Structure of coated pits and vesicles

Purified coated vesicles typically contain clathrin and auxiliary structural proteins of about 100 000 and 50 000 relative molecular mass (Mr). A model is described for the packing of clathrin trimers into the characteristic pentagons and hexagons of the surface lattices of coats. In a coated vesicle, clathrin appears to bind to an inner 'core' of particles containing the 100 000 and 50 000 Mr proteins. These core proteins may, in turn, bind to receptors in the membrane of the vesicle. The vesicle itself surrounds specific content molecules bound to their respective receptors. Budding coated vesicles are believed to act as molecular filters in cells. The known structural features of coated membranes are discussed in terms of this apparent role.