Coexistence of Immiscible Mixtures of Palmitoylsphingomyelin and Palmitoylceramide In Monolayers and Bilayers

Abstract

We investigate the surface height fluctuations of single and double bilayers of DPPE supported on silicon using x-ray photon correlation spectroscopy (XPCS). In this techique, x-rays are incident on the membrane in a grazing incidence geometry and diffusely scattered x-rays are measured using an area detector. Time fluctuations of the scattering pattern can then be analyzed to yield the relaxation rate of surface height fluctuations. Bilayer and double bilayer systems were prepared utilizing combination of Langmuir-Blodgett and Langmuir-Schaeffer depositions. Static structural measurements were also made on these systems as well as on more complicated systems consisting of triple and five-fold bilayers of DPPE. Relationships between structure and dynamics of these systems will be discussed.

The many faces (and phases) of ceramide and sphingomyelin II – binary mixtures

“…Egg Cer increases the solid character of SMbased membranes and decreases their fluidity, thus drastically decreasing the lateral mobilities of embedded objects (Catapano et al 2011). The mixed film containing egg Cer/egg SM (1:2) showed an intermediate viscous character, a fact that can be related to the 1:2 maximal compaction due to the molecular complexation previously hypothesized by Busto et al (2009).…”

“…Monolayer and bilayer approaches were employed to study the mixture of 16:0 SM/ 16:0 Cer. In both systems, 16:0 Cer exerts a number of effects in a composition-dependent manner up to X 16:0 Cer 0.3-0.4 (Busto et al 2009). An interpretation of the data on the basis of lipid bilayer observations (Sot et al 2006) is that 16:0 Cerrich and 16:0 Cer-poor phases are immiscible and phase-segregated.…”

“…As a consequence, such Cers form segregated solid-like condensed domains, in both bilayers and monolayers, that even exclude fluorescent probes and proteins (Carrer and Maggio 1999;Holopainen et al 2001;Härtel et al 2005;Castro et al 2007;Chiantia et al 2008;Busto et al 2009;Karttunen et al 2009;López-Montero et al 2010). Natural mixtures of Cer are mainly composed of long chain Cers.…”

“…16:0 Cer forms condensed domains segregated from fluid phases enriched in 16:0 SM (Busto et al 2009) and unsaturated PCs Pinto et al 2011) even in the presence of low amounts of cholesterol ), leading to the idea that Cer and cholesterol can compete in ordered domains with SM (Staneva et al 2008;Busto et al 2010). Mixtures of Cers and SMs N-acylated with palmitic acid (16:0) at the air−water interface showed a thermodynamically stable point at X 16:0 Cer = 0.4 with molecular area condensation, whereas in bilayer systems, complex DSC thermograms were reported (Busto et al 2009) with increasing melting temperatures at increasing 16:0 Cer content. A similar behavior was also reported for mixtures of 16:0 SM with 12:0, 18:0, and even 24:1 Cers (Westerlund et al 2010).…”

“…The interaction of some species of SM and ceramide (Cer) has been studied in monolayers (Busto et al 2009) and bilayers (Busto et al 2009;Westerlund et al 2010). 16:0 Cer forms condensed domains segregated from more liquid-like phases enriched in SM (Busto et al 2009) and unsaturated PCs Pinto et al 2011) even in the presence of low amounts of cholesterol Ale et al 2012), leading to the idea that Cer and cholesterol can compete in ordered domains with SM (Staneva et al 2008;Busto et al 2010). Mixtures of Cer and SM N-acylated with palmitic acid (16:0) in monolayers show a thermodynamically stable point at X 16:0 Cer = 0.4 with molecular area condensation, whereas in bilayer systems, complex differential scanning calorimetry (DSC) thermograms occur (Busto et al 2009) with increasing melting temperatures at increasing ceramide content.…”