Structural Chemistry of 1,2 Dilauroyl-DL-phosphatidylethanolamine: Molecular Conformation and Intermolecular Packing of Phospholipids

Abstract

Crystals of 1,2 dilauroyl-DL-phosphatidylethanolamine: acetic acid are monoclinic with a = 46.2, b = 7.77, c = 9.95 A, j3 = 92.00; space group P21/c. The structural analysis, based on the visual estimates of 1467 reflection intensities, was achieved by direct methods, and least squares analysis convergence was to R1 = 0.28. There are marked differences between the observed molecular conformation and those that have been predicted theoretically. The mean planes containing the lipid chains are essentially parallel to one another; the phosphodiester moiety has a double gauche conformation, while intermolecular hydrogen bonding modifies the conformation that could be anticipated for an isolated phosphatidylethanolamine molecule. The intermolecular packing produces the classical lipid bilayer structure, adjacent lipid bilayers being separated by acetic acid molecules of crystallization. The hydrocarbon chain packing can be considered either as a quasi-hexagonal type or as a complex orthorhombic subcell arrangement. One-dimensional electron density profiles across the lipid bilayer at increasing resolution clearly demonstrate the origin of features present on the low resolution profiles of both model and natural membranes.Phospholipids, glycolipids, and glycosphingolipids play a key structural and functional role in animal, plant, and bacterial cell membranes (1). Furthermore, phospholipids are important molecular components of the serum lipoproteins responsible for fat transport in the body (2) and of bile secreted by the liver where, together with bile salts, they solubilize cholesterol in a complex, aqueous, mixed micellar system (3).Although much information is available on the behavior of phospholipids in water (4, 5), the mutual interactions of different lipid classes, particularly phospholipid-cholesterol (6) (14), and sugars (15), which determine the different lipid classes, have been described. From this structural information, conformational analyses of different phospholipids have been made and, on this basis, the most likely structures have been predicted (12,16,17).In this paper we describe a single-crystal analysis of a phospholipid, the synthetic compound 1,2 dilauroyl-DL-z HsOJI-OCHsCHr-NHa O_ A knowledge of the molecular conformation and intermolecular packing of phosphatidylethanolamine and other phospholipids will allow a more detailed interpretation of the x-ray diffraction data derived from lipid-water, lipid-protein, and natural membrane systems.

Deuterium magnetic resonance: theory and application to lipid membranes

“…In most parts of the bilayer both fatty acyl chains are extended perpendicular to the bilayer surface except for the first segment of chain 2 which is orientated essentially parallel to the bilayer surface Schindler & Seelig, 1975). This view is supported by X-ray diffraction studies of crystalline bilayers of related dilauroylphosphatidylethanolamine which show that chain 2 is bent at the first segment and penetrates less deeply into the bilayer than chain 1 (Hitchcock et al 1974). The conformational twisting in the vicinity of the polar group is also sensed in other parts of the hydrocarbon chains, since two quadrupole splittings are observed for the C-3 segment and then again for the C-10 to C-15 segments (Seelig & Seelig, 19746, table I).…”

“…A precise picture of the molecular conformation of the ethanolamine head group has been derived for single crystals of dilauroyl-DL-phosphatidylethanolamine (Hitchcock et al 1974) and L-a-glycerylphosphorylethanolamine (DeTitta & Craven, 1971 -CH-CH 2 -O-P-O-CH 2 -CH 2 -NH 2 O O 14 system (torsion angle a 5 ) and the gauche-gauche rotation of the phosphodiester linkage (a 2 , a 3 ) leading to a' boomerang' shape of the ethanolamine group in the crystal (DeTitta & Craven, 1971). The nomenclature used here is that introduced by Sundaralingam (1972).…”

Structures of uranyl-decorated lecithin and lecithin–cholesterol bilayers

“…The length and density of the hydrocarbon core of our Q(z) also agrees well with those reported for ,~ ratty acid multilayer by Lesslauer (1974). Hitchcock, Mason, Thomas & Shipley (1974) have analysed the crystal structure of dilauroyl phosphatidylethanolamine and gave the electron density projection onto the normal to the bilayer at various resolutions. The density profile of the resolution of 5.5 A (the curve (b) in Fig.…”

Conformation and mode of organization of amphiphilic membrane components: a conformational analysis

“…The quantummechanical studies demonstrated that no difference should be expected between ethanolamine phosphate and choline phosphate with respect to the conformation about the a5 rotational angle. An excellent agreement was observed for the value of the a4 rotational angle in the conformational analysis and the X-ray crystallographic study of 1,2-dilauroyl-DLphosphatidylethanolamine (Hitchcock et al, 1974). For the other rotational angles of the polar group, the discrepancies between the two approaches underline the importance of the changes in the orientation of the polar head group during the packing process.…”