Cooperative Partition Model of Nystatin Interaction with Phospholipid Vesicles

Abstract

Nystatin is a membrane-active polyene antibiotic that is thought to kill fungal cells by forming ion-permeable channels. In this report we have investigated nystatin interaction with phosphatidylcholine liposomes of different sizes (large and small unilamellar vesicles) by time-resolved fluorescence measurements. Our data show that the fluorescence emission decay kinetics of the antibiotic interacting with gel-phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine vesicles is controlled by the mean number of membrane-bound antibiotic molecules per liposome, <A>. The transition from a monomeric to an oligomeric state of the antibiotic, which is associated with a sharp increase in nystatin mean fluorescence lifetime from approximately 7-10 to 35 ns, begins to occur at a critical concentration of 10 nystatin molecules per lipid vesicle. To gain further information about the transverse location (degree of penetration) of the membrane-bound antibiotic molecules, the spin-labeled fatty acids (5- and 16-doxyl stearic acids) were used in depth-dependent fluorescence quenching experiments. The results obtained show that monomeric nystatin is anchored at the phospholipid/water interface and suggest that nystatin oligomerization is accompanied by its insertion into the membrane. Globally, the experimental data was quantitatively described by a cooperative partition model which assumes that monomeric nystatin molecules partition into the lipid bilayer surface and reversibly assemble into aggregates of 6 +/- 2 antibiotic molecules.

Lateral Distribution of NBD-PC Fluorescent Lipid Analogs in Membranes Probed by Molecular Dynamics-Assisted Analysis of Förster Resonance Energy Transfer (FRET) and Fluorescence Quenching

“…Large unilamellar vesicles (LUV, ~100 nm diameter) were then prepared by extrusion of lipid dispersions through 100-nm pore diameter polycarbonate membranes as previously described [43]. DPH was added to pre-formed vesicles by injecting a very small volume (<0.1% of LUV suspension volume) of methanol stock solution, mixing thoroughly, and incubating at 50 °C in the dark for 2 h. The resulting lipid dispersions were stored at room temperature and used within 24 h of preparation.…”

Drunken Membranes: Short-Chain Alcohols Alter Fusion of Liposomes to Planar Lipid Bilayers

“…To independently measure fluidity changes in membranes due to ethanol, we took advantage of the fact that nystatin, used for the fusion assay above, also fluoresces in membranes (64). The fluorescence of nystatin has been shown to reflect membrane fluidity (65).…”

Influence of a lipid bilayer on the conformational behavior of amphotericin B derivatives — A molecular dynamics study

“…This result suggests that the stable transition of the polar head to the closed conformational state, as has been observed for the two studied derivatives of improved selectivity, should lead to the decrease of transmembrane channel stability. There is also some evidence that the full expression of the AmB channel-forming activity occurs within the environment of sterol-enriched, liquidordered membrane domains [7,21,55]. These supramolecular structures (e.g., lipid rafts present in the plasma membrane of eukaryotic cells) might be regarded as providing an adequate level of bilayer rigidity for the antibiotic molecules to form of a multimolecular assembly that spans the membrane.…”