Ergosterol in POPC Membranes: Physical Properties and Comparison with Structurally Similar Sterols

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 ((2)H NMR) and vesicle extrusion. For the (2)H 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 degrees C). Adding ergosterol to a concentration of 25 mol % increases POPC-d(31) chain ordering as measured by the NMR spectral first moment M(1) 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 degrees C. For all POPC/sterol membranes investigated in this study, we observed a universal linear relation between lysis tension and M(1). This suggests that changes in acyl chain ordering directly affect the tensile properties of the membrane.

Design of new fluorescent cholesterol and ergosterol analogs: Insights from theory

“…The remaining 120 ns were analyzed with AmberTools14 [48] and GROMACS version 4.6.5[64,65], taking snapshots every 20 ps to yield 6000 snapshots in total per system.As discussed in detail later, the simulations performed in this study indicate that Erg orders POPC bilayers more than Chol at 30 mol-%.This observation is in conflict with literature since at 30 mol-%, Chol orders a membrane of monounsaturated lipids such as POPC more efficiently[66][67][68]. The effects of Erg on the bilayer are believed to saturate at around 25 mol-% Erg[66][67][68]. On the contrary, Erg has a greater ordering effect than Chol on saturated membranes due to the rigidity of its tail, which results in smaller tilt angles of the sterol ring sysTo resolve if this discrepancy was a force field related issue, we reran the simulations of Chol in POPC and Erg in POPC employing the CHARMM force field C36c[70].…”

“…The remaining 120 ns were analyzed with AmberTools14 [48] and GROMACS version 4.6.5[64,65], taking snapshots every 20 ps to yield 6000 snapshots in total per system.As discussed in detail later, the simulations performed in this study indicate that Erg orders POPC bilayers more than Chol at 30 mol-%.This observation is in conflict with literature since at 30 mol-%, Chol orders a membrane of monounsaturated lipids such as POPC more efficiently[66][67][68]. The effects of Erg on the bilayer are believed to saturate at around 25 mol-% Erg[66][67][68].…”

Synthesis-enabled functional group deletions reveal key underpinnings of amphotericin B ion channel and antifungal activities

“…4B). Importantly, extensive solid-state NMR studies have demonstrated that the incorporation of either ergosterol or lanosterol into POPC liposomes causes very similar changes in global membrane properties (61)(62)(63). In the event, titrating AmB with sterol-free and then 10% ergosterol-containing POPC LUVs again caused a substantial increase in the observed net exotherm.…”

Phase Diagram of Ternary Cholesterol/Palmitoylsphingomyelin/Palmitoyloleoyl-Phosphatidylcholine Mixtures: Spin-Label EPR Study of Lipid-Raft Formation

“…Possible reasons why indirect determinations of phase boundaries by fluorescent probes could be misleading are discussed in reference (6), although the appropriate conditions were fulfilled in reference (25). Interestingly, fluid-fluid phase separation is observed as two-component 2 H-NMR spectra in binary mixtures of POPC with ergosterol, although this is said not to involve a L o -phase (43) and such twocomponent spectra are not observed with POPC/chol mixtures (9).…”