Stabilization of sphingomyelin interactions by interfacial hydroxyls — A study of phytosphingomyelin properties

D-ribo-phytosphingosines are biologically significant long-chain bases present in various sphingolipids from yeasts, fungi, plants and mammals. In this study we prepared phytopalmitoylsphingomyelin (phytoPSM) analogs based on the D-ribo-phytosphingosine base. The N-linked acyl chains were either 16:0, 2OH(R)16:0 (natural isomer), or 2OH(S)16:0. The gel-phase of phytoPSM was more stable than that of PSM (Tm 48.6 °C and 41.0 °C, respectively). The gel-liquid crystalline phase transition enthalpies were 9.1 ± 0.4 and 6.1 ± 0.3 kcal/mol for phytoPSM and PSM, respectively. An N-linked 2OH(R)16:0 in phytoPSM destabilized the gel phase relative to phytoPSM (by ~+ 6 °C, based on DPH anisotropy measurements), whereas 2OH(S)16:0 in phytoPSM stabilized it (by ~− 6 °C). All phytoPSM analogs formed sterol-enriched ordered domains in a fluid ternary bilayer, and those containing phytoPSM or 2OH(S)phytoPSM were more thermostable than the domains containing 2OH(R)phytoPSM or PSM. The affinity of cholestatrienol for POPC bilayers containing 20 mol% phytoPSM was higher than for comparable bilayers with an equal amount of PSM. The 2-hydroxylated acyl chains in phytoPSM did not markedly alter sterol affinity. We conclude that phytoPSM is a more ordered sphingolipid than PSM, and is fully capable of interacting with cholesterol.

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► The bilayer membrane properties of phytosphingomyelins were examined.
► The gel-phase of phytoSM was markedly stabilized compared to nonhydroxylated SM.
► Sterols displayed high affinity for bilayers containing phytoSM.
► We speculate that phytoPSM may form highly ordered domains in membranes.