Clathrin-mediated endocytosis This animation shows the process of clathrin-mediated endocytosis of transferrin receptors, focusing on the assembly and disassembly of the clathrin cage. A single triskelion, which is approximately 100nm across at its widest point. Iron-bound transferrin is bound to its receptor on the exterior cell membrane. The transferrin receptor in turn binds to adaptor proteins in the interior of the cell, triggering the formation of a clathrin cage around the bound transferrin receptors. Soon after the vesicle has budded off the membrane, clathrin cage disassembly begins. Disassembly is mediated by HSC70, and its cofactor auxilin. The animation takes place in "real time," as clathrin cages have been observed to assemble in ~ 1 minute and disassemble in a few seconds after budding from the membrane. Endocytosis is the process by which cells are able to internalize membrane and extracellular materials through the formation of a vesicle. The process of membrane budding to form a vesicle is generally mediated by a protein coat, which acts both as a means to deform the membrane and to concentrate specific types of proteins inside the nascent vesicle. Clathrin is a coat protein that has been shown to function in receptor-mediated endocytosis events at the plasma membrane. Celldance 2008, 1st Place Video.