Pressure–temperature phase behaviour of natural sphingomyelin extracts

Abstract

Sphingomyelin is the only sphingolipid occurring naturally in mammalian cells and can form up to 50% of the total phospholipid content of the myelin sheath which surrounds nerves. Having predominantly long, saturated acyl chains, it has a relatively high chain melting temperature and has been strongly associated with formation of lipid microdomains. Here, the lyotropic phase behaviour of sphingomyelin 10 from three different natural sources (bovine brain, egg yolk and milk) in excess water is studied as a function of temperature and pressure by small-and wide-angle X-ray scattering, and solid state NMR. The different hydrocarbon chain length distributions of the three lipid extracts results in significant differences in their gel phase structure; both the bovine brain and egg yolk sphingomyelins can form a ripple gel phase but milk sphingomyelin forms an interdigitated gel phase due to the high degree of chain 15 mismatch in its longer hydrocarbon chain components.

Pressure–Temperature Phase Behavior of Mixtures of Natural Sphingomyelin and Ceramide Extracts

“…As previously observed for pure ESM, diffraction patterns from the ripple phase of ESM rich mixtures are less well resolved than for other sphingomyelin extracts such as that from bovine brain, 7 however the characteristic peak envelope and low intensity, small angle peak (at around 0.0065 Å -1 in Figure 4a) strongly suggest ripple phase formation. Due to the poor resolution, accurate lattice parameter determination is not possible, however we have been able to estimate these by assuming γ (the angle between the a and b lattice parameters) is 90° as previously, In pure ESM, DSC data shows a single peak with an onset of 39.3 °C (ESI Figure S2) corresponding to the ripple to fluid lamellar transition as previously reported.…”

“…Due to the poor resolution, accurate lattice parameter determination is not possible, however we have been able to estimate these by assuming γ (the angle between the a and b lattice parameters) is 90° as previously, In pure ESM, DSC data shows a single peak with an onset of 39.3 °C (ESI Figure S2) corresponding to the ripple to fluid lamellar transition as previously reported. 7 After addition of up to 20 mol% EC, the ripple phase is still visible, and it shows a similar transition temperature however, SAXS data shows that the ripple phase no longer transforms to a fluid lamellar phase but to a flat gel phase.…”

“…Above its main transition temperature of approximately 39 °C, ESM is known to form a fluid lamellar phase, 7 however, ceramides are known to have significantly higher gel -fluid transition temperatures. 4 Increasing the EC content causes an increase in the lattice parameter of up to 1.5 Å.…”

“…7 In particular, ESM exhibits a ripple phase in between the unrippled lamellar gel phase and the fluid lamellar phase, with a narrow coexistence region between the fluid lamellar and ripple gel phases.…”

Polymer resonators sensors for detection of sphingolipid gel/fluid phase transition and melting temperature measurement

“…SPH is especially prominent in myelin, a membranous sheath that surrounds and insulates the axons of numerous neurons [29][30][31][32]. In humans, SPH represents 85% of all sphingolipids, and typically make up 10-20 mol % of plasma membrane lipids with higher concentrations found in nerve tissues, red blood cells, and the ocular lenses… Such a plasma membrane component participates in many signaling pathways.…”