Dynamics of the phosphate group in phospholipid bilayers. A 31P-1H transient Overhauser effect study

Abstract

Two recent studies have addressed the question of the dynamics of the phosphate in egg phosphatidylcholine multilayers by measurement and interpretation of 31P NMR spin-lattice relaxation. In the first (Milburn, M. P., and K. R. Jeffrey. 1987. Biophys. J. 52:791-799), the temperature dependences of the two contributions to the 31P relaxation rate, a dipolar interaction of the phosphorus with neighboring protons and a time-dependent anisotropic chemical shielding interaction were separately measured. A further study (Milburn, M. P., and K. R. Jeffrey. 1989. Biophys. J. 56:543-549) incorporated the anisotropic nature of phospholipid motions into the dynamic model of the headgroup motion by measuring the 31P spin-lattice relaxation time in oriented samples as a function of angle between the bilayer normal and the magnetic field. These angular dependent measurements were made at high field so that analysis could by made using the chemical shielding interaction because the 31P-1H dipolar interaction in phospholipid systems is complex and as such poorly understood. Nuclear Overhauser effect (NOE) studies have attempted to identify the important proton species contributing to the 31P-1H dipolar interaction (Yeagle, P. L., W. C. Hutton, C. Huang, and R. B. Martin. 1975. Biochemistry. 15:2121-2124) and despite some controversy in interpretation (Burns, R. A., R. E. Stark, D. A. Vidusek, and M. F. Roberts. 1983. Biochemistry. 22:5084-5090), it was generally agreed that the choline methyl and methylene protons are the major contributors to the 31P-1H NOE. To further understand the nature of the 31P-1H dipolar interaction, we carried out 31P-1H Transient Overhauser effect (TOE) measurements on egg phosphatidylcholine multilayers. Protons from both the lipids and water are important in understanding the TOE measurements in both D20 dispersions and H20 dispersions of egg PC. A quantitative analysis of the TOE has enabled the cross-relaxation rate between the phosphorus and the two proton types to be determined. It is suggested that these TOE experiments are a direct observation of the interaction between the phospholipid phosphate and surrounding water protons. The correlation time describing the relative motion of the phosphate group and the water molecules is on the order of 10- 11 s. The TOE measurements in phospholipid dispersions can be easily understood in terms of a straight forward model of the dipolar interaction and provide complementary information to NOE and T1 measurements.

Unique Backbone-Water Interaction Detected in Sphingomyelin Bilayers with 1H/31P and 1H/13C HETCOR MAS NMR Spectroscopy

“…One-dimensional 31 P magic-angle spinning (MAS) NMR techniques have been extensively applied to the study of lipid bilayer systems (24)(25)(26)(27)(28)(29)(30)(31)(32) and have been recently utilized to study raft formation in tertiary lipid systems containing cholesterol (33). A few reports on the application of two-dimensional 1 H/ 31 P heteronuclear Overhauser effect spectroscopy (HOESY) (26,34) have appeared on PC and phosphatidylethanolamine lipids, although the bulk of 31 P nuclear Overhauser effect (NOE) studies are of the one-dimensional variety (35)(36)(37)(38)(39)(40). NMR experiments involving 1 H/ 13 C cross-polarization (CP) have also been shown to be useful in the study of lipid membrane systems and have been implemented in both one-dimensional (25,(41)(42)(43)(44) and twodimensional (45)(46)(47) experiments.…”

Water–Surfactant Contact Studied by19F–1H Heteronuclear Overhauser Effect Spectroscopy

“…Those experiments often detected the heteronuclear cross-relaxation between water protons and nuclei of some nonprotonated atoms, such as the 13 C in the carboxylate group of octanoate (9,10) or the 31 P in the phosphate group of phosphatidylcholine (8), and provided information about the average water distance to those atoms.…”

“…The assignment given in Fig. 1 is based on the profound F 2 -F 4 -F 6 -F 8 and F 3 -F 5 -F 7 connectivities; the chain positions are numbered from the carboxylate carbon, and thus the first fluorine is F 2 and the last one is F 8 . Since signals from F 3 and F 5 coincide, only the sum of their intensities (F 3-5 ) can evidently be considered.…”

Imaging human teeth by phosphorus magnetic resonance with nuclear Overhauser enhancement

“…The NOE is the fractional change in the integrated NMR absorption intensity of a nuclear spin system upon saturation of neighbor-coupled spins 22 . 31 P NOE enhancement by 1 H irradiation has been widely reported for phosphate compounds in solutions 23 24 , but never in human mineralized tissue. In this study, a positive 1 H- 31 P NOE enhancement of the signal intensity in 31 P MR images is observed.…”