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Biophys. J. BioFAST: First Published June 23, 2006. doi:10.1529/biophysj.106.085027
© 2006 by the Biophysical Society.

A more recent version of this article appeared on September 15, 2006.
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Temperature and Composition Dependence of the Interaction of {delta}-Lysin with Ternary Mixtures of Sphingomyelin/Cholesterol/POPC

Antje Pokorny 1, Lindsay E Yandek 1, Adekunle I Elegbede 2, Anne Hinderliter 2 and Paulo F Almeida 1*

1 University of North Carolina Wilmington
2 North Dakota State University

* To whom correspondence should be addressed. E-mail: almeidap{at}uncw.edu.

Submitted on March 12, 2006
Revised on April 18, 2006
Accepted on 12 June 2006


  Abstract
The kinetics of carboxyfluorescein (CF) efflux induced by the amphipathic peptide {delta}-lysin from vesicles of porcine brain sphingomyelin (BSM), 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and cholesterol (Chol) were investigated as a function of temperature and composition. Sphingomyelin (SM)/Chol mixtures form a liquid-ordered (Lo) phase whereas POPC exists in the liquid-disordered (Ld) phase at ambient temperature. {delta}-Lysin binds strongly to Ld and poorly to Lo phase. In BSM/Chol/POPC vesicles the rate of CF efflux induced by {delta}-lysin increases as the POPC content decreases. This is explained by the increase of {delta}-lysin concentration in Ld domains, which enhances membrane perturbation by the peptide. Phase separations in the micrometer scale have been observed by fluorescence microscopy in SM/Chol/POPC mixtures for some SM, though not for BSM. Thus, {delta}-lysin must detect heterogeneitiesm (domains) in BSM/Chol/POPC on a much smaller scale. Advantage was taken of the inverse variation of the efflux rate with the Ld content of BSM/Chol/POPC vesicles to estimate the Ld fraction in those mixtures. These results were combined with differential scanning calorimetry to obtain the BSM/Chol/POPC phase diagram as a function of temperature.

Key Words: amphipathic peptide, carboxyfluorescein release, liquid-ordered, phase diagram, phase separation, rafts




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Copyright © 2006 by the Biophysical Society.