A Study of the Angular Dependence of NMR Relaxation Times in Macroscopically Oriented Lyotropic Liquid Crystal Lamellar Phases

Proc. Natl. Acad. Sci. U.S.A.

Simplăceanu²,

Dowd³

et al. 1989

Nuclear spin-lattice relaxation both in the rotating frame and in the laboratory frame is used to investigate the slow and fast molecular motions of phospholipids in oriented bilayers in the liquid crystalline phase. The bilayers are prepared from a perdeuterated phospholipid labeled with a pair of 'IF atoms at the 7 position of the 2-sn acyl chain.Phospholipid-cholesterol or phospholipid-gramicidin interactions are characterized by measuring the relaxation rates as a function of the bilayer orientation, the locking field, and the temperature. Our studies show that cholesterol or gramicidin can specifically enhance the relaxation due to slow motions in phospholipid bilayers with correlation times Ts longer than 10-8 sec. The perturbations of the geometry of the slow motions induced by cholesterol are qualitatively different from those induced by gramicidin. In contrast, the presence of cholesterol or gramicidin slightly suppresses the fast motions with correlation times if = 10-9 to 10-10 sec without significantly affecting their geometry. Weak locking-field and temperature dependences are observed for both pure lipid bilayers and bilayers containing either cholesterol or gramicidin, suggesting that the motions of phospholipid acyl chains may have dispersed correlation times.To establish a relationship among the structure, dynamics, and function of biological membranes requires knowledge of (i) the packing and motion of phospholipid molecules in a membrane and (ii) the mechanisms for lipid-sterol and lipidprotein interactions. During the last three decades, considerable efforts have been devoted to the biophysical studies of phospholipid bilayers, which are often viewed as a simplified model of natural membranes (1). Although the static properties of a lipid bilayer, such as the conformation and order ofphospholipids, have been carefully characterized (2, 3), the dynamic behavior of phospholipids in a bilayer environment is less well understood (4).The physical state of a phospholipid bilayer under physiological conditions is that of a lyotropic liquid crystal surrounded by water molecules. Due to the amorphous packing and prevalence of molecular motions, high-resolution x-ray diffraction cannot be applied to lipid bilayers in a liquid crystalline phase. Hence, magnetic resonance, which can give both static and dynamic information, is of vital importance in the field of membrane biophysics. In particular, when combined with isotopic labeling, nuclear relaxation becomes a unique technique which can monitor the microscopic dynamics of a specific site within a macromolecule or a supermolecular assembly. Normally, the spin-lattice relaxation in the laboratory frame (T1) is sensitive to molecular motions on the time scale of 10-1o to 10-1 sec, while the spin-lattice relaxation in the rotating frame (T1p) is sensitive to motions on the time scale of 10-6 to 10-4 sec (5).A number of nuclear magnetic resonance (NMR) investigations have focused on the molecular motions of phospholipids in a pure lipid bilayer, an...

mentioning

confidence: 99%

Effects of cholesterol or gramicidin on slow and fast motions of phospholipids in oriented bilayers.

Proc. Natl. Acad. Sci. U.S.A.

Simplăceanu²,

Dowd³

et al. 1989

“…It is quite likely that this term exhibits a different orientation dependence compared with the relaxation caused by the local modulation of the orientation of a particular CF2 group. The second reason can also be used to explain the lack of agreement between the orientation dependence of oriented 2-[7,7-'9F2]DMPC-d52 bilayers and the orientation dependence of 'H Tp' reported by Pope et al (1982). In their case, the relaxation originates from the dipolar interactions among all the protons in the molecule.…”

Section: Differences Between Protonated and Perdeuterated Lipidsmentioning

confidence: 95%

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

Tjandra

Simplăceanu

et al. 1989

Biophysical Journal

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.

“…This is also true in the case of the rotating-frame relaxation rate (T -') versus the locking field (HI) for multilamellar liposomes (Fisher and James, 1978). Secondly, the locking-field dependence of the proton rotating-frame spin-lattice relaxation rate of oriented lipid bilayers (Cornell and Pope, 1980;Pope et al, 1982) has been found to be well fitted by the conventional Lorentzian relaxation model with a single correlation time, and, combined with the orientation dependence of the relaxation rate, these data have been interpreted in terms of relaxation through a modulation of intermolecular interactions (Pope et al, 1982).…”

Section: Introductionmentioning

confidence: 91%

“…The slow molecular motions of phospholipids have been investigated by NMR using line-shape analysis (Campbell et al, 1979;Huang et al, 1980), spin-lattice relaxation either in low to medium magnetic fields or in the rotating frame (Fisher and James, 1978;Cornell and Pope, 1980;Pope et al, 1982;Kimmich et al, 1983;Brown et al, 1983 and1986), and spin-spin relaxation (Bloom and Sternin, 1987). Previous relaxation studies of slow motions have led to a few controversial conclusions.…”

Section: Introductionmentioning

confidence: 99%

“…Clear-ly, one has the ability to monitor the slow motions at a specific chain position, thus the model fitting can be more precise and changes of the motion along the acyl chain can be observed. Previous relaxation experiments covering a similar time scale were limited to the 'H nucleus, which can only give relaxation rates averaged over the entire molecule, because many of the individual proton resonances overlap (Fisher and James, 1978;Cornell and Pope, 1980;Pope et al, 1982;Kimmich et al, 1983). Another advantage is that the large chemical shift anisotropy (CSA) of the CF2 group allows us to consider only the intramolecular interactions in analyzing our relaxation data.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Rotating-frame relaxation studies of slow motions in fluorinated phospholipid model membranes

Simplăceanu

Lowe

et al. 1988

Biophysical Journal

Rotating-frame relaxation experiments have been carried out on 19F-labeled dimyristoylphosphatidylcholine model membranes. The lipids are labeled with a single CF2 group in the 4-, 8-, or 12-position of the 2-acyl chain. Both oriented lipid bilayers and multilamellar liposomes have been investigated. The relaxation rate has been measured as a function of the locking-field strength, the sample orientation, the label position, and the temperature. Our results have confirmed that extensive slow motions exist in the bilayer and dominate the low-frequency relaxation. The relaxation rate is quite sensitive to the label position. However, many other features of the relaxation are very similar for all three lipid isomers. The temperature dependence of the relaxation rate for the multilamellar liposomes differs from the oriented bilayers, which may imply that the motions are also different. To fit our data, a working model consisting of a superposition of an anisotropic reorientation term and a director fluctuation term has been proposed. We have also verified that almost all of the relaxation process is caused by modulations of the intramolecular interactions. Based on this, a view of the slow motions at a molecular level is discussed in this paper.