Formation of a macromolecular complex between proteins of the AP-1 adaptor complex and proteins and/or lipoproteins that are going to be transported by a clathrin-coated vesicle. The AP-1 adaptor protein complex is a component of the cytoplasmic coat found on clathrin-coated vesicles, and binds to sorting signals of cargo to facilitate their trafficking.
cargo loading into clathrin-coated vesicle, AP-1-mediated