Figure 2.

The key players involved in the initiation of endocytosis. Adaptor proteins, cargo, lipids, and clathrin accumulate at the plasma membrane to make up the nascent endocytic site. Adaptor proteins, including the AP2 complex, bind to the inner leaflet of the plasma membrane. The adaptors interact with the plasma membrane via lipid-binding domains, many of which bind specifically to PIP₂. The tails of adaptor proteins bind and recruit clathrin triskelions to the plasma membrane where they polymerize to form the clathrin coat. Cargo—consisting of transmembrane receptors and extracellular soluble ligands—is taken up by clathrin-coated vesicles. Adaptors bind to signaling motifs on the intracellular side of the receptors.