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.
Maget-Dana
R
R
Centre de Biophysique Moléculaire, CNRS, Orleans, France.
Lakey
J H
JH
Ptak
M
M
D000900:Anti-Bacterial Agents; D017576:Daptomycin; D036341:Intercellular Signaling Peptides and Proteins; D008074:Lipoproteins; D010455:Peptides; D010456:Peptides, Cyclic; D011487:Protein Conformation; D012996:Solutions; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D000900:Anti-Bacterial Agents; D036341:Intercellular Signaling Peptides and Proteins; D008074:Lipoproteins; D010455:Peptides; D010456:Peptides, Cyclic; D012996:Solutions; C044687:A 21978C1; D017576:Daptomycin