title: Importance of the phosphocholine linkage on sphingomyelin molecular properties and interactions with cholesterol; a study with phosphate oxygen modified sphingomyelin-analogues.
abstract: We have characterized the molecular properties and membrane behavior of synthetically modified sphingomyelin analogues, modified on the oxygen connecting the phosphocholine group to the ceramide backbone. The oxygen was replaced with an S-atom (S-PSM), an NH-group (NH-PSM) or a CH(2)-group (CH(2)-PSM). Diphenylhexatriene and Laurdan anisotropy experiments showed that an S-linkage increased and NH- and CH(2)-linkages decreased the stability of PSM-analogue bilayer membranes as compared to PSM. When the polarity of the interface was probed using Laurdan, S-PSM appeared to have a lower polarity as compared to PSM whereas NH-PSM and CH(2)-PSM had higher polarities of their respective interfaces. Fluorescence quenching-studies with cholestatrienol showed that all compounds formed SM/cholesterol-rich domains. The S-PSM/cholesterol and PSM/cholesterol domains displayed a similar thermostability, whereas NH-PSM/cholesterol and CH(2)-PSM/cholesterol domains were less thermostable. DSC on vesicles containing the PSM-analogues showed a more complex melting behavior as compared to PSM, whereas equimolar mixtures of the PSM-analogues and PSM showed almost ideal mixing with PSM for NH- and S-PSM. Our data show that the properties of the bond linking the phosphocholine head group to the 1-hydroxyl on the ceramide molecule is important for the stability of SM/SM and SM/cholesterol interactions.
authors.affiliation: Department of Biochemistry and Pharmacy, Abo Akademi University, Turku, Finland. abjorkbo@abo.fi
authors.forename: Anders
authors.initials: A
authors.lastname: Björkbom
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kaji
authors.forename: Shuji
authors.initials: S
authors.lastname: Harada
authors.forename: Shigeo
authors.initials: S
authors.lastname: Katsumura
authors.forename: J Peter
authors.initials: JP
authors.lastname: Slotte
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D010767:Phosphorylcholine / Q000737:chemistry*; D013109:Sphingomyelins / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D010710:Phosphates; D013109:Sphingomyelins; D010767:Phosphorylcholine; D002784:Cholesterol; D010100:Oxygen