Nyholm Thomas K M, Grandell Pia-Maria, Westerlund Bodil, Slotte J Peter
Abo Akademi University, Department of biochemistry and pharmacy, Tykistökatu 6A, 20520 Turku, Finland.
Biochim Biophys Acta. 2010 May;1798(5):1008-13. doi: 10.1016/j.bbamem.2009.12.025. Epub 2010 Jan 4.
It is known that ceramides can influence the lateral organization in biological membranes. In particular ceramides have been shown to alter the composition of cholesterol and sphingolipid enriched nanoscopic domains, by displacing cholesterol, and forming gel phase domains with sphingomyelin. Here we have investigated how the bilayer content of ceramides and their chain length influence sterol partitioning into the membranes. The effect of ceramides with saturated chains ranging from 4 to 24 carbons in length was investigated. In addition, unsaturated 18:1- and 24:1-ceramides were also examined. The sterol partitioning into bilayer membranes was studied by measuring the distribution of cholestatrienol, a fluorescent cholesterol analogue, between methyl-beta-cyclodextrin and large unilamellar vesicle with defined lipid composition. Up to 15 mol% ceramide was added to bilayers composed of DOPC:PSM:cholesterol (3:1:1), and the effect on sterol partitioning was measured. Both at 23 and 37 degrees C addition of ceramide affected the sterol partitioning in a chain length dependent manner, so that the ceramides with intermediate chain lengths were the most effective in reducing sterol partitioning into the membranes. At 23 degrees C the 18:1-ceramide was not as effective at inhibiting sterol partitioning into the vesicles as its saturated equivalent, but at 37 degrees C the additional double bond had no effect. The longer 24:1-ceramide behaved as 24:0-ceramide at both temperatures. In conclusion, this work shows how the distribution of sterols within sphingomyelin-containing membranes is affected by the acyl chain composition in ceramides. The overall membrane partitioning measured in this study reflects the differential partitioning of sterol into ordered domains where ceramides compete with the sterol for association with sphingomyelin.
已知神经酰胺可影响生物膜的侧向组织。特别是，神经酰胺已被证明可通过取代胆固醇并与鞘磷脂形成凝胶相结构域来改变富含胆固醇和鞘脂的纳米级结构域的组成。在这里，我们研究了神经酰胺的双层含量及其链长如何影响甾醇在膜中的分配。研究了链长为4至24个碳原子的饱和链神经酰胺的作用。此外，还检测了不饱和的18:1-和24:1-神经酰胺。通过测量荧光胆固醇类似物胆甾三烯醇在甲基-β-环糊精和具有确定脂质组成的大单层囊泡之间的分布，研究了甾醇在双层膜中的分配。向由DOPC:PSM:胆固醇（3:1:1）组成的双层膜中添加高达15 mol%的神经酰胺，并测量其对甾醇分配的影响。在23℃和37℃下，神经酰胺的添加均以链长依赖的方式影响甾醇分配，因此中等链长的神经酰胺在减少甾醇向膜中的分配方面最为有效。在23℃时，18:1-神经酰胺在抑制甾醇向囊泡中的分配方面不如其饱和等效物有效，但在37℃时，额外的双键没有影响。在两个温度下，较长的24:1-神经酰胺的行为与24:0-神经酰胺相同。总之，这项工作表明了含鞘磷脂膜中甾醇的分布是如何受到神经酰胺中酰基链组成影响的。本研究中测量的整体膜分配反映了甾醇在有序结构域中的差异分配，其中神经酰胺与甾醇竞争与鞘磷脂的结合。
