Lo/Ld phase coexistence modulation induced by GM1

Abstract

Lipid rafts are assumed to undergo biologically important size-modulations from nanorafts to microrafts. Due to the complexity of cellular membranes, model systems become important tools, especially for the investigation of the factors affecting "raft-like" Lo domain size and the search for Lo nanodomains as precursors in Lo microdomain formation. Because lipid compositional change is the primary mechanism by which a cell can alter membrane phase behavior, we studied the effect of the ganglioside GM1 concentration on the Lo/Ld lateral phase separation in PC/SM/Chol/GM1 bilayers. GM1 above 1mol % abolishes the formation of the micrometer-scale Lo domains observed in GUVs. However, the apparently homogeneous phase observed in optical microscopy corresponds in fact, within a certain temperature range, to a Lo/Ld lateral phase separation taking place below the optical resolution. This nanoscale phase separation is revealed by fluorescence spectroscopy, including C12NBD-PC self-quenching and Laurdan GP measurements, and is supported by Gaussian spectral decomposition analysis. The temperature of formation of nanoscale Lo phase domains over an Ld phase is determined, and is shifted to higher values when the GM1 content increases. A "morphological" phase diagram could be made, and it displays three regions corresponding respectively to Lo/Ld micrometric phase separation, Lo/Ld nanometric phase separation, and a homogeneous Ld phase. We therefore show that a lipid only-based mechanism is able to control the existence and the sizes of phase-separated membrane domains. GM1 could act on the line tension, "arresting" domain growth and thereby stabilizing Lo nanodomains.

Self assembly of HIV-1 Gag protein on lipid membranes generates PI(4,5)P2/Cholesterol nanoclusters

“…Although accurate in detecting and measuring the size of pre-existing nanodomains, these methods are not fast enough to follow the generation of nanodomains. Therefore, we decided to use indirect approaches such as fluorescence quenching [22,46] or Forster Resonant Energy Transfer (FRET) [27]. FRET or self-quenching occurs when two (similar or different) fluorescent molecules are found together within a 3 to 10 nm radius.…”

Self assembly of HIV-1 Gag protein on lipid membranes generates PI(4,5)P2/Cholesterol nanoclusters

“…Although accurate in detecting and measuring the size of pre-existing nanodomains, direct imaging is not fast enough to follow the generation of nanodomains. Therefore, we decided to use indirect approaches such as fluorescence quenching2425 or Forster Resonant Energy Transfer (FRET)26. FRET or self-quenching occurs when two (similar or different) fluorescent molecules are found together within a 3 to 10 nm radius.…”

Effects of neurosteroids on a model membrane including cholesterol: A micropipette aspiration study

“…Moreover, Allo uptake shifts the relative distribution in favor of the L d phase [30]. It is interesting to note that other studies found that the insertion of exogenous molecules in lipid bilayers in the L o + L d coexistence region leads to a modification of the relative proportions of the two liquid phases [37,38]. In addition, the shift amount depends on the lipid bilayer patch under observation.…”

“…2 to help discussion and interpretation of our data. On the basis of the reported phase diagram, at room temperature, the particular composition that we chose should be inside the two-phase coexistence region but very near to the miscibility border through a critical point [37]. Moreover, considering the phase diagram with fixed 1:1 DOPC\bSM ratio as a function of cholesterol content and focussing on the high cholesterol concentration region, where the 1:1:1 mixture is to be positioned, the miscibility border as a function of cholesterol concentration is very steep [35].…”