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Magnetic resonance investigations of lipid motion in isotropic bicelles
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
2005 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 21, no 7, 7702-7709 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2005. Vol. 21, no 7, 7702-7709 p.
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:su:diva-23832DOI: 10.1021/la0513003OAI: oai:DiVA.org:su-23832DiVA: diva2:194680
Note
Part of urn:nbn:se:su:diva-497Available from: 2005-05-02 Created: 2005-05-02 Last updated: 2017-12-13Bibliographically approved
In thesis
1. The Application of isotropic bicelles as model membranes
Open this publication in new window or tab >>The Application of isotropic bicelles as model membranes
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Institutionen för biokemi och biofysik, 2005. 75 p.
Keyword
Bicelle, membrane, peptide, spectroscopy, NMR
National Category
Biophysics
Identifiers
urn:nbn:se:su:diva-497 (URN)91-7155-043-7 (ISBN)
Public defence
2005-05-20, Magnélisalen, Kemiska övningslaboratoriet, Arrhenius väg 12 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2005-05-02 Created: 2005-05-02Bibliographically approved

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