Transporter associated with antigen processing

Transporter associated with antigen processing (TAP) is a member of the ATP-binding-cassette transporter family. It delivers cytosolic peptides into the endoplasmic reticulum (ER), where they bind to nascent MHC class I molecules.

The TAP structure is formed of two proteins: TAP-1 and TAP-2, which have one hydrophobic region and one ATP-binding region each. They assemble into a heterodimer, which results in a four-domain transporter.