Phase and surface properties of lipid bilayers containing neoglycolipids

The physical properties conferred to DPPC bilayers by including neoglycolip ids composed by two different trisaccharides: mannose-mannose-mannose (3M) and glucose-mannose-glucose (GMG) attached to a cholesterol (cho) and a dis tearylglycerol (diC18) lipid moiety by a spacer were evaluated by means of the measurement of the electrokinetic potential and interfacial fluorescent probes. The phase properties measured with diphenylhexatriene (DPH) were c orrelated with the surface properties measured with merocyanine 540, dansyl , and Laurdan probes. The results show that the surface properties of large unilamellar vesicles depend on the sugar exposure to the water phase and a lso on the hydrocarbon moiety by which it is anchored to the bilayer, The c ombination of the cholesterol moiety with the saccharide attenuates the coo perativity decrease induced by the cholesterol moiety without the sugar por tion. The neoglycolipid GMG-diC18 promotes opposite effects affecting sligh tly the cooperativity at the hydrocarbon core of DPPC and displacing the ph ase transition temperature to higher values, The presence of neoglycolipid with diC18 introduces defects in the packing at the interface of the membra ne in the gel state. It is concluded that a relatively low proportion of ne oglycolipids affects significantly the interfacial properties of DPPC bilay ers in large unilamellar vesicles in the absence of changes at the membrane bulk at 25 degrees C. (C) 1999 Academic Press.