Domain Nucleation Rates and Interfacial Line Tensions in Supported Bilayers of Ternary Mixtures Containing Galactosylceramide
Craig D. Blanchette 1, Wan-Chen Lin 2, Christine A. Orme 3, Timothy V. Ratto 1 and Marjorie L. Longo 2*
1 Lawrence Livermore National Laboratory
2 University of California Davis
3 Lawrence Livermore National Lab
* To whom correspondence should be addressed. E-mail: mllongo{at}ucdavis.edu.
Submitted on September 26, 2007
Revised on October 26, 2007
Accepted on 28 November 2007
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Abstract |
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Domains within the plane of the plasma membrane, referred to as membrane rafts, have been a topic of considerable interest in the field of membrane biophysics. Although model membrane systems have been used extensively to study lipid phase behavior as it relates to the existence of rafts, very little work has focused on either the initial stage of lipid domain nucleation, or the relevant physical parameters such as temperature and interfacial line tension which control nucleation. In this work we utilize a method in which the kinetic process of lipid domain nucleation is imaged by atomic force microscopy (AFM) and modeled using classical theory of nucleation to map interfacial line tension in ternary lipid mixtures. These mixtures consist of a fluid phase lipid component (1,2-Dilauroyl-sn-Glycero-3-Phosphocholine (DLPC), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (POPC), or 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC)), a solid phase component (galactosylceramide (GalCer)) and cholesterol. Interfacial line tension measurements of GalCer-rich domains track with our previously measured area/perimeter (A/P) ratios and height mismatches measured here. Line tension also follows known trends in cholesterol interactions and partitioning, as we observed previously with A/P ratios. Our line tension measurements are discussed in combination with recent line tension measurements by Baumgart and coworkers to address line tension regulation by cholesterol and the dynamic nature of membrane rafts.
Key Words:
atomic force microscopy, chain unsaturation, cholesterol, membrane rafts, miscibility, sphingolipids
