On the structural and functional components of coated vesicles

Despite the diversity of their known functions, coated vesicles from different tissues contain a rather similar spectrum of proteins, in addition to their major coat protein, clathrin. In particular, each coated vesicle preparation shows a doublet of polypeptide species, on sodium dodecyl sulphate-containing gel electrophoresis, of apparent molecular weight in the region 30,000 to 36,000. Using bullock brain as a source, these molecules are found in association with possible trimers or higher multiples of clathrin, obtained by dissolving coated vesicles in cholate. They may play a structural role relating to the vertices or edges of the lattices of pentagons and hexagons of the polyhedral coats. Purified coated vesicles (e.g. from chicken oocytes) seem to contain relatively small amounts of specific proteins in terms of “contents”. This suggests that the bulk of the isolated particles, especially those in the small size range (500 to 800 Å diam.), may be “empty” of contents, although many still retain a lipid vesicle. These empty structures could represent a pool of recycling coated vesicle components formed after release (possibly from larger vesicles (800 to 1500 Å diam.)) of the specific contents, at their particular destination.