Physical properties and surface interactions of bilayer membranes containing N-methylated phosphatidylethanolamines

Abstract

The structure and physical properties of aqueous dispersions of 1,2-diacyl-sn-glycero-3-phosphoethanolamines (PE's) and their N-methylated analogues have been studied by scanning calorimetry, 31P nuclear magnetic resonance, and freeze-fracture electron microscopy. While successive N-methylations of a diacylphosphatidylethanolamine cause only modest decreases in its gel to liquid-crystalline phase transition temperature, the introduction of even a single N-methyl group sharply increases the temperature at which the lipid forms a hexagonal II phase. However, 31P nuclear magnetic resonance and electron microscopy show that unlike pure PE species, N-methylated PE's can form a variety of irregular nonlamellar structures at temperatures well below that at which a well-defined hexagonal II phase is formed. The rate of calcium-induced leakage of encapsulated carboxyfluorescein from large unilamellar vesicles composed of dioleoyl- or dielaidoylphosphatidylserine and the corresponding PE is strongly reduced when PE is replaced by N-methylated derivatives. The rate of calcium-induced intermixing of lipids of PE/phosphatidylserine (PS) vesicles steadily decreases as the PE component is successively replaced by its mono-, di-, and tri-N-methylated (phosphatidylcholine) derivatives. By correlating calorimetrically obtained phase diagrams with measurements of vesicle lipid intermixing, we conclude that dielaidoyl-N-methylphosphatidylethanolamine, like PE, can support direct interactions between the surfaces of PS/N-methyl-PE vesicles without lateral separation of a PS(Ca2+)-rich phase, while dielaidoyl-N,N-dimethyl-PE (and phosphatidylcholine) cannot.(ABSTRACT TRUNCATED AT 250 WORDS)

Thematic Review Series: Glycerolipids. Phosphatidylcholine and choline homeostasis

“…Thus, the requirement of choline for mammalian life is very specific for choline, with its three N-methyl groups, and choline cannot even be replaced by dimethylethanolamine that has one less N-methyl group. This specificity is unexpected, because the physical properties of PC in membranes are very similar to those of phosphatidyldimethylethanolamine (85).…”

Metabolism of phosphatidylcholine and its implications for lipid acyl chain composition in Saccharomyces cerevisiae

“…PC deficiency can be bypassed by its biosynthetic precursor in the methylation pathway PDME provided that the yeast cells are grown in the presence of inositol, substrate for the synthesis of PI [19,20]. Like PC, PI is a bilayer forming phospholipid [92] that compensates for the replacement of PC by PDME that forms somewhat less stable bilayers [93]. The ability of PMME to replace PC in the presence of inositol appears to depend on the strain background [19,20].…”

Modulation by gangliosides of the lamellar-inverted micelle (hexagonal II) phase transition in mixtures containing phosphatidylethanolamine and dioleoylglycerol.

“…The H11 phase transition of pure (Ole)2PtdEtn has been reported between 8 and 12°C when detected by 31P-NMR or HSDSC (20,(22)(23)(24) and is increased to >40°C by inclusion of of a mixture of different proportions of(Ole)2PtdCho (20,24 excimer/monomer ratio in mixtures of TPE containing variable amounts of (Ole)2Gro, a lipid well known to induce formation of the HI, phase (5,16,22). In the presence of gangliosides (Fig.…”