High-Melting Lipid Mixtures and the Origin of Detergent-Resistant Membranes Studied with Temperature-Solubilization Diagrams

Abstract

The origin of resistance to detergent solubilization in certain membranes, or membrane components, is not clearly understood. We have studied the solubilization by Triton X-100 of binary mixtures composed of egg sphingomyelin (SM) and either ceramide, diacylglycerol, or cholesterol. Solubilization has been assayed in the 4-50°C range, and the results are summarized in a novel, to our knowledge, form of plots, that we have called temperature-solubilization diagrams. Despite using a large detergent excess (lipid/detergent 1:20 mol ratio) and extended solubilization times (24-48 h) certain mixtures were not amenable to Triton X-100 solubilization at one or more temperatures. DSC of all the lipid mixtures, and of all the lipid + detergent mixtures revealed that detergent resistance was associated with the presence of gel domains at the assay temperature. Once the system melted down, solubilization could occur. In general adding high-melting lipids limited the solubilization, whereas the addition of low-melting lipids promoted it. Lipidomic analysis of Madin-Darby canine kidney cell membranes and of the corresponding detergent-resistant fraction indicated a large enrichment of the nonsolubilized components in saturated diacylglycerol and ceramide. SM-cholesterol mixtures were special in that detergent solubilization was accompanied, for certain temperatures and compositions, by an independent phenomenon of reassembly of the partially solubilized lipid bilayers. The temperature at which lysis and reassembly prevailed was ∼25°C, thus for some SM-cholesterol mixtures solubilization occurred both above and below 25°C, but not at that temperature. These observations can be at the origin of the detergent resistance effects observed with cell membranes, and they also mean that cholesterol-containing detergent-resistant membrane remnants cannot correspond to structures existing in the native membrane before detergent addition.

Lipids in Mitochondrial Macroautophagy: Phase Behavior of Bilayers Containing Cardiolipin and Ceramide

“…The observation ( Figure 1 , Figure 2 and Figure 4 ) that only two phases are seen in the ePC-based samples is noteworthy. This is probably related to the fact that SM and Cer, but not PC or Cer, exhibit a strong interaction and give rise to very rigid, detergent-resistant, and segregated domains [ 36 , 48 ]. The AFM images in Figure 4 show fractal or irregular contours for Cer-containing, eSM-based samples, suggestive of a rigid–fluid domain interface.…”

The Membrane-Water Partition Coefficients of Antifungal, but Not Antibacterial, Membrane-Active Compounds Are Similar

“…While bacteria do not possess sterol biosynthesis machinery and thus are typically devoid of sterols, in eukaryotes sterols may reach up to 50 mol.% of total lipids in the plasma membrane (Mouritsen and Zuckermann, 2004;Ejsing et al, 2009;Subczynski et al, 2017). Sterols are especially efficient in increasing the resistance of lipid bilayers with respect to lysis via pore formation caused by the membrane-active chemicals (Sot et al, 2014;Mattei et al, 2015;Caritá et al, 2017). The mechanism of this protection can be illustrated using the example of lyso-forms of phosphocholine lipids.…”

Effects of Sterols on the Interaction of SDS, Benzalkonium Chloride, and A Novel Compound, Kor105, with Membranes

“…Sterols significantly change the physico-chemical properties of the membrane [8] and affect the mode of membrane interaction with almost every low-molecular-weight compound. For example, sterols increase the resistance of lipid bilayers to detergents [9,10,11,12]. However, the mechanisms of surfactant interactions with membranes with different levels of sterols are still unclear.…”