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Biomedical subjects

R Maget-Dana

Publications and source records attributed to R Maget-Dana.

At least 37 records · Page 2Linked to original sources
PubMed1989

Interactions of the lipopeptide antifungal iturin A with lipids in mixed monolayers.

The miscibility and the interactions of the antifungal lipopeptide iturin A with lipids, DMPC and cholesterol, are studied in monolayers at the air/water interface and a comparison of the respective behaviour of iturin A and the biologically inactive methylated derivative MeTyr-iturin A is made. Each lipopeptide is miscible with anyone of the lipids. This behaviour is revealed by the dependence of the transition pressure upon composition and by deviations from the additivity rule of the mean molecular area. The thermodynamic properties of the mixed systems are studied by the method of Goodrich. The mixed monolayers are always more stable than the two separate components, subsequently there are interactions between the components. However, the excess free energy of mixing delta Gexm is positive for the iturin A/DMPC system which is an indication that the interactions between lipopeptide and lipid molecules are weaker than the interactions between the pure components themselves. This is compatible with the presence of self-associated lipopeptide molecules. However, delta Gexm is highly negative for the iturin A/cholesterol system giving evidence of the formation of a specific complex between iturin A and cholesterol which is not the case with the methylated derivative. These data are analysed in connection with previous results concerning the pore-forming properties of these lipopeptides and the lack of biological activity of MeTyr-iturin A.

Anti-Bacterial Agents↗
PubMed1989

Methylation of the antifungal lipopeptide iturin A modifies its interaction with lipids.

Iturin A, extracted from the culture media of Bacillus subtilis, is an antifungal lipopeptide, the peptide cycle of which includes a D-Tyr residue in position 2. The antibiotic strength of iturin A is related to a change in the permeability of the membrane cells which leads to a leakage of K+ from the intracellular medium. Methylation of the D-Tyr residue dramatically decreases the biological activity of iturin A. Using the intrinsic fluorescence of D-Tyr we have shown that both iturin A and O-methyl-tyrosine iturin A enter the lipid membranes. When dimyristoylphosphatidylcholine vesicles contain iturin A we observe a change in the order degree of the lipid phase and an increase in the transition temperature. The methylated derivative has no effect. Two model membranes have been used to study the permeability changes induced by iturin A and O-methyltyrosine iturin A. Studying ionic permeability we have found that the conductance of a planar lipid membrane increases very much less when the lipopeptide is methylated. On the other hand, the release of carboxyfluorescein trapped in lipid vesicles is less upon addition of O-methyltyrosine-iturin A. We conclude that the Tyr residue of the peptide cycle plays a role in determining the interactions of iturin A with lipid membrane.

Anti-Bacterial Agents↗
PubMed1988

A comparative monomolecular film study of antibiotic A21978C homologues of various lipid chain length.

A21978C is a calcium-dependent lipopeptide antibiotic whose biological properties are modulated by changes in its lipid chain length. This article reports on the monolayer characteristics of this cyclic lipopeptide and of LY146032 a semi synthetic homologue. The equilibrium spreading pressure pi e increases linearly with the ionic concentration of the subphase and is higher with divalent cations. The nature of the divalent cation plays a crucial role in the spreading as indicated by the variation in the molecular free energy delta Gs.delta Gs decreases in the order K+ greater than Mg2+ greater than Ca2+, which indicates privileged interactions with Ca2+. Also, the larger the lipid chain, the easier the spreading of antibiotic molecules. The compression isotherm curves are shown. The mean area of the uncompressed molecules is around 220-240 A 2 which is compatible with the size of the peptide cycle lying at the interface. The isotherm curves of the natural compounds show a transition region where the molecules are more compressible. At a given area/molecule, the surface pressures increase with the acyl chain length. When the molecules are spread on various salt solutions, the surface pressures increase in the order K+ less than Mg2+ less than Ca2+. The isotherm curves are not reversible upon a compression-expansion cycle and a wide amplitude hysteresis is observed. If a second compression is done, the curve shape is that of a liquid-expanded state and the transition region is no longer observed. This implies a conformational change of the molecules during the first compression process.

Anti-Bacterial Agents↗
PubMed1988

Conformational change on calcium binding by the lipopeptide antibiotic amphomycin. A C.D. and monolayer study.

The acidic linear lipopeptide amphomycin is a calcium dependent antibiotic which is thought to bind to carrier lipids such as dolichol monophosphate. The actual role of Ca++ is not definitely established and in this article we have examined the peptides interactions with a range of divalent cations. By CD we have shown that a conformational change is induced by Ca++, Sr++ and Ba++ but not by Mg++, Zn++, Cd++ or Gd+++. Monolayer studies show a decrease in molecular area and an increase in film stability when the subphase contains Ca++. The ensemble of results provides preliminary evidence for the formation of a beta hairpin structure on ion binding (Ka (Ca++) = 2.4 x 10(3)M-1) which could enhance amphomycin's bilayer solubility.

Anti-Bacterial Agents↗
PubMed1987

Effect of the O-methylation of tyrosine on the pore-forming properties of iturins.

A comparison has been made between the pore-forming properties of the antibiotic lipopeptide iturin A and a derivative methylated on the tyrosine residue which shows a restricted biological activity. It is shown that this derivative increases the ion permeability of planar lipid membranes as does iturin A. Nevertheless, the global conductance of the doped membrane is very much lower at the same lipopeptide/phospholipid ratio and the ion selectivity is inverted (PK/PCl = 6 instead of 0.6 with iturin A). The characteristics of the induced conducting pores are also rather different. This suggests an important role of the D-Tyr2 residue, present in all the compounds of the iturin family, both in the biological and in the pore-forming properties of iturin A.

Anti-Bacterial Agents↗
PubMed1985

Structure of bacillomycin F, a new peptidolipid antibiotic of the iturin group.

The structure of a new antibiotic of the iturin group, bacillomycin F, has been demonstrated. It is a mixture of homologous peptidolipids, essentially C51H80N12O14 and C52N82N12O14. The lipid moiety consists of minor isoC15, anteisoC15 beta-amino acids and major isoC16, isoC17 and anteisoC17 beta-amino acids. The peptide sequence was determined by studying the peptides obtained after mild HCl hydrolysis and by Edman degradation of bacillomycin F treated with N-bromosuccinimide. The sequence was confirmed by two-dimensional NMR spectrometry and fast-atom-bombardment mass spectrometry gave the molecular masses of the homologous compounds. Bacillomycin F is a cyclic peptidolipid; its complete structure is given in the paper.

Amino Acid Sequence↗
PubMed1985

Bacterial lipopeptides induce ion-conducting pores in planar bilayers.

Bacterial lipopeptides, known for their antibiotic activities, have been tested for their ability to interact with lipid membranes. These lipopeptides, Iturin A, Bacillomycin L and D and Peptidolipin NA present analogous structural characteristics: a heptapeptidic cycle is linked to a hydrocarbon chain. We present evidence that these lipopeptides modify the conductance of planar bilayers by forming ion-conducting pores.

Anti-Bacterial Agents↗
PubMed1985

Pore-forming properties of iturin A, a lipopeptide antibiotic.

The addition of iturin A, a lipopeptide antibiotic extracted from Bacillus subtilis, to a bimolecular lipid membrane (BLM) increases dramatically its electrical conductance. For very low concentration of iturin A, discrete conductance steps are observed which are assigned to the formation of conducting pores. The characteristics of these pores depend on the lipid content of the BLM and they change with time. Cholesterol considerably increases the lifetimes of open states. The pores are slightly anion versus cation selective. These first observations unable us to briefly discuss the pore-forming properties of lipopeptides.

Anti-Bacterial Agents↗
PubMed1981

Specificities of limulin and wheat-germ agglutinin towards some derivatives of GM3 gangliosides.

Lipid vesicles containing derivatives of GM3 ganglioside (II3-N-acetylneuraminosyllactosyl ceramide) were used to study the specificities of two lectins (limulin and wheat germ agglutinin) towards N-acetyl neuraminic acid and N-glycoloylneuraminic acid and some of their natural and chemically modified derivatives. The extent of the lectin binding to the gangliosides was related to the aggregation process of the lipid vesicles which was monitored as an absorbance increase. Limulin binds specifically to lipid vesicles containing N-glycoloyl derivatives of GM3. The hydroxyl group at C-4 and the carboxyl group of neuraminic acid have to be free for the binding to limulin. The side chain of neuraminic acid is not involved in the binding site of limulin. Wheat germ agglutinin binds to GM3 ganglioside only when the hydrophilic tail of the neuraminic group is cut off (C7 analogues). The acetamido group but not the carboxyl group is involved in the binding to wheat germ agglutinin. The wheat-germ-agglutinin-induced aggregation of vesicles containing derivatives of GM3-ganglioside is dependent on the pH, on the ionic strength and on the presence of Ca2+ ions. The dependence on ionic strength and Ca2+ is a consequence of the electrostatic repulsion of the vesicles. The wheat-germ-agglutinin-induced aggregation process of vesicles containing any suitable GM3-ganglioside derivative was reversed by the addition of N-acetylglucosamine showing that the N-acetylneuraminic acid derivatives bind to the N-acetylglucosamine binding site.

Calcium↗
PubMed1980

Horse erythrocyte gangliosides: preparation of the major hematoside NeuNG1-Lac-Cer.

A simple method for the isolation of hematoside NeuNG1-Lac-Cer from horse erythrocytes is described. An aliquot of the crude ganglioside fraction was labeled by tritiated sodium borohydride after mild periodate oxidation. The compounds obtained were used as radioactive tracers in column chromatography. Gangliosides were applied onto a silicic acid column and eluted stepwise by solvents of steadily increasing polarity. The major ganglioside, NeuNG1-Lac-Cer, was eluted in a high yield by the solvent mixture chloroform/methanol/water (60:35:8, v/v/v).

Animals↗
PubMed1980

Sugar-lectin interactions: how does wheat-germ agglutinin bind sialoglycoconjugates?

The specific binding of N-acetylneuraminic acid to wheat-germ agglutinin is based on configuration similarities between N-acetylneuraminic acid and N-acetylglucosamine. The N-acetamido group and an adjacent hydroxyl group, both in an equatorial position are shown to be the main determinants. The N-acetylneuraminic acid--wheat-germ agglutinin interaction is increased by the removal of the last two carbons C8 and C9. The interaction between wheat-germ agglutinin and glycoconjugates containing N-acetylneuraminic acid is shown to be dependent on a charge effect and on an avidity effect. Succinylated wheat-germ agglutinin which is negatively charged at physiological pH, in contrast with wheat-germ agglutinin which is positively charged, does not bind cell surface glycoconjugates containing N-acetylneuraminic acid but does bind cell surface glycoconjugates containing N-acetylglucosamine. The use of wheat-germ agglutinin and of succinylated wheat-germ agglutinin leads to the determination of the number of cell surface receptors containing N-acetylneuraminic acid.

Acetylglucosamine↗
PubMed1977

Differences in the modulations of the soluble of plasma-membrane-bound 5'-nucleotidase.

The treatment of plasma membranes by a French pressure cell in sucrose medium devoid of detergents solubilized 20% of the total protein and 95--100% of 5'-nucleotidase activity. The soluble enzyme was 40--90-fold purified by centrifugation in a sucrose gradient with a 10--20% yield with respect to the orginal lysate. The purified fraction retained the same high specificity for 5'-AMP (Km = 20 micron) as in the plasma membranes and was enriched in sphingomyelin. Whereas 5'-AMP at high concentration inhibited the membrane-bound enzyme, it had no effect on the solubilized form. The soluble enzyme was stimulated by 2 X 10(-13)-2 X 10(-15) g concanavalin A without any inhibition with higher doses of lectin. The plasma-membrane bound stimulated and inhibited 5'-nucleotidase was modulated by concanavalin A concentrations higher than 0.1 microgram. Inhibition of the activity of the soluble enzyme by antiphosphorylcholine antibodies was not observed with membranes. The regulation of 5'-nucleotidase acitvity in plasma membranes might be associated with a supramolecular organization.

Adenosine Monophosphate↗