Bilayer Thickness Mismatch Controls Domain Size in Model Membranes
Bilayer Thickness Mismatch Controls Domain Size in Model Membranes
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DOI：
10.1021/ja3113615
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发表时间：
2013-05-08
影响因子：
15
通讯作者：
Katsaras, John
中科院分区：
文献类型：
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作者：
Heberle, Frederick A.;Petruzielo, Robin S.;Katsaras, John
脂双层中横向相分离的观察受到了相当多的关注，特别是与细胞中的脂筏现象有关。人们普遍认为筏在细胞过程中发挥着核心作用，尤其是信号转导。虽然在一些模型膜混合物中观察到微米大小的域，但现在认为在体外和体内都存在比 100 nm 小得多的筏（超出了光学显微镜的范围）。我们使用小角度中子散射（一种无探针技术）以前所未有的精度测量单层囊泡中纳米级膜域的尺寸。这些实验是使用四组分模型系统进行的，该系统包含固定比例的胆固醇和饱和磷脂 1,2-二硬脂酰-sn-甘油-3-磷酸胆碱 (DSPC)，与不同量的不饱和磷脂 1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱 (POPC) 和1,2-二油酰-sn-甘油-3-磷酸胆碱（DOPC）。我们发现液体域尺寸随着酰基链不饱和程度（DOPC：POPC 比率）的增加而增加。此外，我们发现域尺寸与共存的液体有序相和液体无序相的双层厚度不匹配之间存在直接相关性，这表明线张力在控制域尺寸中起主导作用。虽然这一结果是线张力理论所预期的，但我们在自由浮动双层中提供了第一个实验验证。重要的是，我们还发现双层厚度的变化，伴随着脂质链不饱和程度的变化，完全局限于无序相。总之，这些结果表明恒温细胞中功能域的大小如何通过脂质成分的变化来调节。
The observation of lateral phase separation in lipid bilayers has received considerable attention, especially in connection to lipid raft phenomena in cells. It is widely accepted that rafts play a central role in cellular processes, notably signal transduction. While micrometer-sized domains are observed with some model membrane mixtures, rafts much smaller than 100 nm-beyond the reach of optical microscopy-are now thought to exist, both in vitro and in vivo. We have used small-angle neutron scattering, a probe free technique, to measure the size of nanoscopic membrane domains in unilamellar vesicles with unprecedented accuracy. These experiments were performed using a four-component model system containing fixed proportions of cholesterol and the saturated phospholipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), mixed with varying amounts of the unsaturated phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). We find that liquid domain size increases with the extent of acyl chain unsaturation (DOPC:POPC ratio). Furthermore, we find a direct correlation between domain size and the mismatch in bilayer thickness of the coexisting liquid-ordered and liquid-disordered phases, suggesting a dominant role for line tension in controlling domain size. While this result is expected from line tension theories, we provide the first experimental verification in free-floating bilayers. Importantly, we also find that changes in bilayer thickness, which accompany changes in the degree of lipid chain unsaturation, are entirely confined to the disordered phase. Together, these results suggest how the size of functional domains in homeothermic cells may be regulated through changes in lipid composition.