NMR Studies of Membrane Structure and Dynamics

Bocian, David F.; Chan, Sunney I.

doi:10.1146/annurev.pc.29.100178.001515

Cited by 113 publications

(65 citation statements)

References 96 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Artificial lipid bilayers are frequently used as models of cell membranes for investigation of membrane properties and in studies of transmembrane proteins. Although a good deal is known about the structure of artificial membranes (6)(7)(8)(9)(10)(11)(12) and orientational and translational diffusion of lipids and other molecules (7,(13)(14)(15)(16), much less is known about the fast interior structural dynamics of the bilayers, which serve as the dynamic bath modes that can impact membrane processes.…”

mentioning

confidence: 99%

“…However, the results of various studies are not always consistent. Some groups have shown that curvature (vesicle size) does not influence the rates of lipid motions (26)(27)(28)(29) whereas others have provided evidence that there are significant changes with vesicle diameter (14)(15)(16). These are complex experiments, particularly when they recover information on ultrafast time scales that reflect structural fluctuations in contrast to slower processes of translational and orientational diffusion.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes

Kel

Tamimi

Fayer

2014

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

View full text Add to dashboard Cite

The ultrafast structural dynamics inside the bilayers of dilauroylphosphatidylcholine (DLPC) and dipalmitoylphosphatidylcholine vesicles with 70, 90, and 125 nm diameters were directly measured with 2D IR vibrational echo spectroscopy. The antisymmetric CO stretch of tungsten hexacarbonyl was used as a vibrational probe and provided information on spectral diffusion (structural dynamics) in the alkyl region of the bilayers. Although the CO stretch absorption spectra remain the same, the interior structural dynamics become faster as the size of the vesicles decrease, with the size dependence greater for dipalmitoylphosphatidylcholine than for DLPC. As DLPC vesicles become larger, the interior dynamics approach those of the planar bilayer.vesicle bilayer dynamics | vesicle size dependent dynamics | vesicles chainlength dependent dynamics T he plasma membrane provides a boundary between a living cell and its surroundings and between cellular compartments, providing organizational control of proteins and small molecules that are critical for achieving the complexity of biological systems. In addition to a permeability barrier, the second role of the plasma membrane is serving as the solvent for membrane proteins and other biomolecules. The lipid environment of membrane proteins can influence their function (1-5), and so impact cell signaling, metabolism, growth, defense, and a myriad of other biological functions.Membranes have a bilayer structure where the nonpolar chains of the lipids form the interior of bilayer, with zwitterionic or ionic head groups at the interfaces with water. Artificial lipid bilayers are frequently used as models of cell membranes for investigation of membrane properties and in studies of transmembrane proteins. Although a good deal is known about the structure of artificial membranes (6-12) and orientational and translational diffusion of lipids and other molecules (7, 13-16), much less is known about the fast interior structural dynamics of the bilayers, which serve as the dynamic bath modes that can impact membrane processes.Unilamellar vesicles (ULVs) of different sizes, as well as multilamellar vesicles (MLVs), are used as model membranes owing to their ease of preparation and handling. It has been shown that their properties depend on the curvature (size) (8,9,13,(17)(18)(19)(20). Aligned planar multi-bilayers (21) are membrane models that do not have curvature, yet they are less attractive for routine use because they are substantially more difficult to prepare than vesicles.Numerous experiments have been performed to determine which type of model bilayers most closely represents the properties of the plasma membrane. However, no consensus exists because the results obtained by different methods and groups are not in agreement. Some small-angle X-ray scattering and small-angle neutron scattering (SANS) experiments indicate that the structural properties of ULVs and MLVs are curvature independent, the overall bilayer thickness does not dependent on vesicle size, and the thicknesses of...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes

Kel

Tamimi

Fayer

2014

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

View full text Add to dashboard Cite

show abstract

“…The interpretation of NMR relaxation times in terms of lipid bilayer dynamics ultimately rests on the introduction of specific motional models, which must lead to experimentally testable predictions before their physical significance can be evaluated. Most recent literature discussions have tended to focus on one or more of the following paradigms: (i) simple isotropic or anisotropic diffusion models (9, 10) modified to include ordering effects (19)(20)(21), (ii) multiple internal rotation models for acyl chain dynamics (22)(23)(24), and (iii) simplified two-motion models in which the fast component is as in (i) and the slow component is identified either with "rigid body motions" (25,26) or with collective bilayer disturbances (12,27,28).…”

mentioning

confidence: 99%

“…The interpretation of 1H NMR results (9,25,26) is complicated by possible spin diffusion, together with uncertainties in separating intra-from intermolecular effects, making quantitative analysis difficult. Studies with 2H and '3C NMR avoid these difficulties, and 2H NMR, particularly, is widelv viewed as a promising technique because information on both molecular dvnamics and ordering can be obtained (19).…”

mentioning

confidence: 99%

New view of lipid bilayer dynamics from 2H and 13C NMR relaxation time measurements.

Brown¹,

Ribeiro²,

Williams³

1983

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

148

118

View full text Add to dashboard Cite

Natural abundance 13C spin-lattice (TI) relaxation time measurements are reported for unilamellar vesicles of 1,2-dipalmitoylphosphatidylcholine (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), in the liquid crystalline phase, at magnetic field strengths of 1. 40, 1.87, 2.35, 4.23, 7.05, 8.45, and 11.7 tesla (resonance frequencies of 15.0, 20.0, 25.1, 45.3, 75.5, 90.5, and 126 MHz, respectively), and the results are compared to previous 2H T, studies of multilamellar dispersions. For both the 13C and 2H T, studies, a dramatic frequency dependence of the relaxation was observed. At superconducting magnetic field strengths (4.23-11.7 tesla), plots of the 13C TF1 relaxation rates as a function of acyl chain segment position clearly reveal the characteristic "plateau" signature of the liquid crystalline phase, as found previously from 2H NMR studies. The dependence of Tj ' on ordering, determined previously from 2H NMR, and the Tj' dependence on frequency, determined from both '3C and 2H NMR studies, suggest that a unified picture of the bilayer molecular dynamics can be provided by a simple relaxation law of the form T' l ATf + BS2 H W-'1/2. In the above expression, A and B are constants, SCH (=SC-D) is the bond segmental order parameter, and of is the nuclear Larmor frequency. The first (A) term includes contributions from fast, local segmental motions characterized by the effective correlation time Tf, whereas the second (B) term describes slower, collective fluctuations in the local ordering. The value of Tf 10-11 sec, obtained by extrapolating Tj' to infinite frequency, suggests that the segmental microviscosity of the bilayer hydrocarbon region does not differ appreciably from that of the equivalent n-paraffinic liquids of similar chain length.NMR techniques were among the first biophysical methods to be applied to lipid bilayers and biological membranes (1, 2). Perhaps the foremost progress in recent years has been made in applications of NMR lineshape analysis to studies of the molecular ordering and conformations of membranous lipids (3-7). Yet, in spite of early promise (8-11), the interpretation of nuclear spin relaxation experiments has not progressed similarly and, in fact, has remained an outstanding problem in membrane biophysics for more than a decade (cf. ref. 12). The bulk of previous work has involved spin-lattice (TI) relaxation time measurements, which are sensitive to details of the molecular motions in the MHz region. Perhaps the major justification for T, relaxation studies of membranes is their dual character as both solid-like and liquid-like materials. The analogies to simpler liquid crystals point to the necessity of obtaining both static and dynamic information in defining these systems and of distinguishing membranes from other classes of biological macromolecules, such as the globular and fibrous proteins and the nucleic acids. These latter biopolymers, while also rich in dvnamic behavior (13,14), appear to have fairly well-defined average structures that can be directly re...

show abstract

“…In the intervening years, NMR spectroscopy has been used in-vitro and in-vivo to study enzymatic reactions (8,9); measure intracellular pH (10,11); study cell membranes (12)(13)(14); follow metabolic pathways in normal, ischemic and neoplastic states (15)(16)(17)(18); and monitor pharmaceutical interventions (19,20). Nuclei investigated include P-31, H-l, C-13, F-19, Na-23, and C1-35.…”

Section: Thank Youmentioning

confidence: 99%

NMR chemical shift imaging

Brink

Buschmann

Rosen

1989

Computerized Medical Imaging and Graphics

View full text Add to dashboard Cite

Medical Engineering and Medical PhysicsI. ABSTRACT Methods of obtaining nuclear magnetic resonance (NMR) images containing chemical shift information are presented. Using a three-dimensional Fourier Transform approach (two spatial axes and one resonance frequency axis), proton chemical shift images were acquired in phantoms and in-vivo using both spin echo and free induction decay (FID) pulse sequences. A proton resonance frequency of 61.5 MHz, corresponding to a magnetic field strength of 1.44 tesla, was used. In simple phantoms, chemical shift images indicate that spectral resolution of 0.7 parts per million (ppm) is readily achieved at all locations within the image matrix, even when using a magnet not specifically designed for chemical shift spectroscopy. In-vivo images of normal human forearms and cat heads yield separable signals from water and lipid protons. In the cat brain, no appreciable NMR signal originates from membrane lipids (e.g., myelin); images acquired using FID pulse sequences imply T 2 relaxation times less than 2 msec for these protons. The measurement of magnetic susceptibility using this technique is also demonstrated. The effect of susceptibility variations in-vivo appears in general to be less than 1 ppm.Proton chemical shift imaging was used to study fatty liver change in the rat. The correlation between lipid group signal intensity from chemical shift images i'n-viv and liver triglyceride levels measured in-vitro was good (r = .97). In-vivo T 1 relaxation time measurements were made on lipid and water protons separately. Values calculated were corrected for the influence of gaussian plane selection and spin echo data acquisition, and demonstrate different T 1 times reflecting two distinct populations of non-exchanging protons. Proton chemical shift imaging offers enhanced sensitivity over conventional NMR imaging techniques in characterizing fatty liver disease.Selective saturation (solvent suppression) techniques were used in an imaging context in both phantoms and in-vivo. Using a three-dimensional chemical shift imaging approach, data presented demonstrate the feasibility of imaging proton metabolites at low concentration. Phantom studies without solvent suppression failed to detect lactate at 80 mM; however with solvent suppression, lactate at 40 mM was imaged in a reasonable time (approximately 50 minutes). Using a conventional two-dimensional NMR imaging technique preceded by a selective (saturating) pulse, signal from water or lipid protons were eliminated (>95% reduction in signal intensity), resulting in images of -CH 2 -or H 2 0 proton distribution with resolution and imaging times equivalent to conventional proton images. With improvements in imaging systems, these techniques may play an important role in the non-invasive evaluation of tissue ischemia using proton NMR. where Y is the gyromagnetic ratio (defined as the ratio of the nuclear magnetic moment to the spin angular momentum) and B is the magnetic field seen by the nucleus (5). This B field is traditionally rewritte...

show abstract

NMR Studies of Membrane Structure and Dynamics

Cited by 113 publications

References 96 publications

Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes

Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes

New view of lipid bilayer dynamics from 2H and 13C NMR relaxation time measurements.

NMR chemical shift imaging

Contact Info

Product

Resources

About