TABLE OF CONTENTS The present understanding of Clathrin and its functions in cellular contexts comes from the combined efforts in different fields. These include strikingly diverse examples: the developing chicken oocyte as the yolk proteins are internalized, human placenta, nerve synapses and unfortunately, viral infection. Clathrin cage assemblies with adaptor protein AP2 and other components are here described, based on studies by electron cryomicroscopy and X-ray crystallography.
Keywords: Clathrin; coated vesicles; electron cryomicroscopy; clathrin adaptor AP2; AP180; auxilin
Electron micrographs of glutaraldehyde fixed, thin sections of cells first revealed coated membrane and the process of coated vesicle formation. Based on such studies in cells, steps in the endocytic cycle in nutrient uptake and during synaptic transmission were described; coated pit assembly on the cytoplasmic surface of the plasma membrane, invagination and budding, scission of the coated vesicle containing concentrated cargo, uncoating and fusion of the vesicle with an acceptor compartment.
When extracts of particles were made from homogenized brain, structures, negatively stained in 1% uranyl acetate, were observed in electron micrographs and were thought to represent these endocyticcoated profiles. The particles were purified and the major complexes characterized, now well known as clathrin and the AP2 adaptor complex, in association with lipid vesicles. The particles were heterogeneous in size and shape but a small number of symmetrical examples were identified, initially by eye, indicating...
