Adaptor protein (AP) complexes select cargo for inclusion into coated vesicles in the late secretory and endocytic pathways. AP complexes are heterotetramers composed of two large subunits (α, δ, γ or ε, and a β subunit), a medium subunit (μ) and a small subunit (σ). In mammals there are five AP complexes (AP1-5). Drosophila, yeast and C. elegans lack AP4 and AP5 complexes. (Adapted from PMID:10611976, PMID:22022230 and PMID:15066634).