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See detailAnalysis of calcium-induced effects on the conformation of fengycin
Nasir, Mehmet Nail ULg; Laurent, Pascal ULg; Flore, Christelle ULg et al

in Spectrochimica Acta Part A : Molecular and Biomolecular Spectroscopy (2013), 110

A combination of CD, FT-IR, NMR and fluorescence spectroscopic techniques was applied to elucidate the conformation of fengycin, a natural lipopeptide with antifungal and eliciting activities, in a ... [more ▼]

A combination of CD, FT-IR, NMR and fluorescence spectroscopic techniques was applied to elucidate the conformation of fengycin, a natural lipopeptide with antifungal and eliciting activities, in a membrane-mimicking environment and to investigate the effect of calcium ions on the conformation. We mainly observed that fengycin adopts a turn conformation and that the side chain of glutamate residues plays a key role on the stabilization of the peptide ring backbone conformation. More particularly, the binding of calcium ions by the carboxylic moieties has a consequence on the environment of the tyrosine residues. Our data suggest also an arrangement of fengycin molecules into “-sheet like micelles” in a membrane-mimicking environment and the enhancement of this aggregating effect in presence of calcium ions. The modulation of the fengycin conformation by the environmental conditions may influence its biological properties. [less ▲]

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See detaild-Xylose-based bolaamphiphiles: Synthesis and influence of the spacer nature on their interfacial and membrane properties
Deleu, Magali ULg; Gatard, Sylvain; Payen, Emeline et al

in Comptes Rendus Chimie (2012), 15

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See detailStudy of the specific lipid binding properties of Abeta 11-22 fragment at endosomal pH.
Ravault, S.; Flore, Christelle ULg; Saurel, O. et al

in Langmuir (2009), 25(18), 10948-53

Increasing evidence implicates interactions between Abeta peptide and lipids in the development of Alzheimer's disease. More generally, Abeta peptide interactions with membranes seem to depend on the ... [more ▼]

Increasing evidence implicates interactions between Abeta peptide and lipids in the development of Alzheimer's disease. More generally, Abeta peptide interactions with membranes seem to depend on the composition of the lipid bilayer and the structural features of the peptide. One key parameter should be pH, since one site of intracellular Abeta peptide production and/or accumulation is likely to be endosomes. This intracellular endosomal accumulation was suggested to contribute to disease progression. In this paper, we report a study on the 11-22 amphiphilic domain of Abeta in interaction with model membrane; this region contains most of the charged residues of the N-terminal domain of Abeta. We show that the peptide charge, and more precisely the protonation state of histidines 13 and/or 14, is important for the interaction with lipids. Hence, it is only at endosomal pH that a conformational change of the peptide is observed in the presence of negatively charged lipid vesicles, that is, when both lipid headgroups and histidines can interact through electrostatic interactions. Specific interactions of the fragment with phosphatidylserine and to a lesser extent with phosphatidylcholine, but not phosphatidylethanolamine, are further evidenced by the Langmuir monolayer technique. From our results, we suggest that the protonation state of His residues could have a role in the pathogenic surface interaction of the whole Abeta peptide with membranes. [less ▲]

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See detailLipid-Destabilizing Properties Of The Hydrophobic Helices H8 And H9 From Colicin E1
Lins, Laurence ULg; El Kirat, K.; Charloteaux, Benoît ULg et al

in Molecular Membrane Biology (2007), 24(5-6), 419-30

Colicins are toxic proteins produced by Escherichia coli that must cross the membrane to exert their activity. The lipid insertion of their pf domain is linked to a conformational change which enables the ... [more ▼]

Colicins are toxic proteins produced by Escherichia coli that must cross the membrane to exert their activity. The lipid insertion of their pf domain is linked to a conformational change which enables the penetration of a hydrophobic hairpin. They provide useful models to more generally study insertion of proteins, channel formation and protein translocation in and across membranes. In this paper, we study the lipid-destabilizing properties of helices H8 and H9 forming the hydrophobic hairpin of colicin E1. Modelling analysis suggests that those fragments behave like tilted peptides. The latter are characterized by an asymmetric distribution of their hydrophobic residues when helical. They are able to interact with a hydrophobic/hydrophilic interface (such as a lipid membrane) and to destabilize the organized system into which they insert. Fluorescence techniques using labelled liposomes clearly show that H9, and H8 to a lesser extent, destabilize lipid particles, by inducing fusion and leakage. AFM assays clearly indicate that H8 and especially H9 induce membrane fragilization. Holes in the membrane are even observed in the presence of H9. This behaviour is close to what is seen with viral fusion peptides. Those results suggest that the peptides could be involved in the toroidal pore formation of colicin E1, notably by disturbing the lipids and facilitating the insertion of the other, more hydrophilic, helices that will form the pore. Since tilted, lipid-destabilizing fragments are also common to membrane proteins and to signal sequences, we suggest that tilted peptides should have an ubiquitous role in the mechanism of insertion of proteins into membranes. [less ▲]

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See detailLipid-Interacting Properties Of The N-Terminal Domain Of Human Apolipoprotein C-III
Lins, Laurence ULg; Flore, Christelle ULg; Chapelle, L. et al

in Protein Engineering (2002), 15(6), 513-20

The lipid-interacting properties of the N-terminal domain of human apolipoprotein C-III (apo C-III) were investigated. By molecular modeling, we predicted that the 6-20 fragment of apo C-III is obliquely ... [more ▼]

The lipid-interacting properties of the N-terminal domain of human apolipoprotein C-III (apo C-III) were investigated. By molecular modeling, we predicted that the 6-20 fragment of apo C-III is obliquely orientated at the lipid/water interface owing to an asymmetric distribution of the hydrophobic residues when helical. This is characteristic of 'tilted peptides' originally discovered in viral fusion proteins and later in various proteins including some involved in lipoprotein metabolism. Since most tilted peptides were shown to induce liposome fusion in vitro, the fusogenic capacity of the 6-20 fragment of apo C-III was tested on unilamellar liposomes and compared with the well characterized SIV fusion peptide. Mutants were designed by molecular modeling to assess the role of the hydrophobicity gradient in the fusion. FTIR spectroscopy confirmed the predominantly helical conformation of the peptides in TFE solution and also in lipid-peptide complexes. Lipid-mixing experiments showed that the apo C-III (6-20) peptide is able to increase the fluorescence of a lipophilic fluorescent probe. The vesicle fusion was confirmed by core-mixing and leakage assays. The hydrophobicity gradient plays a key role in the fusion process because the mutant with no hydrophobic asymmetry but the same mean hydrophobicity as the wild type does not induce significant lipid fusion. The apo C-III (6-20) fragment is, however, less fusogenic than the SIV peptide, in agreement with their respective mean hydrophobicity. Since lipid fusion should not be the physiological function of the N-terminal domain of apo CIII, we suggest that its peculiar distribution of hydrophobic residues is important for the lipid-binding properties of apo C-III and should be involved in apolipoprotein and lipid exchanges crucial for triglyceride metabolism. [less ▲]

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See detailExperimental And Conformational Analyses Of Interactions Between Butenafine And Lipids
Mingeot-Leclercq, Mp.; Gallet, X.; Flore, Christelle ULg et al

in Antimicrobial Agents and Chemotherapy (2001), 45(12), 3347-54

Butenafine (N-4-tert-butylbenzyl-N-methyl-1-naphtalenemethylamine hydrochloride) is an antifungal agent of the benzylamine class that has excellent therapeutic efficacy and a remarkably long duration of ... [more ▼]

Butenafine (N-4-tert-butylbenzyl-N-methyl-1-naphtalenemethylamine hydrochloride) is an antifungal agent of the benzylamine class that has excellent therapeutic efficacy and a remarkably long duration of action when applied topically to treat various mycoses. Given the lipophilic nature of the molecule, efficacy may be related to an interaction with cell membrane phospholipids and permeabilization of the fungal cell wall. Similarly, high lipophilicity could account for the long duration of action, since fixation to lipids in cutaneous tissues might allow them to act as local depots for slow release of the drug. We have therefore used computer-assisted conformational analysis to investigate the interaction of butenafine with lipids and extended these observations with experimental studies in vitro using liposomes. Conformational analysis of mixed monolayers of phospholipids with the neutral and protonated forms of butenafine highlighted a possible interaction with both the hydrophilic and hydrophobic domains of membrane phospholipids. Studies using liposomes demonstrated that butenafine increases membrane fluidity [assessed by fluorescence polarization of 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene and 1,6-diphenylhexatriene] and membrane permeability (studied by release of calcein from liposomes). The results show, therefore, that butenafine readily interacts with lipids and is incorporated into membrane phospholipids. These findings may help explain the excellent antifungal efficacy and long duration of action of this drug when it is used as a topical antifungal agent in humans. [less ▲]

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