STRUCTURE OF ESCHERICHIA-COLI MEMBRANES - PHOSPHOLIPID CONFORMATION IN MODEL MEMBRANES AND CELLS AS STUDIED BY DEUTERIUM MAGNETIC-RESONANCE

The dynamic conformation of phospholipid molecules in membranes of Escherichia coli has been investigated by means of deuterium magnetic resonance. E. coli strains which were deficient in the synthesis of cardiolipin were grown in the presence of selectively deuterated elaidic acid, oleic acid, and palmitic acid. A total of 50-85% of the natural fatty acids were replaced by the deuterium-labeled analogues, and well-resolved deuterium magnetic resonance spectra of intact E. coli cells could be obtained in less than 1-h measuring time. The spectra reveal a striking similarity between the phospholipid conformation in a biological membrane and that of phospholipid model membranes. If the deuterium label is attached at the C-2 segment of the fatty acyl chains or at the cis double bond, the deuterium magnetic resonance spectra are rather unique and can be considered as spectral fingerprints of the phospholipid conformation in the fluid membrane. Almost identical fingerprints are observed for native E. coli membranes, for liposomes formed from extracted E. coli lipids, and for synthetic phospholipids. The phospholipid conformation in the fluid membrane as derived from these spectral patterns is closely related to the structural model suggested for phospholipids in the gel phase and in the crystalline state. The orientational fluctuations of the fatty acyl chain segments in the membrane are quantitatively described by the deuterium order parameters. A detailed order profile has been established for E. coli membranes by incorporating palmitic acid and oleic acid selectively deuterated at altogether 10 different carbon atoms. The shape of the curve drawn through deuterium order parameters of intact E. coli cells closely resembles that of synthetic l-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. It can be concluded that the order profiles characteristic of saturated and cis unsaturated fatty acyl chains are qualitatively not altered by the presence of membrane proteins. Due to instrumental limitations, lipids in the gel state or lipids tightly bound to membranous proteins cannot be resolved in the present experiments. © 1979, American Chemical Society. All rights reserved.