cell penetrating peptide; Fluorescence microscopy; Giant unilamellar vesicle; Protein–membrane interaction; Transactivator of transcription

Mechanistic insights into the translocation of full length HIV-1 Tat across lipid membranes by Annegret Boll; Aline Jatho; Nadine Czudnochowski; Matthias Geyer; Claudia Steinem (pp. 2685-2693).

Fluorescence methods for lipoplex characterization by Catarina Madeira; Luís M.S. Loura; Maria R. Aires-Barros; Manuel Prieto (pp. 2694-2705).

Since the first reported transfection studies using cationic liposomes in 1987, significant advances have been made on the understanding of the physical properties of DNA/cationic liposome complexes (lipoplexes) in order to improve their transfection efficiencies. In this review a critical survey of the biophysical techniques used in their characterization is presented, with an emphasis on fluorescence methodologies, namely FRET. It is shown that the use of FRET combined with state-of-the-art modeling and data analysis allows detailed structural information in conditions close to the in vivo utilization of these non-viral based vectors. We describe in detail the use of fluorescence-based methods in (i) the assessment of DNA–lipid interaction and kinetics of lipoplex formation; (ii) membrane mixing studies; (iii) characterization of lipoplex molecular structure through the determination of interlamellar distances; and (iv) qualitative and quantitative evaluation of DNA condensation by cationic liposomes. This review aims at providing a framework for future characterization studies of novel liposomal formulations as gene delivery carriers, taking advantage of more sensitive nucleic acid and lipid dyes concomitantly with increasingly sophisticated fluorescence techniques.►We present a critical survey of biophysical techniques for lipoplex characterization. ►Emphasis is given to the use of fluorescence methodologies, namely FRET. ►We provide a framework for the use of novel fluorescence techniques in this context.

Keywords: Cationic lipids; Gene delivery; Lipoplex; Fluorescence techniques; FRET; Plasmid DNA

Fluorescence methods for lipoplex characterization by Catarina Madeira; Luís M.S. Loura; Maria R. Aires-Barros; Manuel Prieto (pp. 2694-2705).

Keywords: Cationic lipids; Gene delivery; Lipoplex; Fluorescence techniques; FRET; Plasmid DNA

Molecular organization of antibiotic amphotericin B in dipalmitoylphosphatidylcholine monolayers induced by K⁺ and Na⁺ ions: The Langmuir technique study by Marta Arczewska; Gagos Mariusz Gagoś (pp. 2706-2713).

The effect of potassium (K⁺) and sodium (Na⁺) ions on the self-association of antibiotic amphotericin B (AmB) in the lipid membrane was reported. Mixed Langmuir monolayers of AmB and dipalmitoylphosphatidylcholine (DPPC) were investigated by recording surface pressure–area isotherms spread on aqueous buffers containing physiological concentration of K⁺ and Na⁺ ions. The analyses of the π–A isotherms and compressional modulus curves indicate the interactions in the AmB–DPPC system. The strength of the AmB–DPPC interactions and the stability of the mixed monolayers were examined on the basis of the excess free energy of mixing values. The obtained results proved a high affinity of AmB towards lipids induced by the presence of K⁺ than Na⁺ ions. The most stable monolayers in the presence of K⁺ and Na⁺ ions were formed by AmB and DPPC with the 1:1 and 2:1 stoichiometry. The understanding of the AmB aggregation processes at the molecular level should contribute to elucidate the mechanisms of action and toxicity of this widely used drug. The presented results are potentially valuable in respect to develop more efficient and less toxic AmB formulations.Display Omitted► K⁺ and Na⁺ ions play an important role in molecular organization of AmB in DPPC monolayers. ► The results proved a high affinity of AmB towards DPPC induced by the presence of K⁺ than Na⁺ ions. ► The stoichiometry of the most stable AmB and DPPC monolayers was 1:1 and 2:1 in presence of K⁺ and Na⁺ ions.

Keywords: Amphotericin B; Molecular organization; Langmuir monolayer; Na; ⁺; ion; K; ⁺; ion

The influence of PAMAM-OH dendrimers on the activity of human erythrocytes ATPases by Michal Ciolkowski; Monika Rozanek; Michal Szewczyk; Barbara Klajnert; Maria Bryszewska (pp. 2714-2723).

Dendrimers are a relatively new and still not fully examined group of polybranched polymers. In this study polyamidoamine dendrimers with hydroxyl surface groups (PAMAM-OH) of third, fourth and fifth generation (G3, G4 and G5) were examined for their ability to influence the activity of human erythrocyte plasma membrane adenosinetriphosphatases (ATPases). Plasma membrane ATPases are a group of enzymes related, among others, to the maintenance of ionic balance inside the cell. An inhibition of their activity may result in a disturbance of cell functioning. Two of examined dendrimers (G4 and G5) were found to inhibit the activity of Na⁺/K⁺ ATPase and Ca²⁺ ATPase by 20–30%. The observed effect was diminished when higher concentrations of dendrimers were used. The experiment with the use of pyrene as fluorescent probe sensitive to the changes in microenvironment's polarity revealed that it was an effect of dendrimers' self-aggregation. Additional studies showed that PAMAM-OH dendrimers were able to decrease the fluidity of human erythrocytes plasma membrane. Obtained results suggest that change in plasma membrane fluidity was not caused by the dendrimer–lipid interaction, but dendrimer–protein interaction. Different pattern of influence of dendrimers on ATPases activity and erythrocyte membrane fluidity suggests that observed change in ATPases activity is not a result of dendrimer–lipid interaction, but may be related to direct interaction between dendrimers and ATPases.► G4 and G5 PAMAM-OH dendrimers inhibit the human erythrocyte membrane ATPases. ► Inhibition of ATPases by PAMAM-OH dendrimers depends on dendrimer generation. ► PAMAM-OH dendrimers are able to decrease human erythrocyte membrane fluidity. ► Change in plasma membrane fluidity may be a result of dendrimer–protein interaction.

Keywords: Abbreviations; ATPase; adenosinetriphosphatase; CH; cholesterol; DLS; dynamic light scattering; DPH; 1,6-diphenyl-1,3,5-hexatriene; EDTA; ethylenediaminetetraacetic acid disodium salt dihydrate; EGTA; ethylene glycol-bis(2-aminoethylether)-N,N,N’,N’-tetraacetic acid; G3, G4, G5; third, fourth and fifth generation of dendrimer; PAMAM; polyamidoamine dendrimer; PAMAM-OH; polyamidoamine dendrimer with hydroxyl surface groups; PC; phosphatidylcholine; PMSF; phenylmethanesulfonyl fluoride; PPI; polypropyleneimine dendrimers; SM; sphingomyelin; TMA-DPH; N,N,N-trimethyl-4-(6-phenyl-1,3,5,-hexatrien-1-yl)phenylammonium p-toluenesulfonate; Tris; tris(hydroxymethyl)aminomethanePAMAM-OH dendrimers; ATPase; Erythrocyte ghosts; Liposomes; Enzyme inhibition; Red blood cell

The influence of PAMAM-OH dendrimers on the activity of human erythrocytes ATPases by Michal Ciolkowski; Monika Rozanek; Michal Szewczyk; Barbara Klajnert; Maria Bryszewska (pp. 2714-2723).

Lipid packing variations induced by pH in cardiolipin-containing bilayers: The driving force for the cristae-like shape instability by Nada Khalifat; Jean-Baptiste Fournier; Miglena I. Angelova; Nicolas Puff (pp. 2724-2733).

Cardiolipin is a four-tailed acidic lipid found predominantly within the inner membrane of mitochondria, and is thought to be a key component in determining inner membrane properties and potential. Thus, cardiolipin may be involved in the dynamics of the inner membrane characteristic invaginations (named cristae) that protrude into the matrix space. In previous studies, we showed the possibility to induce, by localized proton flow, a macroscopic cristae-like shape remodeling of an only-lipid model membrane mimicking the inner mitochondrial membrane. In addition, we reported a theoretical model describing the dynamics of a chemically driven membrane shape instability caused by a modification of the plane-shape equilibrium density of the lipids in the membrane. In the present work, we focus on the lipid-packing modifications observed in a model cardiolipin-containing lipid membrane submitted to pH decrease because this is the driving force of the instability. Laurdan fluorescence and ζ-potential measurements show that under pH decrease, membrane surface charge decreases, but that significant modification of the lipid packing is observed only for CL-containing membranes. Our giant unilamellar vesicle experiments also indicate that cristae-like morphologies are only observed for CL-containing lipid membranes. Taken together, these results highlight the fact that only a strong modulation of the lipid packing of the exposed monolayer leads to membrane shape instability and suggest that mitochondrial lipids, in particular the cardiolipin, play a specific role under pH modulation in inner mitochondrial membrane morphology and dynamics.Display Omitted► Cardiolipin is a key component of the inner mitochondrial membrane. ► pH induced significant lipid packing modifications only for cardiolipin-containing membranes. ► Asymmetry of the best preferred area per lipid leads to membrane shape instability. ► Cristae-like morphologies are only observed for cardiolipin-containing GUVs. ► Lipids play a specific role in inner mitochondrial membrane morphology and dynamics.

Keywords: Abbreviations; CL; cardiolipin (diphosphatidylglycerol); IMM; inner mitochondrial membrane; PC; egg yolk; l; -α-phosphatidylcholine; PE; egg yolk; l; -α-phosphatidylethanolamine; LUV; large unilamellar vesicles; GUV; giant unilamellar vesicles; GP; generalized polarization; Laurdan; 6-dodecanoyl-2-dimethylaminonaphthalene; DPH; 1,6-diphenyl-1,3,5-hexatrieneCardiolipin; pH; Laurdan; Mitochondrion; GUV; Curvature instability

Lipid-mediated membrane binding properties of Disabled-2 by Ruba Alajlouni; Karen E. Drahos; Carla V. Finkielstein; Daniel G.S. Capelluto (pp. 2734-2744).

Disabled-2 (Dab2) is an adaptor protein involved in several biological processes ranging from endocytosis to platelet aggregation. During endocytosis, the Dab2 phosphotyrosine-binding (PTB) domain mediates protein binding to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P₂) at the inner leaflet of the plasma membrane. As a result of platelet activation, Dab2 is released from α-granules and associates with both the αIIbβ3 integrin receptor and sulfatide lipids on the platelet surface through its N-terminal region including the PTB domain (N-PTB), thus, modulating platelet aggregation. Thrombin, a strong platelet agonist, prevents Dab2 function by cleaving N-PTB within the two basic motifs required for sulfatide association, a reaction that is prevented when Dab2 is bound to these sphingolipids. We have characterized the membrane binding properties of Dab2 N-PTB using micelles enriched with Dab2 lipid ligands, sulfatides and PtdIns(4,5)P₂. Remarkably, NMR spectroscopy studies suggested differences in lipid-binding mechanisms. In addition, we experimentally demonstrated that sulfatide- and PtdIns(4,5)P₂-binding sites overlap in Dab2 N-PTB and that both lipids stabilize the protein against temperature-induced unfolding. We found that whereas sulfatides induced conformational changes and facilitated Dab2 N-PTB penetration into micelles, Dab2 N-PTB bound to PtdIns(4,5)P₂ lacked these properties. These results further support our model that platelet membrane sulfatides, but not PtdIns(4,5)P₂, protect Dab2 N-PTB from thrombin cleavage.► Reconstitution of Dab2 N-PTB in sulfatide- and PtdIns(4,5)P₂-enriched micelles. ► Sulfatide- and PtdIns(4,5)P₂-binding sites overlap in Dab2 N-PTB. ► Sulfatides, but not PtdIns(4,5)P₂, induce Dab2 N-PTB structural changes. ► Sulfatides, but not PtdIns(4,5)P₂, contribute to membrane insertion of Dab2 N-PTB.

Keywords: Abbreviations; CD; circular dichroism; Dab2; Disabled-2; DDM; N-dodecyl-β-; d; -maltopyranoside; NMR; nuclear magnetic resonance; N-PTB; N-terminal region of Dab2 containing the PTB domain; PtdIns(4,5)P; ₂; phosphatidylinositol 4,5-bisphosphate; PTB; phosphotyrosine-binding domain; SPR; surface plasmon resonanceDisabled-2; PTB domain; Sulfatide; Phosphatidylinositol 4,5-bisphosphate; Micelle

Lipid-mediated membrane binding properties of Disabled-2 by Ruba Alajlouni; Karen E. Drahos; Carla V. Finkielstein; Daniel G.S. Capelluto (pp. 2734-2744).

Probing membrane permeabilization by the antimicrobial peptide distinctin in mercury-supported biomimetic membranes by Lucia Becucci; Martina Papini; Daniel Mullen; Andrea Scaloni; Gianluigi Veglia; Rolando Guidelli (pp. 2745-2752).

The mechanism of membrane permeabilization by the antimicrobial peptide distinctin was investigated by using two different mercury-supported biomimetic membranes, namely a lipid self-assembled monolayer and a lipid bilayer tethered to the mercury surface through a hydrophilic spacer (tethered bilayer lipid membrane: tBLM). Incorporation of distinctin into a lipid monolayer from its aqueous solution yields rapidly ion channels selective toward inorganic cations, such as Tl⁺ and Cd²⁺. Conversely, its incorporation in a tBLM allows the formation of ion channels permeable to potassium ions only at non-physiological transmembrane potentials, more negative than −340mV. These channels, once formed, are unstable at less negative transmembrane potentials. The kinetics of their formation is consistent with the disruption of distinctin clusters adsorbed on top of the lipid bilayer, incorporation of the resulting monomers and their aggregation into hydrophilic pores by a mechanism of nucleation and growth. Comparing the behavior of distinctin in tBLMs with that in conventional black lipid membranes strongly suggests that distinctin channel formation in lipid bilayer requires the partitioning of distinctin molecules between the two sides of the lipid bilayer. We can tentatively hypothesize that an ion channel is formed when one distinctin cluster on one side of the lipid bilayer matches another one on the opposite side.► Distinctin forms rapidly ion channels selective toward inorganic cations in lipid monolayers. ► Distinctin is adsorbed on lipid bilayers in the form of aggregates. ► Distinctin ion channels in lipid bilayers are formed by nucleation and growth of embedded monomers. ► Distinctin molecules must partition between the two sides of a lipid bilayer in order to form ion channels.

Keywords: Antimicrobial peptide; Ion channel; Lipid monolayer self-assembled on mercury; Tethered bilayer lipid membrane; Nucleation and growth; Partially fused vesicle

Effect of ceramide structure on membrane biophysical properties: The role of acyl chain length and unsaturation by Sandra N. Pinto; Liana C. Silva; Anthony H. Futerman; Manuel Prieto (pp. 2753-2760).

Ceramide is an important bioactive sphingolipid involved in a variety of biological processes. The mechanisms by which ceramide regulates biological events are not fully understood, but may involve alterations in the biophysical properties of membranes. We now examine the properties of ceramide with different acyl chains including long chain (C16- and C18-), very long chain (C24-) and unsaturated (C18:1- and C24:1-) ceramides, in phosphatidylcholine model membranes. Our results show that i) saturated ceramides have a stronger impact on the fluid membrane, increasing its order and promoting gel/fluid phase separation, while their unsaturated counterparts have a lower (C24:1-) or no (C18:1-) ability to form gel domains at 37°C; ii) differences between saturated species are smaller and are mainly related to the morphology and size of the gel domains, and iii) very long chain ceramides form tubular structures likely due to their ability to form interdigitated phases. These results suggest that generation of different ceramide species in cell membranes has a distinct biophysical impact with acyl chain saturation dictating membrane lateral organization, and chain asymmetry governing interdigitation and membrane morphology.► Global biophysical behavior of long chain versus very long chain, and saturated versus unsaturated ceramide species are studied. ► Saturated ceramides have a stronger impact on membrane lateral organization. ► Ceramide chain asymmetry governs interdigitation independently of the degree of unsaturation. ► Ceramide interdigitation is the driven force behind tubular structure formation. ► Saturated-ceramide gel domains have a long range effect in increasing the order of the POPC-rich fluid phase.

Keywords: Abbreviations; C16-ceramide; N-palmitoyl-D-; erythro; -sphingosine; C18:1-ceramide; N-oleoyl-D-; erythro; -sphingosine; C18-ceramide; N-stearoyl-D-; erythro; -sphingosine; C24:1-ceramide; N-nervonoyl-D-; erythro; -sphingosine; C24-ceramide; N-lignoceroyl-D-; erythro; -sphingosine; CerS; ceramide synthases; DPH; 1,6-diphenyl-1,3,5-hexatriene; FCS; Fluorescence correlation spectroscopy; GUV; giant unilamellar vesicles; MLV; multilamellar vesicles; POPC; 1-palmitoyl-2-oleoyl-; sn; -glycero-3-phosphocholine; Rho 110; rhodamine 110; Rho-DOPE; N-rhodamine-dipalmitoylphosphatidylethanolamine; SLs; Sphingolipids; SM; sphingomyelin; t-PnA; trans-parinaric acidCeramide gel domains; Ceramide synthases; Ceramide tubules; Interdigitation; Lipid domain morphology

Fluid phase lipid areas and bilayer thicknesses of commonly used phosphatidylcholines as a function of temperature by Kucerka Norbert Kučerka; Mu-Ping Nieh; John Katsaras (pp. 2761-2771).

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.► Fluid bilayers composed of phosphatidylcholines are studied at several temperatures. ► Structural parameters are determined by neutron and X-ray scattering analysis. ► Thermal behavior of bilayer interactions is dominated by trans–gauche isomerization. ► Van der Waals interactions dictate chain length dependence in saturated lipids. ► Lipid chain dynamics depend strongly on double bond position.

Keywords: Area per lipid; Bilayer structure; Fluid phase; Neutron scattering; X-ray scattering; Phosphatidylcholine

Fluid phase lipid areas and bilayer thicknesses of commonly used phosphatidylcholines as a function of temperature by Kucerka Norbert Kučerka; Mu-Ping Nieh; John Katsaras (pp. 2761-2771).

Keywords: Area per lipid; Bilayer structure; Fluid phase; Neutron scattering; X-ray scattering; Phosphatidylcholine

Sections

Personal tools

BBA - Biomembranes (v.1808, #11)

Sections

Personal tools

Local resources

BBA - Biomembranes (v.1808, #11)