Liquid-Ordered Phase Formation by Mammalian and Yeast Sterols: A Common Feature With Organizational Differences

Abstract

Here, biophysical properties of membranes enriched in three metabolically related sterols are analyzed both in vitro and in vivo. Unlike cholesterol and ergosterol, the common metabolic precursor zymosterol is unable to induce the formation of a liquid ordered (l o) phase in model lipid membranes and can easily accommodate in a gel phase. As a result, Zym has a marginal ability to modulate the passive membrane permeability of lipid vesicles with different compositions, contrary to cholesterol and ergosterol. Using fluorescence-lifetime imaging microscopy of an aminostyryl dye in living mammalian and yeast cells we established a close parallel between sterol-dependent membrane biophysical properties in vivo and in vitro. This approach unraveled fundamental differences in yeast and mammalian plasma membrane organization. It is often suggested that, in eukaryotes, areas that are sterolenriched are also rich in sphingolipids, constituting highly ordered membrane regions. Our results support that while cholesterol is able to interact with saturated lipids, ergosterol seems to interact preferentially with monounsaturated phosphatidylcholines. Taken together, we show that different eukaryotic kingdoms developed unique solutions for the formation of a sterol-rich plasma membrane, a common evolutionary trait that accounts for sterol structural diversity.

C-Glucosylation as a tool for the prevention of PAINS-induced membrane dipole potential alterations

“…The inclusion of PSM in the chosen molar proportion, decreasing the mole fraction of cholesterol from 50 to 33%, which leads to l d and l o segregation in the ternary system, caused a decrease in this ratio to a value close to that observed for pure POPC LUV (2.20 ± 0.03 vs. 2.03 ± 0.02. The results are in overall agreement with our previous measurements in single, two and three component lipid mixtures using either di-8-ANEPPS or a similar probe, di-4-ANEPPS 35 , 50 , 52 .

Figure 2 Membrane dipole potential measurements through the excitation intensity ratio at 420 nm / 520 nm of di-8-ANEPPS in pure POPC, POPC:Chol 1:1 and POPC:Chol:PSM 1:1:1 liposomes (1 mM total lipid) at 23 °C.

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Yeast Sphingolipid-Enriched Domains and Membrane Compartments in the Absence of Mannosyldiinositolphosphorylceramide

“…With di-8-ANEPPS, our results for both fluorescence lifetime and membrane dipole potential measurements, were nearly identical for wt and ipt1 Δ cells, regardless of the model system studied—GUVs, living cells or IPM. This suggests that those biophysical properties, which are strongly dependent on sterol and sterol-lipid interactions [ 51 , 61 ], are less dependent on the major sphingolipid headgroup. In erg6 Δ cells, which have an altered sterol profile, but no noticeable changes in sphingolipid profile when compared to wt cells [ 87 , 88 ], the rigidity of the gel domains is not changed [ 11 ], but the fluorescence lifetime of a sterol sensitive dye is significantly different from wt cells [ 51 ].…”

“…This suggests that those biophysical properties, which are strongly dependent on sterol and sterol-lipid interactions [ 51 , 61 ], are less dependent on the major sphingolipid headgroup. In erg6 Δ cells, which have an altered sterol profile, but no noticeable changes in sphingolipid profile when compared to wt cells [ 87 , 88 ], the rigidity of the gel domains is not changed [ 11 ], but the fluorescence lifetime of a sterol sensitive dye is significantly different from wt cells [ 51 ]. This behavior is opposite to that found for ipt1 Δ cells where the rigidity of the gel domains is increased but the fluorescence properties of di-8-ANEPPS remain unchanged when compared to wt cells.…”

“…Changes in membrane dipole potential were evaluated in IPM suspensions using the ratio of the steady-state fluorescence intensity values obtained from excitation of di-8-ANEPPS at 420 nm and at 520 nm, both with emission at 635 nm [50,51].…”

Plasma membrane vesicles from cauliflower meristematic tissue and their role in water passage

“…These molecules have been linked with different functions, such as lipid packing, since they are able to interact with membrane proteins and fatty acids [ 13 ]. Furthermore, membrane sterols have been documented to regulate membrane water permeability [ 14 ]. For example, it has been reported that the presence of cholesterol in the bilayer makes it less permeable to water [ 15 ].…”