NMR-based conformational analysis of sphingomyelin in bicelles

Abstract

Sphingomyelin (SM) is a common sphingolipid in mammalian membranes and is known to be substantially involved in cellular events such as the formation of lipid rafts. Despite its biological significance, conformation of SM in a membrane environment remains unclear because the noncrystalline property and anisotropic environment of lipid bilayers hampers the application of X-ray crystallography and NMR measurements. In this study, to elucidate the conformation of SM in membranes, we utilized bicelles as a substitute for a lipid bilayer membrane. First, we demonstrated through 31P NMR, 2H NMR, and dynamic light scattering experiments that SM forms both oriented and isotropic bicelles by changing the ratio of SM/dihexanoyl phosphatidylcholine. Then, we determined the conformation of SM in isotropic bicelles on the basis of coupling constants and NOE correlations in 1H NMR and found that the C2–C6 and amide groups of SM take a relatively rigid conformation in bicelles.