Open AccessDirect determination of layer packing for a phospholipid solid solution at 0.32-nm resolution.
Author(s) -
Douglas L. Dorset
Publication year - 1994
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.91.11.4920
Subject(s) - crystallography , bilayer , homologous series , phase (matter) , chemistry , crystal (programming language) , phosphatidylethanolamine , polar , lipid bilayer , solid solution , diffraction , x ray crystallography , phospholipid , analytical chemistry (journal) , membrane , chromatography , physics , organic chemistry , optics , biochemistry , phosphatidylcholine , astronomy , computer science , programming language
Electron diffraction intensity data were collected from a 2:3 binary solid solution of two homologous phosphatidylethanolamines (1,2-dimyristoyl-sn-glycerophosphoethanolamine and 1,2-dipalmitoyl-sn-glycerophosphoethanolamine) epitaxially oriented by cocrystallization with naphthalene. The layer packing was determined directly by predicting the value of 12 of the 17 phases from sigma 1- and sigma 2-triplet invariants in space group P1. A reverse Fourier transform of the resulting potential maps provides estimates for three other phases and the two remaining ones were found by generating maps for the 2(2) = 4 possible phase combinations and then testing the smoothness of the potential profile of the hydrocarbon chain packing. The same phase solution can be found by translating a molecular model (based on the known x-ray crystal structure of a shorter homologue) past the unit cell origin. The solid solution is found to retain a stable polar group packing while the statistical occupancy of two terminal-chain carbons is expressed by a reduced potential profile at the nonpolar interface at the bilayer center.