Search PubMed⌕ Search

Biomedical subjects

J Dufourcq

Publications and source records attributed to J Dufourcq.

53 records · Page 3Linked to original sources
PubMed1982

Structure-function relationships for cardiotoxins interacting with phospholipids.

Four cardiotoxins (CTX I-IV) from Naja mossambica mossambica were compared for their ability to interact with phospholipid vesicles and their capacity to bind erythrocytes. It is concluded that the affinity of the toxins always increases in the order: I approximately equal to II less than III less than IV. The binding is specific for charged lipids even in lipid mixtures. Proteolytic attack of the free and lipid-bound cardiotoxin indicates that at least the first loop Leu1-Thr13 is at the lipid contact. Tryptic and synthetic peptides constitutive of this loop are shown to interact with lipids. Arg5 residue increases the affinity toward the bilayer. The Raman spectra of lipid-bound cardiotoxin indicate a secondary and tertiary structure mainly similar to that of the free toxin. On charged lipids cardiotoxins induce a decrease of the enthalpy and an increase of disorder without change in the transition temperature; at saturating amounts of toxin the transition is abolished. In binary mixtures of phosphatidylcholine and charged lipids the observed effects can be accounted by a phase separation induced by the toxin.

Amino Acid Sequence↗
PubMed1982

Melittin-phospholipid interactions: binding of the mono- and tetrameric form of this peptide, and perturbations of the thermotropic properties of bilayers.

The binding of melittin to phospholipid bilayers and micelles depends on its quaternary structure and on the state of association of lipids. Monomeric melittin only binds to lipids above their cmc, whereas tetrameric melittin exhibits a biphasic binding; the interaction with monomeric lipids being possible without dissociation of the tetramer. In lipid excess, the bound state observed by fluorescence, polarization and ORD are always very similar. We propose the following model: the presence of a lipidic interface is necessary for the binding of monomeric melittin, while the tetramer may interact with lipid monomers without any dissociation: it might increase in size by addition of lipid molecules to form a micelle-like particle. The perturbations induced by melittin on the thermotropic behaviour of charged phospholipids are detected by calorimetry (DSC) and fluorescence polarization of DPH. For the first group of lipids, constituted of mono or divalent C14 and of divalent C16 lipids, the transitions are progressively abolished in the presence of melittin, without any shift of the temperature. For a second group of lipids, essentially constituted of monovalent C16 lipids, a cooperative transition is always observed. Moreover, at lipid to protein molar ratios higher than 8, there are two distinct well-defined transitions, at the same temperature as for pure lipid and 10 degrees C to 15 degrees C lower. All these results are interpreted by a phase separation occurring between quasi-pure lipid regions and the lipid-melittin complex. These last ones either could, or not, give rise to a phase transition, according to the cohesion of the initial bilayer. In the case of binary mixtures, there would be a phase separation between enriched phosphatidylcholine regions and negative lipid-melittin complexes.

Bee Venoms↗
PubMed1980

Snake venom phospholipases A2. A fluorescence study of their binding to phospholipid vesicles correlation with their anticoagulant activities.

The interaction of snake venom phospholipases A2 with phospholipids has been studied by intrinsic fluorescence. This has been performed in order to understand why some enzymes possess anticoagulant properties while others have no action on blood clotting. We show that phospholipases A2 can be distinguished according to their binding properties to phospholipid vesicles. Strong inhibitors of coagulation interact with phospholipids with a significant change of their fluorescence while poor inhibitors have little or no effect. Strong inhibitors have a great affinity toward phosphatidylserine and do not require Ca2+ for interaction. Similar results are obtained with phosphatidylcholine-phosphatidylserine 1:1 mixtures. The diether analogue of phosphatidylcholine shows that formation of the complex is promoted by Ca2+ and can occur whenever the lipids are in crystal or fluid phase. Inactivation of anticoagulant phospholipase A2 decreased the affinity of enzyme for the phospholipids. The change in the intrinsic fluorescence of the phospholipases A2 on binding indicates a modification of the environment of the tryptophan residues. This is discussed in terms of the so-called interface recognition site as seen in the case of pancreatic phospholipase A2. It is concluded that the phospholipases may inhibit coagulation by competing with clotting proteins for the lipid surface. Although not considered in this study, the consequence of the hydrolysis of lipids remains to be estimated.

Animals↗
PubMed1979

Lipid-protein interactions: NMR study of melittin and its binding to lysophosphatidylcholine.

Proton NMR of melittin differs according to the association state of the peptide in the monomer or tetramer. Melittin interacts with lysophosphatidyl-choline micelles, whatever the association state of melittin; well resolved superimposed spectra from both components for all the lipid to peptide molar ratios are observed. Within the complexes, local mobility and fast exchange occurs. On binding concomitant shifts on Trp19 indole lines and on the aliphatic CH2 protons of the lipids are detected. The lipid perturbation is maximum for methylene groups in a alpha and beta of the ester bond, this could allow positionning of Trp19 in the hydrophobic core of the lipids.

Bee Venoms↗
PubMed1976

Lipid-protein interactions in membrane models. Fluorescence polarization study of cytochrome b5-phospholipids complexes.

According to previous authors, cytochrome b5, when extracted from bovine liver by a detergent method, is called cytochrome d-b5. On the other hand, the protein obtained after trypsin action, which eliminates an hydrophobic peptide of about 54 residues, is called cytochrome t-b5. Fluorescence polarization of the dansyl phosphatidylethanolamine probe inserted into phospholipid vesicles is very sensitive to the binding of proteins, and so is a useful method to study lipid-protein interactions. The chromophore mobility, R, decreases markedly when dipalmitoyl phosphatidylcholine vesicles are incubated with cytochrome d-b5, whereas R does not change for cytochrome c and cytochrome t-b5. This can be interpreted as a strengthening of bilayer, only due to the interaction of the hydrophobic peptide tail. Interaction of dipalmitoly phosphatidylcholine vesicles with cytochrome d-b5 occurs either below or above the melting temperature of the aliphatic chains (41 degrees C). Even for a high protein to lipid molar ratio (1 molecule of protein for 40 phospholipid molecules), the melting temperature is apparently unaffected. Phosphatidylserine and phosphatidylinositol do not interact at pH 7.7 with cytochrome d-b5, because electrostatic forces prevent formation of complexes. At low pH, the interaction with the protein occurs, but the binding is mainly of electrostatic nature.

Animals↗