Dolichyl phosphate induces non-bilayer structures, vesicle fusion and transbilayer movement of lipids: a model membrane study

The effect of dolichol and dolichyl phosphate on fusion between large unilamellar vesicles comprised of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) was studied using a fluorescence resonance energy transfer assay. The influence of dolichyl phosphate on the transbilayer movement of DOPC in multilamellar vesicles (MLV) and large unilamellar vesicles (LUV) composed of DOPC and DOPE (1:2) was investigated by using the phosphatidylcholine-specific transfer protein. 31P-NMR and freeze-fracture electron microscopy were employed to study the macroscopic organization of DOPC and DOPE containing model membranes in the absence or presence of dolichyl phosphate. The results indicate that both dolichol and dolichyl phosphate enhance vesicle fusion in a comparable and concentration-dependent way; the amount of exchangeable PC from MLVs is increased by dolichyl phosphate, probably as a result of fusion processes; dolichyl phosphate destabilizes the bilayer organization in MLVs comprised of DOPE and DOPC, resulting in the formation of hexagonal (HII) phase and 'lipidic' particles.