Dynamics of phosphate head groups in biomembranes. Comprehensive analysis using phosphorus-31 nuclear magnetic resonance lineshape and relaxation time measurements

Abstract

Phospholipid head group dynamics have been studied by pulsed phosphorus-31 nuclear magnetic resonance (31P-NMR) of unoriented and macroscopically aligned dimyristoylphosphatidylcholine model membranes in the temperature range, 203-343 K. Lineshapes and echo intensities have been recorded as a function of interpulse delay times, temperature and macroscopic orientation of the bilayer normal with respect to the magnetic field. The dipolar proton-phosphorus (1H-31P) contribution to the transverse relaxation time, T2E, and to lineshapes was eliminated by means of a proton spin-lock sequence. In case of longitudinal spin relaxation, T1Z, the amount of dipolar coupling was evaluated by measuring the maximum nuclear Overhauser enhancement. Hence, the results could be analyzed by considering chemical shift anisotropy as the only relaxation mechanism. The presence of various minima both in T1Z and T2E temperature plots as well as the angular dependence of these relaxation times allowed description of the dynamics of the phosphate head group in the 31P-NMR time window, by three different motional classes, i.e., intramolecular, intermolecular and collective motions. The intramolecular motions consist of two hindered rotations and one free rotation around the bonds linking the phosphate head group to the glycerol backbone. These motions are the fastest in the hierarchy of time with correlation times varying from less than 10(-12) to 10(-6) s in the temperature range investigated. The intermolecular motions are assigned to phospholipid long axis rotation and fluctuation. They have correlation times ranging from 10(-11) s at high temperatures to 10(-3) s at low temperatures. The slowest motion affecting the 31P-NMR observables is assigned to viscoelastic modes, i.e., so called order director fluctuations and is only detected at high temperatures, above the main transition in pulse frequency dependent T2ECP experiments. Comprehensive analysis of the phosphate head group dynamics is achieved by a dynamic NMR model based on the stochastic Liouville equation. In addition to correlation times, this analysis provides activation energies and order parameters for the various motions, and a value for the bilayer elastic constant.

Lipid Internal Dynamics Probed in Nanodiscs

“…Upon increasing the temperature, a steep decrease is detected, which reflects the incoming large membrane dynamics that correspond to the L α fluid phase. For pure DMPC liposomes, a sharp transition is observed from gel to fluid phases and T m can be unambiguously determined from the inflection point at (20±1) °C, in accordance with the value reported for [D 54 ]DMPC (Figure 3, red line) 13. In the presence of cholesterol (Figure 3, red dotted line), the transition is less abrupt, which is also in accordance with the coexistence of several phases (liquid ordered, solid ordered, liquid disordered) over that temperature range.…”

“…Each vector bond gives rise to a characteristic Pake doublet, which is assignable to its C− 2 H pair along the acyl chain 8. Figure 2 shows selected spectra obtained below (Figure 2 A–D, 289 K) and above (Figure 2 E–H, 298 K) the melting temperature ( T m ) of pure and cholesterol‐doped deuterium‐labelled [D 54 ]DMPC liposomes [ T m =(293±1) K] 13. At 289 K, that is, below the T m , an axially asymmetric broad spectrum spanning about 120 kHz is observed for DMPC liposomes; this is typical for L β′ or gel phases (Figure 2 A).…”

Alamethicin Supramolecular Organization in Lipid Membranes from 19F Solid-State NMR

“…Thus, the Lb 0 phase exhibits a crystalline character, and at the higher temperatures of this phase, molecular fluctuations occur. When the temperature is further decreased to <260 K, the free rotation around the P-O bonds is quenched and only bond librations persist (58). These data show that at <250 K, dipolar spin diffusion remains the predominant mechanism of magnetization exchange, and at the same time fast rotation of the CF 3 group makes all three fluorine atoms magnetically equivalent (59).…”

Anionic Phospholipid Interactions of the Prion Protein N Terminus Are Minimally Perturbing and Not Driven Solely by the Octapeptide Repeat Domain

“…In particular, the order of the headgroups can be ascertained from broad line 31 P NMR (49), although relaxation measurements give an insight into the rates of motion of the headgroup (50). The width of the 31 P powder pattern indicates the phase of the lipids, with broader components corresponding to greater order, and narrow com- ponents indicate highly mobile species such as micelles undergoing isotropic motion.…”