Structure and Lipid Interaction of N-Palmitoylsphingomyelin in Bilayer Membranes as Revealed by 2H-NMR Spectroscopy

Abstract

Selectively deuterated N-palmitoyl sphingomyelins were studied by deuterium nuclear magnetic resonance spectroscopy ((2)H-NMR) to elucidate the backbone conformation as well as the interaction of the sphingolipids with glycerophospholipids. Macroscopic alignment of the lipid bilayers provided good spectral resolution and permitted the convenient control of bilayer hydration. Selective deuteration at the acyl chain carbons C(2) and C(3) revealed that the N-acyl chain performs a bend, similar to the sn-2 chain of the phosphatidylcholines. Profiles of C-D bond order parameters were derived from the segmental quadrupolar splittings for sphingomyelin alone and for sphingomyelin-phosphatidycholine mixtures. In the liquid-crystalline state, the N-acyl chain of sphingomyelin alone revealed significantly more configurational order than the chains of homologous disaturated or monounsaturated phosphatidylcholines. The average chain order parameters and the relative width of the order parameter distribution were correlated over a range of bilayer compositions. The temperature dependence of the (2)H-NMR spectra revealed phase separation in bilayers composed of sphingomyelin and monounsaturated phosphatidylcholine, in broad agreement with existing phase diagrams.

Assessing the Nature of Lipid Raft Membranes

“…The overall ordering in S C is much weaker (S CD ¼À0.18) than in the two other systems, but even S C displays lateral heterogeneity, though the domains appear larger, smoother, and with smaller variations in the S CD values. The average S CD values are in line with corresponding experimental order parameter profiles of fluid POPC [53,54] and DPPC-CHOL mixtures with similar CHOL concentrations [45,55].…”

Effect of Low Concentration of DHPC on the DPPC/Sm Bilayer

“…On the other hand, the values of the order parameter obtained for system D are lower than those obtained for system A, suggesting that chains in system D are less ordered with values typically observed for liquid crystal state. This behavior is in agreement with previous reports 41 .…”

Pressure–temperature phase behaviour of natural sphingomyelin extracts

“…24 MAS NMR line width increases are 50 observed for both of these phospholipids prior to chain melting and a similar trend has also been reported previously in 2 H NMR studies of perdeuterated DPPC 25 and palmitoyl-SM. 26 From these experiments, this effect appears to be independent of both headgroup and interfacial structure and we believe that this may be a universal trend related to lipid melting transitions.…”