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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 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 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 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 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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