Cholesterol Orientation and Dynamics in Dimyristoylphosphatidylcholine Bilayers: A Solid State Deuterium NMR Analysis

Abstract

Proton decoupled deuterium NMR spectra of oriented bilayers made of DMPC and 30 mol % deuterated cholesterol acquired at 76.8 MHz (30 degreesC) have provided a set of very accurate quadrupolar splitting for eight C-D bonds of cholesterol. Due to the new precision of the experimental data, the original analysis by. Biochemistry. 23:6062-6071) had to be reconsidered. We performed a systematic study of the influence on the precision and uniqueness of the data-fitting procedure of: (i) the coordinates derived from x-ray, neutron scattering, or force field-minimized structures, (ii) internal mobility, (iii) the axial symmetry hypothesis, and (iv) the knowledge of some quadrupolar splitting assignments. Good agreement between experiment and theory could be obtained only with the neutron scattering structure, for which both axial symmetry hypothesis and full order parameter matrix analysis gave satisfactory results. Finally, this work revealed an average orientation of cholesterol slightly different from those previously published and, most importantly, a molecular order parameter equal to 0.95 +/- 0.01, instead of 0.79 +/- 0.03 previously found for the same system at 30 degreesC. Temperature dependence in the 20-50 degreesC range shows a constant average orientation and a monotonous decrease of cholesterol Smol, with a slope of -0.0016 K-1. A molecular order parameter of 0.89 +/- 0.01 at 30 degreesC was determined for a DMPC/16 mol % of cholesterol.

Sterols and membrane dynamics

“…The same effect is reported using independently chain-labeled phospholipids or ring-labeled cholesterol. Using deuterium-labeled cholesterol offers the advantage of determining the average orientation of the fused ring system with respect to the bilayer normal [18,19]. Cholesterol sits perpendicular to the membrane surface and keeps this orientation independent of temperature [18].…”

The Potential of Fluorescent and Spin-labeled Steroid Analogs to Mimic Natural Cholesterol

“…Because the cholesterol analogs are relatively rigid molecules these distribution profiles determined from a single point on the molecules provide a measure for the amplitude of the transverse cholesterol motions. Although the anisotropic motions of cholesterol are rather complex (22,55,57), from the different transverse motions the suitability of a given cholesterol analog can be assessed.…”

Understanding Sterol‐Membrane Interactions, Part II: Complete 1H and 13C Assignments by Solid‐State NMR Spectroscopy and Determination of the Hydrogen‐Bonding Partners of Cholesterol in a Lipid Bilayer

“…Currently, most of solid-state NMR experiments on phospholipid/cholesterol systems have been focused on the phospholipid component or on the dynamics of cholesterol. [25,[30][31][32][33][34][35] However, chemical shifts are intimately related to the local environment around the nuclei and could reveal the nature of lipid-cholesterol interactions. In recent work, we have shown that the chemical shifts calculated by quantum-chemical methods could be used to reproduce experimental solution-state chemical shifts, both in the presence and in the absence of hydrogen bonds, with a satisfactory degree of accuracy.…”