FUSION OF PHOSPHOLIPID-VESICLES INDUCED BY THE RIBOSOME-INACTIVATING PROTEIN SAPORIN

The single chain ribosome-inactivating protein Saporin-SB (SO-6) induc es the fusion of acid phospholipid vesicles. The extent of fusion was measured by resonance energy transfer assay between the -2-1,3-benzoxa diazol-4-yl)-dimyristoylphosphatidyl lithoanolamine (NBD-PE)(donor) an d N-(lissamine rhodamine B sulphonyl)-diacylphoshaidylethanolamine (Rh -PE) (acceptor) incorporated in the vesicle. The saturated lipid/prote in molar ratio is approx. 100:1. The time course of fusion of vesicles induced by the protein showed that the process was completed within 1 0 minutes, and the size of the particles in the medium was enlarged wh ich conforms the occurrence of the fusion occuring. The fusion is temp erature dependent and the liquid-crystalline state lipid is more apt t o fuse than the gel phase lipid. The effect of SO-6 is also dependent on ionic strength and pH, high salt concentration and basic pH may abo lish fusion, which suggests that both electrostatic and hydrophobic co mponents may be involved in the process.