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See detailModeling of the Iturinic Antimicrobial Lipopeptide Mycosubtilin at Interfaces
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

Conference (2014, June)

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See detailMulti-scale modeling of mycosubtilin lipopeptides at the air/water interface: structure and optical second harmonic generation
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

in Physical Chemistry Chemical Physics [=PCCP] (2014), 16

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 ... [more ▼]

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]. [less ▲]

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See detailReorientation of the helix of the tryptophan-rich gp41W peptide from HIV-1 at interfaces
Matar, Gladys; Benichou, Emmanuel; Nasir, Mehmet Nail ULg et al

in Journal of Chemical Physics (2013), 139

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 ... [more ▼]

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. [less ▲]

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See detailInteractions of iturinic antibiotics with plasma membrane. Contribution of biomimetic membranes.
Nasir, Mehmet Nail ULg; Besson, Françoise; Deleu, Magali ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2013), 17(3), 505-516

Iturinic antibiotics are produced by Bacillus subtilis strains and constitute a family including iturin A, mycosubtilin and bacillomycins D, F and Lc. They are cyclic lipopeptides having -amino fatty ... [more ▼]

Iturinic antibiotics are produced by Bacillus subtilis strains and constitute a family including iturin A, mycosubtilin and bacillomycins D, F and Lc. They are cyclic lipopeptides having -amino fatty acids linked up to a peptide constituted by seven -aminoacids with an invariable LDDLLDL chiral sequence. The first three -aminoacids containing the tyrosyl residue are the same for all members. They are well-known by their strong antifungal activities but they have also antibacterial and hemolytic properties. These biological properties are due to their amphiphilic nature allowing interactions with different membrane components. Sterols found in plasma membranes are the privileged interaction partners of these lipopeptides. Moreover, the tyrosyl residue of the iturinic antibiotics seems to play an important role during their fixation to the plasma membrane, the result of which is often the cellular lysis. Within plasma membranes, there are particular regions with high sterol content. These microdomains have a different composition compared to the rest of the membrane; they are enriched in certain lipids and proteins and they are involved in many key cellular processes. Their perturbation could then have an important impact on the cell. Due to their composition, these microdomains could constitute the preferential target of iturin antibiotics. This review aims to synthetize the works related to the biological activities of iturinic antibiotics and focusses especially to their understanding at the molecular level with a discussion on the key chemical groups of the iturin antibiotics and on the potentiality of microdomains to constitute a target for these molecules [less ▲]

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See detailInfluence of the tyrosine environment on the second harmonic generation of iturinic antimicrobial lipopeptides at the air–water interface
Nasir, Mehmet Nail ULg; Benichou, Emmanuel; Loison, Claire et al

in Physical Chemistry Chemical Physics [=PCCP] (2013), 15

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 ... [more ▼]

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. [less ▲]

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See detailMulti-Scale Modelisation of the Optical Second Harmonic Generation of Tyrosine-Containing Iturinic Antimicrobial Lipopeptides
Loison, Claire; Nasir, Mehmet Nail ULg; Benichou, Emmanuel et al

Poster (2013)

The optical Second Harmonic Generation (SHG) of Mycosubtilin Langmuir Layers at the air/water interface are modeled. In this tyrosine-containing lipopepeptide, the environment of the tyrosine residue is ... [more ▼]

The optical Second Harmonic Generation (SHG) of Mycosubtilin Langmuir Layers at the air/water interface are modeled. In this tyrosine-containing lipopepeptide, the environment of the tyrosine residue is critical in defining the SHG response. To propose reasonable the structure of Mycosubtilin aggregates at the air-water interface, molecular dynamics simulations (all-atom and coarse-grained) are performed. Molecular hyperpolarizability of the lipopeptide are obtained by Quantum Chemistry calculations. Finally, the SHG susceptibilities of the interface are calculated using a simple additive model. The molecular dynamics simulations suggest that lipopeptides aggregate at the interface into half-micelles, and that this phenomena is the origin of a constraint on Tyrosine orientation. In particular the C-OH bond of the Tyrosine residue has a preferential orientation along the interface normal, pointing towards the air. This inhomogneneous orientation distribution, associated with a dominant hyperpolarizability component along the C-OH bond of the Tyrosine, yields a characteristic SHG response. Comparison with experimental data gathered in our lab are proposed. [less ▲]

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See detailSecond harmonic generation from tyrosine containing peptides
Nasir, Mehmet Nail ULg; Bergmann, Emeric; Benichou, Emmanuel et al

in Proceedings of SPIE (2013), 8817

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 ... [more ▼]

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. [less ▲]

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See detailInfluence of the 524-VAAEIL-529 sequence of annexins A6 in their interfacial behavior and interaction with lipid monolayers.
Domon, Magdalena; Nasir, Mehmet Nail ULg; Pikula, Slawomir et al

in Journal of Colloid & Interface Science (2013), In Press

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 ... [more ▼]

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. [less ▲]

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See detailConformational analyses of bacillomycin D, a natural antimicrobial lipopeptide, alone or in interaction with lipid monolayers at the air-water interface
Nasir, Mehmet Nail ULg; Besson, Françoise

in Journal of Colloid & Interface Science (2012), 387(1), 187-193

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 ... [more ▼]

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. [less ▲]

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See detailSimulations of the Antifungal Lipopeptide Mycosubtilin in Langmuir Monolayers of Sterols
Loison, Claire; Nasir, Mehmet Nail ULg; Besson, Françoise

Poster (2012, July)

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See detailInteractions of the antifungal mycosubtilin with ergosterol-containing interfacial monolayers
Nasir, Mehmet Nail ULg; Besson, Françoise

in Biochimica et Biophysica Acta - Biomembranes (2012), 1818(5), 1302-1318

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 ... [more ▼]

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. [less ▲]

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See detailSecond harmonic generation to monitor the interactions of the antimicrobial mycosubtilin with membrane-mimicking interfacial monolayers
Nasir, Mehmet Nail ULg; Benichou, Emmanuel; Guez, Jean-Sébastien et al

in BioNanoScience (2012), 2(2), 108-112

Mycosubtilin is a strong antimicrobial agent belonging to the iturinic lipopeptide family which contains a single tyrosine residue. Its cell target has been shown to be the cytoplasmic membrane. This ... [more ▼]

Mycosubtilin is a strong antimicrobial agent belonging to the iturinic lipopeptide family which contains a single tyrosine residue. Its cell target has been shown to be the cytoplasmic membrane. This tyrosine residue has been previously shown to be essential for the biological activity of mycosubtilin. Since we have previously demonstrated that tyrosine, an aromatic amino acid, can be used as an endogenous probe for the frequency doubling process, the presence of a tyrosine residue in mycosubtilin allowed us to investigate the interactions of mycosubtilin with biomimetic lipid monolayers at the air–water interface by second harmonic generation (SHG). Mycosubtilin was added underneath dipalmitoylphosphatidylcholine or cholesterol monolayers at the air–water interface and significant increases in the surface pressure were observed in both cases. This observation demonstrates that mycosubtilin interacts with these biomimetic membranes. A light polarization resolved analysis of the SHG signals recovered for these two systems was then performed and confirmed that those interactions between the tyrosine residue in mycosubtilin and the membranes could be monitored by SHG. Furthermore, the differences exhibited by the nonlinear optical measurements for different membranes showed that these interactions depend on the nature of the biomimetic membrane present at the air–water interface. [less ▲]

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See detailAnnexins as organizers of cholesterol- and sphingomyelin-enriched membrane microdomains in Niemann-Pick type C disease.
Domon, Magdalena; Nasir, Mehmet Nail ULg; Matar, Gladys et al

in Cellular and Molecular Life Sciences : CMLS (2011), 69(11), 1773-1785

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with ... [more ▼]

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. [less ▲]

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See detailSecond harmonic generation as a tool to probe the interactions of peptides with membrane-mimicking interfacial monolayers
Benichou, Emmanuel; Duboisset, Julien; Matar, Gladys et al

Conference (2011)

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See detailApplication de l’optique non-linéaire à l’analyse des interactions peptide-monocouches à l’interface air-eau
Nasir, Mehmet Nail ULg; Benichou, Emmanuel; Brevet, Pierre-François et al

Scientific conference (2011)

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See detailInteractions de la mycosubtiline avec les membranes biomimétiques. Apport de l’optique non linéaire
Nasir, Mehmet Nail ULg; Besson, Françoise

Scientific conference (2011)

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See detailAnalyses biophysiques des interactions peptide-monocouches à l’interface air-eau
Nasir, Mehmet Nail ULg; Benichou, Emmanuel; Brevet, Pierre-François et al

Poster (2011)

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