Laboratoire de Biogenèse Membranaire, UMR 5200, CNRS-Université Victor Segalen Bordeaux 2, 33076 Bordeaux, France.
Plant Physiol. 2010 Apr;152(4):2173-87. doi: 10.1104/pp.109.149823. Epub 2010 Feb 24.
In this article, we analyzed the lipid composition of detergent-insoluble membranes (DIMs) purified from tobacco (Nicotiana tabacum) plasma membrane (PM), focusing on polyphosphoinositides, lipids known to be involved in various signal transduction events. Polyphosphoinositides were enriched in DIMs compared with whole PM, whereas all structural phospholipids were largely depleted from this fraction. Fatty acid composition analyses suggest that enrichment of polyphosphoinositides in DIMs is accompanied by their association with more saturated fatty acids. Using an immunogold-electron microscopy strategy, we were able to visualize domains of phosphatidylinositol 4,5-bisphosphate in the plane of the PM, with 60% of the epitope found in clusters of approximately 25 nm in diameter and 40% randomly distributed at the surface of the PM. Interestingly, the phosphatidylinositol 4,5-bisphosphate cluster formation was not significantly sensitive to sterol depletion induced by methyl-beta-cyclodextrin. Finally, we measured the activities of various enzymes of polyphosphoinositide metabolism in DIMs and PM and showed that these activities are present in the DIM fraction but not enriched. The putative role of plant membrane rafts as signaling membrane domains or membrane-docking platforms is discussed.
在本文中，我们分析了从烟草（Nicotiana tabacum）质膜（PM）中纯化的去污剂不溶性膜（DIM）的脂质组成，重点研究了多聚磷酸肌醇，这些脂质已知参与各种信号转导事件。与完整的 PM 相比，多聚磷酸肌醇在 DIM 中得到了富集，而所有结构磷脂则从该部分大量耗尽。脂肪酸组成分析表明，多聚磷酸肌醇在 DIM 中的富集伴随着它们与更多饱和脂肪酸的结合。使用免疫金电子显微镜策略，我们能够在 PM 的平面上可视化磷脂酰肌醇 4,5-二磷酸的结构域，60%的表位存在于直径约 25nm 的簇中，40%随机分布在 PM 的表面。有趣的是，磷脂酰肌醇 4,5-二磷酸簇的形成对甲基-β-环糊精诱导的固醇耗竭并不敏感。最后，我们测量了 DIM 和 PM 中各种多聚磷酸肌醇代谢酶的活性，并表明这些活性存在于 DIM 部分，但没有富集。讨论了植物膜筏作为信号转导膜域或膜对接平台的可能作用。
