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

Abstract

A rather widespread idea on the functional importance of sphingolipids in cell membranes refers to the occurrence of ordered domains enriched in sphingomyelin and ceramide that are largely assumed to exist irrespective of the type of N-acyl chain in the sphingolipid. Ceramides and sphingomyelins are the simplest kind of two-chained sphingolipids and show a variety of species, depending on the fatty acyl chain length, hydroxylation, and unsaturation. Abundant evidences have shown that variations of the N-acyl chain length in ceramides and sphingomyelins markedly affect their phase state, interfacial elasticity, surface topography, electrostatics, and miscibility, and that even the usually conceived "condensed" sphingolipids and many of their mixtures may exhibit liquid-like expanded states. Their lateral miscibility properties are subtlety regulated by those chemical differences. Even between ceramides with different acyl chain length, their partial miscibility is responsible for a rich two-dimensional structural variety that impacts on the membrane properties at the mesoscale level. In this review, we will discuss the miscibility properties of ceramide, sphingomyelin, and glycosphingolipids that differ in their N-acyl or oligosaccharide chains. This work is a second part that accompanies a previous overview of the properties of membranes formed by pure ceramides or sphingomyelins, which is also included in this Special Issue.

Keywords: Brewster angle microscopy; Compression isotherms; Langmuir films; Phase diagrams; Surface miscibility.

Fig. 1

Surface behavior and topography of mixed monolayers of ceramides. The upper panels show the compression isotherms of the pure and mixed films as indicated. The lower panels show the monolayer thickness calculated from reflectivity measurement as a function of surface pressure. The expanded phase (open circles) thickens at increasing values of surface pressure up to the transition surface pressure, when domains of condensed phase appear (solid symbols). The insets show representative Brewster angle microscopy images of the corresponding films. All images are 200 × 250 μm in size. Adapted from Dupuy and Maggio (2012)

Fig. 2

Condensation of 16:0 SM induced by the presence of 16:0 Cer. (a) Compression isotherms of pure 16:0 SM (solid line) and pure 16:0 Cer (dashed line) and the extrapolated molecular area for 16:0 SM in a condensed phase at low surface pressures (straight gray line). (b) Variation of the mean molecular area of the 16:0 SM–16:0 Cer mixture with 16:0 Cer mole fractions at 10 mN.m⁻¹. The solid line represents the molecular area for an ideal 16:0 SM–16:0 Cer mixture. The dashed gray line represents the molecular area for the ideal 16:0 SM (in LC phase)–16:0 Cer mixture. (c) Epifluorescence micrographs of pure and mixed 16:0 SM 16:0 SM–16:0 Cer monolayers. The monolayers were doped with 0.5 mol% of the fluorescent probe DiI-C18. All images are 331 × 263 μm in size. Modified from Busto et al. (2009)

Fig. 3

Compression isotherms of binary mixtures of sphingomyelins and ceramides with a high mismatch in the N-acyl chain length. 12:0 SM/24:0 Cer (a) appears rather immiscible, whereas 24:0 SM/10:0 Cer (b) formed mixed expanded phases over the whole range of compositions. Reprinted with permission from Dupuy and Maggio (2014). Copyright 2014 American Chemical Society

Fig. 4

Variation with the film composition of the mixing parameters: (a) mean molecular area, (b) perpendicular dipole moment of the binary mixtures of 24:1 Cer with 12:0, 16:0, and 24:0 SM, and (c) monolayer imaging by Brewster angle microscopy of the mixtures of 24:1 Cer with 12:0, 16:0, and 24:0 SM at 15 mN m⁻¹. Extracted from Dupuy and Maggio (2014)

Fig. 5

Partial molecular area contributions of the components of the mixture 10:0 Cer/16:0 SM at 5mN.m⁻¹ and at 24 °C. Modified from Dupuy and Maggio (2014)

Fig. 6

Monolayer imaging by Brewster angle microscopy of the mixtures at 15 mN.m⁻¹ of 16:0 SM with 24:0 Cer (a) and 10:0 Cer (b). Reprinted with permission from Dupuy and Maggio (2014). Copyright 2014 American Chemical Society

Fig. 7

The surface pressure–molecular area isotherms of mixed monolayers of ceramide and glycosphingolipids or gangliosides: (a) mixed films of ceramide and GlcCer; (b) ceramide and Gg4cCer; (c) ceramide and GM3; and (d) ceramide and GD1a. The insets show the deviation from the ideal behavior (dashed straight line) of the mean molecular area at the surface pressure indicated for the mixed films in the proportions shown in the abscissa. Extracted from Maggio (2004)

Fig. 8

Variation of partial mean molecular area and average surface potential/molecule with the films composition in mixed monolayers of ceramide with GSLs. The variation of the partial mean molecular area (thick lines) or the partial average surface potential/molecule (thin lines) of ceramide (a–c) in the presence of GlcCer (d), Gg4Cer (e), or ganglioside GD1a (f) is shown for mixed films with the proportions of ceramide indicated in the abscissa. As indicated in each panel, the surface pressures points at which the values were derived for both parameters correspond to 5 mN.m⁻¹ (upper curves) and 30 mN.m⁻¹ (lower curves); in c and f, the curves for the surface potential/molecule (thin lines) at 5 and 30 mN.m⁻¹ are essentially superimposed. Reprinted from Maggio (2004), copyright 2004, with permission from Elsevier

Fig. 9

Variation of compression free energy in monolayers of GSLs and excess free energy of compression in mixed films with ceramide. The free energy of compression between 2 and 35 mN.m⁻¹ of the sphingolipid indicated in the abscissa is shown in (a). The variation with the type of oligosaccharide chain in the GSLs can be described by two regression lines with different slopes for the series of neutral GSLs (267 cal/mol/carbohydrate residue, r² = 0.995) and gangliosides (390 cal/mol/carbohydrate residue, r² = 0.999).The excess free energy of compression for films of the GSLs indicated in the abscissa with ceramide in equimolar proportions is shown in (b). Reprinted from Maggio (2004), copyright 2004, with permission from Elsevier