Membrane structure of caveolae and isolated caveolin-rich vesicles |
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Authors: | M Westermann Heiko Leutbecher Helmut W Meyer |
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Institution: | Institut für Ultrastrukturforschung des Klinikums der Friedrich Schiller Universit?t Jena, Ziegelmühlenweg 1, D-07740 Jena, Germany e-mail:i5maws@rz.uni-jena.de Tel. +49-03641-933123; Fax +49-03641-933102, DE Institut für Biochemie II des Klinikums der Friedrich Schiller Universit?t Jena, L?bderstra?e 3, D-07740 Jena, Germany, DE
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Abstract: | Caveolae are specialized invaginated domains of the plasma membrane. Using freeze-fracture electron microscopy, the shape
of caveolae and the distribution of intramembrane particles (integral membrane proteins) were analyzed. The caveolar membrane
is highly curved and forms flask-like invaginations with a diameter of 80–120 nm with an open porus of 30–50 nm in diameter.
The fracture faces of caveolar membranes are nearly free of intramembrane particles. Protein particles in a circular arrangement
surrounding the caveolar opening were found on plasma membrane fracture faces. For isolation of caveolin-enriched membrane
vesicles, the method of Triton X-100 solubilization, as well as a detergent-free isolation method, was used. The caveolin-rich
vesicles had an average size of between 100 and 200 nm. No striated coat could be detected on the surface of isolated caveolin-rich
vesicles. Areas of clustered intramembrane particles were found frequently on membrane fracture faces of caveolin-rich vesicles.
The shape of these membrane protein clusters is often ring-like with a diameter of 30–50 nm. Membrane openings were found
to be present in the caveolin-rich membrane vesicles, mostly localized in the areas of the clustered membrane proteins. Immunogold
labeling of caveolin showed that the protein is a component within the membrane protein clusters and is not randomly distributed
on the membrane of caveolin-rich vesicles.
Accepted: 16 September 1998 |
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