Elucidation of slow motions in glycoglycerolipid bilayers by two-dimensional solid-state deuteron NMR

Membrane solid-state NMR in Canada: A historical perspective

This manuscript presents an overview of more than 40years of membrane solid-state nuclear magnetic resonance (NMR) research in Canada. This technique is a method of choice for the study of the structure and dynamics of lipid bilayers; bilayer interactions with a variety of molecules such as membrane peptides, membrane proteins and drugs; and to investigate membrane peptide and protein structure, dynamics, and topology. Canada has a long tradition in this field of research, starting with pioneering work on natural and model membranes in the 1970s in a context of emergence of biophysics in the country. The 1980s and 1990s saw an emphasis on studying lipid structures and dynamics, and peptide-lipid and protein-lipid interactions. The study of bicelles began in the 1990s, and in the 2000s there was a rise in the study of membrane protein structures. Novel perspectives include using dynamic nuclear polarization (DNP) for membrane studies and using NMR in live cells. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.

Measurement of the lateral diffusion of dipalmitoylphosphatidylcholine adsorbed on silica beads in the absence and presence of melittin: a 31P two-dimensional exchange solid-state NMR study

31P two-dimensional exchange solid-state NMR spectroscopy was used to measure the lateral diffusion, D(L), in the fluid phase of dipalmitoylphosphatidylcholine (DPPC) in the presence and absence of melittin. The use of a spherical solid support with a radius of 320 +/- 20 nm, on which lipids and peptides are adsorbed together, and a novel way of analyzing the two-dimensional exchange patterns afforded a narrow distribution of D(L) centered at a value of (8.8 +/- 0.5) x 10(-8) cm2/s for the pure lipid system and a large distribution of D(L) spanning 1 x 10(-8) to 10 x 10(-8) cm2/s for the lipids in the presence of melittin. In addition, the determination of D(L) for nonsupported DPPC multilamellar vesicles (MLVs) suggests that the support does not slow down the lipid diffusion and that the radii of the bilayers vary from 300 to 800 nm. Finally, the DPPC-melittin complex is stabilized at the surface of the silica beads in the gel phase, opening the way to further study of the interaction between melittin and DPPC.

Phases and phase transitions of the glycoglycerolipids

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. The database is considered comprehensive for glycerophospholipids, glycoglycerolipids, sphingolipids and natural membrane extracts. Here, a review of the LIPIDAT data subset referring to glycoglycerolipids is presented together with an analysis of these data. The glycoglycerolipids subset represents 4% of all LIPIDAT records. It includes data collected over a 20-year period and consists of 419 records obtained from 37 articles in 13 journals. An analysis of the data in the subset has allowed us to identify trends in hydrated glycoglycerolipids phase behavior reflecting differences in hydrocarbon chain length, chain branching, chain-glycerol linkage type (ether vs. ester), sugar headgroup-glycerol linkage type (alpha vs. beta) and sugar headgroup identity. Included is a summary of the data concerning the effect of pH and of stereochemical purity on glycoglycerolipid phase behavior. Information on the mesomorphism of biologically derived and dry glycoglycerolipids is also presented. This review includes 92 references.

Effect of calcium on the dynamic behavior of sialylglycerolipids and phospholipids in mixed model membranes. A 2H and 31P NMR study

DTSL, a sialic acid bearing glyceroglycolipid, has been deuteriated at the C3 position of the sialic acid headgroup and at the C3 position of the glycerol backbone. The glycolipid was studied as a neat dispersion and in multilamellar dispersions of DMPC (at a concentration of 5-10 mol % relative to phospholipid), using 2H and 31P NMR. The quadrupolar splittings, delta v Q, of the headgroup deuterons were found to differ in the neat and mixed dispersion, suggesting different headgroup orientations in the two systems. In DTSL-DMPC liposomes, two quadrupolar splittings were observed, indicating that the axial and equatorial deuterons make different angles with respect to the axis of motional averaging. The splittings originating from the equatorial and axial deuterons were found to increase and decrease with increasing temperature, respectively, indicating a temperature-dependent change in average headgroup orientation. Longitudinal relaxation times, T1Z, were found to be short (3-6 ms). The field dependence of T1Z suggests that more than one motion governs relaxation. At 30.7 MHz a T1Z minimum was observed at approximately 40 degrees C. At 46.1 MHz the T1Z values were longer and increased with temperature, demonstrating that the dominant rigid-body motions of the headgroup at this field are in the rapid motional regime (greater than 10(8) s-1). DTSL labeled at the glycerol C3 position was studied in DMPC multilamellar dispersions. Whereas two quadrupolar splittings have been observed for other glycolipids labeled at this position, only a single delta nu Q was observed. This shows that the orientation of the C2-C3 segment of DTSL relative to the bilayer normal differs from that of other glycolipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular details of anesthetic-lipid interaction

By means of isotopic labeling with deuterium (2H) and observation by nuclear magnetic resonance (NMR), it has been possible to measure the conformational ordering and dynamics of lipids and anesthetics in membranes. The local anesthetic tetracaine causes disordering in the acyl chains of the lipids, very little effect near the glyceryl residue, and minor ordering effects in the charged head group. The anesthetic itself is well ordered within the lipid matrix. The magnitudes of these effects depend upon the nature of the lipid, and upon whether or not the anesthetic is charged. A model can be constructed for the location of the anesthetic within the lipid bilayers. Confirmation of the model comes from Fourier transform infrared spectroscopy (FTIR), which also shows directly the pressure-driven exclusion of local anesthetic from lipid, and the augmentation of this effect by the presence of cholesterol. Future studies by solid-state NMR of protein, and neutron diffraction of specifically deuterated components of anesthetic-nerve systems, should reveal even more precise details of the molecular events involved in anesthesia.

Physical properties of glycosyldiacylglycerols: an infrared spectroscopic study of the gel-phase polymorphism of 1,2-di-O-acyl-3-O-(beta-D-glucopyranosyl)-sn-glycerols

The thermotropic and barotropic gel-phase polymorphism of a homologous series of saturated, straight-chain beta-D-glucosyldiacylglycerols was studied by Fourier transform infrared spectroscopy. Three spectroscopically distinct lamellar gel phases were detected thermotropically. Upon cooling to temperatures below the gel/liquid-crystalline phase transition temperature, all of these lipids form a metastable L beta gel phase characterized by orientationally disordered all-trans acyl chains. The transformation of the metastable L beta phase to a stable crystalline (Lc2) phase first involves the formation of an intermediate which itself is an ordered crystal-like (Lc1) phase. In the intermediate Lc1 phase, the zigzag planes of the polymethylene chains are nearly perpendicular to one another, and one of the ester carbonyl oxygens is engaged in a strong hydrogen bond, probably to the 2-hydroxyl of the sugar headgroup. The transformation of the Lc1 phase to the Lc2 phase involves a reorientation of the all-trans hydrocarbon chains and is probably driven by the strengthening of the hydrogen bond between the carbonyl ester oxygen and its proton donors. Since a "solid-state" reorganization of the acyl chains is an integral part of that process, it tends to become more sluggish as the chain length increases and is not observed with the longer chain homologues (N greater than 16). The spectroscopic characteristics of the most stable gel phases of the odd- and even-numbered members of this homologous series of compounds exhibit only minor differences, indicating that the structures of these phases are generally similar. The barotropic phase behavior of the shorter and longer chain beta-D-glucosyldiacylglycerols is also different. Compression of the L beta phase of the shorter chain compounds results in immediate conversion to their stable lc phases, whereas compression of the L beta phase of the longer chains does not. Furthermore, compression of the longer chain compounds may result in the formation of chain-interdigitated bilayers, whereas this is not the case for the shorter chain homologues. We suggest that the gel phase formed by any given homologue at a given temperature or pressure is that which maximizes the sometimes competing requirements for the optimal packing of the sugar headgroups and the hydrocarbon chains.

Glycerolipids: common features of molecular motion in bilayers

In the present study, analysis of 2H NMR line-shape and spin-lattice relaxation behavior has been used to investigate the dynamics of several glycolipid and phospholipid bilayers. The gel-phase spectra of these lipids labeled at the C3 position of the glycerol backbone are broad (approximately 90 kHz) and characteristic of fast-limit axially asymmetric motion. Moreover, anisotropic spin-lattice relaxation is observed in all of these systems. The line-shape and relaxation features of the lipids in the gel phase were best simulated by using a fast-limit three-site jump model, with relative site populations of 0.46, 0.34, and 0.20. This motion is associated with an internal jump about the C2-C3 bond of the glycerol backbone. A second motion, rotation about the long axis of the molecule, is needed to account for the observed temperature dependence of the quadrupolar echo amplitude and the spectral line shape above and below the gel to liquid-crystalline phase transition temperature. On the other hand, the gel-phase spectra of phospholipids labeled at the C2 position of the glycerol backbone are also characterized by a fast internal motion, which is simulated by a two-site librational jump. The results indicate that the glycerol backbone dynamics of the glycolipid and phospholipid systems investigated in this study can be described in terms of common fast internal motions and a slower whole molecule axial motion. These results are compared with previous dynamic studies of similar systems.