Adaptins are proteins that mediate the formation of vesicles by clathrin-coated pits, through interaction with membrane-bound receptors. There are several types of adaptin, each related to a different group of such receptors.
Adaptins show sequence similarity to some COPI subunits, thus they are thought to have a common evolutionary origin.
Adaptins cluster to form the AP2 complex.
The Adaptin complex is a heterotetramer consisting of two large adaptins (alpha or beta), a medium adaptin (mu), and a small adaptin (sigma):
References
List of adaptins Wikipedia(Text) CC BY-SA