Adaptor proteins (AP) are proteins that form the protein complexes that mediate the transport of molecules to intracellular locations. Adaptor proteins include signal transducing adaptor proteins, vesicular transport adaptor proteins, and clathrin adaptor proteins. They form into five different adaptor protein complexes: AP-1, AP-2, and AP-3 are clathrin associated. The AP2 adaptor complex aids clathrin mediated endocytosis. The complexes protein sort the cargos and via vesicles transport them to distinct targets. Their dysfunction can contribute to a number of genetic disorders.