title: Fluorescence indicates a calcium-dependent interaction between the lipopeptide antibiotic LY146032 and phospholipid membranes.
abstract: LY146032 is one of the A21978C family of calcium-dependent antibiotics. This paper reports on its interactions with membranes as studied by its intrinsic fluorescence. The Trp residue was found to have a low fluorescence yield because of Förster-type energy transfer to the kynurenine residue (Kyn) (epsilon = 5000 at 364 nm). However, the Kyn fluorescence (lambda max = 465 nm in H2O) was a sensitive probe of the membrane interactions, and it was used in steady-state fluorescence measurements including fluorescence polarization anisotropy. Initial binding of the peptide to phospholipid vesicles occurs in calcium-free solutions. When calcium is added, the resulting 10-fold fluorescent enhancement and 15-nm blue shift show that it causes the antibiotic to penetrate further into the lipid bilayer. Calcium is bound with an association constant of 151 M-1, while a phospholipid titration in the presence of calcium gave an association constant of 5 x 10(3) M-1 for egg phosphatidylcholine. Magnesium and cadmium cause very slight fluorescence enhancements, but a more significant effect is caused by the trivalent lanthanide ions. Analysis of these data indicates that the calcium-selective site is on the peptide and that ion binding to the phospholipid headgroups has a secondary role. Comparison with the divalent cation dependent antibiotics bacitracin and amphomycin shows that LY146032 has a quite different activity and that a calcium-dependent membrane interaction could account for results obtained in vivo.
authors.affiliation: Centre de Biophysique Moléculaire, CNRS, Université d'Orléans, France.
authors.forename: J H
authors.initials: JH
authors.lastname: Lakey
authors.forename: M
authors.initials: M
authors.lastname: Ptak
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine; D000900:Anti-Bacterial Agents; D002118:Calcium; D017576:Daptomycin; D004134:Dimyristoylphosphatidylcholine; D007700:Kinetics; D007737:Kynurenine; D008081:Liposomes; D008954:Models, Biological; D010455:Peptides; D010713:Phosphatidylcholines; D013050:Spectrometry, Fluorescence
chemical_list: D000900:Anti-Bacterial Agents; D008081:Liposomes; D010455:Peptides; D010713:Phosphatidylcholines; D015060:1,2-Dipalmitoylphosphatidylcholine; D007737:Kynurenine; D017576:Daptomycin; D002118:Calcium; D004134:Dimyristoylphosphatidylcholine