ATP-binding cassette domain of the Transporter Associated with Antigen Processing, subfamily C
TAP (Transporter Associated with Antigen Processing) is essential for peptide delivery from the cytosol into the lumen of the endoplasmic reticulum (ER), where these peptides are loaded on major histocompatibility complex (MHC) I molecules. Loaded MHC I leave the ER and display their antigenic cargo on the cell surface to cytotoxic T cells. Subsequently, virus-infected or malignantly transformed cells can be eliminated. TAP belongs to the large family of ATP-binding cassette (ABC) transporters, which translocate a vast variety of solutes across membranes.