Interaction of myelin basic protein, melittin and bovine serum albumin with gangliosides, sulphatide and neutral glycosphingolipids in mixed monolayers

Interfacial Aβ fibril formation is modulated by the disorder-order state of the lipids: The concept of the physical environment as amyloid inductor in biomembranes

The behavior of amphiphilic molecules such as lipids, peptides and their mixtures at the air/water interface allow us to evaluate and visualize the arrangement formed in a confined and controlled surface area. We have studied the surface properties of the zwitterionic DPPC lipid and Aβ(1-40) amyloid peptide in mixed films at different temperatures (from 15 to 40 °C). In this range of temperature the surface properties of pure Aβ(1-40) peptide remained unchanged, whereas DPPC undergoes its characteristic liquid-expanded → liquid-condensed bidimensional phase transition that depends on the temperature and lateral pressure. This particular property of DPPC makes it possible to dynamically study the influence of the lipid phase state on amyloid structure formation at the interface in a continuous, isothermal and abrupt change on the environmental condition. As the mixed film is compressed the fibril-like structure of Aβ(1-40) is triggered specifically in the liquid-expanded region, independently of temperature, and it is selectively excluded from the well-visible liquid condensed domains of DPPC. The Aβ amyloid fibers were visualized by using BAM and AFM and they were Thio T positive. In mixed DPPC/Aβ(1-40) films the condensed domains (in between 11 mN/m to 20 mN/m) become irregular probably due to the fibril-like structures is imposing additional lateral stress sequestering lipid molecules in the surrounding liquid-expanded phase to self-organize into amyloids.

Langmuir monolayer of lysozyme at variable subphase pH conditions: a comprehensive study on structure, morphology and hysteresis behaviour

Formation of a pure Langmuir monolayer of lysozyme at the air-water interface and its investigation by means of a surface pressure (π)-mean molecular area (A) isotherm has been accomplished under different subphase pH conditions. A normalized area-time curve confirms the stable nature of the lysozyme monolayer whose compressibility variation with an increased surface pressure at specific subphase pH has also been studied from π-A isotherms. The monolayers exhibit irreversible hysteresis behaviour irrespective of subphase pH conditions, as evidenced from successive compression-expansion π-A isotherm cycles. Comparison of surface thermodynamics under hysteresis with subphase pH variation confirms that the monolayer at subphase pH ≈ 4.0 involves a greater amount of energy to attain and retain the ordered and compact monolayer than the other two pH conditions (pH ≈ 7.0 and 9.5). In situ visualization of lysozyme monolayers by Brewster angle microscopy suggests the homogeneous and stripe-like pattern formation at lower and higher surface pressure respectively. Further investigations of lysozyme films at solid surfaces have been carried out with atomic force microscopy and X-ray reflectivity (XRR) analysis. Structural reversibility of lysozyme molecules under compression-expansion-compression of the monolayer is revealed from the comparison of height profiles of AFM images and electron density profiles as extracted from XRR analysis of the films deposited during both first and second compressions of the monolayer. The mechanism of the structural rearrangement of lysozyme molecules with surface pressure variation at different subphase pH is explored, correlating macroscopic and microscopic information.

In vitro and in vivo antimicrobial activity of self-assembled melittin nanoparticles: A comparative study with melittin peptide

The aim of the present study was to analyse the efficacy of self-assembled melittin nanoparticles (MelNP) and compare with native melittin peptide (Mel). Self-assembly formation of the melittin was promoted by heating at 90 °C for 50 min followed by cooling at room temperature. SEM micrographs revealed the formation of nanovesicles. MIC of MelNP against E. coli, S. aureus and P. aeruginosa was found to be 4, 2, and 2 μM, respectively while it was 8, 8 and 4 μM for Mel peptide. Markedly, MelNP showed 12.6 % hemolysis at 8 μM whereas with Mel it was about 71.63 %. The lytic activity of MelNP was also higher in the presence of trypsin/serum than Mel. Both MelNP and Mel exhibited membranolytic activity with cellular disintegration. Further, toxicity analysis studied up to 72 h showed that MelNP was non-toxic to zebrafish embryos up to 6 μM; however, with Mel exposed embryos showed up 30 dead embryos. Bacterial load was markedly reduced in MelNP and Mel exposed infected embryos than compared to the infected one. Moreover, the peptides were also responsible for reducing the infection and prolonging the survivability in infected embryos. Thus, MelNP could be considered an efficient and safer therapeutic molecule that Mel and wherein further experiments are warranted to affirm the broad spectrum efficiency.

Melittin-solid phospholipid mixed films trigger amyloid-like nano-fibril arrangements at air-water interface

We used the Langmuir monolayers technique to study the surface properties of melittin toxin mixed with either liquid-condensed DSPC or liquid-expanded POPC phospholipids. Pure melittin peptide forms stable insoluble monolayers at the air-water interface without interacting with Thioflavin T (Th-T), a sensitive probe to detect protein amyloid formation. When melittin peptide is mixed with DSPC lipid at 50 % of peptide area proportion at the surface, we observed the formation of fibril-like structures detected by Brewster angle microscopy (BAM), but they were not observable with POPC. The nano-structures in the melittin-DSPC mixtures became Th-T positive labeling when the arrangement was observed with fluorescence microscopy. In this condition, Th-T undergoes an unexpected shift in the typical emission wavelength of this amyloid marker when a 2D fluorescence analysis is conducted. Even when reflectivity analysis of BAM imaging evidenced that these structures would correspond to the DSPC lipid component of the mixture, the interpretation of ATR-FTIR and Th-T data suggested that both components were involved in a new lipid-peptide rearrangement. These nano-fibril arrangements were also evidenced by scanning electron and atomic force microscopy when the films were transferred to a mica support. The fibril formation was not detected when melittin was mixed with the liquid-expanded POPC lipid. We postulated that DSPC lipids can dynamically trigger the process of amyloid-like nano-arrangement formation at the interface. This process is favored by the relative peptide content, the quality of the interfacial environment, and the physical state of the lipid at the surface.

Gangliosides smelt nanostructured amyloid Aβ(1-40) fibrils in a membrane lipid environment

Gangliosides induced a smelting process in nanostructured amyloid fibril-like films throughout the surface properties contributed by glycosphingolipids when mixed with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/Aβ(1-40) amyloid peptide. We observed a dynamical smelting process when pre-formed amyloid/phospholipid mixture is laterally mixed with gangliosides. This particular environment, gangliosides/phospholipid/Aβ(1-40) peptide mixed interfaces, showed complex miscibility behavior depending on gangliosides content. At 0% of ganglioside covered surface respect to POPC, Aβ(1-40) peptide forms fibril-like structure. In between 5 and 15% of gangliosides, the fibrils dissolve into irregular domains and they disappear when the proportion of gangliosides reach the 20%. The amyloid interfacial dissolving effect of gangliosides is taken place at lateral pressure equivalent to the organization of biological membranes. Domains formed at the interface are clearly evidenced by Brewster Angle Microscopy and Atomic Force Microscopy when the films are transferred onto a mica support. The domains are thioflavin T (ThT) positive when observed by fluorescence microscopy. We postulated that the smelting process of amyloids fibrils-like structure at the membrane surface provoked by gangliosides is a direct result of a new interfacial environment imposed by the complex glycosphingolipids. We add experimental evidence, for the first time, how a change in the lipid environment (increase in ganglioside proportion) induces a rapid loss of the asymmetric structure of amyloid fibrils by a simple modification of the membrane condition (a more physiological situation).

Research Development, Optimization and Modifications of Anti-cancer Peptides

Anti-cancer peptides play an important role in the area of cancer inhibition. A variety of anti- cancer peptides have emerged through the extraction and structural modification of peptides from biological tissues. This review provides the research background of anti-cancer peptides, the introduction of the mechanism of anti-cancer peptides for inhibition of cancers, the discovery and development along with optimization and modifications of these peptides in the clinical application. In conclusion, it can be said that anti-cancer peptides will play a major role in the future oncologic clinic.

Aβ-Amyloid Fibrils Are Self-Triggered by the Interfacial Lipid Environment and Low Peptide Content

We studied the surface properties of Aβ(1-40) amyloid peptides mixed with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) (liquid state) or 1,2-disteraoyl-phosphatidylcholine (DSPC) (solid state) phospholipids by using nanostructured lipid/peptide films (Langmuir monolayers). Pure Aβ(1-40) amyloid peptides form insoluble monolayers without forming fibril-like structures. In a lipid environment [phospholipid/Aβ(1-40) peptide mixtures], we observed that both miscibility and stability of the films depend on the peptide content. At low Aβ(1-40) amyloid peptide proportion (from 2.5 to 10% of peptide area proportion), we observed the formation of a fibril-like structure when mixed only with POPC lipids. The stability acquired by these mixed films is within 20-35 mN·m^-1 compatible with the equivalent surface pressure postulated for natural biomembranes. Fibrils are clearly evidenced directly from the monolayers by using Brewster angle microscopy. The so-called nanostructured fibrils are thioflavin T positive when observed by fluorescence microscopy. The amyloid fibril network at the surface was also evidenced by atomic force microscopy when the films are transferred onto a mica support. Aβ(1-40) amyloid mixed with the solid DSPC lipid showed an immiscible behavior in all peptide proportions without fibril formation. We postulated that the amyloid fibrillogenesis at the membrane can be dynamically nano-self-triggered at the surface by the quality of the interfacial environment, that is, the physical state of the water-lipid interface and the relative content of amyloid protein present at the interface.

Melittin inhibits proliferation, migration and invasion of bladder cancer cells by regulating key genes based on bioinformatics and experimental assays

The antitumour effect of melittin (MEL) has recently attracted considerable attention. Nonetheless, information regarding the functional role of MEL in bladder cancer (BC) is currently limited. Herein, we investigated the effect of MEL on critical module genes identified in BC. In total, 2015 and 4679 differentially expressed genes (DEGs) associated with BC were identified from the GSE31189 set and The Cancer Genome Atlas database, respectively. GSE‐identified DEGs were mapped and analysed using Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes analyses to determine BC‐involved crucial genes and signal pathways. Coupled with protein–protein interaction network and Molecular Complex Detection analyses, Modules 2 and 4 were highlighted in the progression of BC. In in‐vitro experiments, MEL inhibited the proliferation, migration, and invasion of UM‐UC‐3 and 5637 cells. The expression of NRAS, PAK2, EGFR and PAK1 in Module 4—enriched in the MAPK signalling pathway—was significantly reduced after treatment with MEL at concentrations of 4 or 6 μg/mL. Finally, quantitative reverse transcription‐polymerase chain reaction and Western blotting analyses revealed MEL inhibited the expression of genes at the mRNA (ERK1/2, ERK5, JNK and MEK5), protein (ERK5, MEK5, JNK and ERK1/2) and phosphorylation (p‐ERK1/2, p‐JNK, and p‐38) levels. This novel evidence indicates MEL exerts effects on the ERK5‐MAK pathway—a branch of MAPK signalling pathway. Collectively, these findings provide a theoretical basis for MEL application in BC treatment.

Behaviour of protein (BSA)-lipid (DMPA) mixed monolayer on the spreading order of the individual component

Surface pressure (π) - mean molecular area (A) isotherms of protein (BSA) - lipid (DMPA) mixed films are examined by varying their ratio and altering the spreading order of BSA and DMPA on the water surface to study the protein-lipid interactions and the corresponding structures and patterns at different interfacial conditions. π-A isotherms and compression-decompression isotherm cycles of protein-lipid mixed monolayers below and above of the isoelectric point of BSA (pI ≈ 4.8) are also examined. Below the isoelectric point of BSA (pH ≈ 4.0), i.e., when BSA is weakly hydrophobic and has net positive charge shows low hysteresis irrespective of the spreading order of the molecules. However, at pH ≈ 7.0, i.e., when the overall charge of BSA is negative and is strongly hydrophobic the protein-lipid mixed films display higher hysteresis value. Besides the properties of the isotherms, the surface morphology and secondary conformations of protein inside the mixed films are obtained from X-ray reflectivity, atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy respectively after depositing the mixed films on solid substrates. Nearly similar information is obtained after altering the spreading order of BSA and DMPA, which indicates that the spreading of molecules on the water surface is one of the better ways of forming the lipid-protein mixed film at the air-water interface.

Melittin Exerts Beneficial Effects on Paraquat-Induced Lung Injuries In Mice by Modifying Oxidative Stress and Apoptosis

Melittin (MEL) is a 26-amino acid peptide with numerous biological activities. Paraquat (PQ) is one of the most widely used herbicides, although it is extremely toxic to humans. To date, PQ poisoning has no effective treatment, and therefore the current study aimed to assess for the first time the possible effects of MEL on PQ-induced lung injuries in mice. Mice received a single intraperitoneal (IP) injection of PQ (30 mg/kg), followed by IP treatment with MEL (0.1 and 0.5 mg/kg) twice per week for four consecutive weeks. Histological alterations, oxidative stress, and apoptosis in the lungs were studied. Hematoxylin and eosin (H&E) staining indicated that MEL markedly reduced lung injuries induced by PQ. Furthermore, treatment with MEL increased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activity, and decreased malonaldehyde (MDA) and nitric oxide (NO) levels in lung tissue homogenates. Moreover, immunohistochemical staining showed that B-cell lymphoma-2 (Bcl-2) and survivin expressions were upregulated after MEL treatment, while Ki-67 expression was downregulated. The high dose of MEL was more effective than the low dose in all experiments. In summary, MEL efficiently reduced PQ-induced lung injuries in mice. Specific pharmacological examinations are required to determine the effectiveness of MEL in cases of human PQ poisoning.

Melittin, a major peptide component of bee venom, and its conjugates in cancer therapy

Melittin (MEL), a major peptide component of bee venom, is an attractive candidate for cancer therapy. This agent has shown a variety of anti-cancer effects in preclinical cell culture and animal model systems. Despite a convincing efficacy data against variety of cancers, its applicability to humans has met with challenges due to several issues including its non-specific cytotoxicity, degradation and hemolytic activity. Several optimization approaches including utilization of nanoparticle based delivery of MEL have been utilized to circumvent the issues. Here, we summarize the current understanding of the anticancer effects of bee venom and MEL on different kinds of cancers. Further, we also present the available information for the possible mechanism of action of bee venom and/or MEL.

Electrostatic field effects on membrane domain segregation and on lateral diffusion

Natural membranes are organized structures of neutral and charged molecules bearing dipole moments which generate local non-homogeneous electric fields. When subjected to such fields, the molecules experience net forces that can modify the lipid and protein organization, thus modulating cell activities and influencing (or even dominating) the biological functions. The energetics of electrostatic interactions in membranes is a long-range effect which can vary over distance within r^-1 to r^-3. In the case of a dipole interacting with a plane of dipoles, e.g. a protein interacting with a lipid domain, the interaction is stronger than two punctual dipoles and depends on the size of the domain. In this article, we review several contributions on how electrostatic interactions in the membrane plane can modulate the phase behavior, surface topography and mechanical properties in monolayers and bilayers.

Composition-driven surface domain structuring mediated by sphingolipids and membrane-active proteins. Above the nano- but under the micro-scale: mesoscopic biochemical/structural cross-talk in biomembranes

Biomembranes contain a wide variety of lipids and proteins within an essentially two-dimensional structure. The coexistence of such a large number of molecular species causes local tensions that frequently relax into a phase or compositional immiscibility along the lateral and transverse planes of the interface. As a consequence, a substantial microheterogeneity of the surface topography develops and that depends not only on the lipid-protein composition, but also on the lateral and transverse tensions generated as a consequence of molecular interactions. The presence of proteins, and immiscibility among lipids, constitute major perturbing factors for the membrane sculpturing both in terms of its surface topography and dynamics. In this work, we will summarize some recent evidences for the involvement of membrane-associated, both extrinsic and amphitropic, proteins as well as membrane-active phosphohydrolytic enzymes and sphingolipids in driving lateral segregation of phase domains thus determining long-range surface topography.

Protein-induced surface structuring in myelin membrane monolayers

Monolayers prepared from myelin conserve all the compositional complexity of the natural membrane when spread at the air-water interface. They show a complex pressure-dependent surface pattern that, on compression, changes from the coexistence of two liquid phases to a viscous fractal phase embedded in a liquid phase. We dissected the role of major myelin protein components, myelin basic protein (MBP), and Folch-Lees proteolipid protein (PLP) as crucial factors determining the structural dynamics of the interface. By analyzing mixtures of a single protein with the myelin lipids we found that MBP and PLP have different surface pressure-dependent behaviors. MBP stabilizes the segregation of two liquid phases at low pressures and becomes excluded from the film under compression, remaining adjacent to the interface. PLP, on the contrary, organizes a fractal-like pattern at all surface pressures when included in a monolayer of the protein-free myelin lipids but it remains mixed in the MBP-induced liquid phase. The resultant surface topography and dynamics is regulated by combined near to equilibrium and out-of-equilibrium effects. PLP appears to act as a surface skeleton for the whole components whereas MBP couples the structuring to surface pressure-dependent extrusion and adsorption processes.

Biophysical properties of a synthetic transit peptide from wheat chloroplast ribulose 1,5-bisphosphate carboxylase

The surface properties of pure RuBisCo transit peptide (RTP) and its interaction with zwitterionic, anionic phospholipids and chloroplast lipids were studied by using the Langmuir monolayer technique. Pure RTP is able to form insoluble films and the observed surface parameters are compatible with an alpha-helix perpendicular to the interface. The alpha-helix structure tendency was also observed by using transmission FT-IR spectroscopy in bulk system of a membrane mimicking environment (SDS). On the other hand, RTP adopts an unordered structure in either aqueous free interface or in the presence of vesicles composed of a zwitterionic phospholipid (POPC). Monolayer studies show that in peptide/lipid mixed monolayers, RTP shows no interaction with zwitterionic phospholipids, regardless of their physical state. Also, with the anionic POPG at high peptide ratios RTP retains its individual surface properties and behaves as an immiscible component of the peptide/lipid mixed interface. This behaviour was also observed when the mixed films were composed by RTP and the typical chloroplast lipids MGDG or DGDG (mono- and di-galactosyldiacylglycerol). Conversely, RTP establishes a particular interaction with phosphatidylglycerol and cardiolipin at low peptide to lipid area covered relation. This interaction takes place with an increase in surface stability and a reduction in peptide molecular area (intermolecular interaction). Data suggest a dynamic membrane modulation by which the peptide fine-tunes its membrane orientation and its lateral stability, depending on the quality (lipid composition) of the interface.

Biophysics of sphingolipids II. Glycosphingolipids: An assortment of multiple structural information transducers at the membrane surface

Glycosphingolipids are ubiquitous components of animal cell membranes. They are constituted by the basic structure of ceramide with its hydroxyl group linked to single carbohydrates or oligosaccharide chains of different complexity. The combination of the properties of their hydrocarbon moiety with those derived from the variety and complexity of their hydrophilic polar head groups confers to these lipids an extraordinary capacity for molecular-to-supramolecular transduction across the lateral/transverse planes in biomembranes and beyond. In our opinion, most of the advances made over the last decade on the biophysical behavior of glycosphingolipids can be organized into three related aspects of increasing structural complexity: (1) intrinsic codes: local molecular interactions of glycosphingolipids translated into structural self-organization. (2) Surface topography: projection of molecular shape and miscibility of glycosphingolipids into formation of coexisting membrane domains. (3) Beyond the membrane interface: glycosphingolipid as modulators of structural topology, bilayer recombination and surface biocatalysis.

Protein-mediated surface structuring in biomembranes

The lipids and proteins of biomembranes exhibit highly dissimilar conformations, geometrical shapes, amphipathicity, and thermodynamic properties which constrain their two-dimensional molecular packing, electrostatics, and interaction preferences. This causes inevitable development of large local tensions that frequently relax into phase or compositional immiscibility along lateral and transverse planes of the membrane. On the other hand, these effects constitute the very codes that mediate molecular and structural changes determining and controlling the possibilities for enzymatic activity, apposition and recombination in biomembranes. The presence of proteins constitutes a major perturbing factor for the membrane sculpturing both in terms of its surface topography and dynamics. We will focus on some results from our group within this context and summarize some recent evidence for the active involvement of extrinsic (myelin basic protein), integral (Folch-Lees proteolipid protein) and amphitropic (c-Fos and c-Jun) proteins, as well as a membrane-active amphitropic phosphohydrolytic enzyme (neutral sphingomyelinase), in the process of lateral segregation and dynamics of phase domains, sculpturing of the surface topography, and the bi-directional modulation of the membrane biochemical reactivity.

Many length scales surface fractality in monomolecular films of whole myelin lipids and proteins

Monomolecular films prepared with all the lipid and protein components of myelin were spread at the air/aqueous buffer interface from isolated bovine spinal cord myelin fully dissolved in chloroform:methanol (2:1) or by surface free energy shock of myelin membrane microvesicles. These monolayers show indistinguishable surface behavior, with similar compositional phase coexistence through all the compression isotherm on several subphase conditions. The domains were observed through epifluorescence and Brewster angle microscopy on the air/water interface and on Langmuir-Blodgett films. Their thickness was measured ellipsometrically. Under molecular packing conditions resembling those found in the natural membrane, the morphology and size of the domains are highly self-similar, displaying no characteristic length scale. These properties are the hallmark of fractal objects. The fractality extends at least three orders of magnitudes, from the micrometer to the millimeter range, the fractal dimension being about 1.7. A possible implication of fractality in membrane structure and/or function is demonstrated through the high fluctuation of the propagation of signals through constrained diffusion in corrals formed by domains in the plane of the monolayer, which restricts the diffusion of a fluorescent probe over many length scale domains.

Favorable and unfavorable lateral interactions of ceramide, neutral glycosphingolipids and gangliosides in mixed monolayers

Interactions among four natural neutral sphingolipids (ceramide, glucosyl-ceramide, lactosyl-ceramide and asialo-GM1) and six gangliosides (GM3, GM2, GM1, GD3, GD1a and GT1b) were studied in binary Langmuir monolayers at the air-buffer interface in terms of their molecular packing, compressibility, dipole potential and mixing behavior. The changes of surface organization can be grouped into three sets: (a) binary films of neutral GSLs, and of the latter with ceramide, exhibit thermodynamically unfavorable mixing with mean molecular area expansions and dipole moment hyperpolarization; (b) mixed monolayers of ceramide, or of GlcCer, and gangliosides occur with thermodynamically favorable interactions leading to mean molecular area condensation and depolarisation; (c) binary mixtures of LacCer or Gg4Cer with gangliosides, and all ganglioside species among them, revealed molecular immiscibility characterized by additive mean molecular area and dipole potential, with composition-independent constant collapse pressure. These results disclose basic tendencies of GSLs to molecularly mix or demix, leading to their surface segregation, which may underlay vectorial separation of their specific biosynthetic pathways.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Evidence of a strong interaction of 2,4-dichlorophenoxyacetic acid herbicide with human serum albumin

The interaction of 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) with human serum albumin (HSA) was studied using fluorescence and differential scanning calorimetry (DSC). Fluorescence displacement of 1-anilino-8-naphtalenesulfonate (ANS) bound to HSA was used to evaluate the binding affinity of 2,4-D to HSA. The binding is associated to a high affinity site of HSA located in the IIIA subdomain. The association constant (Kass) of the herbicide was about 5 microM(-1), several times higher than the affinity found for pharmaceutical compounds. This relatively strong interaction with HSA was evidenced by the increase in HSA protein thermostability induced as consequence of herbicide interaction. 2,4-D induces an increase in the midpoint of thermal denaturation temperature from 60.1 degrees C in herbicide free solution to 75.6 degrees C in full ligand saturating condition. The calorimetric enthalpy and the excess heat capacity also increased upon 2,4-D binding. To investigate the possibility of other/s system/s of 2,4-D transport in blood, besides of HSA, the interaction of the herbicide with lipid monolayers was explored. No interaction was detected with any of the lipids tested. The overall results provided evidence that high affinity 2,4-D-HSA complex exhibits enhanced thermal stability and that HSA is the unique transport system for 2,4-D in blood.

Surface behavior of myelin monolayers

Myelin can be spread as a stable monomolecular layer, with reproducible properties, at the air-water interface. The major lipids and proteins of myelin are represented in this monolayer in molar ratios similar to those in the original membrane. A well-defined collapse point of the myelin monolayer occurs at ca. 46 mN/m. At a surface pressure of ca. 20 mN/m, the surface pressure-molecular area isotherm of the myelin monolayer shows a change in its compressibility, exhibited as a diffuse but reproducible inflection with a clearly marked change of the surface compressional modulus; the surface potential-area curve shows a change of slope at the same surface pressure. The myelin monolayer shows considerable hysteresis during the first compression-decompression cycle; no detectable protein unfolding under expansion; and decreased hysteresis after the first cycle. The average molecular areas, the inflection at 20 mN/m, the variation of the surface potential per unit of molecular surface density, and the hysteresis properties of the myelin monolayer indicate that this membrane undergoes changes of intermolecular organization mostly ascribed to the protein fraction, above a lateral surface pressure of ca. 20 mN/m. The behavior is consistent with a surface pressure-dependent relocation of protein components in the film. This has marked effects on the stability, molecular packing, and dipolar organization of the myelin interface.

Molecular interactions of the major myelin glycosphingolipids and myelin basic protein in model membranes

The molecular organization, interactions, phase state and membrane-membrane interactions of model membranes containing cerebroside (GalCer), sulfatide (Sulf) and myelin basic protein (MBP) were investigated. Sulf shows a larger cross-sectional area than GalCer, in keeping with the lateral electrostatic repulsions in the negatively charged polar head group. The interactions of GalCer with different phospholipids are similar while those with Sulf depend on the phosphoryl choline moiety in the phospholipid. MBP induces a decrease of the phase transition temperature in both lipids but with Sulf this occurs at lower proportions of MBP. In mixtures of Sulf with phosphatidylcholine MBP induces phase separation among Sulf-rich and PC-rich domains. Extensive apposition of bilayers containing Sulf is induced by MBP while GalCer interferes with this process. Few membrane interactions proceed to bilayer merging or whole bilayer fusion and the glycosphingolipids help preserve the membrane integrity.

Interaction of alpha-MSH and substance P with interfaces containing gangliosides

In the present work we studied the interaction of alpha-MSH and substance P neuropeptides with gangliosides using lipid monolayers, fluorescence spectroscopy, and differential scanning calorimetry techniques. The positively charged weak amphiphilic neuropeptides did not show surface activity in the range of concentrations tested (0.1-0.3 muM), but they were preferentially able to penetrate monolayers formed by acidic lipids, showing the best interaction with the more complex gangliosides. The general order of interaction found for both peptides is GTIh > GDIa = GMI > DLPA > sulphatide. Neither neuropeptide interacted with phosphatidylcholine monolayers above 10 mN.m-1. The binding of alpha-MSH to GMI micelles followed by changes in the fluorescence of its tryptophan residue takes place with an increase in the hydrophobic environment of the neuropeptide. An apparent dissociation constant of 13 muM was estimated for this process. Similar result was found with GMI:DMPC vesicles (1:10 molar ratio). The thermotropic profile of GMI micelles is modified in the presence of the neuropeptides. The calorimetric enthalpy of GMI transition increased 21% and 37% in the presence of alpha-MSH and substance P, respectively. Both neuropeptides induced the same increment in the transition temperature Tm from 19 to 20.5 degrees C. The basic physicochemical studies herein indicated that both positively charged neuropeptides, alpha-MSH and substance P, interact with interfaces containing gangliosides in a mainly electrostatic form, whereas the hydrophobic interaction seems to play a secondary role.

Surface behavior of axolemma monolayers: physico-chemical characterization and use as supported planar membranes for cultured Schwann cells

The axolemma membrane forms a stable and reproducible monomolecular layer at the air-aqueous interface. The major lipids and proteins are present in this monolayer in molar ratios similar to the original membrane. Acetylcholinesterase and Na-K-ATPase activities are preserved in the monolayer to levels of 64% and 25%, respectively. The total lipid fraction forms a homogeneously mixed phase. The presence of proteins in the monolayer introduces surface inhomogeneties. Among other features, this is revealed by the presence of two values of lateral pressure at which the monolayer shows partial or total collapse: a broad partial collapse at surface pressures between 13 to 30 mN/m and a sharp collapse point at 46 mN/m. The average molecular areas, the broad collapse point, and the variation of the surface potential per molecule suggest the relocation of protein components at surface pressures between 13 to 30 mN/m. The behavior is consistent with the extrusion and exposure of proteins toward the aqueous medium that depends on the lateral pressure. Schwann cells grown on coverslips coated with axolemma monolayers at 13 mN/m (beginning of the broad collapse) and 34 mN/m (above the broad collapse) recognize the difference in the surface organization of axolemma caused by the lateral pressure which affects their proliferation, morphology, and spatial pattern of organization. Our results show for the first time that response of Schwann cells depends on the intermolecular organization of the axolemma surface with which they interact. These results suggest that the local expression of putative surface molecules of axolemma that may mediate membrane recognition and the signalling of morphological and proliferative changes can be modulated by long range supramolecular properties.

Modulation by glycosphingolipids of membrane-membrane interactions induced by myelin basic protein and melittin

The effect of glycosphingolipids (GSLs) with oligosaccharide chains of different length and charge on membrane-membrane interactions induced by myelin basic protein (MBP) or melittin (Mel) was comparatively investigated with small unilamellar vesicles. MBP induces a fast vesicle aggregation and close membrane apposition. Merging of lipid bilayers and vesicle fusion induced by MBP are slower and less extensive processes compared to membrane apposition. The changes of membrane permeability concomitant to these phenomena are small. The Trp region of MBP remains in a rather polar environment when interacting with vesicles; its accessibility to NO3- or acrylamide quenching depends on the type of GSLs in the membrane. The Trp region of Mel is inserted more deeply into the lipid bilayer and its accessibility to the aqueous quenchers is less dependent on variations of the oligosaccharide chain of the GSLs. Mel induces a faster and more extensive membrane apposition and bilayer merging than does MBP. Extensive vesicle disruption occurs in the presence of Mel. Negatively charged GSLs facilitate membrane proximity and vesicle aggregation but an increase of the oligosaccharide chain length of either neutral or acidic GSLs decreases the interaction among vesicles that are induced by either protein. This effect is independent of the different mode of insertion of MBP and Mel into the membrane. Our results suggest that the modulation by the oligosaccharide chain on the protein-induced interactions between bilayers containing GSLs is probably exerted beyond the level of local molecular interactions between the basic proteins and the lipids.

Calcium-ganglioside interactions and synaptic plasticity: effect of calcium on specific ganglioside/peptide (valinomycin, gramicidin A)-complexes in mixed mono- and bilayers

A controlled exchange of calcium between the extracellular space (mM Ca2+) and the neuroplasm (microM Ca2+) is considered to be an essential prerequisite for almost every stage of neuronal activity. Our research interest is focused on those compounds, which due to their physico-chemical properties and localization within the synaptic membrane might fulfill the task as neuromodulators for functional synaptic proteins. Because of this specific binding properties towards calcium and their peculiar interactions with calcium in model systems gangliosides (amphiphilic sialic acid containing glycosphingolipids) are favorite candidates for a functional involvement in synaptic transmission of information. In this study we used monolayers to investigate the molecular packing and surface potential at the air/water interface, the interaction of gangliosides with the depsipeptide valinomycin (= monovalent ion carrier), and its influenceability by calcium. Furthermore we looked at calcium effects on the single channel conductance and mean channel life-time of the monovalent ion channel gramicidin A in mixed PC/ganglioside bilayers. In pure ganglioside monolayers the addition of 0.01 mM Ca2+ induces monolayer condensation, a rise in collapse pressure (= higher film stability), a shift of phase transition (= change of conformation), and a more negative head group potential (change of electric properties). In mixed ganglioside-valinomycin monolayers the addition of Ca2+ causes phase separation and/or aggregate formation between the ganglioside and the peptide. Single channel conductance fluctuations as well as mean channel life-time were analyzed for gramicidin A incorporated into binary mixed black lipid membranes of negatively charged gangliosides (GM1, GD1a, GT1b, GMix) and neutral lecithin (DOPC) in different molar ratios. At monovalent electrolyte concentrations up to < 250 mM CsCl the single channel conductance was significantly larger in the negatively charged mixed DOPC/ganglioside membranes than in the neutral DOPC membrane. Additionally, in the presence of gangliosides the mean channel life-time is increased. The addition of calcium (0.05 mM) induced a reduction of single channel conductance of gramicidin A in DOPC- and mixed DOPC/ganglioside membranes. These physico-chemical data in connection with new electromicroscopical evidences for a precise localization of calcium, a calcium pump (Ca(2+)-ATPase), a clustered arrangement of gangliosides in synaptic terminals, and biochemical results with regard to activatory nature of exogenous gangliosides for neuronal protein phosphorylation and ATPases, support the hypothesis of a modulatory function of gangliosides in synaptic transmission.

Effect of sulfatide and gangliosides on phospholipase C and phospholipase A2 activity. A monolayer study

The effect of sulfatide and gangliosides GM1, GD1a and GT1b on the activity of phospholipase C from Clostridium perfringens on dilauroylphosphatidylcholine and of porcine pancreatic phospholipase A2 on dilauroylphosphatidic acid was studied in lipid monolayers containing different proportions of glycolipids under zero-order kinetics at various constant surface pressures. The presence of sulfatide in the monolayer increases the activity of phospholipase C at high surface pressures. Gangliosides shift the cut-off pressure to lower values and inhibit the action of phospholipase C. In mixed monolayers with dilauroylphosphatidic acid, sulfatide at a molar fraction of 0.5 increases the activity of phospholipase A2 at surface pressures below 18 mN/m and shows an inhibitory effect at higher pressures. Ganglioside GM1 at a molar fraction of 0.25 completely inhibits the enzyme above 20 mN/m and markedly reduces its activity at lower pressures. Gangliosides GD1a and GT1b abolish the enzyme activity at all pressures at molar fractions of 0.25 and 0.15, respectively. The modified velocity of the enzymatic reaction in the presence of glycosphingolipids is not due to an irreversible alteration of the catalytic activity.

Interaction and fusion of unilamellar vesicles containing cerebrosides and sulfatides induced by myelin basic protein

The effects of myelin basic protein on the aggregation, lipid bilayer merging, intercommunication of aqueous compartments and leakage of small unilamellar vesicles of egg phosphatidylcholine containing different proportions of galactocerebroside and sulfatide were investigated. This was performed employing light scattering, absorbance changes and fluorescence assays (resonance energy transfer, Terbium/dipicolinic acid assay and carboxyfluorescein release). The apposition of membranes rapidly induced by myelin basic protein is enhanced by sulfatide but reduced by galactocerebroside compared to vesicles of egg phosphatidylcholine alone. On the other hand, the presence of either glycosphingolipid in the membrane interferes with the induction by myelin basic protein of lipid bilayer merging, subsequent fusion and changes of the membrane permeability. Our results support an important modulation by sulfatide and galactocerebroside on the interactions among membranes induced by myelin basic protein, depending on the relative proportions of the glycosphingolipids and phosphatidylcholine.

Modulation of phospholipase A2 activity by neutral and anionic glycosphingolipids in monolayers

The effect of neutral (galactocerebroside and asialo-ganglioside GM1) or anionic (sulphatide and gangliosides GM1, GD1a and GT1b) glycosphingolipids on the activity of phospholipase A2 from pig pancreas was studied in mixed monolayers of dilauroyl phosphatidylcholine with the glycosphingolipids in different molar fractions at various constant surface pressures. The activity of the enzyme depends on the proportion and type of glycosphingolipid in the interface. Sulphatide activates the enzyme at all proportions, whereas galactocerebroside shows inhibition or activation depending on its proportion in the film. Asialo-ganglioside GM1 and gangliosides GM1, GD1a and GT1b can strongly inhibit the enzyme at relatively low molar fractions in the film in the following order: asialo-ganglioside GM1 less than ganglioside GM1 less than ganglioside GT1b less than ganglioside GD1a. The changes of activity are not due to a direct action of the lipids on the active centre or interfacial recognition region of the enzyme.

Effect of glycerol on the molecular properties of cerebrosides, sulphatides and gangliosides in monolayers

The presence of glycerol, free from surface-active impurities, modifies the molecular area, surface potential/molecule and thermodynamic parameters of compression of monolayers of galactosylceramide, sulphatide and gangliosides GM1, GD1a and GT1b. This may be due to changes of the composition and structural properties of the glycosphingolipid solvation shell with an influence on the intermolecular organization.

Surface topography of sulfatide and gangliosides in unilamellar vesicles of dipalmitoylphosphatidylcholine

The property of the dyes, acridine orange and methylene blue, to exhibit metachromatic changes upon binding to negatively charged groups that are within a defined spatial separation was employed to study the lateral and transverse topography of sulfatide and gangliosides GM1 and GD1a mixed with dipalmitoylphosphatidylcholine (DPPC) in unilamellar vesicles. The spectral changes of the dyes in the presence of liposomes containing anionic glycosphingolipids (GSLs) (hypochromism and frequency shift) are typical of polyanionic lattices while minor changes are found for neutral lipids. The metachromatic changes are abolished by the presence of Ca2+ in the external medium. The proportion of anionic GSLs accessible to the dyes on the external surface of the liposomes is greater as the GSLs are more complex (sulfatide less than GM1 less than GD1a) and as its proportion in the mixture decreases. The number of molecules of anionic GSLs that are laterally distributed on the external surface in a position favorable for the formation of dye dimers (at intermolecular distances not exceeding 1 nm) is greater for sulfatide than for ganglioside. This is correlated to the greater intermolecular distances and delocalization in ganglioside-, compared to sulfatide-containing interfaces. The experimental values indicate that the mixture with DPPC of any of the anionic GSLs studied behaves as if it was more enriched in the GSLs compared to the proportions of the whole mixture.

Effect of calcium ions on the thermotropic behaviour of neutral and anionic glycosphingolipids

In the concentration range of 10(-5) to 10(-1) M Ca2+ modulates the thermotropic properties of several neutral and anionic glycosphingolipids (galactosylceramide, asialo-GM1, sulfatide, GM1, GD1a, GT1b) and of their mixtures with dipalmitoylphosphatidylcholine. The transition temperature of gangliosides is not appreciably changed while the transition enthalpy increases by 20% in the presence of Ca2+. The more marked effect of Ca2+ is on the thermotropic behavior of systems containing sulfatide. Increasing concentrations of Ca2+ between 10(-5) and 10(-3) M (up to a molar ratio of Ca2+/sulfatide 1:2) induce a progressive increase of both the transition temperature and enthalpy. Further increases up to 10(-1) M Ca2+ induce a new phase transition at a lower temperature. No evidence is found for induction of phase separation of pure glycosphingolipid-Ca2+ domains in mixtures of any of the glycosphingolipids with dipalmitoylphosphatidylcholine. The modification of the phase behavior of anionic glycosphingolipids by Ca2+ does not involve detectable variations of the intermolecular packing but is accompanied by marked modifications of the dipolar properties of the polar head group region.

Interactions of ovalbumin and of its putative signal sequence with phospholipid monolayers. Possible importance of differing lateral stabilities in protein translocation

Surface properties of ovalbumin and of its putative signal sequence, and their interactions with phospholipids at an air-water interface, have been studied. The mature protein can form an interfacial film spontaneously from its bulk solution, whereas the signal sequence cannot. Mature ovalbumin also penetrates phospholipid monolayers from the subphase (independently of the type of phospholipid present), whereas its signal sequence does not. The surface stability of a spread film of the signal sequence is, however, higher than that of a film of mature ovalbumin. Above specific threshold concentrations of signal peptide and of mature ovalbumin in mixed films with phospholipids, two separate phases are formed. In such immiscible films, the signal sequence peptide is also able to support a higher lateral surface pressure than mature ovalbumin, at corresponding areas of peptide and mature protein in the mixed monolayers. It is suggested that the differing lateral stabilities of ovalbumin and of its putative signal sequence may be relevant to the translocation of ovalbumin across the membrane of the endoplasmic reticulum, and a scheme for its translocation is proposed that is based on these properties.

Molecular interactions and thermotropic behavior of glycosphingolipids in model membrane systems

The oligosaccharide chain of glycosphingolipids (GSLs) has a marked influence on their thermotropic behavior, intermolecular packing and surface electrical potential. The transition temperature and enthalpy of GSLs decrease proportionally to the complexity of the polar head group and show a linear dependence with the intermolecular spacings. Interactions occurring among GSLs and phospholipids induce changes of the molecular area and surface potential that depend on the type of GSLs. Increasing proportions of phospholipids perturb the thermodynamic properties of the GSLs up to a point where phase separated phospholipid domains separate out but no phase separation of pure GSLs occurs. Heterogeneous equilibria among different structures occur for some systems. Large changes of the molecular free energy, eccentricity, asymmetry ratio and phase state of the GSLs-containing structure can be triggered by small changes of the molecular parameters, lipid composition and lateral surface pressure. The thermotropic behavior of GSLs is considerably perturbed by myelin basic protein. Phase separation occurs depending on the amount of protein and type of GSLs. The protein induces a decrease of the lipid molecular area, the more so the more complex the oligosaccharide chain in the GSLs. These membrane systems can not be described only on the basis of the individual properties of the molecules involved in a simple causal manner. Still scarcely explored long range thermodynamic, geometric and field effects that belong simultaneously to the intervening molecules, to the morphological properties of the structure involved and to the aqueous environment, are important determinants of their behavior.

Sulfatide-binding proteins

Sulfatides (galactosyl ceramide-I3-sulfate) and other sulfated glycolipids are found in many tissues. The cell adhesion proteins laminin, thrombospondin, and von Willebrand factor bind specifically to sulfated glycolipids. Methods for characterizing the specificity of these interactions using surface-adsorbed glycolipids are reviewed. The three proteins do not bind to other anionic lipids, including gangliosides, phospholipids, or cholesterol 3-sulfate. Binding to sulfatides is saturable and of relatively high affinity. Relative binding avidity depends on the oligosaccharide structure of the glycolipids. Binding to sulfatides in erythrocyte membranes can account for the hemagglutinating activities of the three proteins and may play a role in the interactions of these proteins with other cell types.

Properties of signal-sequence peptides at an air-water interface

The surface behaviour of three signal-sequence polypeptides (the pretrypsinogen 2 signal sequence, a synthetic consensus signal sequence and the putative signal sequence of ovalbumin) were studied at an air-water interface. It was found that the surface stabilities of the spread polypeptide films were higher than those of polypeptides and proteins previously investigated (including melittin and membrane proteins), and that the signal peptides had a much lower affinity for the interface than had other peptides and proteins. The observed molecular areas of the signal-sequence peptides indicated that the molecules have a considerable degree of secondary structure at the surface interface.

Molecular parameters and physical state of neutral glycosphingolipids and gangliosides in monolayers at different temperatures

The effect of temperature on the behaviour of four different gangliosides (GM3, GM1, GD1a and GT1b), sulphatide, ceramide (Cer) and three neutral glycosphingolipids (GalCer, Gg3Cer, Gg4Cer) was investigated in monolayers at the air-NaCl (145 mM) interface. GM1, GD1a and GT1b are liquid-expanded in the range of temperatures studied (5-65 degrees C). GM3, sulphatide, Cer and neutral glycosphingolipids show isothermal liquid-expanded----liquid-condensed transitions. The collapse pressure of ganglioside monolayers decreases with temperature, whereas neutral glycosphingolipids may show some maximum values at particular temperatures. The reduction of the molecular area of liquid-expanded glycosphingolipids under compression occurs with a favorable positive entropy change and an unfavorable negative enthalpy. By contrast, the compression of interfaces with a two-dimensional phase transition occurs with an unfavorable entropy but a favorable enthalpy change. From the temperature dependence of the surface pressure at which the two-dimensional phase transition takes place, a minimal temperature above which the isotherm becomes totally liquid-expanded can be obtained. For the different glycosphingolipids this temperature decreases in the order Cer greater than GalCer greater than sulphatide greater than Gg3Cer greater than Gg4Cer greater than GM3 greater than GM1 greater than GD1a greater than GT1b. This sequence is similar to that found for the calorimetrically determined transition temperatures (cf. Maggio, B., Ariga, T., Sturtevant, J.M. and Yu, R.K. (1985) Biochemistry 24, 1084-1092).

Molecular parameters and conformation of globoside and asialo-GM1

Comparative studies of the individual properties and intermolecular organization of asialo-GM1 (Gg4Cer) and globoside (Gb4Cer) were made employing lipid monolayers and high-sensitivity differential scanning calorimetry. The surface pressure-area isotherm of Gb4Cer is more expanded than that of Gg4Cer. This results in greater molecular areas and compressibilities, and lower intermolecular interaction energies, for Gb4Cer compared to Gg4Cer at all surface pressures. This looser intermolecular packing may be responsible for a lower transition temperature (40.5 degrees C) and enthalpy of transition (delta Hcal) (2.0 kcal mol-1) found for the phase transition of Gb4Cer compared to Gg4Cer (54.0 degrees C and 4.2 kcal mol-1). The surface potential per molecule and resultant molecular dipole moment vector values are greater for Gb4Cer than for Gg4Cer at comparable values of surface pressure and molecular area. All these results reflect the existence of a rigid L-shape in the oligosaccharide chain of Gb4Cer that prevents a close intermolecular packing compared to the straight orientation of the polar head group of Gg4Cer. Significant movements of the oligosaccharide chain may occur depending on the lateral surface pressure. At low surface pressures the orientation of the oligosaccharide chain of Gg4Cer may be displaced an angle of up to about 40 degrees compared to the perpendicular position adopted at high surface pressures. In agreement with an enhanced liquid character of the interface, the oligosaccharide chain of Gb4Cer exhibits a greater freedom of movement and the displacement from the position perpendicular to the interface can reach to about 65 degrees.

Thermotropic behavior of binary mixtures of dipalmitoylphosphatidylcholine and glycosphingolipids in aqueous dispersions

The thermotropic behavior of mixtures of dipalmitoylphosphatidylcholine (DPPC) with natural glycosphingolipids (galactosylceramide, phrenosine, kerasine, glucosylceramide, lactosylceramide, asialo-GM1, sulfatide, GM3, GM1, GD1a, GT1b) in dilute aqueous dispersions were studied by high sensitivity differential scanning calorimetry over the entire composition range. The pretransition of DPPC is abolished and the cooperativity of the main transition decreases sharply at mole fractions of glycosphingolipids below 0.2. All systems exhibit non-ideal temperature-composition phase diagrams. The mono- and di-hexosylceramides are easily miscible with DPPC when the proportion of glycosphingolipids in the system is high. A limited quantity (1-6 molecules of DPPC per molecule of glycosphingolipid (GSL) can be incorporated into a homogeneously mixed lipid phase. Domains of DPPC, immiscible with the rest of a mixed GSL-DPPC phase that shows no cooperative phase transition, are established as DPPC exceeds a certain proportion in the system. One negative charge (sulfatide) or four neutral carbohydrate residues (asialo-GM1) in the oligosaccharide chain of the glycosphingolipids results in phase diagrams exhibiting coexistence of gel and liquid phases over a broad temperature-composition range. Systems containing gangliosides show complex phase diagrams, with more than one phase transition. However, no evidence for phase-separated domains of pure ganglioside species is found. The thermotropic behavior of systems containing DPPC and glycosphingolipids correlates well with their interactions in mixed monolayers at the air/water interface.