Alpha adaptin is a hetero tetramer which regulates clathrin-bud formation. The carboxyl-terminal appendage of the alpha subunit regulates translocation of endocytic accessory proteins to the bud site.

1: Crystal structure of the alpha appendage of AP-2 reveals a recruitment platform for clathrin-coat assembly Traub LM, Downs MA, Westrich JL, Fremont DH; Proc Natl Acad Sci U S A 1999;96:8907-8912. PMID:10430869