Direct evidence for the partial dehydration of phosphatidylethanolamine bilayers on approaching the hexagonal phase.
X-ray diffraction studies on oriented multilayers of 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE) in the lamellar gel (L beta) and inverted hexagonal (HII) phases at various temperatures (5-50 degrees C) and relative humidities (0-100%) are reported. One-dimensional electron density profiles of the L beta phase bilayers were constructed to a resolution of better than 4 A using direct methods to solve for the phase problem. In addition, the electron density profiles were fitted favorably using a model in which the atomic groups were assumed to be Gaussian distributed [Wiener, M. C., & White, S. H. (1992) Biophys. J. 61, 434-447]. The X-ray data clearly demonstrate that, at 100% relative humidity (RH), POPE samples exist in two distinct L beta phases, differing primarily in the amount of water between the lamellae. As the hexagonal phase transition temperature is approached, 100% RH POPE samples partially dehydrate, releasing approximately 5 water molecules per phospholipid and experiencing on average a 3-A decrease in repeat spacing. The lower temperature hydrated L beta phase POPE electron density distribution resembles that obtained from the L beta phase 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayers and is unlike the partially dehydrated POPE bilayers.
Katsaras
J
J
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
Jeffrey
K R
KR
Yang
D S
DS
Epand
R M
RM
D003890:Desiccation; D006813:Humidity; D008051:Lipid Bilayers; D008433:Mathematics; D008962:Models, Theoretical; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D014961:X-Ray Diffraction
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine