title: Comprehensive molecular motion capture for sphingomyelin by site-specific deuterium labeling.
abstract: Lipid rafts have attracted much attention because of their significant functional roles in membrane-associated processes. It is thought that sphingomyelin and cholesterol are essential for forming lipid rafts; however, their motion characteristics are not fully understood despite numerous studies. Here we show accurate local motions encompassing an entire sphingomyelin molecule, which were captured by measuring quadrupole splittings for 19 kinds of site-specifically deuterated sphingomyelins (that is, molecular motion capture of sphingomyelin). The quadrupole splitting profiles, which are distinct from those reported from perdeuterated sphingomyelins or simulation studies, reveal that cholesterol enhances the order in the middle parts of the alkyl chains more efficaciously than at the shallow positions. Comparison with dimyristoylphosphocholine bilayers suggests that cholesterol is deeper in sphingomyelin bilayers, which likely explains the so-called umbrella effect. The experiments also demonstrate that (i) the C2'-C3' bond predominantly takes the gauche conformation, (ii) the net ordering effect of cholesterol in sphingomyelin bilayers is not larger than that in phosphatidylcholine bilayers, (iii) cholesterol has no specific preference for the acyl or sphingosine chain, (iv) the acyl and sphingosine chains seem mismatched by about two methylene lengths, and (v) the motion of the upper regions of sphingomyelin chains is less temperature dependent than that of lower regions probably due to intermolecular hydrogen bond formation among SM molecules. These insights into the atomic-level dynamics of sphingomyelin provide critical clues to understanding the mechanism of raft formation.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. matsmori@chem.sci.osaka-u.ac.jp
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Matsumori
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Yasuda
authors.forename: Hiroki
authors.initials: H
authors.lastname: Okazaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsuchikawa
authors.forename: Mototsugu
authors.initials: M
authors.lastname: Doi
authors.forename: Tohru
authors.initials: T
authors.lastname: Oishi
authors.forename: Michio
authors.initials: M
authors.lastname: Murata
mesh_terms: D002784:Cholesterol / Q000737:chemistry; D003903:Deuterium; D008051:Lipid Bilayers / Q000737:chemistry; D021962:Membrane Microdomains / Q000737:chemistry*; D008968:Molecular Conformation; D009038:Motion; D019906:Nuclear Magnetic Resonance, Biomolecular; D010713:Phosphatidylcholines / Q000737:chemistry; D013109:Sphingomyelins / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D002784:Cholesterol; D003903:Deuterium