Slow motions in oriented phospholipid bilayers and effects of cholesterol or gramicidin. A 19F-NMR T1 rho study

Abstract

In an extension of our earlier work (Peng, Z.-y., V. Simplaceanu, I. J. Lowe, and C. Ho. 1988. Biophys. J. 54:81-95), the rotating-frame nuclear spin-lattice relaxation (T1 rho) technique has been used to investigate the slow molecular motions (10(-4) - 10(-6) s) in lipid bilayers prepared from protonated or perdeuterated 19F-labeled phospholipids in the absence and presence of cholesterol or gramicidin as membrane-interacting molecules. Complications caused by the 19F-1H cross-polarization observed previously can be removed by the substitution of 2H for 1H in the acyl chains. Only a weak dependence of the T-1(1 rho) on the locking field strength is found for a phospholipid molecule with perdeuterated acyl chains, indicating that there are no slow motions with a single, well-defined correlation time between 5 x 10(-6) and 4 x 10(-5) s. However, the orientation dependences of the T-1(1 rho) can be well fitted by motional models with either one slow motion having an unspecified geometry or with a superposition of two specific types of slow motions. Cholesterol and gramicidin show distinct effects in altering either the geometry or the weighting of slow motions in phospholipid bilayers, as reflected by changes in the orientation dependence. These two additives also exhibit quite different label-position specificities. A qualitative understanding of the induced effects of cholesterol and gramicidin on the dynamics of phospholipid bilayers will be discussed.

Lipid-cholesterol interactions. Monte Carlo simulations and theory

“…In addition to the above equilibrium measurements, there have been several NMR studies of the dynamical aspects of lipid-cholesterol interactions (7,8). These studies indicate that cholesterol strongly affects the slower, cooperative molecular motions of the lipids but has a smaller effect on the fast timescale motions.…”

Cross-Correlated 19F Relaxation Measurements for the Study of Fluorinated Ligand–Receptor Interactions

“…This arises from the secular spectral density contribution J CD u (0) shown in Eq. [5]. As a consequence, the magnitude of η xy increases with slower molecular tumbling (longer correlation time), and becomes amplified in the bound state.…”

“…The transverse rate constant η xy has a nearly linear dependence on τ c as a consequence of the secular J CD u (0) term in Eq. [5]. This implies a more efficient F x,y ↔ 2I z F x,y cross-relaxation for larger molecules.…”

“…The relaxation measurements have consisted of either standard auto-relaxation measurements (i.e., R 1 = 1/T 1 , R 2 = 1/T 2 , and R 1ρ = 1/T 1ρ ) or heteronuclear 19 F-1 H NOE measurements (see, e.g., (2,(5)(6)(7)(8)(9)(10)). However, studies of cross-correlated fluorine relaxation have been fewer and restricted mainly to theoretical analyses…”

A generalized approach for NMR studies of lipid–protein interactions based on sparse fluorination of acyl chains

“…5,6 Complementary studies on fluorinated lipids focused on analyzing lipid phase properties. [7][8][9][10] Use of fluorinated lipids and 19 F NMR to investigate protein-lipid interactions was suggested before, 11 but not explored presumably for technical deficiencies with regard to (i) preparing the required quantities of membrane protein with isotope enrichment and reconstituted in micelles or bicelles; (ii) synthesizing sparsely fluorinated lipids; and (iii) NMR methodology and hardware. Advances in these fields 12 now make it possible to develop the experimental approach delineated here.…”