title: Fusion of phospholipid vesicles produced by the anti-tumour protein alpha-sarcin.
abstract: The anti-tumour protein alpha-sarcin causes fusion of bilayers of phospholipid vesicles at neutral pH. This is demonstrated by measuring the decrease in the efficiency of the fluorescence energy transfer between N-(7-nitro-2-1,3-benzoxadiazol-4-yl)-dimyristoylphosphatidylethano lamine (NDB-PE) (donor) and N-(lissamine rhodamine B sulphonyl)-diacylphosphatidylethanolamine (Rh-PE) (acceptor) incorporated in dimyristoylphosphatidylcholine (DMPG) vesicles. The effect of alpha-sarcin is a maximum at 0.15 M ionic strength and is abolished at basic pH. alpha-Sarcin promotes fusion between 1,6-diphenylhexa-1,3,5-triene (DPH)-labelled DMPG and dipalmitoyl-PG (DPPG) vesicles, resulting in a single thermotropic transition for the population of fused phospholipid vesicles. Bilayers composed of DMPC and DMPG, at different molar ratios in the range 1:1 to 1:10 PC/PG, are also fused by alpha-sarcin. Freeze-fracture electron micrographs corroborate the occurrence of fusion induced by the protein. alpha-Sarcin also modifies the permeability of the bilayers, causing the leakage of calcein in dye-trapped PG vesicles. All of the observed effects reach saturation at a 50:1 phospholipid/protein molar ratio, which is coincident with the binding stoichiometry previously described.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Química, Universidad Complutense, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Gasset
authors.forename: M
authors.initials: M
authors.lastname: Oñaderra
authors.forename: P G
authors.initials: PG
authors.lastname: Thomas
authors.forename: J G
authors.initials: JG
authors.lastname: Gavilanes
mesh_terms: D001230:Aspergillus / Q000378:metabolism*; D004722:Endoribonucleases; D004735:Energy Transfer; D005452:Fluoresceins / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers; D008854:Microscopy, Electron; D009994:Osmolar Concentration; D010743:Phospholipids / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D005452:Fluoresceins; D005656:Fungal Proteins; D008051:Lipid Bilayers; D010743:Phospholipids; C014801:alpha-sarcin; D004722:Endoribonucleases; C007740:fluorexon