| 41. |
- Orädd, Greger, et al.
(författare)
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Lateral diffusion coefficients of separate lipid species in a ternary raft-forming bilayer: A Pfg-NMR multinuclear study
- 2005
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Ingår i: BIOPHYSICAL JOURNAL. - : Elsevier BV. - 0006-3495. ; 89:1, s. 315-20
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Tidskriftsartikel (refereegranskat)abstract
- By isotopical labeling lipid lateral diffusion coefficients for each of the membrane constituents, including cholesterol, have been measured by H-1, H-2, and F-19 pulsed field gradient NMR spectroscopy in macroscopically oriented lipid bilayers. This provides a means of obtaining detailed dynamic and compositional information in raft-forming lipid bilayers without introducing foreign molecules into the systems. The raft systems studied contained dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DPPC)/cholesterol at the molar ratios of 42.5: 42.5: 15 and 35: 35: 30 in excess water. At temperatures below 30 degrees C the raft system forms large (>1 mu m) domains of a liquid ordered (l(o)) phase, in which the lipid lateral diffusion was; 5 times slower than for the lipids in the surrounding liquid disordered (l(d)) phase. Within each domain all lipid species showed the same diffusion coefficient, despite the very different structures of cholesterol and phospholipids. DPPC partitions exclusively into the l(o) domains, whereas cholesterol and dioleoylphosphatidylcholine were distributed in both l(o) and l(d) phases. The cholesterol concentration was found to be 10-20 mol% in the l(d) domain and 30-40 mol% in the l(o) domain. Comparison of these results with data from sphingomyelin-containing systems suggests that DPPC interacts more weakly with cholesterol than does sphingomyelin.
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| 42. |
- Orädd, Greger, et al.
(författare)
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Lateral Diffusion of Cholesterol and Dimyristoylphosphatidylcholine in a Lipid Bilayer Measured by Pulsed Field Gradient NMR Spectroscopy
- 2002
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Ingår i: Biophys Journal. ; 83:5, s. 2702-4
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Tidskriftsartikel (refereegranskat)abstract
- The pulsed field gradient NMR method for measuring self-diffusion has been used for a direct determination of the lateral diffusion coefficient of cholesterol, fluorine labeled at the 6-position, for an oriented lamellar liquid-crystalline phase of dimyristoylphosphatidylcholine (DMPC)/cholesterol/water. It is found that the diffusion coefficients of DMPC and cholesterol are equal over a large temperature interval. The apparent energy of activation for the diffusion process (58 kJ/mol) is about the same as for a lamellar phase of DMPC/water, whereas the phospholipid lateral diffusion coefficient is approximately four times smaller in the presence of cholesterol.
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| 43. |
- Orädd, Greger, et al.
(författare)
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Lateral diffusion studied by pulsed field gradient NMR on oriented lipid membranes
- 2004
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581. ; 42:2, s. 123-31
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Tidskriftsartikel (refereegranskat)abstract
- This mini-review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is proposed to have appreciable potential for future biophysical investigations in the field of membrane biology. Topics such as transport of molecules both across and in the plane of the membrane can be successfully studied, and the formation of lipid domains and their intrinsic dynamics can also be scrutinized. First, a short introduction to the NMR technique is given together with a brief discussion on methods of obtaining a good bilayer orientation. Then, a number of recent results on biophysical/biological membrane systems of great interest is presented, in which some unique conclusions on so-called raft membranes are reached. It is shown for systems with large two-phase areas of liquid disordered and liquid ordered phases that lipid lateral diffusion is faster in the former phase and has a smaller apparent activation energy. Further, on the time-scale of the experiments (50-250 ms), exchange between the two phases is fast in the phospholipid-cholesterol-water ternary system, whereas it is slow in the sphingomyelin-dioleoylphosphatidylcholine-cholesterol-water quaternary system.
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| 44. |
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| 45. |
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| 46. |
- Orädd, Greger, 1961-
(författare)
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NMR diffusion studies on lyotropic liquid crystalline systems
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The pulsed field gradient fourier transform nuclear magnetic resonance (PFG-FTNMR) method to measure translational diffusion coefficients in multicomponent systems has been applied to amphiphilic molecules forming liquid crystalline phases.By analyzing the concentration dependence of the diffusion coefficients of water and amphiphile in a micellar system of N,N-dimethyldodecy lamine oxide (DDAO) in water it was possible to conclude that the micelles formed were polydisperse in size and shape. It was also shown that solubilization of small amounts of hydrophobic molecules into the micelles induces spherical micelles of a narrow size distribution. From the magnitude of the lateral diffusion coefficient in the cubic phase of DDAO/water it was concluded that this phase is built up of bicontinous aggregates.The lipid lateral diffusion in the cubic phase of monooleoylglycerol (MO)/water has been measured. The decrease in the lateral diffusion of MO in this phase, when the water was replaced by glycerol, was ascribed to changes in viscosity in the polar region. Measurements by electron spin resonance and time-resolved fluorescence spectroscopy showed that changes in viscosity of the solvent also affected the motions in the hydrocarbon region.The diffusion coefficients of all three components in the cubic phase located in the lowwater region of the ternary system of diacylglycerol (DAG)/soybean phosphatidylcholine (SPC)/water have been determined. Conclusive evidence was provided for that this cubic phase is built up of reversed micelles containing mainly SPC in a continous matrix of mainly DAG.The effect on the phase properties of DDAO upon incorporation of the peptide gramicidin D has been investigated. It was shown that gramicidin D induces a lamellar phase at all water contents. The change in the order parameter profile of the C-2H bonds in perdeuterated DDAO upon incorporation of gramicidin D is compatible with theoretical calculations for proteins exhibiting a positive hydrophobic mismatch.A method for using the PFG FTNMR technique in measurements of the transmembrane exchange rate of small molecules in vesicular suspensions is discussed and some preliminary data is shown.
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| 47. |
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| 48. |
- Orädd, Greger, et al.
(författare)
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NMR studies of binary and ternary systems of phosphatidylcholines
- 2007
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Ingår i: European Biophysics Journal, 2007 July, Volume 36, Supplement 1. ; , s. 1-278
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lipid lateral segregation in biomimicking model membranes has recently become a topic of great interest due to the biological coupling to the concept of functional rafts. In the studies of liquid-liquid phase coexistence it is found that lateral phase separation into liquid ordered and liquid disordered phases takes place in ternary systems consisting of one unsaturated and one saturated lipid, together with a sterol. The phase behavior is critically dependent on the components with respect to chain length, degree of unsaturation and sterol structure and the driving force of the phase separation is closely related to the ordering effect of the sterol on the lipid chains. This study presents NMR data for binary and ternary systems composed of mixtures of sphingomyelins, phosphatidylcholines and cholesterol. Order parameters were obtained from perdeuterated chains in the saturated lipid and diffusion data of both the saturated and unsaturated lipids were measured with the pulsed field gradient NMR method. Data were analyzed with regard to phase separation into liquid and solid phases.
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| 49. |
- Orädd, Greger, et al.
(författare)
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NMR Studies of Lipid Lateral Diffusion in the DMPC/Gramicidin D/Water System: Peptide Aggregation and Obstruction Effects
- 2004
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495. ; 87, s. 980-7
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Tidskriftsartikel (refereegranskat)abstract
- The PFG-NMR method has been used in macroscopically oriented bilayers to investigate the effect of the peptide gramicidin D on the lateral diffusion of dimyristoylphosphatidylcholine. By varying both the temperature (21–35°C) and the gramicidin content (0–5 mol %) we have introduced solid obstacles into the lipid liquid crystalline bilayer. It was shown that the obstruction effect exerted by the peptide can be described with several different theoretical models, each based on different premises, and that the fit of the models to experimental data gave reasonable results. We found that each gramicidin molecule was surrounded by approximately one layer of bound lipids and that the obstruction from gel phase patches can be described as small solid obstacles. No evidence of linear aggregates of gramicidin, such as those reported by atomic force microscopy in the gel phase, was found.
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| 50. |
- Orädd, Greger
(författare)
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NMR Studies of Oriented Domain-Forming Model Membranes
- 2007
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Ingår i: Bioactive Lipids in the Lipidomics Era (C2).
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Summary of MeetingThe identification of many receptors and targets of bioactive lipid mediators has led to research uncovering their roles in regulating many important normal and pathophysiological processes. It has become evident that the biological activities and functions of lipid signaling molecules are dependent on both their molecular structures and complex cell-specific interactions among the different pathways involved in their biosynthesis and metabolism. The growing complexity of these interactions and the thousands of cellular lipids, together with genomics and proteomics technology already in place, has emphasized the need for development of complementary lipidomics technology. The goal of this meeting is to bring investigators studying signaling and metabolism of bioactive lipids together with researchers who are now developing lipidomics methods for exhaustive characterization and systematic measurement by mass spectrometry of the lipidome, ie cellular lipids, their precursors and their metabolites. The program of this meeting has been designed to foster and synergize research in these areas.
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