Cholesterol Decreases the Interfacial Elasticity and Detergent Solubility of Sphingomyelins

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• 作者：Xin-Min Li ; Maureen M. Momsen ; Janice M. Smaby ; Howard L. Brockman ; and Rhoderick E. Brown
• 刊名：Biochemistry
• 出版年：2001
• 出版时间：May 22, 2001
• 年：2001
• 卷：40
• 期：20
• 页码：5954 - 5963
• 全文大小：145K
• 年卷期：v.40,no.20(May 22, 2001)
• ISSN：1520-4995

文摘

The interfacial interactions of cholesterol with sphingomyelins (SMs) containing varioushomogeneous acyl chains have been investigated by Langmuir film balance approaches. Low in-planeelasticity 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 ofsphingolipid-sterol rafts. Changes in the in-plane elastic packing, produced by cholesterol, werequantitatively assessed by the surface compressional moduli (C_s^-1) of the monolayer isotherms. Of specialinterest were C_s^-1 values determined at high surface pressures (>30 mN/m) that mimic the biomembranesituation. 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 theywere fluid or gel phase without cholesterol. The magnitude of the reduction in in-plane elasticity inducedby 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 thanmonounsaturated. At similar high cholesterol mole fractions, the in-plane elasticity within SM-cholesterolliquid-ordered phase was significantly lower than that of PC-cholesterol liquid-ordered phase, even whenPCs were chain-matched to the SMs. Sphingoid-base functional groups (e.g., amide linkages), whichfacilitate 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 structuralfeatures that predominates in naturally occurring SMs permits very effective resistance to solubilizationby Triton X-100.