Clathrin-Coated Vesicles and Targeting

Abstract

In eukaryotic cells, receptor-mediated endocytosis and exit of specific trans-Golgi network cargo proteins (newly synthesized lysosome enzymes and secretory proteins) occur by way of clathrin-coated pits and clathrin-coated vesicles (CCVs). The major structural proteins of the coat are the heavy and light chains of clathrin. Along with clathrin, CCVs contain clathrin-associated proteins called assembly polypeptides (AP), because of their apparent ability to promote the polymerization of clathrin triskelions into polyhedral coat structures under physiological conditions. They have been renamed adaptors, since it was shown that they selectively bind cell-membrane receptors carrying endocytosis signals on their cytoplasmic tails. Pulled by the clathrin coat, membrane invaginates and pinches off, forming CCVs. The clathrin coat and parts of the adaptors are rapidly shed from the vesicle, which will be recycled for repeated rounds of coated pits assembly, invagination, and budding. Then the decoated vesicle carrying receptor-ligand complexes is suited to fuse with the acceptor compartment (for review, see refs. 1 and 2).