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Deuterium NMR Study of the Effect of Ergosterol on POPE Membranes |
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| Authors: | Ya-Wei Hsueh Chi-Jung Weng Jenifer Thewalt Martin Zuckermann |
| Institution: | † Department of Physics, National Central University, Jhong-li 320, Taiwan ‡ Center for Complex Systems, National Central University, Jhong-li 320, Taiwan § Institute of Biophysics, National Central University, Jhong-li 320, Taiwan ¶ Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada ‖ Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada |
| Abstract: | We study the effect of ergosterol on the physical properties of 1-2H31]palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) multibilayers using deuterium nuclear magnetic resonance. NMR spectra were taken as a function of temperature and ergosterol concentration up to 70 mol %. The spectral first moments show that there is a dramatic difference in the ability of ergosterol to disorder the gel phase and to order the liquid-crystalline phase of POPE membranes, an unusual behavior among lipid/sterol systems studied up to now. Further investigation of the liquid-crystalline phase shows that ergosterol (erg) increases the chain order of POPE-d31, but that this effect saturates at 10 mol % ergosterol. This is in marked contrast to the effect of cholesterol (chol) on POPE membranes: the chain order of POPE increases with cholesterol to at least 45 mol %. Moreover, we found that at higher ergosterol concentrations (>40 mol %) ergosterol decreases the POPE-d31 chain order, which, to our knowledge, has not been directly observed in other lipid/sterol systems. The temperature-composition phase diagram is presented. Finally, at all ergosterol concentrations, the chain order of liquid-crystalline-phase POPE is much smaller than that of comparable POPE/chol membranes. This implies that there is no liquid-ordered phase behavior for POPE/erg membranes. |
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