n-Alcohol Length Governs Shift in Lo-Ld Mixing Temperatures in Synthetic and Cell-Derived Membranes

Abstract

A persistent challenge in membrane biophysics has been to quantitatively predict how membrane physical properties change upon addition of new amphiphiles (e.g., lipids, alcohols, peptides, or proteins) in order to assess whether the changes are large enough to plausibly result in biological ramifications. Because of their roles as general anesthetics, n-alcohols are perhaps the best-studied amphiphiles of this class. When n-alcohols are added to model and cell membranes, changes in membrane parameters tend to be modest. One striking exception is found in the large decrease in liquid-liquid miscibility transition temperatures (Tmix) observed when short-chain n-alcohols are incorporated into giant plasma membrane vesicles (GPMVs). Coexisting liquid-ordered and liquid-disordered phases are observed at temperatures below Tmix in GPMVs as well as in giant unilamellar vesicles (GUVs) composed of ternary mixtures of a lipid with a low melting temperature, a lipid with a high melting temperature, and cholesterol. Here, we find that when GUVs of canonical ternary mixtures are formed in aqueous solutions of short-chain n-alcohols (n ≤ 10), Tmix increases relative to GUVs in water. This shift is in the opposite direction from that reported for cell-derived GPMVs. The increase in Tmix is robust across GUVs of several types of lipids, ratios of lipids, types of short-chain n-alcohols, and concentrations of n-alcohols. However, as chain lengths of n-alcohols increase, nonmonotonic shifts in Tmix are observed. Alcohols with chain lengths of 10–14 carbons decrease Tmix in ternary GUVs of dioleoyl-PC/dipalmitoyl-PC/cholesterol, whereas 16 carbons increase Tmix again. Gray et al. observed a similar influence of the length of n-alcohols on the direction of the shift in Tmix. These results are consistent with a scenario in which the relative partitioning of n-alcohols between liquid-ordered and liquid-disordered phases evolves as the chain length of the n-alcohol increases.

The Affinity of Sterols for Different Phospholipid Classes and Its Impact on Lateral Segregation

“…5). Commonly, the thermal stability of lateral domains is used as a measure of how prone a lipid mixture is to form domains (41,(48)(49)(50)(51). This parameter is mostly dependent on the lipid composition of the domains, and the higher the fraction of sterol and saturated PL is, the higher the melting temperature becomes.…”

Impact of Acyl Chain Mismatch on the Formation and Properties of Sphingomyelin-Cholesterol Domains

“…Another commonly used parameter to describe the lateral segregation propensity of mixed lipid bilayers is the thermostability of the formed ordered domains (17,20,48,60). We used both deuterium NMR and FRET to study the influence of the acyl chain length in the PC molecules on the thermostability of the PSM-enriched ordered domains (Figs.…”

Giant Plasma Membrane Vesicles: An Experimental Tool for Probing the Effects of Drugs and Other Conditions on Membrane Domain Stability

“…This miscibility transition occurs at a temperature called T mix , and was first observed experimentally in giant vesicles and black lipid membranes in 2001 (Dietrich, Bagatolli, Volovyk, Thompson, Levi, Jacobson et al 2001; Samsonov, Mihalyov and Cohen 2001), and is also observed in extracted and isolated biological membranes (Dietrich 2001; Baumgart, Hammond, Sengupta, Hess, Holowka, Baird et al 2007) (Figure 1). While all hydrophobic impurities are expected to lower the main chain transition temperature to roughly the same extent, the magnitude and sign of an impurity’s effect on the miscibility transition temperature depends more strongly on the membrane composition and the detailed molecular structure of the impurity (Allender and Schick 2017; Cornell, McCarthy, Levental, Levental, Brooks and Keller 2017). We recently found that several anesthetic n-alcohols lower T mix in vesicles isolated from RBL-2H3 membranes, but two non-anesthetic n-alcohols do not (Gray, Karslake, Machta and Veatch 2013; Machta, Gray, Nouri, McCarthy, Gray, Miller et al 2016).…”