Depth-Dependent Segmental Melting of the Sphingomyelin Alkyl Chain in Lipid Bilayers
Depth-Dependent Segmental Melting of the Sphingomyelin Alkyl Chain in Lipid Bilayers
复制标题
脂质双层中鞘磷脂烷基链的深度依赖性片段熔化
DOI：
10.1021/acs.langmuir.2c00092
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发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Murata Michio
中科院分区：
文献类型：
--
作者：
Tsuchikawa Hiroshi;Monji Mami;Umegawa Yuichi;Yasuda Tomokazu;Slotte J. Peter;Murata Michio
脂双层的链熔融通常使用量热方法，如差示扫描量热法（DSC）进行详细研究，并且所得的主转变温度被认为是模型膜实验中最重要的参数之一。然而，并不总是清楚脂质的烃链是沿着脂质双层的深度逐渐熔化，还是它们都在非常窄的温度范围内同时熔化，如DSC所暗示的。在本研究中，我们重点关注了作为成筏脂质的一个例子的硬脂酰-d-鞘磷脂（SSM）。我们在4′，10′和16′位置合成了氘标记的SSM，并使用固态氘NMR通过改变温度1.0 °C测量了它们的深度依赖性熔融，并与饱和脂质棕榈酰硬脂酰磷脂酰胆碱（PSPC）的观察结果进行比较。结果表明，SSM表现出特征的深度依赖性熔化，这是没有观察到的PSPC。鞘磷脂酰胺部分之间的强分子间氢键可能导致链熔融从链末端开始通过中间部分并在上部结束。这种依赖于深度的熔融意味着SSM的小凝胶状域保持在略高于主转变温度的温度下。这些鞘磷脂的功能可能是负责SM为基础的脂筏的生物学特性。
The chain melting of lipid bilayers has often been investigated in detail using calorimetric methods, such as differential scanning calorimetry (DSC), and the resultant main transition temperature is regarded as one of the most important parameters in model membrane experiments. However, it is not always clear whether the hydrocarbon chains of lipids are gradually melting along the depth of the lipid bilayer or whether they all melt concurrently in a very narrow temperature range, as implied by DSC. In this study, we focused on stearoyl-d-sphingomyelin (SSM) as an example of raft-forming lipids. We synthesized deuterium-labeled SSMs at the 4′, 10′, and 16′ positions, and their depth-dependent melting was measured using solid-state deuterium NMR by changing the temperature by 1.0 °C, and comparing with that observed from a saturated lipid, palmitoylstearoylphosphatidylcholine (PSPC). The results showed that SSM exhibited a characteristic depth-dependent melting, which was not observed for PSPC. The strong intermolecular hydrogen bonds between the sphingomyelin amide moiety probably caused the chain melting to start from the chain terminus through the middle part and end in the upper part. This depth-dependent melting implies that the small gel-like domains of SSM remain at temperatures slightly above the main transition temperature. These sphingomyelin features may be responsible for the biological properties of SM-based lipid rafts.