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- Andersson, August, et al.
(författare)
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Magnetic resonance investigations of lipid motion in isotropic bicelles
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 21:7, s. 7702-7709
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.
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| 4. |
- Andersson, August, 1974-
(författare)
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The Application of isotropic bicelles as model membranes
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Isotropic bicelles are disc-shaped aggregates of lipids and detergents, and are suitable model systems for high-resolution NMR studies of membrane-interacting peptides. In this thesis the structures for the two peptides motilin and transportan were determined by homonuclear 1H methods in the presence of bicelles, and the structure of the bovine prion protein peptide (bPrPp) was solved in the presence of DHPC micelles. All of these peptides were found to be largely a-helical when bound to the model membranes. In subsequent experiments both motilin and transportan were shown to reside on the surface of the bicelles, whereas bPrPp is more likely to have a transmembrane configuration. NMR translational diffusion experiments revealed that the isotropic bicelles studied here are very large objects compared to what is regularly indicated by high-resolution NMR spectroscopy. Furthermore, these studies showed that all three peptides examined interact strongly with bicelles. Investigation of the NMR-relaxation of labeled sites in the peptides motilin and penetratin demonstrated that the overall rotational correlation times for these peptides do not reflect the bicellar size. Such decoupling of NMR relaxation from the dependence of overall size is also seen for the dynamics of the lipid molecules in the bicelles. It is therefore concluded that the overall size is not the sole determinant of the linewidths in NMR spectra, but that extensive motions within the bicelles also exert significant effects. Another interesting observation is that the membrane-bound structures of the peptides motilin, transportan, penetratin and bPrPp are very similar, even though these peptides have very different biological functions. In contrast, considerably more variation is observed in the membrane-positioning and molecular dynamics of these peptides. Since the bicelles have been found to induce differences in membrane positioning and molecular dynamics compared to micelles, these model membranes are likely to be important in order to enhance our understanding of the biological function of membrane interacting peptides.
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- Bárány-Wallje, Elsa, et al.
(författare)
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Dynamics of transportan in bicelles is surface charge dependent.
- 2006
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Ingår i: J Biomol NMR. - 0925-2738. ; 35:2, s. 137-47
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigated the dynamic behavior of the chimeric cell-penetrating peptide transportan in membrane-like environments using NMR. Backbone amide 15N spin relaxation was used to investigate the dynamics in two bicelles: neutral DMPC bicelles and partly negatively charged DMPG-containing bicelles.The structure of the peptide as judged from CD and chemical shifts is similar in the two cases. Both the overall motion as well as the local dynamics is, however, different in the two types of bicelles. The overall dynamics of the peptide is significantly slower in the partly negatively charged bicelle environment, as evidenced by longer global correlation times for all measured sites.The local motion, as judged from generalized order parameters, is for all sites in the peptide more restricted when bound to negatively charged bicelles than when bound to neutral bicelles (increase in S2 is on average 0.11±0.07). The slower dynamics of transportan in charged membrane model systems cause significant line broadening in the proton NMR spectrum, which in certain cases limits the observation of 1H signals for transportan when bound to the membrane. The effect of transportan on DMPC and DHPC motion in zwitterionic bicelles was also investigated, and the motion of both components in the bicelle was found to be affected.
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- Bárány-Wallje, Elsa, et al.
(författare)
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NMR solution structure and position of transportan in neutral phospholipid bicelles.
- 2004
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Ingår i: FEBS Lett. - 0014-5793. ; 567:2-3, s. 265-9
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Tidskriftsartikel (refereegranskat)abstract
- Transportan is a chimeric cell-penetrating peptide constructed from the peptides galanin and mastoparan, which has the ability to internalize living cells carrying a hydrophilic load. In this study, we have determined the NMR solution structure and investigated the position of transportan in neutral bicelles. The structure revealed a well-defined -helix in the C-terminal mastoparan part of the peptide and a weaker tendency to form an -helix in the N-terminal domain. The position of the peptide in relation to the membrane, as studied by adding paramagnetic probes, shows that the peptide lies parallel to, and in the head-group region of the membrane surface. This result is supported by amide proton secondary chemical shifts.
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- Strömqvist, Johan, 1976-, et al.
(författare)
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Nitroxide Spin-Label Quenching of Fluorophore’s Triplet Stateas a Tool for Studying Diffusion Mediated Reactions in LipidMembranes
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Annan publikation (populärvet., debatt m.m.)abstract
- In this work, we introduce an approach to study bimolecularinteractions in model lipid bilayers and biologicalmembranes, which exploits the influence of membrane-associatedElectron Spin Resonance (ESR) labels on the fluorescencesignal of likewise membrane-bound fluorophoremarkers. It is shown how one can exploit the high detectionsensitivity of the fluorescence signal without loosing the abilityto follow low-frequency molecular interactions, takingplace on a time scale well beyond that of the fluorescencelifetimes. The approach utilizes triplet state monitoring byFluorescence Correlation Spectroscopy (FCS), whereby thefluctuations in a strong fluorescence signal is used to characterizetransition rates to and from the lowest triplet stateof the fluorophores, which take place on a time scale 3 to 6orders of magnitude slower than the fluorescence lifetimesof the fluorophores. FCS measurements were performed onthe dye Lissamine Rhodamine B (LRB) in aqueous solutionsand bound to a lipid in a liposome, and in the presence of differentlocal concentrations of the ESR label TEMPO. Bothin the aqueous solution and in the lipid membrane measurements,the measured relative changes in the singlet-triplettransitions rates were found to well reflect the collisionalfrequencies between the LRB and TEMPO molecules. Theproposed approach, allowing low-frequency interactionsto be monitored with a bright fluorescence signal offers abroad applicability, both in terms of read-out means, typesof molecular interactions that can be followed, and in whatenvironment these interactions can be measured. From thispoint of view, it can prove useful for a broad category ofmolecular interaction studies.
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