Spatial and functional heterogeneity of sphingolipid-rich membrane domains
Spatial and functional heterogeneity of sphingolipid-rich membrane domains
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DOI：
10.1074/jbc.m502244200
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发表时间：
2005-06-24
影响因子：
4.8
通讯作者：
Kobayashi, T
中科院分区：
文献类型：
--
作者：
Kiyokawa, E;Baba, T;Kobayashi, T
人们对生物膜中脂质的组织知之甚少。脂筏被定义为膜上富含鞘磷脂和胆固醇的簇。脂筏中脂质分布的细节没有得到很好的描述，主要是因为缺乏适当的探针。长期以来，神经节苷脂GM1特异性蛋白霍乱毒素一直是脂筏的唯一脂质探针。最近的研究表明，蚯蚓毒素Lysenin能特异性识别富含鞘磷脂的膜结构域。Lysenin与鞘磷脂的结合伴随着毒素的寡聚，导致靶膜上形成孔。在这项研究中，我们产生了一个截短的Lysenin突变体，它不会寡聚，因此是无毒的。利用这个突变的Lysenin，我们发现Jurkat T细胞中富含神经鞘磷脂的膜结构域与富含神经节苷脂GM1的膜结构域在空间上是不同的。与T细胞受体的激活和GM1的交联化一样，神经鞘蛋白的交联会诱导细胞内钙内流和ERK的磷酸化。然而，与CD3或GM1不同的是，鞘磷脂的交联不会诱导显著的蛋白质酪氨酸磷酸化。赖氨酸酶和鞘磷脂酶联合作用提示G蛋白偶联受体参与了鞘磷脂介导的信号转导。因此，这些结果表明，富含鞘磷脂结构域提供了一个不同于T细胞受体或GM1所提供的功能信号级联平台。因此，我们的研究阐明了脂筏的空间和功能异质性。
Little is known about the organization of lipids in biomembranes. Lipid rafts are defined as sphingolipid- and cholesterol-rich clusters in the membrane. Details of the lipid distribution of lipid rafts are not well characterized mainly because of a lack of appropriate probes. Ganglioside GM1-specific protein, cholera toxin, has long been the only lipid probe of lipid rafts. Recently it was shown that earthworm toxin, lysenin, specifically recognizes sphingomyelin-rich membrane domains. Binding of lysenin to sphingomyelin is accompanied by the oligomerization of the toxin that leads to pore formation in the target membrane. In this study, we generated a truncated lysenin mutant that does not oligomerize and thus is non-toxic. Using this mutant lysenin, we showed that plasma membrane sphingomyelin-rich domains are spatially distinct from ganglioside GM1-rich membrane domains in Jurkat T cells. Like T cell receptor activation and cross-linking of GM1, cross-linking of sphingomyelin induced calcium influx and ERK phosphorylation in the cell. However, unlike CD3 or GM1, cross-linking of sphingomyelin did not induce significant protein tyrosine phosphorylation. Combination of lysenin and sphingomyelinase treatment suggested the involvement of G-protein-coupled receptor in sphingomyelin-mediated signal transduction. These results thus suggest that the sphingomyelin-rich domain provides a functional signal cascade platform that is distinct from those provided by T cell receptor or GM1. Our study therefore elucidates the spatial and functional heterogeneity of lipid rafts.