Yaghmur, A, Laggner, P, Sartori, B et al. (1 more author) (2008) Calcium triggered L alpha-H2 phase transition monitored by combined rapid mixing and time-resolved synchrotron SAXS. PLoS One, 3 (4). e2072 - e2072. ISSN 1932-6203
Abstract
BACKGROUND: Awad et al. reported on the Ca(2+)-induced transitions of dioleoyl-phosphatidylglycerol (DOPG)/monoolein (MO) vesicles to bicontinuous cubic phases at equilibrium conditions. In the present study, the combination of rapid mixing and time-resolved synchrotron small-angle X-ray scattering (SAXS) was applied for the in-situ investigations of fast structural transitions of diluted DOPG/MO vesicles into well-ordered nanostructures by the addition of low concentrated Ca(2+) solutions. METHODOLOGY/PRINCIPAL FINDINGS: Under static conditions and the in absence of the divalent cations, the DOPG/MO system forms large vesicles composed of weakly correlated bilayers with a d-spacing of approximately 140 A (L(alpha)-phase). The utilization of a stopped-flow apparatus allowed mixing these DOPG/MO vesicles with a solution of Ca(2+) ions within 10 milliseconds (ms). In such a way the dynamics of negatively charged PG to divalent cation interactions, and the kinetics of the induced structural transitions were studied. Ca(2+) ions have a very strong impact on the lipidic nanostructures. Intriguingly, already at low salt concentrations (DOPG/Ca(2+)>2), Ca(2+) ions trigger the transformation from bilayers to monolayer nanotubes (inverted hexagonal phase, H(2)). Our results reveal that a binding ratio of 1 Ca(2+) per 8 DOPG is sufficient for the formation of the H(2) phase. At 50 degrees C a direct transition from the vesicles to the H(2) phase was observed, whereas at ambient temperature (20 degrees C) a short lived intermediate phase (possibly the cubic Pn3m phase) coexisting with the H(2) phase was detected. CONCLUSIONS/SIGNIFICANCE: The strong binding of the divalent cations to the negatively charged DOPG molecules enhances the negative spontaneous curvature of the monolayers and causes a rapid collapsing of the vesicles. The rapid loss of the bilayer stability and the reorganization of the lipid molecules within ms support the argument that the transition mechanism is based on a leaky fusion of the vesicles.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2008 Yaghmur et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. |
Keywords: | Calcium; Glycerides; Lipid Bilayers; Phase Transition; Phosphatidylglycerols; Salts; Scattering, Small Angle; Static Electricity; Synchrotrons; Temperature; Time Factors; Unilamellar Liposomes; X-Ray Diffraction |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Food Science and Nutrition (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 27 Mar 2015 11:44 |
Last Modified: | 27 Mar 2015 11:44 |
Published Version: | http://dx.doi.org/10.1371/journal.pone.0002072 |
Status: | Published |
Publisher: | Public Library of Science |
Refereed: | Yes |
Identification Number: | 10.1371/journal.pone.0002072 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:83609 |