Melting-Temperature-Dependent Interactions of Ergosterol with Unsaturated and Saturated Lipids in Model Membranes

Abstract

Sterols such as cholesterol (Chol) and ergosterol (Erg) are known to regulate membrane properties in higher eukaryotes and in lower eukaryotes, respectively. To better understand the modulation of membrane properties by Erg, binary lipid membranes composed of Erg and diacylglycerophosphocholine (PC) were studied in Langmuir monolayer and bilayer vesicle systems. From the excess area measured by pressure−area isotherms, attractive interactions between Erg and saturated PC were significant above the melting temperature (T m ) of PC. Conversely, repulsive interactions were observed at temperatures below T m . From the analyses of membrane fluidity and polarity using fluorescence probes, similar trends were observed for bilayer systems where Erg had an ordering effect on saturated PC vesicles in the fluid state. However, Chol had a stronger ordering effect than Erg. In unsaturated PC systems, Erg did not alter membrane ordering. These findings demonstrate that the interaction of Erg with the fluid-state PC lipids will maintain lower-eukaryote membranes in a more ordered state, similar to the effect of cholesterol in higher eukaryotes.

Effect of Cholesterol vs. Ergosterol on DPPC Bilayer Properties: Insights from Atomistic Simulations

“…A number of computational and experimental studies have focused on the comparison of binary mixtures of cholesterol and ergosterol with saturated lipids including DPPC (16:0) and DMPC (14:0). The outcome of these studies, however, are not in agreement with one another [6,15,16,18,22,24,39,40,[42][43][44][45][46][47][48]. A similar disagreement is also observed at the ternary level [33,35,38].…”

“…The above discussion indicates that the comparative studies of cholesterol and ergosterol even considering only DPPC/sterol systems have reported different results [6,24,39,40,42,45,47]. Among the different methods of study, computer simulations can have an essential role to provide insights into the underlying mechanisms in lipid bilayer systems at the atomic resolution even though they are limited in terms of simulation time and system size as well as the accuracy of the present force fields.…”

“…At the binary level, in an NMR study on DPPC/sterol systems at relatively high temperatures, cholesterol had higher impact on the order of the lipid chains [45]. In a recent work, using steady-state fluorescence polarization for DPPC/sterol mixtures in monolayers and bilayer vesicles above the phase transition temperature of the pure DPPC bilayer, lower fluidity values were obtained for cholesterol, meaning its higher ordering effect as compared to ergosterol [42]. Also recently, using the X-ray diffraction method on the DMPC/sterol binary mixtures, ergosterol was found to be three times less potent than cholesterol to condense the DMPC bilayers [22].…”

“…In this paper we inspect this hypothesis and will see how these extra double bonds can affect the planarity of the ring part. Furthermore, it has been shown that ergosterol also promotes the formation of the L o phase [5,23,33,38], and is nearly as effective as cholesterol in this respect [5,33,[39][40][41][42].…”

【Original Contribution】Potential Interaction Behavior of Lanosterol and Unsaturated Phosphocholine in Monolayer Membrane

“…Erg, dominant in lower Eukaryotes and insects 1,16) , has two additional double bonds in B ring and tail, and an additional methyl group at C24 carbon atom in tail. As results, Erg lead to almost no ordering effect in the bilayer composed of unsaturated phosphocholine (PC) 14) , while Erg shows a potent ordering effect in the membrane enriched saturated lipids 15,17,18) .…”