Model for the architecture of caveolae based on a flexible, net-like assembly of Cavin1 and Caveolin discs

Stoeber, Miriam; Schellenberger, Pascale; Siebert, C. Alistair; Leyrat, C.; Helenius, Ari; Grünewald, Kay

doi:10.1073/pnas.1616838113

Cited by 94 publications

(138 citation statements)

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“…These particles bound robustly to liposomes containing phosphatidylserine (PS) or phosphatidic acid, as seen previously using recombinant cavin proteins (10,11), and showed a propensity to form relatively well-ordered lattices of protein on the membrane surface. Interestingly, in this in vitro system the full-length Cavin1 protein could be observed on the interior surface of the vesicles, which Stoeber et al (6) suggest may be because of the occurrence of frequent inward invagination of the PS-containing liposomes. Most remarkably, Cavin1 appeared to form membrane-dependent polygonal arrays, which begins to suggest a potential for protein-protein and protein-membrane interactions to generate a structural scaffold from a loose net-like assembly of soluble cavin oligomers.…”

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confidence: 66%

“…By high-resolution scanning electron microscopy (EM) and frozen deepetch transmission EM, caveolae have been shown to be coated with striations (1,2) or to possess spike-like structures (3), very different from other well-characterized vesicle coats, such as clathrin (4,5). In PNAS, Stoeber et al use a combination of biochemical dissection and EM to provide important insights into the underlying architecture of the caveola protein coat (6).…”

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confidence: 99%

“…Most remarkably, Cavin1 appeared to form membrane-dependent polygonal arrays, which begins to suggest a potential for protein-protein and protein-membrane interactions to generate a structural scaffold from a loose net-like assembly of soluble cavin oligomers. Next, Stoeber et al (6) probed the importance of the HR1 and HR2 domains of Cavin1 for oligomerization, membrane association, and membrane remodeling activity. Both HR1 and HR2 were found to be equally important for membrane localization in cells; however, although removal of HR1 prevented oligomer formation altogether, removing HR2 still yielded partial oligomers, albeit smaller than the 60S particles of the wild-type Cavin1 protein.…”

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confidence: 99%

“…Stoeber et al (6) next extended their analyses to the other major structural component of caveolae, the integral membrane protein, CAV1. Although this necessitated the use of detergents and negative staining, rather than cryoEM, the detergent solubilized 8S CAV1 oligomers were found to form relatively homogeneous disk-shaped particles ∼15 nm in diameter, which also resemble particles of recombinant CAV3 seen previously when Cavins possess two regions of α-helical structure, termed HR1 and HR2, which are rich in basic residues.…”

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confidence: 99%

“…They also possess a conserved sequence suggested to be involved in oligomerization (oligomerization domain, OD) and a sequence with potential roles in protein-protein interactions (caveolin scaffolding domain, CSD), although this is controversial (20). (C) Proposed model for caveolar assembly by Stoeber et al (6). CAV1 can be isolated as disk-shaped oligomers ∼15 nm in diameter that are proposed to be underlying building blocks of the caveolar coat.…”

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Unraveling the architecture of caveolae

Parton

Collins

2016

Proc. Natl. Acad. Sci. U.S.A.

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The eukaryotic cell surface is composed of many distinct membrane domains that are formed by the cooperative interactions of different proteins and lipids. These domains are important for membrane trafficking and cell signaling and are modulated in turn by changes in the cell environment. Caveolae ("little caves") are ∼60-nm membrane invaginations ( Fig. 1) that are a dominant surface feature of many mammalian cells, including muscle fibers, endothelia, and adipocytes, where they play a role in membrane homeostasis, signaling, and cellular mechanoprotection. Formation of caveolae in vertebrate cells requires two distinct protein families: the membrane-embedded caveolins (CAV1-3) and the peripheral membrane cavins (Cavin1-4). Although the general morphology of caveolae has been known for decades, the atypical structures of the protein subunits has meant that progress has been slow with regards to the high-resolution studies of caveola architecture. By high-resolution scanning electron microscopy (EM) and frozen deepetch transmission EM, caveolae have been shown to be coated with striations (1, 2) or to possess spike-like structures (3), very different from other well-characterized vesicle coats, such as clathrin (4, 5). In PNAS, Stoeber et al. use a combination of biochemical dissection and EM to provide important insights into the underlying architecture of the caveola protein coat (6).The first protein component of caveolae to be identified and shown to be essential for caveola formation was CAV1 (7-9). Subsequently, it was found that both CAV2 and muscle-specific CAV3 homologs are also localized to caveolae. Caveolin proteins are ∼20 kDa and possess two membrane-inserted α-helices with cytoplasmic N-and C-terminal sequences. These proteins form oligomeric complexes at the plasma membrane that line the cytoplasmic leaflet of the invaginated caveola structures. Cavins, although equally important for caveola formation, were only identified in the past decade through proteomic and cellular studies from several groups. Cavins also possess a conserved and unique structural organization, in this case consisting of conserved N-and C-terminal α-helical domains (HR1 and HR2) interspersed by disordered linker sequences (DR1, DR2, DR3) (10). Although recent studies have begun to tease out the functions of these domains in membrane recruitment, remodeling, and protein-protein interactions, our understanding is still limited. For example, how do caveolin oligomers assemble within caveolae, and what drives cavin oligomerization and recruitment to caveolar domains at the cell surface?In their report, Stoeber et al. (6) propose a model for the arrangement of the caveolin and cavin proteins that begins to address some of the ongoing questions in the field. Affinity purification of Cavin1 expressed in HEK293 cells revealed the presence of heterogeneous particles with a mesh-like appearance by cryoEM and 3D electron tomography. These particles bound robustly to liposomes containing phosphatidylserine (PS) or phosphatidic acid, as...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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