transporter associated with antigen processing §

Delivers peptides to the partially folded MHC class I molecule across the ER membrane.

TAP1 and TAP2 form a heterodimer to transport proteins from the cytosol into the ER. The genes TAP1 and TAP2 are located in the MHC locus and like most related genes, the expression is enhanced by interferons, produced in response to viral infection.

The TAP complex has limited specificity for peptides it will transport:

• between 8 and 16 amino acids
• hydrophobic / basic residues at the C-terminus

TAP has a bias against proline in the first three amino-terminal residues.

![[CleanShot 2023-12-10 at 17.18.23@2x.png]]

Note

Most of the peptides transported by TAP will not bind to the MHC class I molecules and are rapidly cleared out of the ER by Sec61.