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Linoleic and linolenic acid hydroperoxides (HPOs) constitute key intermediate oxylipins playing an important role as signaling molecules during plant defense processes in response to biotic or abiotic stress. They have also been demonstrated in vitro as antimicrobial agents against plant fungi and bacteria. To reach the phytopathogens in vivo, the HPOs biosynthesized in the plant cells must cross the plant plasma membrane (PPM) where they can also interact with plasma membrane lipids and have an effect on their organization. In the present study, we have investigated the interaction properties of HPOs with PPM at a molecular level using biophysical tools combining in vitro and in silico approaches and using plant biomimetic lipid systems. Our results have shown that HPOs are able to interact with PPM lipids and perturb their lateral organization. Glucosylceramide (GluCer) is a privileged partner, sitosterol lessens their binding and the presence of both GluCer and sitosterol further reduces their interaction. Hydrophobic effect and polar interactions are involved in the binding. The chemical structure of HPOs influences their affinity for PPM lipids. The presence of three double bonds in the HPO molecule gives rise to a higher affinity comparatively to two double bonds, which can be explained by their differential interaction with the lipid polar headgroups.

Films based on xylose and peanut protein isolate (PPI) were prepared by solution casting. The effects of xylose content (1%, 2%, 5%, 10%, 20% PPI, w/w) on the structure and mechanical properties of PPI–xylose (PPI–X) film were systematically investigated. The xylose-modified PPI was firstly prepared by crosslinking and modifying of peanut isolated protein with xylose. The degree of glycosylation and surface hydrophobicity significantly increased from 5.6% to 10.9% and from 130.6 to 370.0, respectively, with the increase of the xylose content. Maillard reactions occurring between PPI and xylose were confirmed by Fourier transform infrared spectroscopy. Then the xylose-modified PPI was developed into films. PPI–X films showed markedly increased tensile strength (increased by 77%) and elongation (increased by 67%) and decreased solubility (from 96.6% to 43.4%) compared to PPI films, suggesting that the incorporation of xylose could markedly enhance the mechanical properties and the water resistance of films. This property improvement was correlated to the increased protein surface hydrophobicity and sulfhydryl group content with the addition of xylose. No significant differences were detected among L*, a*, b* colour values of all films (P > 0.05). The scanning electron microscope images of the PPI–X film showed that the addition of xylose up to 10% produced a more homogeneous and denser structure. Finally, the improvement mechanism of the PPI–X film was proposed.

International audience; Glycolipids constitute a class of molecules with various biological activities. Among them, sugar-based bolaamphiphiles characterized by their biocompatibility, biodegradability and lower toxicity, became interesting for the development of efficient and low cost lipid-based drug delivery systems. Their activity seems to be closely related to their interactions with the lipid components of the plasma membrane of target cells. Despite many works devoted to the chemical synthesis and characterization of sugar-based bolaamphiphiles, their interactions with plasma membrane have not been completely elucidated. In this work, two sugar-based bolaamphiphiles differing only at the level of their sugar residues were chemically synthetized. Their interactions with membranes have been investigated using model membranes containing or not sterol and with in silico approaches. Our findings indicate that the nature of sugar residues has no significant influence for their membrane interacting properties, while the presence of sterol attenuates the interactions of both bolaamphiphiles with the membrane systems. The understanding of this distinct behavior of bolaamphiphiles towards sterol-containing membrane systems could be useful for their applications as drug delivery systems.

By manipulating the various physicochemical properties of amino acids, the design of peptides with specific self-assembling properties has been emerging for more than a decade. In this context, short peptides possessing detergent properties (so-called &ldquo, peptergents&rdquo, ) have been developed to self-assemble into well-ordered nanostructures that can stabilize membrane proteins for crystallization. In this study, the peptide with &ldquo, peptergency&rdquo, properties, called ADA8 and extensively described by Tao et al., is studied by molecular dynamic simulations for its self-assembling properties in different conditions. In water, it spontaneously forms beta sheets with a &beta, barrel-like structure. We next simulated the interaction of this peptide with a membrane protein, the bacteriorhodopsin, in the presence or absence of a micelle of dodecylphosphocholine. According to the literature, the peptergent ADA8 is thought to generate a belt of &beta, structures around the hydrophobic helical domain that could help stabilize purified membrane proteins. Molecular dynamic simulations are here used to image this mechanism and provide further molecular details for the replacement of detergent molecules around the protein. In addition, we generalized this behavior by designing an amphipathic peptide with beta propensity, which was called ABZ12. Both peptides are able to surround the membrane protein and displace surfactant molecules. To our best knowledge, this is the first molecular mechanism proposed for &ldquo

Plasma membranes are complex entities common to all living cells. The basic principle of their organization appears very simple, but they are actually of high complexity and represent very dynamic structures. The interactions between bioactive molecules and lipids are important for numerous processes, from drug bioavailability to viral fusion. The cell membrane is a carefully balanced environment and any change inflicted upon its structure by a bioactive molecule must be considered in conjunction with the overall effect that this may have on the function and integrity of the membrane. Conceptually, understanding the molecular mechanisms by which bioactive molecules interact with cell membranes is of fundamental importance.Lipid specificity is a key factor for the detailed understanding of the penetration and/or activity of lipid-interacting molecules and of mechanisms of some diseases. Further investigation in that way should improve drug discovery and development of membrane-active molecules in many domains such as health, plant protection or microbiology.In this review, we will present complementary biophysical approaches that can give information about lipid specificity at a molecular point of view. Examples of application will be given for different molecule types, from biomolecules to pharmacological drugs. A special emphasis is given to cyclic lipopeptides since they are interesting molecules in the scope of this review by combining a peptidic moiety and a lipidic tail and by exerting their activity via specific interactions with the plasma membrane.

International audience; Natural and synthetic amphiphilic molecules including lipopeptides, lipopolysaccharides, and glycolipids are able to induce defense mechanisms in plants. In the present work, the perception of two synthetic C14 rhamnolipids, namely, AlkRL and Ac-RL, differing only at the level of the lipid tail terminal group have been investigated using biological and biophysical approaches. We showed that Alk-RL induces a stronger early signaling response in tobacco cell suspensions than does Ac-RL. The interactions of both synthetic RLs with simplified biomimetic membranes were further analyzed using experimental and in silico approaches. Our results indicate that the interactions of Alk-RL and Ac-RL with lipids were different in terms of insertion and molecular responses and were dependent on the lipid composition of model membranes. A more favorable insertion of Alk-RL than Ac-RL into lipid membranes is observed. Alk-RL forms more stable molecular assemblies than Ac-RL with phospholipids and sterols. At the molecular level, the presence of sterols tends to increase the RLs’ interaction with lipid bilayers, with a fluidizing effect on the alkyl chains. Taken together, our findings suggest that the perception of these synthetic RLs at the membrane level could be related to a lipid-driven process depending on the organization of the membrane and the orientation of the RLs within the membrane and is correlated with the induction of early signaling responses in tobacco cells.

Many Pseudomonas spp. produce cyclic lipodepsipeptides (CLPs), which, besides their role in biological functions such as motility, biofilm formation and interspecies interactions, are antimicrobial. It has been established that interaction with the cellular membrane is central to the mode of action of CLPs. In this work, we focus on the CLPs of the so-called viscosin group, aiming to assess the impact of the main structural variations observed within this group on both the antimicrobial activity and the interaction with model membranes. The antimicrobial activity of viscosin, viscosinamide A, WLIP and pseudodesmin A were all tested on a broad panel of mainly Gram-positive bacteria. Their capacity to permeabilize or fuse PG/PE/cardiolipin model membrane vesicles is assessed using fluorescent probes. We find that the Glu2/Gln2 structural variation within the viscosin group is the main factor that influences both the membrane permeabilization properties and the minimum inhibitory concentration of bacterial growth, while the configuration of the Leu5 residue has no apparent effect. The CLP-membrane interactions were further evaluated using CD and FT-IR spectroscopy on model membranes consisting of PG/PE/cardiolipin or POPC with or without cholesterol. In contrast to previous studies, we observe no conformational change upon membrane insertion. The CLPs interact both with the polar heads and aliphatic tails of model membrane systems, altering bilayer fluidity, while cholesterol reduces CLP insertion depth.

Surfactants are molecules able to spontaneously self-assemble to form aggregates with well-defined properties, such as spherical micelles, planar bilayers, cylindrical micelles or vesicles. Micelles have notably several applications in many domains, such as drug delivery or membrane protein solubilization. In this context, the study of micelle formation in relation with the structural and physico-chemical properties of surfactants is of great interest to better control their use in the different application fields. In this work, we use the MD approach developed by Yoshii et al. and extend it to surfactants with different structures. We aim to systematically investigate different micellar properties as a function of the aggregates size by a molecular dynamics approach, to get an insight into the micellar organization and to collect some relevant descriptors about micelle formation. For this, we perform short MD simulations of preformed micelles of various sizes and analyze three parameters for each micelle size, namely the eccentricity of the micelles, the hydrophobic/hydrophilic surface ratio and the hydrophobic tails hydration. If these parameters are known descriptors of micelles, they were not yet studied in this way by MD. We show that eccentricity, used as "validator" parameter, exhibits minimal values when the aggregate size is close to the experimental aggregation number for surfactants that are known to form spherical micelles. This hence indicates that our methodology gives consistent results. The evolution of the two descriptors follows another scheme, with a sharp increase and decrease, respectively, followed by a leveling-off. The aggregate sizes at which this stabilization starts to occur are close to the respective aggregation number of each surfactant. In our approach, we validate the use of these descriptors to follow micelle formation by MD, from "simple" surfactants to more complex structures, like lipopeptides. Our calculations also suggest that some peculiar behavior, like that of TPC, can be highlighted by our approach. In the context of peptidic surfactants, our methodology could further help to improve computer simulations combined to molecular thermodynamic models to predict micellar properties of those more complex amphiphilic molecules.

Based on its outstanding antifungal properties, it is reasonable to believe that fengycin might be efficient to topically treat localized dermatomycoses. Since most of the fungi species involved in the formation of those mycotic skin diseases colonize primarily the stratum corneum (SC), studying the interaction between fengycin and SC-mimicking lipid membranes is a primary step to determine the potential of fengycin to overcome the physical barrier of the skin. In this respect, multilamellar lipid vesicles (MLVs), with a lipid composition mimicking that of the SC, were prepared and characterized by differential scanning calorimetry (DSC). The critical micelle concentration (CMC) of fengycin was also assessed under skin conditions and found to be 1.2±0.1μM. The molecular interactions of fengycin with SC-mimicking MLVs were investigated by both DSC and isothermal titration calorimetry (ITC). Results showed that the interactions were considerably affected by changes in lipid phase behaviour. At 40°C and below, fengycin induced exothermic changes in the lipid structures suggesting that less-ordered lipid domains became more-ordered in presence of fengycin. At 60°C, clearly endothermic interaction enthalpies were observed, which could arise from the "melting" of remaining solid domains enriched in high melting lipids that without fengycin melt at higher temperatures.

International audience; Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm2. In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C–OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C–OH bond of the tyrosine, yields a ratio of the susceptibility elements χ(2)ZZZ/χ(2)ZXX consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919].Previous Article | Next Article PaperMulti-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generationClaire Loison,*a Mehmet Nail Nasir,b Emmanuel Benichou,a Françoise Bessonb and Pierre-François Breveta Show AffiliationsPhys. Chem. Chem. Phys., 2014,16, 2136-2148DOI: 10.1039/C3CP53101EReceived 23 Jul 2013, Accepted 27 Nov 2013First published online 28 Nov 2013| |Share on citeulike|Share on facebook|Share on twitter|| More PDF Rich HTML Buy PDF Add PDF to Basket (£38*) *Exclusive of taxes This article contains 13 page(s)Download CitationHelpRequest PermissionsAccess DeniedPlease choose one of the options provided in the log in section to gain access to this content: Abstract Cited by Related Content Metrics Monolayers of the lipopeptide mycosubtilin are studied at the air/water interface. Their structure is investigated using molecular dynamics simulations. All-atom models suggest that the lipopeptide is flexible and aggregates at the interface. To achieve simulation times of several microseconds, a coarse-grained (CG) model based on the MARTINI force field was also used. These CG simulations describe the formation of half-micelles at the interface for surface densities up to 1 lipopeptide per nm2. In these aggregates, the tyrosine side chain orientation is found to be constrained: on average, its main axis, as defined along the C–OH bond, aligns along the interface normal and points towards the air side. The origin of the optical second harmonic generation (SHG) from mycosubtilin monolayers at the air/water interface is also investigated. The molecular hyperpolarizability of the lipopeptide is obtained from quantum chemistry calculations. The tyrosine side chain contribution to the hyperpolarizability is found to be dominant. The orientation distribution of tyrosine, associated with a dominant hyperpolarizability component along the C–OH bond of the tyrosine, yields a ratio of the susceptibility elements χ(2)ZZZ/χ(2)ZXX consistent with the experimental measurements recently reported by M. N. Nasir et al. [Phys. Chem. Chem. Phys., 2013, 15, 19919].

Mycosubtilin, an antimicrobial lipopeptide produced by Bacillus subtilis , is characterized by strong antifungal activities. The molecular mechanisms of its biological activities on the membranes of the sensitive yeasts or fungi have not yet been clearly elucidated. Our purpose was to mimic the mycosubtilin interactions with these membranes using various Langmuir monolayers. Since the major sterol of yeasts or fungi is ergosterol, the interactions of mycosubtilin with monolayers constituted by ergosterol, DPPC/ergosterol or DPPC/sphingomyelin/ergosterol were examined at different initial surface pressures (Πi). Plotting the mycosubtilin-induced surface pressure increases versus Πi allowed to determine that the exclusion pressures of mycosubtilin from these different monolayers is higher than the surface prevailing within the biological membranes. However, this behavior was lost when mycosubtilin was interacting with ergosteryl acetate-containing monolayers. This suggests the involvement of the sterol alcohol group in the mycosubtilin interactions within membranes. Furthermore, the behavior of mycosubtilin with stigmasterol, similar to that observed with ergosterol, differs from that previously observed with cholesterol, suggesting a role of the alkyl side chain of the sterols. The adsorption of mycosubtilin to ergosterol monolayers induced changes in the lipopeptide orientation at the air–water interface as revealed by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Moreover, imaging the air–water interface by Brewster angle microscopy (BAM) indicates that mycosubtilin induced changes in the organization and morphology of monolayers containing pure ergosterol with the appearance of small condensed dots, suggesting again that the target of mycosubtilin might be the ergosterol present in the membranes of the sensitive yeasts or fungi.

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with pathogens, and viral infection, etc. Recently some members of the annexin family of conserved calcium and membrane-binding proteins have been recognized as cholesterol-interacting molecules and suggested to play a role in the formation, stabilization, and dynamics of membrane microdomains to affect membrane lateral organization and to attract other proteins and signaling molecules onto their territory. Furthermore, annexins were implicated in the interactions between cytosolic and membrane molecules, in the turnover and storage of cholesterol and in various signaling pathways. In this review, we focus on the mechanisms of interaction of annexins with lipid microdomains and the role of annexins in membrane microdomains dynamics including possible participation of the domain-associated forms of annexins in the etiology of human lysosomal storage disease called Niemann-Pick type C disease, related to the abnormal storage of cholesterol in the lysosome-like intracellular compartment. The involvement of annexins and cholesterol/sphingomyelin-enriched membrane microdomains in other pathologies including cardiac dysfunctions, neurodegenerative diseases, obesity, diabetes mellitus, and cancer is likely, but is not supported by substantial experimental observations, and therefore awaits further clarification.

International audience; Mycosubtilin is a natural antimicrobial lipopeptide produced by Bacillus subtilis strains. It is characterized by its hemolytic and strong antifungal activities. Mycosubtilin interacts with the plasma membranes of sensitive cells. However, the molecular mechanisms of its biological activities have not been completely elucidated. Our purpose was therefore to analyze the interactions of mycosubtilin with biological membranes by using biomimetic membranes such as Langmuir monolayers and multilayers. Structural changes of mycosubtilin, involving its peptide backbone and the side chain of its tyrosyl residue, were observed when the lipopeptide was interacting with cholesterol-containing multilayers. The interactions of mycosubtilin with monolayers constituted by pure lipids and by phosholipid/cholesterol or phospholipid/sphingomyelin/cholesterol were also examined. An original behavior of mycosubtilin toward cholesterol-containing monolayers was found. However, this original behavior was lost when mycosubtilin was interacting with pure cholesterylacetate monolayers. This suggests the involvement of the alcohol group of cholesterol in mycosubtilin-cholesterol interactions within membranes. Moreover, mycosubtilin induced changes in the organization and morphology of cholesterol-containing monolayers, and large condensed domains with different levels of condensation appeared only in the case of DPPC/sphingomyelin/cholesterol monolayer.

Among the secondary metabolite lipopeptides produced by Bacillus subtilis, mycosubtilin is characterized by its strong antifungal activities. Even though its structure and its cellular target, the cytoplasmic membrane, have been determined, the molecular mechanisms of the biological activity of mycosubtilin have not been completely elucidated. In this work, the interactions between mycosubtilin and cytoplasmic membranes were modelled by using biomimetic systems such as Langmuir monolayers at the air-water interface and lipid multilamellar vesicles. The interactions of mycosubtilin with these biomimetic systems were examined, for the first time, by using specific techniques such as polarization modulation infrared reflection absorption spectroscopy, Brewster angle microscopy and high-resolution magic angle spinning NMR. Our findings indicate that mycosubtilin alone, at the air-water interface, forms a monolayer film and keeps its turn conformation. In the presence of DMPC, mycosubtilin binds to phospholipid monolayers, in a surface pressure-dependent manner. This binding results in the appearance of condensed domains which can be due to the formation of mycosubtilin clusters and/or to the lipopeptide aggregation with some phospholipid molecules and/or the formation of liquid-condensed domains of DMPC. Furthermore, in multilamellar vesicles, the mycosubtilin-DMPC interactions take place at the level of the aliphatic chains of the phospholipid because the phase transition temperature of DMPC decreased in the presence of mycosubtilin.

International audience; The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes. Two model peptides were selected. The first one, an alanine-rich peptide, K3A18K3, was shown to be in alpha-helix structures in TFE, a membrane environment-mimicking solvent, while it was mostly beta-sheeted in aqueous buffer as revealed by infrared spectroscopy. The other, alamethicin, a natural peptide, was in a stable alpha-helix structure. To determine the role of the peptide conformation on the nature of its interactions with lipids, we compared the structure and topology of the conformational-labile peptide K3A18K3 and of the alpha-helix rigid alamethicin in both aqueous and phospholipid environments (Langmuir monolayers and multilamellar vesicles). K3A18K3 at the air-water interface showed a pressure-dependent orientation of its beta-sheets, while the alpha-helix axis of alamethicin was always parallel to the interface, as probed by polarization modulation infrared reflection absorption spectroscopy. The beta-sheeted K3A18K3 peptide was uniformly distributed into DPPC condensed domains, while the helical-alamethicin insertion distorted the DPPC condensed domains, as evidenced by Brewster angle microscopy imaging of the air/interface. The beta-sheeted K3A18K3 interacted with DMPC multilamellar vesicles via hydrophilic interactions with polar heads and the helical-alamethicin via hydrophobic interactions with alkyl chains, as shown by infrared spectroscopy and solid state NMR. Our findings are consistent with the prevailing assumption that the conformation of the peptide predetermines the mode of interaction with lipids. More precisely, helical peptides tend to be inserted via hydrophobic interactions within the hydrophobic region of membranes, while beta-sheeted peptides are predisposed to interact with polar groups and stay at the surface of lipid layers.

International audience; The glycoprotein gp41 from the Human Immunodeficiency Virus type 1 (HIV-1) has an amino acid sequence enriched in tryptophan residues, the so-called gp41W peptide (i.e., KWASLWNWFNITNWLWYIK) and plays a crucial role in HIV-1 host cell infection. Using the coupling of Second Harmonic Generation targeting the tryptophan residues with lateral surface tension measurements, we investigate the interaction of gp41W with a neat air/water and a lipid/water interfaces. At the air/water interface, gp41W presents a well-defined orientation and this orientation is strongly modified at the lipid/water interface, depending on the surface pressure. These results show that this strategy is well suited to monitor tryptophan containing α-helices orientation at lipid/water interfaces.

International audience; The second harmonic generation (SHG) response at the air-water interface from the tyrosine-containing natural iturinic cyclo-lipopeptides mycosubtilin, iturin A and bacillomycin D is reported. It is shown that this response is dominated by the single tyrosine residue present in these molecules owing to the large first hyperpolarizability arising from the non-centrosymmetric aromatic ring structure of this amino acid. The SHG response of these iturinic antibiotics is also compared to the response of surfactin, a cyclo-lipopeptide with a similar l,d-amino acid sequence but lacking a tyrosine residue, and PalmATA, a synthetic linear lipopeptide possessing a single tyrosine residue but lacking the amino acid sequence structuring the cycle of the iturinic antibiotics. From the light polarization analysis of the SHG response, it is shown that the tyrosine local environment is critical in defining the SHG response of these peptides at the air-water interface. Our results demonstrate that tyrosine, similar to tryptophan, can be used as an endogenous molecular probe of peptides and proteins for SHG at the air-water interface, paving the way for SHG studies of other tyrosine-containing bioactive molecules.

International audience; The two step synthesis of a new bolaamphiphile derived from alkenyl l-rhamnosides was described. The general synthetic strategy of bolaamphiphiles derived from l-rhamnose was based on a previous work describing the synthesis of bolaamphiphiles derived from d-xylose. The conformational properties of this new compound were investigated by FTIR spectroscopy in an aqueous film in order to obtain a reference for further studies about the membrane-interacting properties. Moreover, the surface activity of this new bolaamphiphile was analyzed by Langmuir balance technology and was compared with that of the analogous bolaamphiphile derived from alkenyl D-xylosides. The findings indicate that the rhamnoside-based bolaform has an increased surface activity and a better ability to form aggregates than xyloside-based one.

International audience; Annexin A6 (AnxA6), a calcium- and membrane-binding protein, is expressed in mammalian cells in two isoforms: AnxA6-1 and AnxA6-2, the latter lacking the 524-VAAEIL-529 sequence at the start of repeat 7. The different intracellular localization of these two isoforms suggests distinct function in membrane dynamics. The aim of this work was to analyze the behavior of AnxA6 isoforms at the air/water interface alone and in the presence of membrane mimicking lipid monolayers. Using Langmuir technique showed that AnxA6-2 was less adsorbed to the neat air-water interface than AnxA6-1 at acidic pH and minor differences in their PM-IRRAS spectra were observed. Both isoforms exhibited similar behavior towards cholesterol monolayer. However, the interactions of AnxA6-2 with cholesterol ester monolayer were most favorable compared to AnxA6-1. Our experimental data are discussed in relation with the different intracellular localization of the two isoforms and with our constructed model of AnxA6-2 with the known crystal structure of AnxA6-1 showing the persistence of the 516-529 α-helix in AnxA6-2 despite the absence of the 524-VAAEIL-529 sequence.

Sugar-based biosurfactants such as xylose-derived bolaforms have interesting properties, for example high biocompatibility and biodegradability which make them potential useful molecules in the pharmaceutical and cosmetic fields. Until now, no detailed analyses of the physico-chemical properties of these compounds have been undertaken. Two symmetrical D-xylose-based bolaforms were chemically synthesized where the two xylose heads are linked via an acetal link to a hydrocarbon chain containing 18 carbon atoms and an unsaturation. The two bolaforms differ only by their anomeric configuration: αα or ββ. The αα bolaform exhibits interfacial properties at the air-water interface which is not the case for the ββ. FTIR spectroscopy showed that the interactions between the αα bolaform and POPC, a model phospholipid, involve the carbonyl groups of the phospholipid. .

International audience; The Second Harmonic Generation (SHG) response from Tyrosine-containing peptides at the air-water interface is presented. First, the quadratic hyperpolarizability of the aromatic amino acid Tyrosine obtained by Hyper Rayleigh Scattering is reported, demonstrating its potentiality as an endogenous molecular probe for SHG studies. Then, the single Tyrosine antimicrobial peptide Mycosubtilin is monitored at the air-water interface and compared to another peptide, Surfactin, lacking a Tyrosine residue. Adsorption kinetics and polarization analysis of the SHG intensity for the peptide monolayers clearly demonstrate that the SHG response from Mycosubtilin arises from Tyrosine. Besides, it confirms that indeed Tyrosine can be targeted as an endogenous molecular probe.

Fengycin is a natural lipopeptide with antifungal and eliciting properties and able to inhibit the activity of phospholipase A2. A combination of CD, FT-IR, NMR and fluorescence spectroscopic techniques was applied to elucidate its conformation in a membrane-mimicking environment and to investigate the effect of calcium ions on it. We mainly observed that fengycin adopts a turn conformation. Our results showed that calcium ions are bound by the two charged glutamates. The calcium binding has an influence on the fengycin conformation and more particularly, on the environment of the tyrosine residues. The modulation of the fengycin conformation by the environmental conditions may influence its biological properties.

Bacillomycin D is a natural antimicrobial lipopeptide belonging to the iturin family. It is produced by Bacillus subtilis strains. Bacillomycin D is characterized by its strong antifungal and hemolytic properties, due to its interaction with the plasma membrane of sensitive cells. Until now, only few limited analyses were conducted to understand the biological activities of bacillomycin D at the molecular level. Our purpose was to analyze the conformation of bacillomycin D using IR spectroscopy and to model its interactions with cytoplasmic membranes using Langmuir interfacial monolayers. Our findings indicate that bacillomycin D contains turns and allow to model its three-dimensional structure. Bacillomycin D formed a monolayer film at the air-water interface and kept its turn conformation, as shown by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To identify the membrane lipid target of bacillomycin D, its interactions with pure lipid monolayers were analyzed and an original behavior of the lipopeptide toward cholesterol-containing monolayers was shown. This original behavior was lost when bacillomycin D was interacting with pure cholesteryl acetate monolayers, suggesting the involvement of the alcohol group of cholesterol in the lipopeptide-cholesterol interaction.

International audience; The HIV-1 envelope glycoprotein 41 (gp41) undergoes large-scale conformational changes in order to induce the fusion of the virus and cell membranes. Thus, we investigated a possible structure transit at the air-water interface for the tryptophan-rich peptide of gp41 (gp41W). The synthetic peptide (KWASLWNWFNITNWLWYIK), corresponding to gp41W, shows interfacial properties on pure water and Tris buffer at pH 8.5. Isotherm measurements and Brewster angle microscopy (BAM) imaging showed that the behavior of the peptide monolayer was dependent on the subphase composition. A homogenous film was formed on buffer during the peptide monolayer compression, while the appearance of condensed domains on pure water could indicate the oligomerization of gp41W during the surface pressure increase. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) showed that, whatever the subphase, gp41W adopts an α-helix structure at the air-water interface and does not transit for any other structure even at high surface pressures.