title: 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.
authors.affiliation: Centro de Química-Física Molecular, Instituto Superior Técnico, Av. Rovisco Pais, P-1049-001 Lisbon, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Coutinho
authors.forename: Manuel
authors.initials: M
authors.lastname: Prieto
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D001665:Binding Sites; D003198:Computer Simulation; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances; D008560:Membrane Fluidity; D008956:Models, Chemical; D008958:Models, Molecular; D009761:Nystatin / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D046911:Macromolecular Substances; D010713:Phosphatidylcholines; D010743:Phospholipids; D011108:Polymers; D009761:Nystatin; D015060:1,2-Dipalmitoylphosphatidylcholine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine