Ludwig Alexander, Nichols Benjamin James, Sandin Sara
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551 Singapore
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
J Cell Sci. 2016 Aug 15;129(16):3077-83. doi: 10.1242/jcs.191262. Epub 2016 Jul 1.
Caveolae are specialized membrane domains that are crucial for the correct function of endothelial cells, adipocytes and muscle cells. Caveolins and cavins are both required for caveolae formation, and assemble into a large (80S) caveolar coat complex (80S-CCC). The architecture of the 80S-CCC, however, has not been analyzed. Here, we study the 80S-CCC isolated from mammalian cells using negative stain electron microscopy and 3D cryo-electron tomography. We show that the 80S-CCC is a hollow sphere with a diameter of 50-80 nm, and so has the same size and shape as individual caveolar bulbs. This provides strong evidence that the distinctive membrane shape of caveolae is generated by the shape of the 80S-CCC itself. The particle appears to be made up of two layers, an inner coat composed of polygonal units of caveolins that form a polyhedral cage, and an outer filamentous coat composed of cavins. The data suggest that the peripheral cavin coat is aligned along the edges of the inner polyhedral cage, thereby providing a mechanism for the generation of a morphologically stable caveolar coat.
小窝是特殊的膜结构域，对内皮细胞、脂肪细胞和肌肉细胞的正常功能至关重要。小窝蛋白和小窝相关蛋白都是小窝形成所必需的，并组装成一个大型（80S）小窝衣被复合体（80S-CCC）。然而，80S-CCC的结构尚未得到分析。在这里，我们使用负染电子显微镜和三维冷冻电子断层扫描技术研究了从哺乳动物细胞中分离出的80S-CCC。我们发现80S-CCC是一个直径为50-80纳米的空心球体，与单个小窝泡的大小和形状相同。这有力地证明了小窝独特的膜形状是由80S-CCC本身的形状产生的。该颗粒似乎由两层组成，一层是由小窝蛋白的多边形单元构成的内壳，形成一个多面体笼，另一层是由小窝相关蛋白构成的外壳丝状结构。数据表明，外周的小窝相关蛋白外壳沿着内多面体笼的边缘排列，从而为形成形态稳定的小窝衣被提供了一种机制。
