Domain formation and stability in complex lipid bilayers as reported by cholestatrienol

¹ Abo Akademi University
² Utrecht University

^* To whom correspondence should be addressed. E-mail: boramste{at}abo.fi.

Submitted on October 18, 2004
Revised on November 17, 2004
Accepted on 9 March 2005

	Abstract

In this study we have used cholestatrienol (cholesta-5,7,9(11)-trien-3-beta-ol; CTL) as a fluorescent reporter molecule to study sterol-rich Lo-domains in complex lipid bilayers. CTL is a fluorescent cholesterol analogue, which mimics the behavior of cholesterol well. The ability of 1-palmitoyl-2-stearoyl-(12-DOXYL)-sn-glycero-3-phosphocholine (12SLPC) to quench the fluorescence of cholestatrienol gives a measure of the amount of sterol included in Lo-domains in mixed lipid membranes. The stability of sterol-rich domains formed in complex lipid mixtures containing saturated sphingomyelins, phosphatidylcholines or galactosylceramide as potential domain-forming lipids were studied. The amount of sterol associated with sterol-rich domains seemed to always increase with increasing temperature. The quenching efficiency was highly dependent on the domain-forming lipid present in complex lipid mixtures. Sphingomyelins formed stable sterol-enriched domains and was able to shield CTL from quenching better than the other lipids included in this study. The saturated phosphatidylcholines also formed sterol-rich domains, but the quenching efficiency in membranes with these was higher than with sphingomyelins and the domains melted at lower temperatures. PGalCer was not able to form sterol-enriched domains. However, we found that PGalCer stabilized sterol-rich domains formed in PSM-containing bilayers. Using a fluorescent ceramide analog we could also demonstrate that N-palmitoyl-ceramide displaced the sterol from sphingolipid-rich domains in mixed bilayer membranes.

Key Words: ceramide, differential scanning calorimetry, fluorescence quenching, galactosylceramide, sphingomyelin, sterol-rich domains

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