Adaptins are components of the adaptor complexes which link clathrin to receptors in coated vesicles. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration. Beta adaptin is a subunit of the plasma membrane adaptor (By similarity). Adaptor protein complex 3 (AP-3) is a heterotetramer composed of 2 large adaptins (apl5 and apl6), a medium adaptin (apm3) and a small adaptin (aps3). Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex. Belongs to the adaptor complexes large subunit family.