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Abstract
ABSTRACTCaveolae 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.
Highlights
Caveolae are abundant flask- or cup-shaped invaginations in the plasma membrane that are found in almost all vertebrate cells (Stan, 2005)
Caveolin-1 and cavin-1 are essential for the formation of caveolae in vivo (Drab et al, 2001; Hill et al, 2008; Liu and Pilch, 2008), and mutations in caveolin or cavin genes lead to a variety of human diseases (Ding et al, 2014; Liu et al, 2008; Woodman et al, 2004; Rajab et al, 2010; Hayashi et al, 2009)
We have recently demonstrated that caveolins and cavins assemble into a distinct 80S particle, which we termed the caveolar coat complex (80S-CCC) (Ludwig et al, 2013)
Summary
Caveolae are abundant flask- or cup-shaped invaginations in the plasma membrane that are found in almost all vertebrate cells (Stan, 2005). We have recently demonstrated that caveolins and cavins assemble into a distinct 80S particle, which we termed the caveolar coat complex (80S-CCC) (Ludwig et al, 2013). To investigate the overall shape and structure of the purified 80SCCC, we studied the complex by negative stain electron microscopy (Fig. 1E).
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