Ergosterol in POPC membranes: physical properties and comparison with structurally similar sterols |
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Authors: | Hsueh Ya-Wei Chen Mei-Ting Patty Philipus J Code Christian Cheng John Frisken Barbara J Zuckermann Martin Thewalt Jenifer |
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Institution: | * Department of Physics, National Central University, Chung-li 320, Taiwan † Center for Complex Systems, National Central University, Chung-li 320, Taiwan ‡ Institute of Biophysics, National Central University, Chung-li 320, Taiwan § Department of Physics, Simon Fraser University, Burnaby, BC Canada V5A 1S6 ¶ Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC Canada V5A 1S6 |
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Abstract: | The physical properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/ergosterol bilayers in the liquid-crystalline phase were determined using deuterium nuclear magnetic resonance (2H NMR) and vesicle extrusion. For the 2H NMR experiments, the sn-1 chain of POPC was perdeuterated, and spectra were taken as a function of ergosterol concentration and temperature. Analysis of the liquid-crystalline spectra provides clear evidence that two types of liquid-crystalline domains, neither of which is a liquid-ordered phase, having distinct average chain conformations coexist in 80:20 and 75:25 POPC/ergosterol membranes over a wide temperature range (from −2 to at least 31°C). Adding ergosterol to a concentration of 25 mol % increases POPC-d31 chain ordering as measured by the NMR spectral first moment M1 and also increases the membrane lysis tension, obtained from vesicle extrusion. Further addition of ergosterol had no effect on either chain order or lysis tension. This behavior is in marked contrast to the effect of cholesterol on POPC membranes: POPC/cholesterol membranes have a linear dependence of chain order on sterol concentration to at least 40 mol %. To investigate further we compared the dependence on sterol structure and concentration of the NMR spectra and lysis tension for several POPC/sterol membranes at 25°C. For all POPC/sterol membranes investigated in this study, we observed a universal linear relation between lysis tension and M1. This suggests that changes in acyl chain ordering directly affect the tensile properties of the membrane. |
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