Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy
Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy
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DOI：
10.1073/pnas.1418088112
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发表时间：
2015-04-14
影响因子：
11.1
通讯作者：
Sodeoka, Mikiko
中科院分区：
文献类型：
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作者：
Ando, Jun;Kinoshita, Masanao;Sodeoka, Mikiko
细胞膜上富含鞘磷脂（SM）和胆固醇（chol）的结构域称为脂筏，被认为具有与膜信号传导和蛋白质运输相关的重要生物学功能。为了通过拉曼显微镜观察SM在脂筏中的分布，我们设计并合成了一种带有拉曼活性二炔部分的SM类似物（diyne-SM）。Diyne-SM在拉曼沉默区显示出强峰，该区域不受脂质固有振动模式的干扰，并且似乎不会改变含SM单层的性质。因此，我们使用拉曼显微镜直接可视化的分布，二炔-SM的筏模拟域中形成的SM/二油酰磷脂酰胆碱/胆固醇三元单层。拉曼图像可视化的二炔-SM，这表明显着的变化，即使在一个单一的有序域的不均匀分布。具体而言，二炔-SM是丰富的筏域的中心区域相比，周边区域。这些结果似乎不符合普遍接受的筏模型，筏和nonraft相显示出明显的两相分离。其中一个可能的原因是SM浓度的逐渐变化发生在SM富集和SM贫乏区域之间，以最小化疏水错配。我们相信，我们的技术的高光谱拉曼成像的一个单一的脂质单层打开了大门，定量分析的脂质膜提供化学信息和空间分布与高（衍射限制）的空间分辨率。
Sphingomyelin (SM) and cholesterol (chol)-rich domains in cell membranes, called lipid rafts, are thought to have important biological functions related to membrane signaling and protein trafficking. To visualize the distribution of SM in lipid rafts by means of Raman microscopy, we designed and synthesized an SM analog tagged with a Raman-active diyne moiety (diyne-SM). Diyne-SM showed a strong peak in a Raman silent region that is free of interference from intrinsic vibrational modes of lipids and did not appear to alter the properties of SM-containing monolayers. Therefore, we used Raman microscopy to directly visualize the distribution of diyne-SM in raft-mimicking domains formed in SM/dioleoylphosphatidylcholine/chol ternary monolayers. Raman images visualized a heterogeneous distribution of diyne-SM, which showed marked variation, even within a single ordered domain. Specifically, diyne-SM was enriched in the central area of raft domains compared with the peripheral area. These results seem incompatible with the generally accepted raft model, in which the raft and nonraft phases show a clear biphasic separation. One of the possible reasons is that gradual changes of SM concentration occur between SM-rich and -poor regions to minimize hydrophobic mismatch. We believe that our technique of hyperspectral Raman imaging of a single lipid monolayer opens the door to quantitative analysis of lipid membranes by providing both chemical information and spatial distribution with high (diffraction-limited) spatial resolution.