title: Cholesterol decreases the interfacial elasticity and detergent solubility of sphingomyelins.
abstract: The interfacial interactions of cholesterol with sphingomyelins (SMs) containing various homogeneous acyl chains have been investigated by Langmuir film balance approaches. Low in-plane elasticity among the packed lipids was identified as an important physical feature of the cholesterol-sphingomyelin liquid-ordered phase that correlates with detergent resistance, a characteristic property of sphingolipid-sterol rafts. Changes in the in-plane elastic packing, produced by cholesterol, were quantitatively assessed by the surface compressional moduli (C(s)(-1)) of the monolayer isotherms. Of special interest were C(s)(-1) values determined at high surface pressures (>30 mN/m) that mimic the biomembrane situation. To identify structural features that uniquely affect the in-plane elasticity of the sphingomyelin-cholesterol lateral interaction, comparisons were made with phosphatidylcholine (PC)-cholesterol mixtures. Cholesterol markedly decreased the in-plane elasticity of either SM or PC regardless of whether they were fluid or gel phase without cholesterol. The magnitude of the reduction in in-plane elasticity induced by cholesterol was strongly influenced by acyl chain structure and by interfacial functional groups. Liquid-ordered phase formed at lower cholesterol mole fractions when SM's acyl chain was saturated rather than monounsaturated. At similar high cholesterol mole fractions, the in-plane elasticity within SM-cholesterol liquid-ordered phase was significantly lower than that of PC-cholesterol liquid-ordered phase, even when PCs were chain-matched to the SMs. Sphingoid-base functional groups (e.g., amide linkages), which facilitate or strengthen intermolecular hydrogen bonds, appear to be important for forming sphingomyelin-cholesterol, liquid-ordered phases with especially low in-plane elasticity. The combination of structural features that predominates in naturally occurring SMs permits very effective resistance to solubilization by Triton X-100.
authors.affiliation: The Hormel Institute, University of Minnesota, 801 16th Avenue NE, Austin, Minnesota 55912, USA.
authors.forename: X M
authors.initials: XM
authors.lastname: Li
authors.forename: M M
authors.initials: MM
authors.lastname: Momsen
authors.forename: J M
authors.initials: JM
authors.lastname: Smaby
authors.forename: H L
authors.initials: HL
authors.lastname: Brockman
authors.forename: R E
authors.initials: RE
authors.lastname: Brown
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000818:Animals; D002417:Cattle; D002645:Chickens; D002784:Cholesterol / Q000737:chemistry*; D003902:Detergents / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D004548:Elasticity; D005231:Fatty Acids, Unsaturated / Q000737:chemistry; D017830:Octoxynol / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D012995:Solubility; D013109:Sphingomyelins / Q000737:chemistry*
chemical_list: D003902:Detergents; D005231:Fatty Acids, Unsaturated; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D015060:1,2-Dipalmitoylphosphatidylcholine; C086029:1-myristoyl-2-palmitoyl-sn-glycero-3-phosphocholine; D017830:Octoxynol; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine