Structure and lipid interaction of N-palmitoylsphingomyelin in bilayer membranes as revealed by 2H-NMR spectroscopy.

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.

The 3-hydroxy group and 4,5-trans double bond of sphingomyelin are essential for modulation of galactosylceramide transmembrane asymmetry.

The structural features of SPM that control the transbilayer distribution of beta-GalCer in POPC vesicles were investigated by (13)C- and (31)P-NMR spectroscopy using lipid analogs that share physical similarities with GalCer or SPM. The SPM analogs included N-palmitoyl-4,5-dihydro-SPM, 3-deoxy-SPM, 1-alkyl-2-amidophosphatidylcholine, and dipalmitoylphosphatidylcholine, a popular model "raft lipid". The transbilayer distributions of the SPM analogs and SPM in POPC vesicles were similar by (31)P-NMR.