Membrane domain formation, interdigitation and morphological alterations induced by the very long chain asymmetric C24:1 ceramide
Sandra N Pinto 1, Liana C Silva 1*, Rodrigo F. M. de Almeida 1 and Manuel Jose Prieto 1
1 Instituto Superior Técnico
* To whom correspondence should be addressed. E-mail: lianacsilva{at}ist.utl.pt.
Submitted on January 18, 2008
Revised on February 20, 2008
Accepted on 11 June 2008
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Abstract |
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Ceramide (Cer) is involved in the regulation of several biological processes, such as apoptosis and cell signaling. The alterations induced by Cer in the biophysical properties of the membranes are thought to be one of the major routes for Cer action. To gain further knowledge on the alterations induced by Cer, membrane reorganization by the very long chain asymmetric nervonoyl-Cer (NCer) was studied. The application of an established fluorescence multiprobe approach, together with X-ray diffraction, differential scanning calorimetry and confocal fluorescence microscopy, allowed the characterization of NCer and the determination of the phase diagram of palmitoyloleoylphosphatidylcholine (POPC)/NCer binary mixtures. NCer undergoes a transition from a mixed interdigitated gel phase into a partially interdigitated gel phase at ~20°C, and a broad main transition to the fluid phase at ~52°C. The solubility of NCer in the fluid POPC is low, driving gel-fluid phase separation, and the binary phase diagram is characterized by the presence of multiple and large coexistence regions between the interdigitated gel phases and the fluid phase. At 37°C, the relevant phases are the fluid and the partially interdigitated gel. Moreover, the formation of NCer interdigitated gel phases leads to strong morphological alterations in the lipid vesicles, driving the formation of cochleate-type tubular structures.
Key Words:
confocal fluorescence microscopy, gel-fluid phase separation, giant unilamellar vesicles, nervonoylceramide, sphingolipids, tubular structures
